16108547 Diagnostic Medical Imaging

2004 Syllabus
Emergency Radiology
Categorical Course in Diagnostic Radiology
EDITOR Frederick A. Mann, MD SEATTLE, WASH

The Board of Directors of the Radiological Society of North America and the Society’s Refresher Course Committee acknowledge with warm appreciation the scientific contributions of Fredrick A. Mann, MD, in his role as editor of this syllabus.

Robert R. Hattery, MD
Chairman Board of Directors

Robert A. Novelline, MD
Chairman Refresher Course Committee

Presented at the 90th Scientific Assembly and Annual Meeting of the Radiological Society of North America November 28–December 3, 2004

The Radiological Society of North America is a nonprofit organization. The Radiological Society of North America subsidizes the production of categorical and special course syllabi. Financial losses incurred in syllabi production are absorbed by the RSNA. Any net revenues from the sale of syllabi are transferred to the RSNA Research and Education Foundation. ©2004 by the Radiological Society of North America, Inc 820 Jorie Blvd, Oak Brook, IL 60523-2251

Contents

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Preface Frederick A. Mann, MD The Emergence of Emergency Radiology
Robert A. Novelline, MD

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Imaging the Pediatric Patient with Acute Abdominal Disease Carlos J. Sivit, MD The Role of CT in Acute Abdominal Disease: Pitfalls and Their Lessons Dean D. T. Maglinte, MD, James T. Rhea, MD, and M. Stephen Ledbetter, MD The Contemporary Role of Conventional Radiographs in Evaluating the Acute Abdomen Stephen R. Baker, MD Imaging of Cervical Spine Trauma C. Craig Blackmore, MD, MPH Imaging Spine Trauma in the Elderly
Friedrich M. Lomoschitz, MD, C. Craig Blackmore, MD, MPH, and Frederick A. Mann, MD

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Nontraumatic Neurologic Emergencies A. Gregory Sorensen, MD Traumatic Brain Injury: Imaging Update 2004 Alisa D. Gean, MD, Christine Glastonbury, MBBS, and D. Christian Sonne, MD CT for Thromboembolic Disease: Protocols, Interpretation, and Pitfalls Lacey Washington, MD CT of Nontraumatic Aortic Emergencies O. Clark West, MD, and Sanjeev Bhalla, MD Cardiac Applications for Multi–Detector Row CT in the Emergency Department Udo Hoffmann, MD, Ricardo C. Cury, MD, Maros Ferencik, MD, PhD, Fabian Moselewski, BS, Suhny Abbara, MD, and Thomas J. Brady, MD Imaging of Blunt Chest Trauma Nisa Thoongsuwan, MD, Jeffrey P. Kanne, MD, and Eric J. Stern, MD Imaging Diagnosis of Thoracic Aorta and Great Vessel Injuries Stuart E. Mirvis, MD CT of Abdominal Trauma: Part I James T. Rhea, MD CT of Abdominal Trauma: Part II Kathirkamanathan Shanmuganathan, MD 159 133

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Imaging of Thoracolumbar Spine Trauma Georges Y. El-Khoury, MD Imaging of Upper Extremity Injuries in Children Diego Jaramillo, MD, MPH High-Energy Blunt-Force Injuries to the Upper Extremity Thurman Gillespy III, MD Imaging Low-Energy Upper Extremity Injuries Viktor M. Metz, MD, and Marcel O. Philipp, MD Low-Energy Injuries of the Lower Limb Philip M. Hughes, MBBS, MRCP, FRCP Pediatric Lower Extremity Trauma Susan D. John, MD
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Contributors
Suhny Abbara, MD
Department of Radiology Massachusetts General Hospital Boston, Mass

Philip M. Hughes, MBBS, MRCP, FRCP
Department of Radiology Derriford Hospital Plymouth University Hospitals Plymouth, England

Robert A. Novelline, MD
Department of Radiology Massachusetts General Hospital Boston, Mass

Stephen R. Baker, MD
Department of Radiology University Hospital New Jersey Medical School Newark, NJ

Marcel O. Philipp, MD
Department of Radiology Medical University of Vienna Vienna, Austria

Diego Jaramillo, MD, MPH
Department of Radiology Children’s Hospital of Philadelphia Philadelphia, Pa

James T. Rhea, MD
Department of Radiology Massachusetts General Hospital Boston, Mass

Sanjeev Bhalla, MD
Mallinckrodt Institute of Radiology Washington University School of Medicine St Louis, Mo

Susan D. John, MD
Department of Radiology University of Texas Houston Medical School Houston, Tex

Kathirkamanathan Shanmuganathan, MD
Department of Radiology University of Maryland School of Medicine Baltimore, Md

C. Craig Blackmore, MD, MPH
Department of Radiology Harborview Medical Center University of Washington Seattle, Wash

Jeffrey P. Kanne, MD
Department of Radiology Harborview Medical Center University of Washington Seattle, Wash

Carlos J. Sivit, MD
Case Western Reserve University School of Medicine Rainbow Babies and Children’s Hospital Cleveland, Ohio

Thomas J. Brady, MD
Department of Radiology Massachusetts General Hospital Boston, Mass

M. Stephen Ledbetter, MD
Department of Radiology Brigham and Women’s Hospital Boston, Mass

Ricardo C. Cury, MD
Department of Radiology Massachusetts General Hospital Boston, Mass

Friedrich M. Lomoschitz, MD
Department of Radiology Vienna Medical School University of Vienna Vienna, Austria

D. Christian Sonne, MD
Department of Radiology University of California, San Francisco San Francisco, Calif

Georges Y. El-Khoury, MD
Department of Radiology University of Iowa Hospitals and Clinics Iowa City, Iowa

A. Gregory Sorensen, MD
Department of Radiology Massachusetts General Hospital Boston, Mass

Dean D. T. Maglinte, MD
Department of Radiology Indiana University School of Medicine Indianapolis, Ind

Maros Ferencik, MD, PhD
Department of Radiology Massachusetts General Hospital Boston, Mass

Eric J. Stern, MD
Department of Radiology Harborview Medical Center University of Washington Seattle, Wash

Frederick A. Mann, MD
Department of Radiology Harborview Medical Center Seattle, Wash

Alisa D. Gean, MD
Department of Radiology University of California, San Francisco San Francisco, Calif

Viktor M. Metz, MD
Department of Radiology Medical University of Vienna Vienna, Austria

Nisa Thoongsuwan, MD
Department of Radiology Harborview Medical Center University of Washington Seattle, Wash

Thurman Gillespy III, MD
Department of Radiology University of Washington Harborview Medical Center Seattle, Wash

Stuart E. Mirvis, MD
Department of Radiology Maryland Shock-Trauma Center University of Maryland School of Medicine Baltimore, Md

Lacey Washington, MD
Department of Radiology Medical College of Wisconsin Milwaukee, Wis

Christine Glastonbury, MBBS
Department of Radiology University of California, San Francisco San Francisco, Calif

O. Clark West, MD
Department of Radiology University of Texas Medical School at Houston Houston, Tex

Fabian Moselewski, BS
Department of Radiology Massachusetts General Hospital Boston, Mass

Udo Hoffmann, MD

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Department of Radiology Massachusetts General Hospital Boston, Mass

Preface
Why a categorical course on Emergency Radiology? Although it has been a while since the last such course, the curriculum responds to the manifold challenges of communityfocused health care organization that have been caused by accelerating demographic, cultural, and technologic changes. Interactions between structural and fiscal changes in health care delivery and financing have altered the traditional triage and clearing-house roles of emergency departments, which increasingly provide primary care and definitive diagnoses and treatments. The resultant overburdening of emergency departments leads to pressures to shorten the length of the in-facility stay, which begets greater use of adjunct tests, and pressures to obtain and interpret images quickly—not to mention accurately—24/7. Enter enabling imaging technologies (eg, multi–detector row CT) and information technologies (eg, PACS, RIS). Substantial synthesis of new and well-found knowledge is reviewed in this syllabus, and even more will be presented during the course by an exceptional faculty. None of this could or would occur without the leadership and support of the RSNA. In particular, I especially need to acknowledge the assistance and forbearance of Robert A. Novelline, MD, Chair of the RSNA Refresher Course Committee, and Mss Diane Lang, Ann Blair, Annette Savage, and Eileen Brazelton. I can only hope you learn and enjoy reading these chapters as much as I have. Best wishes.

Frederick A. Mann, MD

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Robert A. Novelline, MD

The Emergence of Emergency Radiology1
Emergency radiology is the subspecialty of radiology that deals with the imaging of acutely ill and injured patients and the imaging management of such cases (1). Emergency radiology is one of the newest subspecialties of radiology and one of the fastest growing. In recent years, emergency radiology has emerged into the spotlight. The current drive to improve quality of care and decrease health care costs is demanding faster and more sophisticated diagnostic imaging of patients at emergency centers at the same time that the volume of patients seeking care at emergency centers is increasing. In addition, the demand for immediate off-hours radiologic interpretation for emergency cases is changing the practice of radiology. According to the National Center for Health Statistics of the U.S. Department of Health and Human Services (2), currently more than 100 million U.S. residents (110.2 million in 2002) come annually to an emergency center for evaluation of an acute condition. The annual number of U.S. injury-related visits is currently more than 39 million (39.2 million in 2002). Nearly all patients seen in an emergency department undergo at least one imaging examination as part of their diagnostic evaluation, and many will undergo several, including radiographic, ultrasonographic (US), computed tomographic (CT), and magnetic resonance (MR) imaging examinations. Emergency imaging examinations must be of the highest quality, and images must be obtained and interpreted in a timely manner so that a quick and accurate diagnosis can be made. The National Center of Health Statistics (2) has reported a steady increase in the volume of patients seen at emergency departments. For 1996, the center reported 34 annual visits per 100 persons; in 2002, this number had increased to 39 visits per 100 persons. In the period from 1995 to 1996, there were 36 million injury-related emergency department visits recorded in the United States, and today that annual number is more than 39 million. At Massachusetts General Hospital, we have been observing a steady 5% annual increase in the volume of patients seen at the emergency department during the past decade. Currently, our emergency department treats more than 80.000 patients annually, and emergency radiology personnel perform nearly 80.000 imaging examinations per year, approximately one imaging examination per patient. To provide emergency imaging services for this patient population, the Emergency Radiology Division of Massachusetts General Hospital is equipped with three digital radiography rooms, two multi–detector row CT scanners, a 1.5-T MR imager, and US equipment. Imaging in the division is completely digital, with five picture archiving and communication system (PACS) workstations and a three-dimensional workstation for image management and consultations. In-house staff radiologists provide interpretations 24 hours per day, 7 days per week. The Emergency Radiology Division also serves

RSNA Categorical Course in Diagnostic Radiology: Emergency Radiology 2004; pp 7–9.
1From the Department of Radiology, Harvard Medical School, Massachusetts General Hospital, 32 Fruit St, PO Box 9657, Boston, MA 02114 (e-mail: [email protected]).

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the radiologic needs of the remainder of the medical center during off hours, performing a wide array of emergency inpatient and outpatient imaging examinations during evenings and weekends. Fortunately, there have been spectacular advances in diagnostic imaging during the past decade to meet the demands placed on emergency radiology. CT (3) alone has revolutionized imaging diagnosis for trauma patients, and a new revolution is currently under way with multi–detector row CT scanners, which can scan patients faster, with thinner sections, at higher spatial resolution, and with less radiation exposure than earlier scanners. Ten years ago, it took 20 minutes to perform a CT scan of the head; today a 16–detector row CT examination of the head can be performed in less than 10 seconds. Ten years ago, imaging a patient with multiple trauma who needed CT scans of the head, cervical spine, chest, abdomen, and pelvis would have required 1–2 hours in the CT scanner suite, including the frustrating 5–10-minute waiting periods between scan segments to allow the x-ray tube to cool. This length of time in the radiology area was potentially hazardous for trauma patients and required valuable nursing and physician staff-hours to manage trauma cases in the radiology area. Today, a “total-body” trauma scan can be performed in less than 5 minutes (4). The 16–detector row CT scanners are so fast that one actually has to slow down the scanning of trauma patients with programmed delays so that the scanner will not scan ahead of the movement of the intravenously administered contrast material. In the past, many trauma patients who were seriously injured or were in potentially unstable condition were not able to spend long periods of time in the radiology area to receive the benefits of CT diagnosis; most of these patients today can be examined with multi–detector row CT. Because trauma is the leading cause of death of U.S. citizens younger than 40 years old and is the third most common cause of death of all U.S. citizens (5), the advances in CT diagnosis for trauma cases can profoundly affect U.S. health care. In addition to the increased speed, the advances in multi–detector row CT with 16–detector row CT scanners have also provided dramatic improvements in CT reformations (two-dimensional, three-dimensional, and curved planar reformations), CT angiography, and CT perfusion and cardiac-gated CT examinations. Sagittal and coronal reformations of the spine of trauma patients examined with chest-abdomen CT are so high in quality that thoracolumbar spine radiographs are no longer required. Coronal and sagittal multi–detector row CT reformations now are used to assist in the diagnosis of facial fractures, sternal fractures, diaphragm rupture, gallbladder avulsion, pelvic fractures, and dozens of other injuries not optimally depicted in the transverse plane. Three-dimensional reformations of

fractures provide excellent displays to show the position and alignment of fracture fragments. With 16–detector row CT technology, CT angiography is so improved that it is replacing lengthy conventional arteriography as the imaging modality of choice for patients suspected of having injuries of the aorta and major blood vessels of the head, neck, chest, abdomen, pelvis, and extremities. Cardiac gating of chest CT performed because of trauma can eliminate the aortic pulsatile motion artifact that has been responsible for many indeterminate interpretations of CT images obtained in patients suspected of having aortic trauma. Perfusion CT imaging can be used to diagnose cerebral ischemia associated with traumatic dissection or other injuries of the carotid or vertebral arteries and has potential for use in diagnosing traumatic ischemia of other organs, such as the kidneys. CT has also revolutionized the work-up of nontraumatic emergency conditions and currently is the diagnostic procedure of choice in most emergency centers for patients suspected of having appendicitis, diverticulitis, renal stone disease, bowel obstruction, aortic dissection, aortic aneurysm, or pulmonary embolism (3). CT performed in the emergency center can be used (a) to expedite management and treatment by providing confirmation when disease is present and (b) to prevent unnecessary surgery and/or hospitalization by identifying patients without disease or those with an alternative diagnosis. The 16–detector row CT scanners can scan faster than four–detector row or single–detector row CT scanners do and produce excellent scans with less patient radiation, a marked benefit for children and pregnant woman who require an emergency CT diagnosis. Advances in MR imaging also have been of great diagnostic value in the emergency department. MR is the imaging modality of choice for the diagnosis of acute ischemic stroke and contributes substantially to the diagnosis of other acute conditions of the central nervous system. MR imaging is indicated for patients with spinal trauma who have neurologic deficits and for patients with acute musculoskeletal trauma when the conventional radiographic findings are indeterminate or when a soft-tissue injury is suspected. MR is also indicated for the diagnostic imaging of acute aortic and other vascular conditions in patients who cannot be examined with contrast material–enhanced CT because of a history of allergic reaction to contrast material or impaired renal function. Recently developed fast MR imaging protocols may play a future role in the diagnosis of acute thoracic and abdominal conditions in children and pregnant woman as an alternative to examinations that use ionizing radiation. Today, MR imagers are more readily available to patients in the emergency department. Emergency US is another valuable technique in the management of cases in the emergency department.

Novelline

US is the procedure of choice for patients suspected of having deep venous thrombosis, acute cholecystitis, painless jaundice, or hydronephrosis. US is indicated for nearly all acute gynecologic, obstetric, and acute scrotal conditions. A distinct benefit of US in the trauma patient who is in unstable condition is the fact that US can be performed at the bedside to screen for intraperitoneal hemorrhage and injuries to the major abdominal organs. Fortunately, digital imaging and PACS have developed in concert with recent advances in cross-sectional imaging. A typical total-body trauma scan of the head, cervical spine, chest, abdomen, and pelvis with coronal, sagittal, and other reformations may produce from 500 to 700 images, and these unusually large data sets require viewing each section with soft-tissue, bone, and lung windows. It would be incredibly burdensome to print hard-copy film images of all of these images at various windows and then view the film images on light boxes. Panning through such large image series on PACS while continuously changing windows accelerates the viewing and interpretation of images from trauma and other emergency cross-sectional examinations. In many medical centers, a considerable number of hospital admissions are arranged today through the emergency department, with patients having their initial imaging work-up done and the imaging diagnosis made in the emergency radiology section. Consequently, emergency radiology is becoming one of the important “diagnostic centers” of the institution. At Massachusetts General Hospital, 46% of the inpatients are admitted through the emergency department, with their initial diagnostic imaging examinations performed and interpreted in the emergency radiology division. Off-hours coverage of emergency radiology services is provided today either by an on-site radiologist or through teleradiology. On-site coverage is easier to arrange in academic centers, where the off hours are usually covered by evening, night, and weekend residents. The residents provide preliminary off-hours interpretations that are subsequently checked by staff on the next morning. However, corrections made during “overreads” of resident interpretations may lead to delays in correct diagnosis and delays in patient treatment. Consequently, many academic centers are now instituting full-time in-house staff coverage by using “nighthawk” staff radiologists (staff radiologists working the night shift). Off-hours coverage at nonacademic centers is more difficult to provide because of the current shortage of radiologists. Some private groups do now provide 24-hour staff coverage or have contracted with teleradiology nighthawk services. The demands for radiologists with specialization in emergency radiology and the professional opportunities available today have stimulated great interest in this subspecialty as a career choice. The American Society of Emergency Radiology (ASER) was founded in

1988 to serve the needs of those interested in the field of emergency radiology. ASER now has more than 450 U.S. and international members and an annual scientific meeting with more than 200 registrants. ASER publishes the journal Emergency Radiology: A Journal of Practical Imaging and has sponsored a core curriculum in emergency radiology for residents, medical students, and fellows in emergency radiology. The specialty of emergency radiology has been recognized by the American College of Radiology, which has offered a seat on the council for an ASER representative. Both the Radiological Society of North America and the American Roentgen Ray Society have recognized emergency radiology in the planning of scientific sessions and instructional refresher courses in emergency radiology, as well as including sections of emergency radiology in their respective journals, Radiology and AJR: American Journal of Roentgenology. Research in emergency radiology has involved both retrospective and prospective investigations of new imaging modalities and protocols for the diagnosis of trauma and nontraumatic emergency conditions. Because of the current concerns about rising health care costs and possible overuse of imaging resources, a recent direction in research is the investigation of (a) criteria for selecting patients for emergency imaging examinations, such as the National Emergency X-Radiography Utilization Study (6); or (b) criteria (7) to select the most appropriate imaging examination once the decision to image has been made. As chairman of the RSNA Refresher Course Committee, it gives me great pleasure to invite you to attend the RSNA 2004 Categorical Course in Diagnostic Radiology: Emergency Radiology and/or read this categorical course syllabus prepared by the participants. This course will cover the spectrum of emergency radiology, highlighting cutting-edge technologies and imaging approaches. I am most grateful to all of the invited speakers, who have prepared excellent written materials and presentations for this course.

Emergence of Emergency Radiology

References
1. 2. Harris JH Jr. Reflections: emergency radiology. Radiology 2001; 218:309–316. Emergency department visits. NCHS FASTATS page. National Center for Health Statistics Web site. Available at: www.cdc.gov /nchs/fastats/ervisits.htm. Accessed April 16, 2004. Novelline RA, Rhea JT, Rao PM, Stuk JL. Helical CT in emergency radiology. Radiology 1999; 213:321–339. Ptak T, Rhea JT, Novelline RA. Experience with a continuous, single-pass whole-body multidetector CT protocol for trauma: the three minute multiple trauma CT scan. Emerg Radiol 2001; 8:250– 255. National Safety Council. Injury facts: 2003 edition. Itasca, Ill: National Safety Council, 2003. Hoffman JR, Wolfson AB, Todd K, Mower WR. Selective cervical spine radiography in blunt trauma: methodology of the National Emergency X-Radiography Utilization Study (NEXUS). Ann Emerg Med 1998; 32:461–469. Blackmore CC, Emerson SS, Mann FA, Koepsell TD. Cervical spine imaging in patients with trauma: determination of fracture risk to optimize use. Radiology 1999; 211:759–765.

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A. Gregory Sorensen, MD

Nontraumatic Neurologic Emergencies1

There are a few life-threatening neurologic illnesses in which emergent imaging can play a key role. This chapter will describe the role of imaging in these diseases and also will highlight some of the common neurologic illnesses that are identified with neuroimaging in the acute-care setting of the modern North American emergency department. Unfortunately, the most common diseases of the brain are not yet amenable to assistance with neuroimaging. These diseases include the neuropsychiatric illnesses, such as major depression, bipolar disorder, and schizophrenia, and alcoholism, substance abuse, and addiction. It may be that in the future, our imaging tools will provide us with insight into these diseases and will be used to assist in their acute management. Another class of acute neurologic illness, trauma, is covered in other chapters of this syllabus. This leaves still a sizable number of neurologic illnesses; this syllabus chapter will focus only on the most common. These include stroke (ischemic and hemorrhagic), stroke mimics (such as posterior leukoencephalopathy syndrome), acute demyelinating disease, new adult-onset seizures, and infection. Finally, because a common request for imaging is to determine the safety of proceeding with lumbar puncture to sample cerebrospinal fluid, a short discussion of this topic will also be presented.

STROKE
Stroke is a term that describes a rapid onset of neurologic impairment. Eighty-five percent of all strokes are ischemic stroke, and the vast majority of these are caused by blockages of arterial flow to brain tissue, with subsequent cellular impairment and/or death. Fifteen percent of all strokes are hemorrhagic; this includes both intraparenchymal hemorrhage and subarachnoid hemorrhage, with the latter most commonly caused by rupture of an intracranial aneurysm. For each of these entities, the patient deserves emergent neuroimaging for diagnosis and treatment planning.

RSNA Categorical Course in Diagnostic Radiology: Emergency Radiology 2004; pp 11–15.
1From the Department of Radiology, Massachusetts General Hospital, A. A. Martinos Center, Bldg 149, 13th St, Charlestown, MA 02129 (e-mail: [email protected]).

A.G.S. receives research support from, is a consultant for, or has spoken on behalf of the following companies within the last year: Siemens Medical Systems; General Electric Medical Systems; Glaxo SmithKline; Novartis Pharmaceuticals; Descartes Therapeutics; Schering AG; Hemedex, Inc; Pfizer, Inc; StemCells, Inc; and Transkaryotic Therapies, Inc. In addition, A.G.S. has an equity position in and holds the position of Medical Director at EPIX Medical, Inc, a specialty pharmaceutical company based in Cambridge, Mass, engaged in developing targeted contrast agents for cardiovascular MR imaging.

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Ischemic Stroke Stroke occurs about 700.000 times per year in the United States and is the leading cause of adult morbidity and a leading cause of death. In the past 10 years, the treatment of stroke has begun to shift from initial palliative care, followed by an emphasis on secondary prevention, to a focus on acute treatment, with secondary preventive measures still important but not emergent. This evolution in therapy is due to the approval in 1996 by the Food and Drug Administration of a thrombolytic agent, alteplase (recombinant tissue plasminogen activator, or rt-PA). The results of a number of wellcontrolled clinical trials have demonstrated that administration of alteplase leads to decreased morbidity and mortality when treatment is initiated within 3 hours from the onset of symptoms (1) (Fig 1). Imaging plays a crucial role in alteplase therapy for two reasons. First, alteplase must not be given if the stroke is hemorrhagic, rather than ischemic. Although these two types of stroke can often be distinguished clinically, imaging is still required to rule out hemorrhage prior to administering alteplase. Because computed tomography (CT) is typically available rapidly in the emergency setting and because it is widely accepted as a very sensitive tool for the detection of acute hemorrhage, CT is the standard initial imaging modality. Naturally, any sign of hemorrhage at CT is a contraindication to thrombolytic therapy. This is because the rate of symptomatic hemorrhage increases in stroke patients treated with alteplase from 1% to 7% or more. Hemorrhage is a feared complication of alteplase administration and therefore is the main sign sought at the initial CT examination. However, there are additional signs at CT that are considered to be contraindications for acute chemical thrombolysis. These signs are all ways of estimating the size and the age of the infarct. Current thinking is that the risk of hemorrhage is higher in the larger and more advanced infarcts, probably because of the increased chance of reperfusion injury accompanied by symptomatic hemorrhage. For example, a standard rule of thumb is that treatment with alteplase is contraindicated if more than one-third of the middle cerebral artery territory of the brain has evidence of low attenuation on CT images obtained at the acute CT examination. An example of this is shown in Figure 2. Hemorrhage can be a complication of ischemic stroke even without the administration of any thrombolytic therapy. Attention to the window level settings may provide greater sensitivity to subtle signs of stroke (2). Other signs of severe stroke, such as midline shift, are also thought to represent contraindications to therapy. Although no well-controlled trials have been performed to demonstrate the benefit of adding CT angiography to the initial imaging study, many practitioners do add CT angiography because it is thought to identify clot, if present, in the proximal intracerebral ar-

Sorensen

Figure 1. Model-estimated odds ratio (OR) for favorable outcome at 3 months in alteplase-treated patients, compared with controls, by time from onset of symptoms (OTT). Odds ratio was adjusted for age, baseline glucose concentration, baseline National Institutes of Health Stroke Scale (NIHSS) score, baseline diastolic blood pressure, previous hypertension, and interaction between age and baseline NIHSS measurement. (Reprinted, with permission, from reference 1.)

teries. The presence of clot can confirm the cause of the stroke. However, it is not yet clear to what degree the initial CT angiographic findings correlate with outcome or to what extent they should be used to guide treatment because CT angiography does not always allow good evaluation of the distal collateral vessels. Although CT has become the accepted standard for imaging acute stroke, many groups are also exploring the utility of magnetic resonance (MR) imaging in acute stroke. MR imaging is being explored for a number of reasons. One is to distinguish infarction from transient ischemic attack. Transient ischemic attack is now also considered a medical emergency because of the high frequency of cerebrovascular events after transient ischemic attack (3). Identifying the cause of a transient ischemic attack, such as a dissection (Fig 3), can assist in the work-up and prevention of the transient ischemic attack culminating in a full-fledged infarct. Diffusion-weighted MR imaging is the most sensitive and specific single imaging modality for diagnosis of stroke, and the identification of tissue damage at neuroimaging, even if symptoms have quickly resolved, will have therapeutic implications. A second reason for the use of MR imaging is that, despite the confirmed efficacy of chemical thrombolysis, only a small fraction (estimated at 5%) of stroke victims receive alteplase. This is in part because many patients are outside the 3-hour window of time, after which the risk of hemorrhage goes up substantially. Nevertheless, there have been suggestions that many patients may have lesions that would still be amenable to treatment at this later time, and MR imaging is thought to be the way to identify such patients. The use of MR imaging, particularly identification of a diffusion-perfusion mismatch, is believed to suggest the presence of salvageable tissue. Although this concept is still somewhat the subject of debate, most practitioners believe that a large diffusion-perfusion mismatch

Nontraumatic Neurologic Emergencies

Figure 2. Left: CT images from initial CT examination of the head performed 2 hours 45 minutes after the onset of symptoms in a 42year-old man show hypoattenuation covering more than one-third of the middle cerebral artery territory. Right: CT images from follow-up CT scan performed 6 hours after onset of symptoms show hemorrhagic transformation with midline shift.

Figure 3. Dissection of combined extra- and intracranial carotid artery. Left: Two-dimensional time-of-flight MR angiogram shows absence of right internal carotid artery above bifurcation. Top center: Three-dimensional time-of-flight MR image of circle of Willis shows attenuation of flow in right middle cerebral artery and absent flow in right distal internal carotid artery. Bottom center: Twodimensional phase-contrast MR angiogram of circle of Willis shows cross-filling and retrograde flow through precommunicating part of right anterior cerebral artery (A1 segment). Right: T1-weighted MR image with fat saturation shows hyperintense thrombus in vessel wall in right internal carotid artery in neck just below skull base.

suggests the need for more aggressive treatment. The concept of the ischemic penumbra is similar to the socalled stunned myocardium in the heart, and the development of imaging tools to study this has been a major effort during the past decade. A third use for emergent MR imaging in stroke is when there is a question of venous thrombosis. MR venography and CT venography have not been formally compared in any well-controlled trials that

studied patients with acute stroke (4,5), but most practitioners, extrapolating from other data, believe that MR venography may have higher accuracy.

Hemorrhagic Stroke The 15% of all strokes that are due to hemorrhage can be categorized as either parenchymal or subarachnoid. Both types are easily distinguished at CT in routine practice, and a review of these findings is not necessary here.

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Sorensen
Figure 4. Brain abscess in 33-year-old woman with 3-day history of vomiting and seizure. A, T1-weighted MR image obtained after administration of gadolinium-based contrast material shows ring enhancement. B, T2-weighted MR image shows edema surrounding mass, and differential diagnosis includes both abscess and tumor. C, Diffusion-weighted MR image shows hyperintensity in the center of the abnormality. D, Map of apparent diffusion coefficient shows low apparent diffusion coefficient in center of abnormality. Surgical drainage demonstrated yellow pus that grew streptococci.

There are a few important updates: First, CT angiography increasingly is being used in the emergency setting to evaluate the location and nature of the aneurysm. Familiarity with CT angiography and with the locations of aneurysms is therefore increasingly being driven into the emergency department, rather than the neuroangiography suite. A second important shift is due to changes in clinical practice driven by the results from the International Subarachnoid Aneurysm Trial. This study compared 1-year clinical outcomes after either coiling or clipping of aneurysms. The group undergoing clipping had a substantially greater morbidity at 1 year. Although this appears to show clinical superiority for the less-invasive approach, the clearest assessment of the benefits of coiling will come after the 5-year follow-up data are assembled. This further suggests that radiologists will play an important role in the diagnosis and management of aneurysmal disease.

STROKE MIMICS
A number of disease processes can mimic the appearance of stroke, especially at CT. Fortunately, knowledge of the clinical manifestations of these illnesses, combined with a clear understanding of the most powerful tool in the diagnostic armamentarium for acute ischemic stroke, that is, diffusion-weighted MR imaging, will allow a clear diagnosis in most cases. One relatively recently recognized syndrome is that termed reversible posterior leukoencephalopathy syndrome (6). Although initially thought to be a complication of malignant hypertension and/or associated with toxemia of pregnancy, this syndrome has now been described in subjects with a range of illnesses. Beyond hypertension and toxemia, these additional illnesses include chronic renal disease, pheochromocy-

toma, and acute glomerulonephritis, and the syndrome has been seen as a side effect of chemotherapy. Clinical reversible posterior leukoencephalopathy syndrome is typically accompanied by headache or other symptoms ranging from nausea and/or vomiting to convulsions, stupor, or coma. On pathologic examination, microscopic hemorrhages and infarcts may be evident, although early MR imaging shows increases in the apparent diffusion coefficient, rather than reductions. Lowering the blood pressure is the major form of treatment and should be done before stroke (hemorrhagic or ischemic) occurs. There have been some documented cases of reversible posterior leukoencephalopathy syndrome without hypertension. There is a range of other stroke mimics: lesions that may have similar findings with one or more types of MR imaging. However, careful analysis of imaging, particularly diffusion-weighted images, usually can be used to sort these out. One particularly important step is understanding the difference on diffusion-weighted images between hyperintense signal intensity caused by restricted water mobility—that is, lowered values for the apparent diffusion coefficient—and hyperintense signal intensity on diffusion-weighted images despite normal or even elevated water mobility. This can occur when a region has such hyperintense signal intensity on T2-weighted MR images that even after the diffusion encoding gradients are applied, there is still residual hyperintense signal intensity: the socalled T2 shine-through effect.

OTHER ACUTE NEUROLOGIC ILLNESSES
Although stroke remains the most common neurologic emergency, a variety of other illnesses can be diagnosed for the first time in the emergency department with the aid of imaging. One of these is acute demyelinating

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disease. Demyelinating disease is located typically in the white matter and can be due to either multiple sclerosis or acute disseminated encephalomyelitis, and these entities can look identical. Although the formal diagnosis of multiple sclerosis requires “multiple” events (ie, dissemination of lesions in time and space [7]), many practitioners do not always wait for the multiple events to occur before beginning presumptive treatment for multiple sclerosis with the new disease-modifying agents, such as the interferon-beta class. Although optic neuritis can be an isolated finding, the frequency of this progressing to multiple sclerosis is high enough to lead to immediate treatment, with tapering of the treatment if no symptoms occur. Acute disseminated encephalomyelitis is therefore usually distinguished by history: There is usually a history of immunization and/or a viral prodrome (8). Intracranial abscesses or encephalitis can also occur (9), but these findings are relatively uncommon (about 1 in 100.000 per year) (10). In modern series, intracranial abscesses and encephalitis are typically found in immunocompromised patients, and the usual infections are from toxoplasmosis, Nocardia, etc. Typical causes include contiguous spread (eg, from severe otitis media), hematogenous spread, or a sequela after some breach of physical defenses (eg, after trauma or neurosurgery). Some 20%–30% of these infections are cryptogenic. Diffusion-weighted MR imaging has been reported to show restricted water mobility in the center of the abscess (Fig 4). New onset of seizures is another neurologic illness in which imaging can play a role in the emergency department. However, in this case, the role is to exclude anatomic lesions amenable to focused intervention because most new seizures are idiopathic (some 62% in one series) (11). However, vascular disease (eg, stroke) is frequent in older patients (49% of the older patients with new seizures in that same series), and tumor accounted for 11%. Therefore, routine MR imaging can be helpful in both ruling in and ruling out disease.

fluid, lumbar puncture can result in herniation (12). As a result, some clinicians seek to rule out such masses in clinical settings in which herniation is thought to be a risk. Our role in such settings is to exclude a compartment syndrome. Because the total daily volume of cerebrospinal fluid production is about three times that of the total cerebrospinal fluid volume (total volume in an adult is about 150 mL, with daily production of about 450 mL), if the flow of cerebrospinal fluid from one compartment to another is blocked, a compartment syndrome can arise. Hence, to clear a patient for lumbar puncture simply means to ensure that no blockages to flow are present; this is most easily ascertained by a lack of brain shift.

Nontraumatic Neurologic Emergencies

References
1. Hacke W, Donnan G, Fieschi C, et al. Association of outcome with early stroke treatment: pooled analysis of ATLANTIS, ECASS, and NINDS rt-PA stroke trials. Lancet 2004; 363:768–774. 2. Lev MH, Farkas J, Gemmete JJ, et al. Acute stroke: improved nonenhanced CT detection—benefits of soft-copy interpretation by using variable window width and center level settings. Radiology 1999; 213:150–155. 3. Albers GW, Caplan LR, Easton JD, et al. Transient ischemic attack: proposal for a new definition. N Engl J Med 2002; 347:1713–1716. 4. Ciccone A, Canhao P, Falcao F, Ferro JM, Sterzi R. Thrombolysis for cerebral vein and dural sinus thrombosis. Cochrane Database Syst Rev 2004; 1:CD003693. 5. Campbell BG, Zimmerman RD. Emergency magnetic resonance of the brain. Top Magn Reson Imaging 1998; 9:208– 227. 6. Mukherjee P, McKinstry RC. Reversible posterior leukoencephalopathy syndrome: evaluation with diffusion-tensor MR imaging. Radiology 2001; 219:756–765. 7. Poser CM, Brinar VV. Diagnostic criteria for multiple sclerosis: an historical review. Clin Neurol Neurosurg 2004; 106: 147–158. 8. Gabis LV, Panasci DJ, Andriola MR, Huang W. Acute disseminated encephalomyelitis: an MRI/MRS longitudinal study. Pediatr Neurol 2004; 30:324–329. 9. Tattevin P, Bruneel F, Clair B, et al. Bacterial brain abscesses: a retrospective study of 94 patients admitted to an intensive care unit (1980 to 1999). Am J Med 2003; 115: 143–146. 10. Das P. Infectious disease surveillance update. Lancet Infect Dis 2004; 4:259. 11. Sander JW, Hart YM, Johnson AL, Shorvon SD. National General Practice Study of Epilepsy: newly diagnosed epileptic seizures in a general population. Lancet 1990; 336: 1267–1271. 12. van Crevel H, Hijdra A, de Gans J. Lumbar puncture and the risk of herniation: when should we first perform CT? J Neurol 2002; 249:129–137.

CAN I PERFORM LUMBAR PUNCTURE?
Although neuroimaging has become more common than lumbar puncture for neurologic diagnosis, cerebrospinal fluid sampling is still required for many work-ups. If the intracranial pressure is raised or if a mass is blocking the normal flow of cerebrospinal

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NOTES

Alisa D. Gean, MD, Christine Glastonbury, MBBS, and D. Christian Sonne, MD

Traumatic Brain Injury: Imaging Update 20041
Trauma continues to be the number one cause of death in individuals younger than 44 years old (1). In the United States alone, the cost of head trauma to the public is estimated to be $40 billion annually (2). During the past decade, considerable advances have been made in the field of neuroimaging of these patients. For computed tomography (CT), the acquisition time has decreased with the development of helical, and now multi–detector row, CT scanners. Magnetic resonance (MR) imaging has become more accessible, with faster acquisition times for pulse sequences, newer sequences with greater sensitivity for subtle abnormalities, and the potential for evaluating functional abnormalities subsequent to trauma. Indeed, apart from imaging acute subarachnoid hemorrhage and skull base fractures, MR imaging is superior to CT in the depiction of virtually all manifestations of traumatic brain injury. The lack of beam-hardening artifacts, combined with the ability to perform multiplanar reconstructions, allows MR detection of small extraaxial collections, which is particularly useful in identifying the imaging manifestations of child abuse or domestic violence (3). MR imaging can also be used to temporally stage intracranial hemorrhage, which may be important in diagnosing abuse because multiple sites of hemorrhage at different stages of evolution suggest recurrent trauma. In addition, the signal abnormality caused by prior hemorrhage is seen on MR images far longer than the attenuation abnormality seen on CT images, thus allowing detection of lesions caused by earlier abuse. Further, white matter shearing injuries often are identified only with MR imaging. The lack of ionizing radiation with MR imaging is an added bonus, particularly if serial studies are necessary. More recently, MR spectroscopy, MR diffusion imaging, and functional imaging techniques such as positron emission tomography (PET), single photon emission CT (SPECT), and functional MR imaging have yielded insights into traumatic brain injury. These modalities are likely to have a prognostic role in the care of trauma patients. In spite of these MR imaging advantages, CT continues to be the initial study of choice for evaluating acute traumatic brain injury. In this chapter, we review the current imaging approach and imaging findings in adult traumatic brain injury. We also discuss the newer techniques that may not necessarily alter the acute management of traumatic brain injury but are likely to lead us to a better understanding of its pathophysiology.

CLASSIFICATION OF TRAUMATIC BRAIN INJURY
There are several ways to classify traumatic brain injury (4,5). First, one can divide acute head injuries into primary and secondary lesions. A primary lesion occurs at the

RSNA Categorical Course in Diagnostic Radiology: Emergency Radiology 2004; pp 17–32.
1From the Department of Radiology, University of California, San Francisco, 1001 Potrero Ave, San Francisco, CA 94110 (e-mail: [email protected]).

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time of injury, as a direct result of the traumatic force (eg, cortical contusion, skull fracture, cranial nerve injury, white matter shearing injury). A secondary lesion generally occurs as a consequence of a primary lesion (eg, vasospasm, hypoxia, seizures, and intracranial hypertension from expanding mass lesions or edema). This division is clinically important because secondary injury is often preventable, whereas primary lesions have already occurred by the time the patient is first seen in the emergency department. This classification also underscores the fact that traumatic brain injury is not a static event but is, in fact, a progressive injury that is complex at the cellular level. Traumatic brain injury may also be classified according to lesion location (ie, intra- vs extraaxial), mechanism of injury (penetrating/open vs blunt/ closed), and clinical severity (minor, mild, moderate, or severe). Eighty percent of the injuries classified as traumatic brain injury consist of mild head injuries (defined as a score on the Glasgow coma scale ≥ 13), 10% are moderate (Glasgow coma score, 9–12), and another 10% are severe (Glasgow coma score, 3–8).

mas and demonstrate the extent of mass effect, cisternal compression, and/or hydrocephalus. CT allows optimal evaluation of the calvaria, skull base, and facial bones within the same scan or with the addition of thin sections through a defined region. The introduction of the multi–detector row CT scanner allows more rapid evaluation of the head, neck, and body of injured patients, with markedly reduced imaging times and reduced scanner heat loading. At San Francisco General Hospital, the routine CT protocol for evaluating acute craniocerebral trauma is performed without intravenous contrast material, and images are viewed at three window settings: bone (level, 500 HU; width, 2000 HU), brain (level, 40 HU; width, 80–100 HU), and blood (level, 75 HU; width, 150 HU). The digital lateral scout view, which serves as a “pseudo-skull film,” should always be assessed for a skull fracture or upper cervical spine fracture that may not be visible on the axial images. In rare situations, MR imaging may be recommended in the acute setting when neurologic findings remain unexplained after CT.

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WHO SHOULD BE IMAGED?
Emergency CT of the head in the setting of acute trauma is indicated for the following criteria: (a) Glasgow coma score less than 8 or a decrease of more than 3 in the Glasgow coma score, (b) persistent neurologic deficit, (c) anterograde amnesia, (d) unexplained pupillary inequality, (e) prolonged loss of consciousness for longer than 5 minutes, (f) depressed skull fracture, (g) penetrating injury, or (h) a bleeding diathesis or anticoagulant therapy (6). In the setting of minor head injury (defined as Glasgow coma score = 15, loss of consciousness, and normal findings on brief neurologic examination), less than 10% of the patients have positive CT findings, and less than 1% require neurosurgical intervention (7,8). Investigators in one study suggested that in this group of patients, the presence of one or more of the following seven clinical criteria requires CT scanning: (a) headache, (b) vomiting, (c) age older than 60 years, (d) drug or alcohol intoxication, (e) short-term memory deficits, (f) seizure, and (g) physical evidence of trauma above the clavicles (9).

Subacute or Chronic Traumatic Brain Injury Once the condition of the patient has stabilized, MR imaging may be indicated because of its superior sensitivity to the manifestations of traumatic brain injury. However, the widespread use of MR imaging in the acute setting is limited by the time involved in performing MR imaging coupled with a reduced ability to monitor a critically ill patient or one whose condition is potentially unstable. MR imaging is more useful in the subacute or chronic setting, in which its inherent increased sensitivity to cortical contusions and shear injuries is an important advantage over CT, particularly in the evaluation of a patient whose condition is clinically worse than would be predicted from the CT findings. On routine T2-weighted MR images, inflammatory cells, edema, secondary ischemia, and certain stages of blood products typically are hyperintense. Specific MR pulse sequences have been found to be more sensitive for the depiction of these injuries and are described in more detail subsequently. Functional MR imaging and nuclear medicine techniques such as PET and SPECT may also be helpful in the nonacute setting because they offer insights into the pathophysiologic function of trauma and the resultant functional deficits.

HOW SHOULD THEY BE IMAGED?
Acute Traumatic Brain Injury For the acutely injured patient, CT is the initial imaging modality of choice. Its widespread accessibility, speed, relatively low cost, compatibility with life-support devices, and CT angiographic capability make CT particularly attractive for the evaluation of the critically ill patient. Nonenhanced axial scans rapidly provide accurate localization of space-occupying hemato-

IMAGING CHOICES
Fluid-attenuated Inversion-Recovery Imaging The fluid-attenuated inversion-recovery (FLAIR) pulse sequence increases the conspicuity of focal areas of increased T2 signal abnormality by eliminating (or “nulling”) the high signal intensity of cerebrospinal fluid. Thus, focal bright abnormalities of the gray matter (eg, contusions) or white matter (eg, shear injuries) are more easily appreciated against adjacent dark

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Figure 1. Role of FLAIR imaging in traumatic brain injury. (a) Axial FLAIR MR image at level of centrum semiovale demonstrates a focal area of increased signal intensity within the left frontal subcortical white matter (white arrow), consistent with a shearing lesion. A focal T2 hyperintense lesion (black arrow) is seen involving the cortex of the right frontal lobe, consistent with a cortical contusion, and a linear focus of increased signal intensity (circle) is seen within a left parietal sulcus, consistent with subarachnoid hemorrhage. (b) On the corresponding axial T2-weighted spin-echo MR image, the lesions are much less conspicuous.

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cerebrospinal fluid spaces (Fig 1). Sagittal and coronal FLAIR images are particularly helpful in the appreciation of diffuse axonal injury involving the fornix and corpus callosum, two areas that are difficult to distinguish from adjacent cerebrospinal fluid on routine T2weighted images (10). The FLAIR sequence also has increased sensitivity for the presence of acute or subacute subarachnoid hemorrhage, which appears as areas of hyperintensity within the sulci and cisterns (11). An important pitfall with FLAIR imaging is paradoxical cerebrospinal fluid hyperintensity in the sulci and cisterns of ventilated patients who are receiving a high inspired oxygen fraction of more than 0.60 (12). In addition, cerebrospinal fluid flow artifacts in the basilar cisterns seen with FLAIR imaging can make evaluation of brainstem pathologic abnormalities somewhat difficult.

Susceptibility-weighted Imaging Several years ago, E. Mark Haacke, PhD, designed a high-spatial-resolution three-dimensional fast lowangle shot MR imaging technique that is extremely sensitive to susceptibility changes and, therefore, hemorrhage (15). This sequence has subsequently been termed susceptibility-weighted imaging. Researchers at Loma Linda University Medical Center have detected more shearing lesions with susceptibilityweighted imaging compared with conventional GRE imaging (16). Although susceptibility-weighted imaging is not yet widely available, it holds promise in the diagnosis of the extent of diffuse axonal injury, as well as providing valuable prognostic information. Specifically, preliminary findings have shown that the extent of hemorrhage is strongly correlated with the initial severity of injury and long-term outcome. Diffusion-weighted Imaging and Diffusion-Tensor Imaging A diffusion-weighted imaging sequence is a rapidly acquired MR sequence that detects alteration in the free mobility (or diffusibility) of water molecules through tissues (17). Reduction or restriction of normal diffusibility appears as increased signal intensity on diffusion-weighted MR images. The degree of diffusibility (or apparent diffusion coefficient) can be calculated and also represented in an image. When fluid motion is restricted, there is a low coefficient, and the region appears dark relative to normal tissues on the apparent diffusion coefficient map and bright on the diffusion-weighted MR image. Anisotropic diffusion (ie, preferential flow) is observed in normal myelinated white matter where diffusion is greatest parallel to the fibers and lowest perpendicular to them. Diffusion-weighted imaging in traumatic brain injury can be used to depict abnormalities even when conventional MR images are normal (18,19). In one

Gradient-recalled Echo Imaging The presence of ferromagnetic blood-breakdown products results in minute alterations in the local magnetic field of tissue. Gradient-recalled echo (GRE) sequences are exquisitely sensitive to this field alteration, showing a marked drop in signal intensity, and thus making tiny hemorrhagic lesions readily apparent (13). Chronic blood-degradation products such as hemosiderin and ferritin remain for months to years after injury, which makes the GRE sequence a powerful tool in the evaluation of remote injury long after abnormalities on T2-weighted and FLAIR images have resolved. Currently, the GRE sequence is the most widely used MR sequence to detect parenchymal hemorrhage, although conventional MR imaging is still relatively insensitive to microscopic changes of diffuse axonal injury (14). Unfortunately, because of susceptibility artifact adjacent to the paranasal sinuses and mastoid air cells, GRE images are somewhat limited in the evaluation of cortical contusions involving the inferior frontotemporal lobes.

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study comparing conventional MR imaging (T2weighted, FLAIR, and GRE imaging) with diffusionweighted imaging in traumatic brain injury, investigators found that diffusion-weighted imaging identified more shearing injuries but was less sensitive for hemorrhagic lesions than GRE (20). Diffusion-tensor imaging capitalizes on the principles of the apparent diffusion coefficient and diffusion-weighted imaging because water diffuses more freely along intact white matter fibers than across them (ie, white matter anisotropy). Directionally encoded color maps and three-dimensional tractography are performed to assess fiber integrity. In one study of patients with mild traumatic brain injury and normal CT images obtained acutely (within 24 hours of injury), investigators showed focal areas of reduced anisotropy, particularly in the corpus callosum and internal capsule (21). These abnormalities were less apparent at 1 month in the two patients who underwent repeat imaging. The role of diffusion-weighted imaging and diffusion-tensor imaging in the care of patients needs further research, but these techniques are providing insight into the pathophysiologic function of traumatic brain injury.

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verity of injury as measured with the Glasgow coma scale or length of posttraumatic amnesia (24).

3-T Imaging The relatively new 3-T imaging machines lack some of the advantages that have evolved for 1.5-T imaging, including larger bores and wider fields of view. Currently, claustrophobia and body size may limit how many patients can benefit from imaging in a 3-T machine. In addition, because 3-T images are more prone to susceptibility artifacts, surface contusions may be missed. Nevertheless, the increased signal-to-noise ratio inherent in a 3-T machine is roughly double that at 1.5 T, and this higher signalto-noise ratio can be used to reduce image acquisition time and/or improve resolution. Advanced applications, such as functional studies that are based on blood oxygen level–dependent contrast, MR spectroscopy, and diffusion-tensor imaging, are likely to benefit from 3 T. Further, new phased-array coil systems combined with “parallel imaging” technique offer the promise of even faster imaging, which is particularly helpful in the world of trauma imaging. SPECT Imaging Brain SPECT imaging is performed with a gamma camera 2 hours following the intravenous injection of technetium 99m hexamethylpropyleneamine oxime. The normal adult brain shows a bilateral symmetric tracer distribution, with higher activities in (a) temporal, parietal, and occipital cortices, (b) basal nuclei, (c) thalami, and (d) the cingulate gyrus. Focal or regional areas of hypoperfusion may be evident in traumatic brain injury and have been found to correlate better with the acute clinical status than with structural images (27). In another study, investigators found an association of acute areas of hypoperfusion with brain atrophy at 6 months, suggesting secondary ischemic damage (28). Normal findings on brain SPECT study have been found to be reliable in the exclusion of the clinical sequelae of mild head injury. PET Imaging Much of the work in brain PET imaging has centered on the cerebral utilization of glucose (as fluorine 18 fluorodeoxyglucose). There is an increase in glucose metabolism following severe traumatic brain injury, which reflects the injury-induced energy crisis, with an increase in glucose utilization, a decrease in oxidative metabolism, and an uncoupling of cerebral blood flow. Some investigators have suggested a greater sensitivity of PET for the detection of abnormalities in patients with mild and moderate traumatic brain injury with normal MR studies who have persistent cognitive or behavioral complaints (29). Because a nearby cyclotron is needed to generate the radioactivity, PET imaging is not widely available.

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Proton MR Spectroscopy Proton MR spectroscopy (1H MR spectroscopy) allows noninvasive in vivo assessment of brain tissue through the quantification of cerebral metabolites (22). The primary metabolites include N-acetylaspartate, creatine, choline, glutamate, and lactate. N-acetylaspartate is a cellular amino acid and a marker for neuronal and axonal integrity. It is quantified from a small selected volume of tissue (voxel) and is usually expressed as a ratio with respect to choline or creatine. Creatine, which produces a composite signal consisting predominantly of creatine and phosphocreatine, is considered to be a measure of cellular density and is especially high in glial cells (eg, posttraumatic gliosis). Increased choline signal may be due to myelin injury and accumulation of membrane myelin-degradation products. Tissue injury is seen as a reduction in the N-acetylaspartate–creatine ratio and may be seen in injured brain within 24 hours after traumatic brain injury (23). As is the case with the other previously mentioned MR techniques, MR spectroscopy is a tool that can be used to identify abnormalities in the setting of a normal conventional MR examination. Specifically, lactate, a by-product of anaerobic glycolysis, may be diffusely elevated in otherwise normal-appearing brain and has been correlated with a poor clinical outcome. In addition, MR spectroscopy can be used to depict an abnormality in otherwise normal-appearing white matter in the subacute and chronic period (24–26). A correlation has been shown between the reduction of N-acetylaspartate, the elevation of choline, and the se-

Figure 2. Role of scrutinizing the scout view. This 62-year-old woman with a prior history of traumatic brain injury came to the emergency department following a seizure. (a) Axial CT image at admission demonstrates left frontal posttraumatic encephalomalacia subjacent to a craniotomy. No acute intracranial abnormality is seen. (b) Lateral scout view, however, reveals a displaced fracture of cervical vertebra C2 (circle).

Traumatic Brain Injury

Functional MR Imaging In functional MR imaging, the activity of the brain is observed through the detection of an alteration in the ratio of cerebral blood deoxyhemoglobin to oxyhemoglobin in response to particular tasks (30). Neuronal activation within the cerebral cortex leads to an overcompensation of blood flow relative to the increase in oxygen consumption, which results in a decrease in capillary and venous deoxyhemoglobin concentrations. Because deoxyhemoglobin is an endogenous paramagnetic contrast agent, a decrease in its concentration is reflected as an increase in signal intensity on GRE images. To perform functional MR imaging, a high-resolution, three-dimensional, spoiled gradient-recalled acquisition in the steady state (steady-precession GRE) T1-weighted whole-brain study is initially performed. Then, for collection of functional MR imaging data, GRE echo-planar imaging is performed. The magnetic evoked responses to the stimulated tasks (eg, working memory) are subsequently coregistered with the highresolution MR images. Functional MR imaging research in traumatic brain injury has centered primarily on the assessment of deficits after mild traumatic brain injury, but functional MR imaging also offers promise in the understanding of the ability of the brain to reorganize after injury (14). Brain SPECT, PET, and functional MR imaging show promise, but many of the currently available data rely on small case series or case reports. Note that disturbances in cerebral blood flow can also be measured with CT perfusion or MR perfusion imaging.

EXTRAAXIAL INJURIES
Fractures This is CT territory. Although the primary role of CT in evaluating acute traumatic brain injury is to quickly identify a neurosurgical lesion, CT images optimally

demonstrate fractures of the calvaria, skull base, and facial skeleton. Newer three-dimensional technology, which allows remarkable display of complex fractures, is now expeditious and user friendly and is becoming more widely available. In addition to routine scrutiny of the axial sections, vertex and horizontal calvarial fractures should be sought on the sagittal scout image, where they may occasionally be better depicted. The presence of fluid levels in the sphenoid sinuses or fluid within the mastoid air cells and/or middle ear cavity should alert one to the possibility of a skull base or temporal bone fracture. An air-fluid level in a maxillary sinus raises concern about an orbital floor fracture (ie, facial trauma), although such an air-fluid level is also frequently noted in intubated patients as a result of retained sinus secretions. The 5-mm-thick sections through the brain for a routine head scan are insufficient to evaluate these areas further, and additional axial 1-mm sections through the skull base or orbits may be helpful. Indeed, 60% of temporal bone fractures may be missed on routine CT images (31). Air in the ipsilateral temporomandibular joint is a helpful secondary manifestation of temporal bone trauma (32). All fractures should be assessed for the presence of a scalp laceration and radiopaque foreign bodies, both of which increase the likelihood of infection. On the lowest axial section of a routine brain scan, the first cervical vertebra is often identified, and its relation to the dens should be noted. It is unusual, however, to see any further portion of the cervical spine, although the lateral scout image may again provide clues to cervical injury (Fig 2). For complete rapid evaluation of the cervical spine when radiographs are abnormal or insufficient, 1-mm helical sections should be obtained, ideally at the time of the brain study, and reformatted in the sagittal and coronal planes. In highrisk patients, radiographs are becoming obsolete.

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Epidural Hematoma The epidural hematoma occurs in the potential space located between the dura and the inner table of the skull (Fig 3) (4). More than 75% occur in the region of the temporal squamosa, and a vast majority of epidural hematomas are associated with an underlying skull fracture (6). The characteristic hyperattenuating biconvex contour of an epidural hematoma results from tense distention of the epidural space with arterial blood, typically from the middle meningeal artery. The venous epidural hematoma, as an exception to this, occurs at three classic sites: (a) in the posterior fossa from rupture of the torcular or the transverse sinus, (b) in the middle cranial fossa from disruption of the sphenoparietal sinus, and (c) at the vertex, with hemorrhage from the superior sagittal sinus (33). The latter lesion can be difficult to diagnose with axial CT images, although it can be readily confirmed with direct coronal images or coronal reconstructions of the axial data. Unlike the arterial epidural hematoma, the venous epidural hematoma rarely expands beyond the initial injury because of the lower pressure generated by venous extravasation. An important CT finding suggestive of rapid expansion of an arterial epidural hematoma is the presence of low-attenuation areas within an otherwise hyperattenuating hematoma. This appearance has been referred to as “the swirl sign” and is thought to represent active bleeding (Fig 4) (34,35). A heterogeneous epidural hematoma is an ominous finding that should be followed closely. Although differentiation from the subdural hematoma usually is straightforward, several imaging features are useful in making this distinction. First, because the dura is tightly adherent at sutures, it is uncommon for the epidural hematoma to cross a suture line (with the exception of the sagittal suture). Second, the epidural hematoma can cross the midline, in contrast to the subdural hematoma, which is limited by the falx. Third, the epidural hematoma is seen as a sharply localized lentiform mass, with the displaced dura seen on the MR image as an intact low-signal-intensity line between the brain and the epidural mass (Fig 5). This hypointense line is a valuable finding when the shape and location of the extraaxial collection are inconclusive. Fourth, the epidural hematoma can extend from the supratentorial to the infratentorial space, whereas the subdural hematoma is limited by the tentorium. Fifth, 99% of epidural hematomas are located at the coup site, whereas the subdural hematoma is usually found at the contrecoup site. Finally, because the venous sinuses are composed of both dural layers, their displacement confirms an epidural mass. The clinical manifestation of the epidural hematoma is governed by the mass effect produced and by

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Figure 3. Subdural hematoma versus epidural hematoma. Coronal schematic through the level of superior sagittal sinus (S) illustrates the relationship of a subdural hematoma and an epidural hematoma to normal meningeal anatomic structures. Note that dura is a bilayered structure and that the layers split to form dural venous sinuses and falx. The epidural hematoma (EDH) is located above the outer dural layer (ie, periosteum). The subdural hematoma (SDH) is located beneath the inner dural layer. (Reprinted, with permission, from reference 4.)

the associated neuronal injuries. Brain injury, however, is much less common with an epidural hematoma than with a subdural hematoma. The classic manifestation is that of a patient who experiences a lucid conscious interval that is soon followed by neurologic deterioration. The lucid interval is attributed to the absence of underlying brain injury, with subsequent enlargement of the epidural hematoma resulting in progressive neurologic decline. However, this classic manifestation is seen in only 25% of the patients (36,37).

Subdural Hematoma The subdural hematoma is a serosanguineous fluid collection located between the arachnoid mater and the dura. Subdural hematoma is seen in 10%–20% of patients with closed head trauma and is the most common operable intracranial hematoma (38). The subdural hematoma is usually due to laceration of the bridging cortical veins (Fig 6). An increased incidence of subdural hematoma is seen in elderly patients because cerebral atrophy allows increased relative motion between the brain parenchyma and calvaria and because the atrophic brain is less capable of tamponade of a small subdural hematoma. The degree of brain distortion in these individuals, however, may be relatively minor because of the abundant extracerebral space (39). Rapid decompression of obstructive hydrocephalus can also result in a subdural hematoma if the brain surface recedes from the dura faster than the parenchyma reexpands after having been compressed by the distended ventricles. Other causes of a subdural hematoma include injury to pial vessels, pacchionian granulations (arachnoid granulations), or the great veins. The acute subdural hematoma is associated with a skull fracture in less than 50% of the cases and is typically a contrecoup lesion. Most subdural hemato-

Figure 4. Active bleeding within an epidural hematoma. (a) Admission axial CT image and (b) 3-hour follow-up axial CT image demonstrate marked interval enlargement of a right temporal epidural hematoma. Note the intrinsic hypoattenuation that represents active bleeding (arrow); the high-attenuation area represents clotted blood. Also note the marked increase in scalp soft-tissue swelling (double-headed arrow) at the coup site.

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Figure 5. Venous epidural hematoma (displaced dura). Intermediate-weighted axial MR image demonstrates a thin black line (arrow) at the medial margin of the hyperintense collection. This line represents the displaced dura, and its presence confirms the epidural location of lesion. Current epidural hematoma was secondary to interruption of the right transverse sinus. Whether venous or arterial, all epidural hematomas show displaced dura at MR imaging. A contrecoup left orbitofrontal contusion (circle) is also noted.

mas are semisolid within 1–10 days and thus require a craniotomy, rather than burr hole evacuation. With time, the subdural hematoma organizes via activated fibroblasts and blood vessels that invade the hematoma from the dura. These vessels are fragile and are prone to episodes of repeat bleeding (hence, the problem of the “chronic recurrent subdural hematoma”). The CT appearance of the typical acute subdural hematoma consists of a hyperattenuating, homogeneous, crescentic contrecoup lesion that frequently tracks along the entire hemisphere. The degree of mass effect seen in association with the subdural hematoma often appears excessive for the size of the hematoma because of the presence of underlying parenchymal injury. If appropriate midline shift is not seen, then a contralateral mass lesion should be suspected. An “atypical” acute subdural hematoma tends to be less crescentic in shape, is heterogeneous

in attenuation, and is associated with greater mass effect than expected for the size of the collection (Fig 7). The heterogeneity represents recent unclotted hemorrhage, anemia, a paucity of hemoglobin within the hematoma, or admixing with cerebrospinal fluid from torn arachnoid mater (4,40). In contrast to a heterogeneous acute subdural hematoma, a heterogeneous chronic subdural hematoma shows fluid-fluid levels, septa, and loculations, indicating its chronicity and its fragile vascular lining membrane. The frequent absence of associated intraaxial injury is an additional imaging finding that helps differentiate the heterogeneous acute subdural hematoma from repeat bleeding into a preexisting chronic subdural hematoma. As mentioned previously, the subdural hematoma (unlike the epidural hematoma) crosses calvarial sutures and can extend along the tentorium and the falx cerebri. The subdural hematoma does not, however, typically travel from the supratentorial space into the posterior fossa. A vast majority of subdural hematomas are supratentorial in location. The posterior fossa subdural hematoma is uncommon in adults, probably because of the greater restriction of rotational movement of the cerebellum and diminished shearing stress on superficial veins. Although the shape of the typical acute subdural hematoma tends to be crescentic, the formation of dural adhesions (eg, following trauma or infection) can result in a more convex collection, thus mimicking the epidural hematoma. This is particularly challenging in the elderly patient. There are two relatively common pitfalls in the CT evaluation of the subdural hematoma (Fig 8). The first pitfall occurs with a thin-convexity hematoma, which can be difficult to appreciate adjacent to the hyperattenuating skull unless the CT image is viewed with wide windows (so-called blood windows). The introduction of a picture archiving and communications

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system allows the film reviewer to adjust the window settings readily. The second pitfall in the CT evaluation of the subdural hematoma is subacute bleeding that has become isoattenuating with adjacent brain. Recognition of secondary signs, such as displacement of gray matter, white matter buckling, mass effect, and midline shift, is helpful, although it can be difficult when the subdural hematoma is bilateral. Contrast opacification of the displaced cortical veins (or MR imaging) can provide confirmatory evidence of the isoattenuating subdural hematoma (41–43). The chronic subdural hematoma is frequently bilateral and, in the absence of recurrent hemorrhage, may appear uniformly low in attenuation, thus mimicking a subdural hygroma (Fig 9) or even cerebral atrophy. The presence of mass effect, however, should exclude the latter.

Figure 6. Bridging cortical veins. (a) Coronal and (b) axial contrastenhanced T1weighted MR images demonstrate enhancement of several veins (arrows) traversing the subdural and subarachnoid space. These vessels are the ones that are torn during sudden acceleration and deceleration, thus leading to subdural hematoma.

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Subdural Hygroma The traumatic subdural hygroma is thought to arise from cerebrospinal fluid leakage and a “one-way” rent in the arachnoid mater. The traumatic subdural hygroma generally develops more than 3 days after traumatic brain injury. These fluid collections have cerebrospinal fluid attenuation on CT images and may be indistinguishable from a chronic subdural hematoma (Fig 9). A comparison study can be invaluable in these cases. The distinction can sometimes be made by evaluating the attenuation of the collection (Hounsfield units), which is equivalent to that of cerebrospinal fluid for the subdural hygroma. MR imaging is capable of clarifying any ongoing confusion because it is more sensitive than CT to the presence of blood products in a subdural hematoma. On MR images, the subdural hygroma follows cerebrospinal fluid in signal intensity, whereas a chronic subdural hematoma is of higher signal intensity with all pulse sequences. The signs and symptoms of a subdural hygroma are sometimes indistinguishable from those of a subacute subdural hematoma. Most patients, however, are asymptomatic, and their condition is managed conservatively (44). In 85% of the patients with clinical symptoms referable to a subdural hygroma, the condition responds to burr hole evacuation. Subarachnoid Hemorrhage The most common cause of subarachnoid hemorrhage is trauma. The blood can arise from direct pial injury, extension from an underlying parenchymal contusion, or contiguous extension of intraventricular hemorrhage. The interpeduncular cistern and sylvian fissures are two common sites for the accumulation of traumatic subarachnoid hemorrhage (Fig 10). Therefore, establishing a clinical history can be crucial to avoid mistaking traumatic subarachnoid hemorrhage for a ruptured cerebral aneurysm (45,46). Although uncommon, aneurysmal rupture

Figure 7. Acute "atypical" subdural hematoma. This left holohemispheric subdural hematoma is termed atypical because of its heterogeneity, its disproportionate mass effect for its size, and its slightly convex shape. Atypical subdural hematoma has a particularly ominous prognosis. Another highly unusual finding in this case is brain injury at the coup site (note left-sided scalp soft-tissue swelling). Extensive subarachnoid blood overlying left hemisphere is an additional poor prognostic sign.

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Figure 8. Two potential pitfalls in CT evaluation of subdural hematoma. (a) Coronal T1weighted MR image demonstrates thin linear hyperintense lesions (arrows) beneath left occipital lobe, as well as lateral to right cerebellar hemisphere, consistent with small subacute subdural hemorrhages. Because of the small size of the collection and obscuration by beam-hardening artifact of the calvaria, the corresponding CT study was interpreted as normal. (b) Nonenhanced axial CT image of a different patient shows bilateral medial displacement of cortical surface (double-headed arrows) and "white matter buckling," consistent with bilateral isodense subdural hematoma.

Traumatic Brain Injury

Figure 9. Acute subdural hygroma. (a) Axial CT image on admission shows left parieto-occipital scalp soft-tissue swelling (arrow) and no intracranial abnormality. (b) Three-day follow-up axial CT image demonstrates interval development of small bifrontal low-attenuation subdural collections. If prior CT images were not available, the appearance could be confused with chronic subdural hematomas.

Figure 10. Traumatic subarachnoid hemorrhage (two common locations). (a) Axial CT image shows small amount of hyperattenuating blood (arrow) within the interpeduncular fossa. Brain is otherwise normal. (b) Axial CT image from another patient shows subarachnoid hemorrhage within the right sylvian fissure. Note characteristic contrecoup location of subarachnoid hemorrhage, identified opposite the scalp injury (arrow). In these two cases, the cause of the hemorrhage is likely secondary to shearing of perimesencephalic and insular veins, respectively.

may cause the trauma, resulting in imaging features of both conditions. On CT images, acute subarachnoid hemorrhage is seen as abnormal linear areas of high attenuation interdigitating between sulci and fissures. As is the case with

the majority of traumatic lesions, the largest amount of subarachnoid hemorrhage is usually located at the contrecoup site. With time, the blood becomes isoattenuating with brain and ultimately resolves. In the subacute and chronic phase, MR imaging is still able to

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Figure 11. Subacute traumatic subarachnoid hemorrhage. Coronal FLAIR MR image demonstrates horizontal linear hyperintensity (arrow) within several left temporal-occipital sulci. Corresponding CT study was normal.

depict subtle residual blood, particularly with FLAIR and GRE sequences (Fig 11). Subarachnoid hemorrhage is toxic to the underlying cortex and can also interfere with normal cerebrospinal fluid resorption at the level of the pacchionian granulations, thus leading to communicating hydrocephalus.

Intraventricular Hemorrhage Traumatic intraventricular hemorrhage can occur by one of three methods: (a) contiguous extension from a parenchymal hematoma, (b) shearing of subependymal veins that line the ventricular cavities, or (c) retrograde reflux of subarachnoid hemorrhage through the foramina of the fourth ventricle. Traumatic intraventricular hemorrhage may be isolated, but it is usually associated with superficial contusions and subarachnoid hemorrhage. Subtle intraventricular hemorrhage can be detected by the appearance of a fluid-fluid level layering dependently within the occipital horns of the lateral ventricles (so-called hematocrit effect), because fibrinolytic activators within cerebrospinal fluid inhibit clotting (38). In some cases, the choroid plexus may act as a nidus for the blood to clot and form a ventricular cast or tumefactive blood clot (Fig 12). In the absence of recurrent hemorrhage, the blood rarely persists for more than 1–2 weeks. Large amounts of intraventricular blood may impede cerebrospinal fluid flow and result in noncommunicating hydrocephalus.

Figure 12. Isolated intraventricular hemorrhage. (a) Axial CT image demonstrates hyperattenuating blood layering within the occipital horn of the left lateral ventricle, producing the socalled hematocrit effect (arrow). Image is otherwise normal. (b) T1weighted axial MR image of a different patient is remarkable for small round hyperintense nodules (arrows) located within anterior right temporal horn and dependently within left occipital horn, consistent with tumefactive clots. In both of these cases, intraventricular hemorrhage is likely secondary to shearing of subependymal veins.

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INTRAAXIAL INJURIES
Traumatic Dysautoregulation With normal circumstances, the amount of cerebral blood flow to the brain remains constant despite vacillations in blood pressure. This ability to regulate blood flow, which is termed autoregulation, stems from the unique capacity of the cerebral vasculature to dilate in response to a decrease in blood pressure and constrict in response to an increase in blood pressure. The loss of this ability, or dysautoregulation, is a wellrecognized sequela of traumatic brain injury that is particularly common in younger individuals. In the early stages of dysautoregulation, the hyperemic swelling appears on CT and MR images as ill-defined focal

Figure 13. Dysautoregulation. Axial CT image shows asymmetry of the sylvian fissure and temporal sulci, with preservation of graywhite differentiation. In addition to hyperemic swelling of right temporal lobe, the differential diagnosis would include isodense subarachnoid hemorrhage overlying right hemisphere, meningitis, a small right subdural hematoma, and asymmetric atrophy involving left hemisphere.

or diffuse sulcal effacement with preservation of the gray-white differentiation (Fig 13). With increasing severity, the hyperemia may progress to cerebral edema.

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Cortical Contusion Cortical contusions are hemorrhagic parenchymal “bruises.” They are peripheral lesions, involving the

Figure 14. Cortical contusion. (a) Parasagittal T1-weighted MR image demonstrates multiple wedge-shaped areas of hyperintensity (arrows), consistent with subacute cortical contusions. Lesions involve the surface of brain. They are wedge-shaped, with their base abutting calvarial surface and their apex pointing centrally. (b) T2-weighted axial MR image shows well-defined wedgeshaped areas of hyperintensity (arrow) within left temporal cortex, consistent with remote trauma (posttraumatic encephalomalacia). Without a proper clinical history, lesion could be mistaken for remote ischemic infarction.

Traumatic Brain Injury

Figure 15. Coup-contrecoup mechanism. On impact, a decrease in parenchymal pressure occurs within the frontal lobes as they are transiently displaced away from skull. Frontal bridging cortical veins are also lacerated at this time. In contrast, the occipital lobes experience momentary increase in pressure as they are thrust against the coup site. Negative pressure gradients are toxic to the brain. Resultant injury classically consists of scalp swelling, skull fracture, and epidural hematoma at the coup site, with a contrecoup subdural hematoma and intraaxial hemorrhage. (Reprinted, with permission, from reference 4.)

cation makes detection with CT difficult, particularly when patient motion occurs and there is streak artifact. MR imaging offers an important advantage in the detection of these often subtle injuries because the calvaria does not distort the signal. MR imaging is also capable of providing images in multiple planes, obviating partial volume artifacts from one plane alone. On T2-weighted MR images, contusions are seen as areas of increased signal intensity (depending on the extent of hemorrhage) and are particularly conspicuous with the FLAIR sequence. Although currently the most sensitive MR techniques for blood products are multiplanar gradient-recalled imaging and susceptibilityweighted MR imaging, susceptibility artifact from the skull limits evaluation of surface contusions. With time, the lesion shrinks into a gliotic scar. An old contusion is seen as a wedge-shaped area of peripheral encephalomalacia, with the apex of the wedge pointing centrally and the broad base facing the irregular surface of the skull. In the chronic stage, this triangular shape can resemble a remote ischemic infarct (Fig 14).

Figure 16. Coupcontrecoup injury. Axial CT image shows epidural hematoma and scalp injury at the coup site and subdural hematoma and intraaxial injury at the contrecoup site. Extent of midline shift is less because of the balanced mass effect from the two lesions.

gyral crests, particularly those in contact with irregular contours of the skull (eg, the orbital roof, petrous ridge, and sphenoid ridge) (38,40). This superficial lo-

Cerebral Hematoma Unlike the cerebral contusion, the cerebral hematoma is located deeper in the brain. In the acute setting, the hematoma is hyperattenuating on CT images. Within days, a peripheral rim of low attenuation is seen, consistent with edema and pressure necrosis. In the subacute phase, ring enhancement can be noted with either CT or MR imaging because of the proliferation of new capillaries lacking a complete bloodbrain barrier. Indeed, in the absence of prior studies or an accurate clinical history, it may not be possible to differentiate a hematoma with ring enhancement from an abscess, neoplasm, or infarct. In the chronic phase, a smaller area of nonenhancing encephalomalacia results, with compensatory dilatation of the ipsilateral ventricle and sulci. On CT images, this appearance is nonspecific, but the presence of blood products can be detectable with MR imaging for years. The “coup-contrecoup” mechanism refers to the fact that the moving skull comes to an abrupt stop while the brain continues to move for another brief moment (Figs 15, 16) (4,47–50). The portion of the

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Figure 17. Delayed traumatic hematoma. (a) Admission axial CT image reveals effacement of the right occipital horn but no definite intraaxial hemorrhage. (b) Six-hour follow-up CT image shows interval development of a large right temporal hematoma with a fluid-fluid level (arrow).

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brain opposite the impact site initially pulls away from the dura but on recoil strikes the dura with force. Injury at the impact site is termed the coup injury, whereas that on the opposite side is termed the contrecoup injury. The coup site is identified by the presence of a skull fracture, epidural hematoma, or scalp injury. Although both coup and contrecoup lesions can result in hemorrhage, it is far more common at the contrecoup site. Interestingly, contrecoup lesions are rarely seen in the cerebellum or occipital lobes after a frontal impact because of the thick smooth inner surface of the occipital bone and because the falx and tentorium act to stabilize the adjacent brain parenchyma. Occasionally, patients with head injuries develop a delayed hematoma in an area previously shown to be nonhemorrhagic on CT or MR images (Fig 17) (51– 53). Such hematomas tend to be lobar, are frequently multiple, and often occur in areas that demonstrated contusion on initial images. Most delayed hematomas occur within 2–4 days of injury and are associated with a poor prognosis. The pathogenesis of these lesions is controversial, but it probably is related to the fact that ischemic tissue is extremely vulnerable to reperfusion hemorrhage. Possible causes include vasospasm with subsequent vasodilation, hypotension with subsequent hypertension, and a preexisting or acquired coagulopathy. The attenuation of acute hemorrhage on CT images is related to the globin moiety of hemoglobin (not to the iron component). Acute blood normally has an attenuation value of 50–70 HU, whereas brain parenchyma measures 20–30 HU. Acute hematomas in anemic patients (hemoglobin level, <11 mg/dL) may thus appear isoattenuating with brain parenchyma. The attenuation of an acute clot may increase in the first few days as the clot retracts. Subsequent proteolysis results in a decrease in attenuation. The MR imaging features of hemorrhage are influenced by the fol-

Figure 18. Diffuse axonal injury. (a) Conventional T2-weighted axial spin-echo MR image demonstrates several subtle punctate foci of hypointensity (arrows) within the frontal subcortical white matter. (b) Coronal GRE MR image of same patient better demonstrates the extent of signal abnormality. This loss of signal is due to the ferromagnetic effect of blood products such as hemosiderin and ferritin.

lowing: (a) location (subarachnoid or subdural or intraaxial), (b) field strength (magnetic susceptibility is proportional to field strength [2]), (c) pulse sequence, (d) lesion size, (e) clot retraction, (f) red blood cell integrity, (g) the presence or absence of continued bleeding, (h) hemoglobin oxygenation state, (i) local tissue pH, and (j) oxygen tension. The details of these factors are complex and beyond the scope of this chapter. Cerebral edema, seen as a pe-

Figure 19. Diffuse axonal injury of the corpus callosum. (a) T1-weighted midsagittal MR image demonstrates a slightly prominent splenium of the corpus callosum with minimal hypointensity (arrow). (b) Corresponding T2-weighted midsagittal MR image clearly shows the central splenial signal abnormality, with subtle sparing of the callosal surface (arrow).

Traumatic Brain Injury

Figure 20. There are currently a number of MR pulse sequences that are used to identify diffuse axonal injury (DAI). (See text for advantages and disadvantages.) ADC = apparent diffusion coefficient map, DTI = diffusion-tensor imaging, DWI = diffusionweighted imaging, MPGR = multiplanar gradient-recalled imaging, SWI = susceptibilityweighted imaging.

ripheral zone of low attenuation surrounding the hemorrhage, appears at about 8 hours and is maximal 3–5 days after the initial injury. The degree of edema is a function of both the extent of the initial injury and the state of hydration of the patient.

Diffuse Axonal Injury Although diffuse axonal injury is a nonsurgical injury, its presence has long-term implications with respect to patient prognosis. It is well accepted that CT remains limited in the detection of diffuse axonal injury, with images frequently being discordant with the clinical status of the patient (14,54–58). In the acute phase, discrete small (usually <1-cm) foci of hypoattenuation may be depicted in the white matter at the gray-white junction. Acute hemorrhagic shear injuries are more easily identified, but brainstem and posterior fossa diffuse axonal injury often remains elusive

because of beam-hardening artifact. In addition, the hemorrhage may resolve quickly and not be visible on the follow-up images. Because of the relatively poor sensitivity of CT in the detection of diffuse axonal injury, MR imaging may be helpful in the first 2 weeks to better evaluate the extent of injury. GRE and susceptibility-weighted MR images are particularly helpful because of their enhanced sensitivity to the presence of blood products (Fig 18) (16,59,60). It is important to remember that fast spin-echo imaging is less sensitive to diffuse axonal injury (and to hemorrhage, in general) than is conventional spin-echo MR imaging. The most common shearing lesions are seen in the frontal parasagittal white matter. With increasing shearing force, the corpus callosum, typically the splenium, is injured (Figs 19, 20) (61). The most severe shearing forces result in dorsolateral brainstem injury

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(ie, “the deeper the lesion location, the more severe the injury”). These three locations (parasagittal white matter, corpus callosum, and dorsolateral brainstem) are called the shear injury triad. Acute nonhemorrhagic lesions of diffuse axonal injury are bright on diffusion-weighted images, with a corresponding decrease in apparent diffusion coefficient (19). As mentioned previously, diffusion-tensor imaging is being investigated as a means to detect more subtle axonal injury that can reflect dysfunction of white matter tracts. Injury disrupts the preferential mobility (anisotropy) of water along the fiber tracts, and the findings can be displayed quantitatively in the form of fractional anisotropy or with visual depiction on color tensor maps. Findings from diffusion-tensor imaging may be abnormal with normal MR and CT images. After about 3 weeks, diffuse axonal injury is often associated with atrophic enlargement of the ventricles and sulci.

Figure 21. Brainstem contusion. Axial CT image through the midbrain shows dorsolateral hyperattenuation within the left tectal plate, consistent with a focal contusion secondary to direct impact with the rigid dural margin of the tentorium. Brain is otherwise unremarkable.

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Penetrating Injuries More than 80% of the gunshot wounds to the head penetrate the skull, and most of these patients die. Brainstem involvement is uniformly fatal, as is bihemispheric injury unless the injury is limited to the cerebral surface. Forty percent of the surviving patients suffer posttraumatic epilepsy. The bullet trajectory can be determined by examining the calvaria and adjacent brain parenchyma (62–64). At the entry site, the inner table of the skull is beveled, whereas at the exit site (usually larger), the outer table of the skull is beveled. The exit site also tends to show greater bone destruction. Highvelocity bullets cause more extensive direct tissue laceration and can result in severe contusion injuries at remote locations because of transmission of radial shock waves. Penetrating and perforating injuries may be complicated by fragments of bone or scalp within the brain. It is the organic material, rather than the inorganic metal fragments, that accounts for the majority of infections after penetrating injuries. Traumatic Brainstem Injury Evaluating the brainstem and posterior fossa with CT is particularly difficult because of beam-hardening artifact from bone. Indeed, CT depicts only 20% of the acute brainstem injuries that are identified subsequently with MR imaging. Nevertheless, in the acute setting, CT remains the imaging modality of choice because the brainstem contusion and shearing injuries are managed conservatively. MR imaging may be warranted in the subacute setting to investigate unexplained neurologic deficits and to determine prognosis. In addition, the ability to better image these areas with MR has furthered our understanding of traumatic brain injury. Primary injuries to the brainstem have a predilection for the dorsolateral mesencephalon and include direct contusions and shear injuries (Fig 21) (65–70). Contusions may be isolated and typically result from

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the impact of the brainstem against the tentorium. Contusions always extend to the brainstem surface. Shearing injuries may occasionally be difficult to distinguish from contusions, but shearing injuries often do not extend to the brainstem surface and are almost always associated with supratentorial diffuse axonal injury. The secondary types of brainstem injury include those resulting from hypoxic-ischemic damage or from abrupt downward herniation of the brainstem (Duret hemorrhage) (Fig 22). In the latter injury, brainstem descent causes stretching and shearing of perforating basilar arterial branches, which produces hemorrhage within the brainstem. The Duret hemorrhage also can arise either from vessel wall rupture caused by hypoxic damage or from venous infarction. In contrast to the brainstem shearing injury and the direct brainstem contusion, both of which have a predilection for the dorsolateral brainstem, the Duret hemorrhage typically is seen in the central pons or midbrain. Duret hemorrhage is associated with an extremely poor prognosis. Uncommon causes of traumatic brainstem injury include the pontomedullary rent and hypoxic-ischemic injury. In summary, although CT remains the mainstay for assessment of patients with acute traumatic brain injury, MR imaging has a greater sensitivity for the detection of pathologic findings. MR imaging is currently used primarily for patients with unexplained brain dysfunction after traumatic brain injury. The use of specialized MR imaging techniques, such as diffusion-tensor imaging, diffusion-weighted imaging, susceptibilityweighted imaging, and MR spectroscopy, and functional studies such as functional MR imaging, PET, and SPECT may not yet alter immediate surgical care, but these techniques do increase our understanding of the pathophysiology of trauma and of long-term neurologic disability. This, in turn, may allow more accurate prediction of patient outcome, may play a role in clinical drug trials, and may alter the direction of treatment and rehabilitation of the patient with head injury.

Figure 22. Duret hemorrhage. (a) Preoperative axial CT image demonstrates a right temporal extraaxial collection (arrow) and a normal brainstem. Imaging manifestations of downward herniation were noted on more cranially located CT images. (b) Postoperative axial CT image shows hemorrhage within the central pons.

Traumatic Brain Injury

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Lacey Washington, MD

CT for Thromboembolic Disease: Protocols, Interpretation, and Pitfalls1
Pulmonary embolism (PE) is, unfortunately, a common event. Approximately 600.000 episodes of PE occur each year in the United States, and it is considered the third most common acute cardiovascular event, after cardiac ischemia and stroke. However, PE is a much more complex diagnostic challenge than ischemic heart disease and stroke. Complicating its diagnosis is the fact that PE is really only one manifestation of a larger disease entity, venous thromboembolism, which also includes deep venous thrombosis. Until recently, the diagnosis of PE was made predominantly with pulmonary arteriography or ventilation-perfusion scintigraphy (ventilation-perfusion scans). Important limitations to each of these techniques precluded diagnosis of PE in many patients. The diagnosis of deep venous thrombosis was approached separately, and many techniques have been used in its diagnosis, including physical examination, impedance plethysmography, contrast venography, and ultrasonography (US). Each of these techniques has its own limitations. Since the early 1990s, a new approach to the diagnosis of venous thromboembolism has developed, as computed tomographic (CT) pulmonary arteriography was added to the armamentarium of diagnostic techniques for PE. Multi–detector row CT has since increased the image quality and popularity of this technique. CT pulmonary arteriography is an increasingly common examination, as everyone who cares for patients in emergency settings knows. To improve the efficiency of diagnosis of the whole spectrum of venous thromboembolism, a second CT technique has also been developed: delayed CT through the deep venous system of the pelvis and lower extremities, or “indirect CT venography.” CT pulmonary arteriography and CT venography are, in some ways, straightforward techniques, and they appeal to clinicians because the direct visualization of clot within a vessel is immediately comprehensible. However, there are some challenges involved with using and refining these techniques. It is important to be familiar with data concerning sensitivity and specificity of CT pulmonary arteriography. These data help to shape an imaging algorithm for patients suspected of having venous thromboembolism, placing CT pulmonary arteriography in an appropriate context. An approach to reviewing images must be selected—an increasing challenge given the large data sets now being produced with multi–detector row CT scanners. It is important for readers to be aware of the findings of acute and chronic thromboembolic disease and to be aware of artifacts and other findings that may simulate clots, both in the pulmonary vessels and in the lower extremities. Distinctive features of chronic PE and deep
RSNA Categorical Course in Diagnostic Radiology: Emergency Radiology 2004; pp 33–45.
1From the Department of Radiology, Medical College of Wisconsin, 9200 W Wisconsin Ave, Milwaukee, WI 53226-3596 (e-mail: [email protected]).

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venous thrombosis must also be recognized, so that patients do not receive excessive or unnecessary treatment.

SENSITIVITY AND SPECIFICITY OF CT TECHNIQUES
CT Pulmonary Arteriography CT evaluation for PE has become popular rapidly for a number of reasons: CT is readily available, the images are easily understood, and alternate diagnoses are commonly made at CT in patients without evident thromboembolic disease (1,2). Some authors, however, continue to argue that the popularity of CT pulmonary arteriography is not well justified by data. There are two substantial reasons for the difficulty in proving the validity of CT techniques: One is the lack of a robust reference standard; the second is the rapid evolution of CT technology. The only true reference standard for the diagnosis of PE is autopsy. For obvious reasons, it is not possible to validate CT with autopsy in any large series of human patients. Autopsy data have other less obvious limitations. The rate of detection of PE with autopsy depends to a large extent on the amount of attention given to small vessels. If careful attention is given to the smallest vessels, as many as 90% of patients may have emboli, either acute or chronic (3). The lung is thought to act normally as a filter, preventing emboli from reaching the systemic arterial circulation, and it is unlikely that emboli are contributing factors in 90% of all deaths. In any individual case, it is difficult to assess the contribution of an embolus to the death of a patient. In addition, because this level of attention is seldom given to the pulmonary vessels, the use of autopsy to exclude PE as a contributing factor in the death of any given patient is problematic—small emboli may be present but not found. In most studies of CT pulmonary arteriography, investigators have compared CT pulmonary arteriographic results with pulmonary angiography, considering angiography to be the reference standard because it is the existing validated imaging technique. Pulmonary angiography is accepted because it has been shown to be safe to withhold anticoagulation therapy in patients with negative pulmonary angiography. However, the results of studies in the 1990s have suggested that arteriography has its own limitations. Interreader variability for arteriography is substantial (4,5). In at least one study, investigators have attempted to approach the problem of anatomic truth. In a study with an animal model, a methacrylate cast of pulmonary vessels was analyzed after the animals were sacrificed, and both CT and angiographic results were compared with the autopsy results. CT was as sensitive as angiography and had a comparable positive predictive value (6). Interestingly, if angiography was assumed to be the reference standard, the appar-

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ent sensitivity of CT dropped to values similar to those reported in clinical trials in humans that use arteriography as a reference standard. The second problem with assessing CT has been the rapid evolution of technology. In multiple studies, investigators have compared single-detector helical CT with pulmonary angiography. Early studies of the sensitivity of CT with respect to angiography reported sensitivities of single-detector helical CT for PE in the range of 90%, when investigators were predominantly looking at segmental or more central emboli (7–9). The results of occasional studies have shown lower sensitivities, usually because of a decreased sensitivity for small subsegmental emboli (10). In relatively few studies have investigators even attempted to assess the accuracy of newer multi–detector row CT scanners (11– 13). Increasingly short scan times with multi–detector row CT scanners allow thin-collimation images to be obtained through the entire volume of the lungs. Images with thinner collimation result in higher detection rates of PE and in improved interreader agreement (14). As expected, two–detector row CT is more accurate than single–detector row CT when each is compared with angiography (12), and the results of studies and subjective opinion suggest that increasing the number of CT detector rows, with the corresponding decrease in scan times, will further increase accuracy. Ironically, while research is attempting to determine whether multi–detector row CT can adequately detect small subsegmental emboli, actual practice seems to be faced with the opposite problem: how to care for patients with small, isolated subsegmental pulmonary emboli found at multi–detector row CT (Fig 1). The overall clinical importance of subsegmental emboli is controversial, and the prevalence of isolated subsegmental emboli differs in various studies, probably reflecting differences among study populations. In studies that used pulmonary angiography, isolated subsegmental PE appears to occur in less than 10% of patients (4,12,15). Some of the emboli now found with multi– detector row CT clearly would have been undetected with previous imaging modalities, particularly in patients with extensive lung disease. Because such patients would have had other possible explanations for their symptoms, clinicians would have been reluctant to subject such patients to angiography, and scintigraphy is unlikely to yield diagnostic results in patients with substantial lung disease. As a result, there are no good historical data about the importance of these emboli. Patients with good cardiopulmonary reserve and indeterminate ventilation-perfusion scans who have no evidence of deep venous thrombosis on serial noninvasive studies of the lower extremities have clinically good outcomes (16). Certainly, some of these patients can be assumed to have PE. It is therefore clear that in the absence of deep venous thrombosis, patients with good cardiopulmonary reserve tolerate

Figure 1. Isolated subsegmental acute PE. (a, b) Axial CT images show complete filling defect in subsegmental right lower lobe pulmonary artery (arrow) that extends for several contiguous images.

CT for Thromboembolic Disease

subsegmental emboli. Unfortunately, this result does not apply to patients with poor cardiopulmonary reserve, even in the absence of deep venous thrombosis. It also does not apply to patients with a single negative lower extremity US study and cannot be readily extrapolated to CT venographic results. At this time, the Prospective Investigation of Pulmonary Embolism Diagnosis (PIOPED) II trial is under way in an attempt to meet the need for large-scale prospective studies of CT pulmonary arteriography, with preliminary results soon to be presented. In addition, the results of numerous outcome studies have shown low rates of morbidity and mortality from subsequent PE in patients with no evidence of PE at CT pulmonary arteriography who did not receive anticoagulant therapy (17–24). Because of doubts about the accuracy of angiography, these outcome studies may eventually become more important than those that use angiography as a reference standard.

vantage of CT venography over US is that the pelvic veins and profunda femoris veins are also imaged. The findings from some magnetic resonance (MR) venographic studies have shown a higher than previously suspected incidence of isolated pelvic vein thrombosis, suggesting that imaging these veins may have a substantial effect on patient care (33,34).

DIAGNOSTIC ALGORITHM
At the author’s institution, the following algorithm is used in evaluating patients suspected of having thromboembolic disease. First, those patients who present with signs and symptoms of deep venous thrombosis alone (with no clinical evidence of PE) undergo US imaging because of the high sensitivity of lower extremity US in this patient population. Patients who present with signs and symptoms suggestive of PE initially undergo chest radiography. Those with normal chest radiographs are referred for scintigraphy. It has been shown that patients with a normal chest radiograph are more likely to have a definitive ventilation-perfusion scan result (ie, normal findings, very low probability of PE, or high probability of PE) (35,36). Patients with abnormal chest radiographs undergo CT scans that include evaluation of the pulmonary arteries and the lower extremity veins unless there is a contraindication to the intravenous administration of contrast material, in which case patients may be referred for US and/or scintigraphy as the initial evaluation. Patients who have nondiagnostic scintigraphy or CT may be referred for further testing as indicated. For example, if enhancement of the lower extremity veins is less than optimal and the clinical scenario is suggestive of the possibility of deep venous thrombosis, or if there is substantial mixing artifact on the CT scan and the presence of deep venous thrombosis is questioned, the patient is referred for US. Although scintigraphy has

CT Venography Until the late 1990s, deep venous thrombosis was an occasional incidental finding at abdominal and pelvic CT examinations, and “direct” CT venography with injections into the pedal veins had been investigated as an alternative to conventional contrast venography and to US (25). However, in 1998, Loud et al (26) introduced a technique that took advantage of the contrast material administered for CT pulmonary arteriography to assess the lower extremity veins. With the introduction of this technique (called “indirect” CT venography), CT became a single practical, clinically available test for both deep venous thrombosis and PE. Because CT venography is a newer technique than CT pulmonary arteriography, there are fewer studies assessing its accuracy. However, the findings from those studies show moderately good interobserver agreement (27), with good sensitivity and specificity, when compared with US (28–32). An important ad-

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not been shown generally to provide additional information in patients who have undergone CT, in specific cases in which a single area is questioned at CT, scintigraphy may be helpful in evaluating perfusion to a particular portion of the lungs. Patients may undergo pulmonary arteriography in cases in which poor pulmonary arterial enhancement or severe motion artifacts render CT pulmonary arteriography nondiagnostic. Occasionally, limited arteriographic studies are suggested for evaluation of a single vessel in which an embolus is questioned at CT pulmonary arteriography. When CT pulmonary arteriography and CT venography are of less than optimal quality, recent data from our institution show that clinicians tend to behave as if PE is confidently excluded (37). In this small retrospective series, this behavior did not have any negative consequences. Nevertheless, this approach is certainly not well validated. Although studies are continuing to demonstrate good outcomes in patients who do not receive anticoagulant therapy after negative findings at CT pulmonary arteriography, some published diagnostic algorithms continue to allow for the potential risks of missed PE at CT. To account for potential false-negative studies, patients may be stratified according to the pretest probability of PE (38). According to one such strategy, patients with a high pretest probability and normal ventilation-perfusion scan results can be safely assumed to have no PE. In contrast, patients with a high or intermediate pretest probability and negative findings at CT are grouped with those who have low- or intermediate-probability ventilation-perfusion results and undergo lower extremity US. Unless deep venous thrombosis is demonstrated, this algorithm requires pulmonary angiography in this group of patients. Patients with a low pretest probability of PE may undergo a highly sensitive D-dimer assay— which is considered sufficiently sensitive to exclude venous thromboembolism only in patients with a low pretest probability of PE. Patients with positive D-dimer assays or those seen at institutions where the sensitive version of such an assay is not available undergo CT pulmonary arteriography or ventilation-perfusion scanning. Patients with negative findings at CT pulmonary arteriography undergo lower extremity US, but in contrast to those patients with a high pretest probability of venous thromboembolism, in the lowprobability group the combination of negative findings at CT pulmonary arteriography and negative findings at lower extremity US is considered to exclude venous thromboembolism. As more data accumulate, it is likely that fewer algorithms will insist on pulmonary angiography in patients with negative findings on good-quality multi– detector row CT examinations. Recent guidelines from the British Thoracic Society (39) state that “patients with a good quality negative CTPA do not require fur-

ther investigation or treatment for PE.” A more conservative conclusion is drawn by Kearon (40), who concludes that on the basis of results with single-detector CT pulmonary arteriography, negative findings at CT and at lower extremity US in combination exclude PE, but only in patients with a low or intermediate pretest probability of venous thromboembolism. CT venography, as a newer technique, is not included in most published algorithms for the diagnosis of venous thromboembolism. At our institution, nevertheless, it is routinely performed. This approach is controversial because the results of some studies have suggested that there is relatively little diagnostic yield for routine CT venography. A recent review of 1435 patients scanned during a 27-month period at our institution showed that 51 patients (3.6%) had deep venous thrombosis at CT venography but no PE at CT pulmonary arteriography (37). A separate study of 609 patients at the same institution showed that 11% (21 patients) of the 183 patients with venous thromboembolism at CT had deep venous thrombosis alone, with no PE (41). While this finding is probably, in itself, an adequate rationale for the use of CT venography, the technique becomes even more useful if clinicians are following an algorithm that assumes poor negative predictive value of negative findings at CT. Because these imaging algorithms require evaluation for deep venous thrombosis in all patients with negative findings at CT pulmonary arteriography, the use of CT venography will prevent a large number of lower extremity US examinations—at the cost of some additional radiation to the patient. The amount of additional radiation will depend on the design of the CT venographic protocol, and the effect of the additional radiation can be limited by avoiding CT venography in young patients and in patients who have already undergone lower extremity US.

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CT PULMONARY ARTERIOGRAPHIC TECHNIQUE
The rapid changes in CT scanner technology make it difficult to comment on technical aspects of protocol design for CT pulmonary arteriography in a chapter such as this one, because there are so many possible detector configurations. The portion of the lungs that can be imaged in a reasonable breath hold depends on the speed of the CT scanner. The earliest protocols were designed for single-detector helical scanners, which only allowed imaging from the inferior pulmonary veins to the aortic arch in a reasonable time interval. As scanners improved, protocols were designed to include larger and larger volumes of the lungs, and most recently, the entire volume of the lungs can be included in a single thin-section helical series with the newest multidetector row CT scanners. At the most basic level, protocols should be designed to image as much of the lung as is possible in a reasonable breath-hold interval, with adequate peak

kilovoltage and mAs to prevent excessive image noise. In general, thinner-collimation CT yields better depiction of peripheral vessels and greater sensitivity for small subsegmental PE. With multi–detector row CT scanners, subsecond images can be obtained with 1- or 1.25-mm collimation, depending on the manufacturer, without excessive image noise, except in large patients. This results in better depiction of subsegmental and higher-order vessels (42) and diminishes motion artifacts (43). In larger patients, images with thin collimation may have unacceptable amounts of image noise. With multi–detector row CT scanners, the images can be retrospectively combined to create thicker sections if there is excessive noise on initially viewed thin-section images. As CT tables become more tolerant of increased patient weight, there are more patients in whom image noise is an important factor limiting the quality of CT imaging. Dose can be decreased in smaller patients to limit radiation exposure. Beyond these specifics, there are many parameters of CT pulmonary arteriographic protocols that can be applied regardless of differences among scanners.

Scanning Parameters Although not all investigators agree, some have suggested that caudal-to-cranial scanning improves the quality of many studies. Image degradation caused by respiratory motion is usually most severe at the lung bases and least severe at the apices. With relatively slow scanner speeds that necessitate long breath-hold intervals, it is theoretically desirable to image the lower portion of the lung early in the breath hold, to minimize motion artifact if the patient cannot maintain a breath hold for the entire imaging time. The use of oxygen therapy administered with nasal cannula may help patients maintain longer breath holds, thus reducing motion artifact. With the newest most rapid scanners, the length of the breath hold has become important only in patients with the worst dyspnea. In this group, scanning during quiet breathing may be more successful than a failed attempt at breath holding. Theoretically, patients undergoing mechanical ventilation can be held in apnea with chemical paralysis. If this is done, respiration should ideally be suspended at high lung volumes, to increase pulmonary resistance and improve opacification (44). At our institution, mechanical ventilation is almost never suspended. Instead, mechanical ventilators are set to minimal tidal volume and rate for the duration of the scan. Timing of Imaging At many institutions, fixed scan delays have been found to be adequate, with only a minority of patients having poorly enhanced pulmonary arteries if imaging is obtained at a delay of, for example, 28 seconds from the start of contrast material administration

(45). However, with four– or eight–detector row CT scanners, we believe that image quality seems to be improved by the use of scan delays tailored to individual patients. There are two approaches to timing contrast administration: (a) a preliminary time-density curve or (b) commercially available bolus-tracking software. With both approaches, initial nonenhanced images are obtained to locate the pulmonary artery. To create a time-density curve, 10 low-dose images are then obtained over the main pulmonary artery during the injection of 18 mL of contrast material. The time delay for the diagnostic study is calculated by using a time to peak enhancement +5 seconds. With bolustracking software, contrast material is injected, and low-dose images are obtained over the pulmonary artery until contrast material appears, at which time diagnostic imaging is initiated. The difficulty with the use of bolus-tracking software is the unpredictable nature of the start of breath holding, which may lead to relatively little advance warning to the patient about the start of a breath hold and thus to respiratory motion on the initial images. If a fixed delay is used, it is helpful to increase the length of the delay or to obtain a time-density curve in patients who are thought to have cardiac dysfunction, pulmonary arterial hypertension, or central venous stenoses. The short scan times used with the rapid, new multi–detector row CT scanners have decreased the need for precise timing. With an eight– detector row CT scanner, a volume through the lungs can be scanned in approximately 10–12 seconds, and with a 16–detector row scanner, the lungs can be scanned in 5–6 seconds. If 120 mL of intravenous contrast material is injected at a rate of 4 mL/sec, it is possible to initiate scanning at a delay of 25 seconds, a longer delay than was almost ever necessary with carefully timed contrast material boluses, and to finish scans within a few seconds of the end of the injection, essentially guaranteeing that imaging will not be performed too late in contrast material administration.

CT for Thromboembolic Disease

Contrast Material Nonionic intravenous contrast material is used almost always for CT pulmonary arteriography. Early in the experience with CT pulmonary arteriography, some authors recommended using low concentrations of contrast material at high flow rates to reduce streak artifact from high contrast material density in the superior vena cava (46); however, this artifact is seldom now considered to be particularly problematic. At our institution, 120 mL of nonionic contrast material (iohexol; 360 mg/mL) is injected at a rate of 4 mL/sec. Patients with a mildly elevated serum creatinine are given 125 mL of iso-osmolar contrast material (iodixanol; 320 mg/mL), with hydration both before and after the examination. Protocols ranging from injection rates of 2 mL/sec to 5 mL/sec have been advocated by various

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Figure 2. Paddle-wheel reconstruction. (a) Sagittal reformation is used as scout. Slab reformations are obtained rotating around central axis. (b) On slab image, webs (black arrows), narrowed artery (white arrows), and areas of focal stenosis (arrowheads) are seen in this patient with chronic thromboembolic pulmonary hypertension.

investigators (45). With faster scanners, smaller quantities of intravenous contrast material may adequately opacify the pulmonary arteries. However, at least 100 mL and probably 120 mL must be given to achieve adequate enhancement of the lower extremity veins at CT venography (and in larger patients, even this quantity is sometimes inadequate). The average CT attenuation of thrombus has been reported to range from 31 to 50 HU (30,47), and Bruce et al (48) have reported mean enhancement values of between 91 and 97 HU with administration of 150 mL of iodinated contrast material, which should allow for the visualization of thrombus.

CT VENOGRAPHY
Technique As with CT pulmonary arteriography, multiple different protocols have been used by different investigators to image the lower extremity veins. Some investigators advocate continuous helical imaging from the level of the renal veins to the level of the popliteal fossae (31). However, Loud and colleagues (26), who performed the first studies of CT venography, obtained only noncontiguous axial 10-mm images at 5cm intervals. In our experience, continuous helical imaging through the pelvis creates partial-volume artifacts secondary to the obliquity of the iliac veins, and this makes these images more difficult to interpret. For this reason, a compromise protocol has been implemented: 5-mm-thick axial CT images at 2-cm intervals are obtained from the level of the iliac crests to

the level of the popliteal fossae. When the veins are enhanced to 80 HU, contrast is considered to be adequate to exclude thrombosis; at lower degrees of enhancement, clots may be diagnosed on occasion, but they cannot be confidently excluded. Initial studies of indirect CT venography were performed with imaging at 3 minutes after the initiation of contrast material administration (26). Some authors have advocated earlier imaging (49,50), while others have suggested that a delay of 4 minutes may be preferable, at least in patients suspected of having abnormal hemodynamics or slow flow (32). Timing for CT venography appears, however, to be much less crucial than that for CT pulmonary arteriography.

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Image Viewing The large numbers of images generated with CT pulmonary arteriography and CT venography are most easily evaluated on a workstation. At institutions that use picture archiving and communications systems (PACS) for all clinical work, CT pulmonary arteriographic images, like images from other studies, are stored and called back up from the PACS system. Workstation review is essential for accurate interpretation of CT pulmonary arteriographic studies. Even prior to the installation of a PACS system, the practice at our institution was to review all studies on a CT workstation. Although selected images from the studies (every third image) are still filmed at both lung and mediastinal windows, it is impractical to interpret CT pulmonary arteriographic studies on hard-copy images. Even when other cases

Figure 3. Acute PE. Axial CT image shows bilateral upper lobe partial filling defects (arrows). Note also a small complete filling defect in subsegmental right upper lobe vessel.

Figure 4. Subsegmental acute PE. Axial CT image shows that subsegmental right upper lobe artery (arrow) is completely filled with clot and appears distended. Remaining vessels at same level (arrowheads) are well enhanced and smaller in diameter.

CT for Thromboembolic Disease

Figure 5. Multiple bilateral acute pulmonary emboli. Axial CT image shows incomplete filling defect (straight arrow) in right basilar artery trunk. Mural thrombus (arrowhead) forms acute angles with vessel wall in left anteromedial basal segmental artery. Complete filling defect (curved arrow) is seen in right medial basal segmental artery. Smaller emboli are seen in other vessels.

plane of section (51) (Fig 2). Most radiologists are accustomed to reading axial images and are reluctant to attempt to use other imaging planes for diagnostic evaluation of images. However, CT pulmonary arteriography with multi–detector row CT scanners produces such large numbers of images that there will probably be increasing interest in alternate ways of viewing these images.

CT FINDINGS IN PE
Acute PE The findings of PE at CT are the same as those described in the earliest discussions of PE (46), although with current technology, these findings may be sought in much smaller vessels. Acute pulmonary emboli may cause partial or complete filling defects; they also may create a “railway-track sign” or mural defects. A partial filling defect is a clot seen in the center of a vessel surrounded by contrast material (Fig 3). When the entire artery fails to opacify because of a central clot, this is a complete filling defect. In the setting of acute PE, arteries that are completely filled with clot may be distended and appear larger than vessels of the same generation that are free of emboli (Fig 4). A railway-track sign is a clot floating within a vessel, surrounded by contrast material, and is commonly seen in central vessels that are parallel to, rather than perpendicular to, the plane of section. Mural defects are clots that adhere to the wall of the vessel. Mural emboli are frequently seen in chronic as well as in acute PE; acute mural emboli commonly make acute angles with the vessel walls. Emboli with several of these manifestations are seen in Figure 5. Secondary signs of acute PE include depiction of the CT equivalent of a Hampton hump, the pulmonary “infarct.” These peripheral wedge-shaped areas of consolidation represent hemorrhage, frequently without true tissue necrosis, and are seen in only a minority of patients. Nonspecific findings in patients with PE include atelectasis and pleural effusions; these findings are common in patients with and without PE.

were being reviewed or read on hard-copy images, CT pulmonary arteriographic studies were always restored from optical disks, and current and comparison studies were reviewed together on the workstation. If only small clots are found, selected magnified demonstration images may be filmed as a record. The theoretical utility of these hard-copy images is that the images can be taken with the patient to another facility; however, increasing numbers of institutions are supplying patients and other facilities with images on CDs rather than on film, and CDs will probably continue to supplant the frequently awkward film record.

Postprocessing Techniques Multiplanar reformations may occasionally be used to clarify diagnoses at CT pulmonary arteriography. These reformations are most commonly used when it is difficult to separate perihilar lymphatic soft tissue from mural thrombus or wall thickening, particularly in patients who are suspected of having chronic PE. Multiplanar reformations also can be useful in separating motion artifacts from real emboli. One group has advocated use of a “paddle-wheel” reformation technique, to try to depict all of the vessels in the

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Figure 6. Chronic PE. (a) On contrast-enhanced axial CT image, mural calcification in right pulmonary artery is subtle. (b) Nonenhanced axial CT image shows mural calcification (arrows) clearly.

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Figure 7. Chronic PE. Axial CT image shows bilateral central mural emboli (arrows) making obtuse angles with the vessel walls, suggesting chronicity.

The main differential diagnostic considerations when filling defects are seen in pulmonary arteries are chronic PE and artifact. In an emergency setting, it may be valuable to distinguish small chronic emboli, which may not require anticoagulant therapy, from similar acute emboli. In addition, patients may present with chronic thromboembolic pulmonary hypertension without any previously diagnosed acute PE, and it is important to separate these patients from patients with massive acute PE, who may, perhaps, be candidates for thrombolytic therapy. Rarely, filling defects may represent neoplasms—either primary sarcomas or central tumor emboli from neoplasms such as hepatocellular carcinoma or renal cell carcinoma.

Figure 8. Bilateral webs in chronic PE. Axial CT image shows thin linear filling defects (arrows) bilaterally in a patient with chronic thromboembolic pulmonary hypertension. On a single image, these filling defects may be mistaken for vascular bifurcations, particularly when vessel has an irregular shape as a result of chronic PE. On contiguous axial images, contrast material columns on both sides of web extend in parallel for several contiguous images.

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Chronic PE The most specific finding for chronic PE is calcification within a clot. However, this finding is insensitive, and unless there is considerable noncalcified mural thrombus, calcification may be difficult to detect in the presence of contrast material enhancement (Fig 6). Other findings (and the clinical history) may be more helpful in making this diagnosis. Chronic emboli are frequently eccentric and contiguous with the vessel wall, and when they are eccentric, they more commonly make obtuse angles, rather than

Figure 9. Chronic PE. Axial CT image shows that right basilar segmental arteries (arrows) are completely nonenhanced and small in caliber. In contrast, left basilar segmental arteries (arrowheads) are normal in caliber, although there is some mural thickening.

acute angles, with the vessel wall (Fig 7). Vascular webs are thin linear or planar filling defects and strongly suggest chronicity (Fig 8). Areas of arterial stenosis may be evident. Stenosis can be difficult to perceive on images obtained perpendicular to a vessel plane but should be suspected when an enhancing vessel is markedly smaller than the adjacent bronchus and other vessels of a similar generation. Multiplanar reformations may help to

Figure 10. Unopacified pulmonary veins. (a) Image at CT pulmonary angiographic window setting shows both adequately enhanced vessels (arrows) and poorly enhanced vessels (arrowheads). (b) Axial CT image viewed at lung window settings demonstrates that the poorly enhanced vessels (arrowheads) are independent of and medial to bronchi, indicating that vessels are veins.

CT for Thromboembolic Disease

image these. Stenosis in isolation is not diagnostic of chronic PE but may support the diagnosis when other findings are present. Abrupt cutoff of the contrast column in a vessel may be seen, with a narrowed (rather than dilated) nonenhancing distal vessel (Fig 9). Vessels containing chronic emboli are apt to be smaller than uninvolved vessels of the same order, in contrast to the enlarged vessels frequently seen with acute PE. Dilation of the main pulmonary arteries is seen in pulmonary arterial hypertension, including that caused by chronic PE. There may be prominent bronchial collateral arteries. Mosaic attenuation in the lungs is more commonly seen in chronic PE than in acute emboli. This finding is not specific for chronic PE, and more patients with it will have small airways disease than chronic PE. Mosaic attenuation may also be seen with other causes of pulmonary arterial hypertension. Expiratory images have been used to distinguish small airways disease from diseases with vascular obstruction; mosaic perfusion secondary to small airways disease will show a dramatic increase in contrast between low- and high-attenuation regions on expiratory images. In a recent article, however, investigators suggested that this change in contrast (air trapping) may also be seen in acute or chronic thromboembolic disease (52). Small subpleural areas of scar, which are probably sequelae of old areas of infarction, are a nonspecific finding that is also common in patients with chronic PE.

Many areas of confusion can be easily avoided by reviewing scans on a workstation.

ARTIFACTS AND PITFALLS
Multiple artifacts that could be confused with emboli have been described. To help avoid confusion, it is best to look for sharply demarcated areas of low attenuation in vessels and to diagnose emboli only when these are seen on more than one sequential image, at least on vessels imaged in cross section. Acute emboli are unlikely to be so small that they will be seen in cross section for a distance of only 1–3 mm.

Anatomic Pitfalls At least a minimal understanding of pulmonary arterial anatomic structures is necessary to interpret CT pulmonary arteriographic studies. However, there are many variants of pulmonary arterial anatomic structures, and the naming of vessels is frequently confusing. It helps to remember that an artery is usually named according to the segmental bronchus that it accompanies. Pulmonary veins course independent of the bronchi. If imaging is performed early in the administration of the contrast material bolus, unopacified pulmonary veins can be confused with PE (Fig 10). This mistake can easily be avoided by workstation review, which will allow the reader to trace vessels back either to their origins at the pulmonary arteries or to their terminations at the left atrium. It is also helpful to keep in mind that the lower lobe pulmonary arteries are peripheral to the accompanying bronchi, whereas lower lobe veins are central to the bronchi. In the upper lobes, the arteries are central to the corresponding bronchi. Another misinterpretation that can be avoided with the use of workstation review is mistaking mucoid impaction of a bronchus for a pulmonary embolus. Mucoid impaction of the bronchus causes central lower attenuation with peripheral higher attenuation, which on a single image can look much like a pulmonary embolus. Following a structure on lung window settings to a section on which it appears aerated helps to make this distinction (Fig 11). Hilar lymph nodes could also potentially be mistaken for emboli, most commonly for chronic emboli, rather than acute emboli. Again, workstation review helps to avoid this interpretive pitfall because lymph nodes will not extend through multiple sections. The most common imaging artifacts seen on CT pulmonary arteriographic studies are streak artifacts

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Figure 11. Mucoid impaction of bronchi. (a) Axial CT image at soft-tissue window setting shows low-attenuation tubular structures (arrows) adjacent to enhanced pulmonary arteries. (b, c) Axial CT images viewed at lung window settings show low-attenuation structures (arrows) continuing to aerated regions, indicating that the structures represent mucus-filled bronchi. They are also seen to run parallel to arteries on contiguous images.

and motion artifacts. Streak artifacts often arise from dense contrast opacification of the superior vena cava or may arise from calcified nodes, metallic surgical clips, pacemakers, and other implanted devices. These artifacts can cause focal areas of low attenuation in the vessel. Streak artifacts are seldom sufficiently well defined to truly cause confusion with emboli and usually continue beyond the vessel and do not extend through multiple consecutive images. Motion artifacts, on the other hand, can convincingly simulate emboli. Partial volume averaging of the lung surrounding vessels occurs with motion, causing low attenuation to appear to be located within an otherwise enhanced vessel. The easiest way to avoid confusing motion artifact with emboli is to evaluate scans on a workstation and switch window and level settings from the soft-tissue windows used to evaluate for PE to lung windows. Motion artifacts are much more easily seen at lung window settings. In addition, workstation review will enable the reader to see that the vessel changes position rapidly from one section to another, confirming that there is motion. Multiplanar reformations may also demonstrate motion. The area most prone to motion artifact is the portion of the left lung immediately behind the heart that receives transmitted cardiac pulsations.

There may, however, be a pitfall with deep inspiration. Recently, a new artifact has been described, which is most commonly seen in young patients. This artifact is thought to be caused by rapid, deep inspiration (often occurring at the beginning of a breath hold), which results in negative intrathoracic pressures and an influx of unopacified blood from the inferior vena cava, diluting the contrast material bolus (53). This is particularly confusing because the vessels will be well enhanced more proximally, and there may be good pulmonary venous enhancement, indicating that the delay to the initiation of imaging is adequate. This artifact should be considered as a possible cause when multiple poorly enhanced arteries are seen at the same anatomic level, and the artifact can theoretically be prevented by careful instructions to patients to avoid a rapid deep inspiration at the beginning of a scan. Another potential cause of confusion is the partial volume averaging that occurs at vascular bifurcations or in small vessels seen in the axial plane. A low-attenuation region at a vascular bifurcation that does not extend to more than one or two images should not be interpreted as PE. Multiplanar reformations may be helpful in distinguishing these low-attenuation regions from true emboli.

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Other Pitfalls It is important to avoid interpreting poor enhancement of vessels as emboli. This pitfall is usually easy to avoid because the degree of enhancement is generally uniform throughout the images or may perhaps be uniformly low in the earliest images or the latest images, suggesting imaging either too early or too late with respect to contrast enhancement. Higher levels of pulmonary vascular resistance lead to better enhancement, and imaging at maximal inspiration is recommended to increase pulmonary vascular resistance and optimize arterial enhancement.

Intravascular Neoplasm Intravascular tumor is a rare cause of intraarterial filling defects. Occasionally, large central intraarterial metastases will occur; this is most common in hepatocellular and renal cell carcinomas. The possibility of intraarterial metastasis should be considered in patients with other evidence of metastatic disease from one of these two primary tumors. Primary sarcomas of the pulmonary arteries are rare. Marked expansion of the vessel and large central unifocal filling defects may suggest the possibility of pulmonary artery sarcoma. When intraarterial neoplasm is suspected, delayed imaging

Figure 12. Acute deep venous thrombosis of left profunda femoris vein. Axial CT image shows that left profunda femoris vein (white arrow) is distended, with mural enhancement and perivenous edema. Note normal-caliber, normally enhancing right profunda femoris vein (black arrow).

through the pulmonary arteries may show enhancement of the low-attenuation region, indicating that it is not bland but tumor thrombus.

dic hardware; unfortunately, this patient population is at increased risk for deep venous thrombosis. These patients may require additional imaging with US if such imaging is clinically feasible. In conclusion, clinical practice with respect to evaluation of patients with venous thromboembolism is changing rapidly, and CT pulmonary arteriography and CT venography are increasingly important parts of radiologic practice in emergency settings. As more studies validate the safety of withholding anticoagulant therapy from patients with negative CT findings for PE, CT pulmonary arteriography will probably continue to increase in popularity. CT of the lower extremity veins may add to the confidence with which venous thromboembolism is excluded in a given patient. Using multi–detector row CT scanners increases depiction of small peripheral vessels, and workstation review increases confidence in the diagnosis or exclusion of PE. Familiarity with the findings of venous thromboembolism and with potential diagnostic pitfalls will ensure accurate interpretation of these ever more common studies.

CT for Thromboembolic Disease

References
1. van Rossum AB, Pattynama PM, Mallens WM, Hermans J, Heijerman HG. Can helical CT replace scintigraphy in the diagnostic process in suspected pulmonary embolism? a retrospective-prospective cohort study focusing on total diagnostic yield. Eur Radiol 1998; 8:90–96. 2. Cross JJ, Kemp PM, Walsh CG, Flower CD, Dixon AK. A randomized trial of spiral CT and ventilation perfusion scintigraphy for the diagnosis of pulmonary embolism. Clin Radiol 1998; 53:177–182. 3. Wagenvoort CA, Mooi WJ. Biopsy pathology of the pulmonary vasculature. London, England: Chapman & Hall, 1989. 4. Diffin DC, Leyendecker JR, Johnson SP, Zucker RJ, Grebe PJ. Effect of anatomic distribution of pulmonary emboli on interobserver agreement in the interpretation of pulmonary angiography. AJR Am J Roentgenol 1998; 171:1085–1089. 5. Stein PD, Henry JW, Gottschalk A. Reassessment of pulmonary angiography for the diagnosis of pulmonary embolism: relation of interpreter agreement to the order of the involved pulmonary arterial branch. Radiology 1999; 210: 689–691. 6. Baile EM, King GG, Muller NL, et al. Spiral computed tomography is comparable to angiography for the diagnosis of pulmonary embolism. Am J Respir Crit Care Med 2000; 161:1010–1015. 7. Remy-Jardin M, Remy J, Deschildre F, et al. Diagnosis of pulmonary embolism with spiral CT: comparison with pulmonary angiography and scintigraphy. Radiology 1996; 200:699–706. 8. Mayo JR, Remy-Jardin M, Muller NL, et al. Pulmonary embolism: prospective comparison of spiral CT with ventilation-perfusion scintigraphy. Radiology 1997; 205:447–452. 9. Garg K, Welsh CH, Feyerabend AJ, et al. Pulmonary embolism: diagnosis with spiral CT and ventilation-perfusion scanning—correlation with pulmonary angiographic results or clinical outcome. Radiology 1998; 208:201–208. 10. Goodman LR, Curtin JJ, Mewissen MW, et al. Detection of pulmonary embolism in patients with unresolved clinical and scintigraphic diagnosis: helical CT versus angiography. AJR Am J Roentgenol 1995; 164:1369–1374.

FINDINGS OF DEEP VENOUS THROMBOSIS
Like PE, deep venous thrombosis appears at CT as a filling defect in an otherwise enhanced vessel. A filling defect may be focal or partial, or the vein may be completely filled with clot. Like an artery, a vein that is completely filled with acute thrombus is usually enlarged. Findings of acute deep venous thrombosis that are not seen in PE include perivenous stranding and mural enhancement (Fig 12). Stranding in the fat around the vein is caused by perivenous edema associated with acute deep venous thrombosis. These findings should be sought not only in the portions of the venous system easily accessible to compression US but also in the pelvis and in the profunda femoris veins. Like chronic PE, chronic deep venous thrombosis may result in calcification of the vein. There may be prominent collateral veins. The vein is usually smaller than the accompanying artery, in contrast to the normal state and to the distension seen with acute deep venous thrombosis. If the vein appears markedly less well enhanced than the artery, a Hounsfield unit measurement should be obtained; imaging may have occurred early in the circulation of contrast material, and caution should be used in interpreting the study. Unfortunately, similar findings may be seen in patients with extensive bilateral thrombosis; a few delayed images may help to distinguish artifact from real thrombosis, and examination of the entire venous system for areas of better enhancement may also be helpful. Artifacts that may be seen at CT venography include mixing and streak artifacts. Streak artifacts may be particularly problematic in patients with orthope-

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11. Coche E, Verschuren F, Keyeux A, et al. Diagnosis of acute pulmonary embolism in outpatients: comparison of thin-collimation multi–detector row spiral CT and planar ventilationperfusion scintigraphy. Radiology 2003; 229:757–765. 12. Qanadli SD, Hajjam ME, Mesurolle B, et al. Pulmonary embolism detection: prospective evaluation of dual-section helical CT versus selective pulmonary arteriography in 157 patients. Radiology 2000; 217:447–455. 13. Blachere H, Latrabe V, Montaudon M, et al. Pulmonary embolism revealed on helical CT angiography: comparison with ventilation-perfusion radionuclide lung scanning. AJR Am J Roentgenol 2000; 174:1041–1047. 14. Schoepf UJ, Holzknecht N, Helmberger TK, et al. Subsegmental pulmonary emboli: improved detection with thin-collimation multi–detector row spiral CT. Radiology 2002; 222: 483–490. 15. Stein PD, Henry JW. Prevalence of acute pulmonary embolism in central and subsegmental pulmonary arteries and relation to probability interpretation of ventilation/perfusion lung scans. Chest 1997; 111:1246–1248. 16. Hull RD, Raskob GE, Coates G, Panjuu AA, Gill GJ. A new noninvasive management strategy for patients with suspected pulmonary embolism. Arch Intern Med 1989; 149: 2549–2555. 17. Garg K, Sieler H, Welsh CH, Johnston RJ, Russ PD. Clinical validity of helical CT being interpreted as negative for pulmonary embolism: implications for patient treatment. AJR Am J Roentgenol 1999; 172:1627–1631. 18. Lomis NN, Yoon HC, Moran AG, Miller FJ. Clinical outcomes of patients after a negative spiral CT pulmonary arteriogram in the evaluation of acute pulmonary embolism. J Vasc Interv Radiol 1999; 10:707–712. 19. Goodman LR, Lipchik RJ, Kuzo RS, Liu Y, McAuliffe TL, O’Brien DJ. Subsequent pulmonary embolism: risk after a negative helical CT pulmonary angiogram—prospective comparison with scintigraphy. Radiology 2000; 215:535–542. 20. Gottsater A, Berg A, Centergard J, Frennby B, Nirhov N, Nyman U. Clinically suspected pulmonary embolism: is it safe to withhold anticoagulation after a negative spiral CT? Eur Radiol 2001; 11:65–72. 21. Musset D, Parent F, Meyer G, et al. Diagnostic strategy for patients with suspected pulmonary embolism: a prospective multicentre outcome study. Lancet 2002; 360:1914–1920. 22. van Strijen MJ, de Monye W, Schiereck J, et al. Single-detector helical computed tomography as the primary diagnostic test in suspected pulmonary embolism: a multicenter clinical management study of 510 patients. Ann Intern Med 2003; 138:307–314. 23. Swensen SJ, Sheedy PF II, Ryu JH, et al. Outcomes after withholding anticoagulation from patients with suspected acute pulmonary embolism and negative computed tomographic findings: a cohort study. Mayo Clin Proc 2002; 77: 130–138. 24. Tillie-Leblond I, Mastora I, Radenne F, et al. Risk of pulmonary embolism after a negative spiral CT angiogram in patients with pulmonary disease: 1-year clinical follow-up study. Radiology 2002; 223:461–467. 25. Baldt MM, Zontsich T, Stumpflen A, et al. Deep venous thrombosis of the lower extremity: efficacy of spiral CT venography compared with conventional venography in diagnosis. Radiology 1996; 200:423–428. 26. Loud PA, Grossman ZD, Klippenstein DL, Ray CE. Combined CT venography and pulmonary angiography: a new diagnostic technique for suspected thromboembolic disease. AJR Am J Roentgenol 1998; 170:951–954. 27. Garg K, Kemp JL, Russ PD, Baron AE. Thromboembolic disease: variability of interobserver agreement in the interpretation of CT venography with CT pulmonary angiography. AJR Am J Roentgenol 2001; 176:1043–1047.

28. Loud PA, Katz DS, Bruce DA, Klippenstein DL, Grossman ZD. Deep venous thrombosis with suspected pulmonary embolism: detection with combined CT venography and pulmonary angiography. Radiology 2001; 219:498–502. 29. Coche EE, Hamoir XL, Hammer FD, Hainaut P, Goffette PP. Using dual-detector helical CT angiography to detect deep venous thrombosis in patients with suspicion of pulmonary embolism: diagnostic value and additional findings. AJR Am J Roentgenol 2001; 176:1035–1038. 30. Duwe KM, Shiau M, Budorick NE, Austin JH, Berkmen YM. Evaluation of the lower extremity veins in patients with suspected pulmonary embolism: a retrospective comparison of helical CT venography and sonography—2000 American Roentgen Ray Society Executive Council Award I. AJR Am J Roentgenol 2000; 175:1525–1531. 31. Cham MD, Yankelevitz DF, Shaham D, et al. Deep venous thrombosis: detection by using indirect CT venography—the Pulmonary Angiography-Indirect CT Venography Cooperative Group. Radiology 2000; 216:744–751. 32. Garg K, Kemp JL, Wojcik D, et al. Thromboembolic disease: comparison of combined CT pulmonary angiography and venography with bilateral leg sonography in 70 patients. AJR Am J Roentgenol 2000; 175:997–1001. 33. Spritzer CE, Arata MA, Freed KS. Isolated pelvic deep venous thrombosis: relative frequency as detected with MR imaging. Radiology 2001; 219:521–525. 34. Stern JB, Abehsera M, Grenet D, et al. Detection of pelvic vein thrombosis by magnetic resonance angiography in patients with acute pulmonary embolism and normal lower limb compression ultrasonography. Chest 2002; 122:115–121. 35. Lesser BA, Leeper KV Jr, Stein PD, et al. The diagnosis of acute pulmonary embolism in patients with chronic obstructive pulmonary disease. Chest 1992; 102:17–22. 36. Goldberg SN, Palmer EL, Scott JA, Fisher R. Pulmonary embolism: prediction of the usefulness of initial ventilation-perfusion scanning with chest radiographic findings. Radiology 1994; 193:801–805. 37. Eyer B, Goodman LR, Washington L, Lipchik RJ. Isolated subsegmental pulmonary embolism (PE) or indeterminate PE discovered on helical CT: clinician response and patient outcome. AJR Am J Roentgenol (in press). 38. Fedullo PF, Tapson VF. Clinical practice: the evaluation of suspected pulmonary embolism. N Engl J Med 2003; 349: 1247–1256. 39. British Thoracic Society Standards of Care Committee Pulmonary Embolism Guideline Development Group. British Thoracic Society guidelines for the management of suspected acute pulmonary embolism. Thorax 2003; 58:470–483. 40. Kearon C. Excluding pulmonary embolism with helical (spiral) computed tomography: evidence is catching up with enthusiasm. CMAJ 2003; 168:1430–1431. 41. Cosmic MS, Goodman LR, Lipchik RJ, Washington L. Detection of deep venous thrombosis with combined helical CT scan of the chest and CT venography in unselected cases of suspected pulmonary embolism. Presented at the 98th International Conference of the American Thoracic Society, Atlanta, Ga, May 17–22, 2002. 42. Ghaye B, Szapiro D, Mastora I, et al. Peripheral pulmonary arteries: how far in the lung does multi-detector row spiral CT allow analysis? Radiology 2001; 219:629–636. 43. Boiselle PM, Rosen M, Raptopoulos V. Comparison of CT pulmonary angiography image quality on single and multidetector scanners (abstr). In: American Roentgen Ray Society 101st Annual Meeting Abstract Book. Leesburg, Va: American Roentgen Ray Society, 2001; 20. 44. Remy-Jardin M, Remy J, Artaud D, Fribourg M, Beregi JP. Spiral CT of pulmonary embolism: diagnostic approach, interpretive pitfalls and current indications. Eur Radiol 1998; 8:1376–1390.

Washington

45. Yankelevitz DF, Shaham D, Shah A, Rademacker J, Henschke CI. Optimization of contrast delivery for pulmonary CT angiography. Clin Imaging 1998; 22:398–403. 46. Remy-Jardin M, Remy J, Wattinne L, Giraud F. Central pulmonary thromboembolism: diagnosis with spiral volumetric CT with the single-breath-hold technique—comparison with pulmonary angiography. Radiology 1992; 185:381–387. 47. Loud PA, Katz DS, Klippenstein DL, Shah RD, Grossman ZD. Combined CT venography and pulmonary angiography in suspected thromboembolic disease: diagnostic accuracy for deep venous evaluation. AJR Am J Roentgenol 2000; 174:61–65. 48. Bruce D, Loud PA, Klippenstein DL, Grossman ZD, Katz DS. Combined CT venography and pulmonary angiography: how much venous enhancement is routinely obtained? AJR Am J Roentgenol 2001; 176:1281–1285. 49. Matar LD, Ramirez JA, McAdams HP, Farrell MB, Herndon JE. Optimal timing of CT venography following CT pulmonary angiography using a multidetector row helical scanner: work in progress (abstr). Radiology 1999; 213(P):472.

50. Patel S, Kazerooni EA. Venous enhancement in the pelvis and thigh on multi-detector CT with variable scan delay times. In: Thoracic imaging 2000: proceedings of the 18th annual meeting of the Society of Thoracic Radiology, March 12–16, 2000, San Diego, Calif. Rochester, Minn: Society of Thoracic Radiology, 2000; 73. 51. Chiang EE, Boiselle PM, Raptopoulos V, Reynolds KF, Rosen MP, Simon M. Detection of pulmonary embolism: comparison of paddlewheel and coronal CT reformations— initial experience. Radiology 2003; 228:577–582. 52. Arakawa H, Kurihara Y, Sasaka K, Nakajima Y, Webb WR. Air trapping on CT of patients with pulmonary embolism. AJR Am J Roentgenol 2002; 178:1201–1207. 53. Gosselin MV, Thieszen SL, Yoon CH. Contrast dynamics during pulmonary CT angiogram (PCTA): analysis of an inspiration-induced artifact (abstr). In: Thoracic imaging 2001: proceedings of the 19th annual meeting of the Society of Thoracic Radiology, April 4–8, 2001, Boca Raton, Fla. Rochester, Minn: Society of Thoracic Radiology, 2001; 186.

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CT for Thromboembolic Disease

NOTES

O. Clark West, MD, and Sanjeev Bhalla, MD

CT of Nontraumatic Aortic Emergencies1

Emergency evaluation of the aorta usually takes place in one of two clinical settings: the acute thoracic aortic syndrome or the suspected ruptured abdominal aortic aneurysm. Conventional angiography has been the reference standard in the past for both clinical syndromes, but the past 2 decades have seen increasing roles for computed tomography (CT), magnetic resonance (MR) imaging, and ultrasonography (US). In the only modern study (to our knowledge) to compare modern techniques for detection of aortic dissection, investigators found that single–detector row helical CT was equivalent to multiplanar transesophageal echocardiography and spin-echo MR imaging on a 0.5-T MR imager in its ability to detect aortic dissection (1). All modalities performed nearly perfectly, with 100% sensitivity for all modalities and high specificity, ranging from 94% to 100%. CT was superior to the other modalities in establishing the presence or absence of aortic arch involvement by dissection: The sensitivity was 93% for CT, 60% for transesophageal echocardiography, and 67% for MR imaging; and specificity was 97% for CT, 85% for transesophageal echocardiography, and 88% for MR imaging (1). In the emergency center equipped with a modern CT scanner, CT is often the preferred modality for urgent evaluation of the aorta. The use of CT in the nontraumatized emergency patient is the focus of this syllabus chapter. The chapter first reviews the pathology and imaging findings in nontraumatic emergency conditions of the aorta. The principles of helical single– and multi–detector row CT evaluation of the aorta are then reviewed, and the chapter concludes with known problems and pitfalls in the evaluation of the aorta with CT.

ACUTE AORTIC SYNDROME
Acute aortic syndrome is characterized by aortic pain coexisting with hypertension (2). Aortic pain is distinct from angina pectoris and is characterized by severe, intense, acute searing or tearing, throbbing, and migratory chest pain (3). Pain may radiate to the anterior portion of the chest, neck, throat, or jaw, particularly when the pain originates in the ascending aorta, and may radiate to the back and abdomen when the pain originates in the descending aorta. The pain associated with classic aortic dissection is similar to the pain experienced by patients with penetrating aortic ulcer and intramural aortic hematoma. Together, these conditions can be lumped together as acute aortic syndrome, and imaging is usually performed for “chest pain; rule out aortic dissection.”

RSNA Categorical Course in Diagnostic Radiology: Emergency Radiology 2004; pp 47–57.
1From

the Department of Radiology, the University of Texas Medical School at Houston, MSB 2.100, 6431 Fannin, Houston, TX 77030 (O.C.W.); and Mallinckrodt Institute of Radiology, Washington University School of Medicine, St Louis, Mo (S.B.).

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Clinical diagnosis of aortic dissection is problematic. The results of a meta-analysis based on 21 articles published from 1996 to 2000 indicate that most patients with thoracic aortic dissection have severe pain with an abrupt onset (4). The absence of sudden onset decreases the probability that aortic dissection is present. Potentially useful symptoms of aortic dissection are (a) a “tearing” or “ripping” character of the pain or (b) pain that migrates from one location in the chest to another. Physical findings are present in one-third or fewer of the cases (4). A pulse deficit or focal neurologic deficit indicates a high likelihood of thoracic aortic dissection in the appropriate clinical setting. A normal aortic and mediastinal contour on the chest radiograph diminishes the likelihood that aortic dissection is present (4).

Aortic Dissection Pathology.—The aorta and great vessels are composed of three layers of tissue: the intima, the media, and the adventitia. In acute aortic dissection, the layers of the aortic wall are torn apart, creating a false lumen within the substance of the aortic media that runs parallel to the true lumen (5). Aortic dissection begins with tearing in the aortic intima and the inner layer of the aortic media, which permits entry of blood along a false lumen within the aortic media (5). The false lumen splits the aortic media into inner and outer layers. The intimomedial flap is composed of the intima and the attached inner layer of the media and separates the true and false lumina. The outer wall of the false lumen is composed of the outer layer of the media and the attached adventitia. Intimal tears occur at points of high shear force, created by the jet of blood expelled under pressure from the heart (6). Most intimal tears occur in the ascending aorta along the right lateral wall (7). The tear then propagates along the greater curvature of the aortic arch and continues caudally along the descending aorta. The tear may also propagate in a retrograde fashion toward the aortic valve. Tears originating beyond the ascending aorta most often occur immediately distal to the left subclavian artery (7). Isolated dissection of the abdominal aorta

is much less common than extension of thoracic aortic dissection into the abdominal aorta (8). Predisposing factors for aortic dissection include systemic hypertension, bicuspid aortic valve, coarctation of the aorta, Marfan syndrome, Ehlers-Danlos syndrome, Turner syndrome, giant cell arteritis, thirdtrimester pregnancy, cocaine abuse, trauma, intraaortic catheterization, and previous aortic valve replacement (4). Atherosclerosis is not a risk factor for acute aortic dissection. Classification.—Both the Stanford and the DeBakey classification systems are widely used to describe aortic dissection (9,10). The Stanford system is simple, but the information conveyed in the DeBakey system is important for complete description of the extent of dissection. Aortic dissections involving the ascending aorta are classified as Stanford type A. Type A dissections may also involve the aortic arch and descending aorta (Fig 1). Aortic dissections involving only the descending aorta are classified as Stanford type B (Fig 2). The more detailed DeBakey system effectively subdivides Stanford type A dissections into those involving the ascending aorta, aortic arch, and descending aorta (type I) and those confined to the ascending aorta (type II). Stanford type B dissections are subdivided into those that are confined to the descending thoracic aorta (type IIIa) and those that involve both the descending thoracic aorta and the abdominal aorta (type IIIb). In general, untreated type A dissections have a high mortality rate and are managed with urgent surgical repair. Type B dissections are often managed with medical therapy, with elective surgical repair in selected cases. Recognition of ascending aortic involvement (type A vs type B) is of paramount importance in determining initial management. The radiology report should also include both the proximal and distal extent of the lesion. Dividing the aorta into zones allows clear reporting. One practical system divides the aorta into the aortic root, ascending aorta, aortic arch (from the origin of the brachiocephalic trunk to the origin of the left subclavian artery), proximal descending aorta (from the origin of the left subclavian artery to the top of the left atrium), distal descending aorta (from the top of the left atrium to the diaphragm), juxtaceliac

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Figure 1. Type A aortic dissection with intramural hematoma and cardiac tamponade. (a–d) Unenhanced transverse CT images show (a) displaced intimal calcifications in aortic arch, (b) intramural hematoma in left half of wall of ascending aorta, and (c, d) large amount of blood in pericardial sac. (e–h) Contrast-enhanced transverse CT images obtained during contrast material injection show intimomedial flap extending longitudinally along course of intimal calcification, separating anterior false lumen from posterior true lumen. (f) False lumen on right side of ascending aorta is enhanced and compresses true lumen. (f–h) Posterior false lumen in descending aorta is unenhanced at this early stage of contrast material distribution. (g) Large mediastinal hematoma is easier to recognize after contrast material administration and causes mass effect on pulmonary arteries. (i–l) Contrast-enhanced transverse CT images obtained after delay show that true and false lumina are now equally enhanced. Delayed enhancement of false lumen illustrates that blood flow is slower in larger false lumen relative to smaller true lumen. (k) At 11 o’clock position, acute angle formed between anterior wall of aorta and intimomedial flap is beak sign (arrow), which is characteristic feature of false lumen. (Figure on facing page.)

Nontraumatic Aortic Emergencies

Figure 1. (caption on facing page).

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Figure 2. Type B aortic dissection in a patient with Marfan disease. (a) Contrast-enhanced transverse CT image at origin of left subclavian artery shows proximal extent of large false lumen. (b) In distal descending aorta, larger false lumen compresses anterior true lumen. (c) Contrast-enhanced and (d) unenhanced transverse CT images at same level show some intimal calcification from posterior wall displaced far anteriorly along intimomedial flap.

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aorta, juxta–superior mesenteric artery aorta, juxtarenal aorta, and infrarenal aorta (11). Further, the report should identify any related complications, including signs of aortic rupture, aneurysm formation, or infarction resulting from compromise of coronary, renal, or mesenteric arteries. CT findings.—Helical CT is highly sensitive and specific for the detection of acute aortic dissection (12). Direct CT signs include (a) detection of an intimomedial flap (Figs 1, 2), (b) compression of the true lumen by a contrast material–enhanced or unenhanced false lumen (Fig 1), and (c) displaced intimal calcification on unenhanced CT images (Fig 2d) (13). Less specific signs include widening of the aorta and thickening of the aortic wall. When endovascular therapy is planned, distinguishing the true from the false lumen becomes important. In most cases, the true lumen is identified by its continuity with the undissected portion of the aorta (14). Additional useful CT signs have been described (14). The beak sign, a feature of the false lumen, is an acute angle formed between the intimomedial flap and the outer wall of the aorta. The beak may be white (filled with contrast material) or gray (filled with hematoma) (Fig 1k). Larger lumen size on cross-sectional images is a feature of the false lumen. In most cases, the true lumen collapses and is compressed by the larger false lumen (Fig 1). Intimomedial rupture has been depicted recently with multi–detector row CT

Figure 3. Type A aortic dissection with intimomedial rupture. Contrastenhanced transverse CT image shows that free edges of intimomedial tear point from true lumen on patient’s left into false lumen on patient’s right.

(15). In 8% of the cases, the free edges of the intimomedial tear point from the true lumen into the false lumen (Fig 3). When multiple phases of scanning are performed after the intravenous administration of contrast material, the false lumen may be noted to have delayed enhancement and delayed washout compared with the true lumen (Fig 1).

Intramural Hematoma Pathology.—The second member of the acute aortic syndrome family, intramural hematoma, was first described in 1920 by Krukenburg (16) but was not widely recognized in the English language radiology literature until the 1990s. Patients with intramural hematoma present with the acute aortic syndrome, clinically indistinguishable from acute aortic dissection. In

Nontraumatic Aortic Emergencies
Figure 4. Type B intramural hematoma that resolved after 4 months. (a, b) Unenhanced transverse CT images show crescentic high-attenuation hematoma on posteromedial aspect of descending thoracic aorta. (c, d) Contrast-enhanced transverse CT images show that intramural hematoma is visible as thickened region of aortic wall. Smooth contour of contrast-filled lumen without intimomedial tear and absence of enhancement help distinguish this intramural hematoma from type B aortic dissection. There are no intimal calcifications to help distinguish intramural hematoma from mural thrombus, but shape and long craniocaudal extent of pathologic findings are typical of intramural hematoma. (e, f) Contrast-enhanced transverse CT images obtained after 4 months of medical therapy show that wall of aorta is uniformly thin, without region of high attenuation, indicating that intramural hematoma has resolved.

acute aortic dissection, the initial lesion is tearing of the intima. In contrast, the initial lesion in intramural hematoma is rupture of the vasa vasorum, resulting in hemorrhage into the aortic media without tearing of the intima (5). Because the lesion is confined to the aortic wall, no false lumen develops. Systemic hypertension and blunt chest trauma are risk factors for development of intramural hematoma (17). Intramural hematoma may progress to aortic dissection. Intramural hematoma involving the ascending aorta (Stanford type A) and the presence of pericardial effusion are predictors of subsequent development of aortic dissection (18). Because of this potential complication, intramural hematoma involving the ascending aorta is usually treated surgically. Intramural hematoma involving the descending aorta is usually treated medically. Intramural hematoma may regress when managed medically (18). CT findings.—The major CT finding of intramural hematoma is a hyperattenuating crescentic eccentrically located region of aortic wall thickening on unenhanced CT images (Fig 4) (13). The hematoma may compress the aortic lumen. The lesion may not

be detectable on contrast-enhanced CT images because the unenhanced hematoma has nearly the same attenuation as the aortic wall when displayed with the window setting sufficiently wide to display the highattenuation contrast material in the aortic lumen. Indeed, the lack of enhancement helps to distinguish intramural hematoma from acute aortic dissection. Intramural hematoma may resolve (Fig 4), may progress to acute aortic dissection, or may rupture (Fig 5). Intramural hematoma should be distinguished from mural thrombus, which is induced by thrombogenic atheroma or alteration in laminar blood flow. Intramural hematoma is a subintimal process, while mural thrombus occurs on the surface of the intima. If the intima is calcified on unenhanced CT images, its position relative to the thrombus or hematoma allows easy distinction between these two entities.

Penetrating Atherosclerotic Ulcer Pathology.—The third member of the acute aortic syndrome family, penetrating atherosclerotic ulcer, was described initially by Shennan in 1934 (19). Stanson and colleagues (20) provided a more complete description

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Figure 5. Ruptured intramural hematoma. (a–c) Unenhanced transverse CT images through descending thoracic aorta demonstrate high-attenuation crescentic region of thickened aortic wall anteriorly and laterally. (c) High-attenuation area extends into aneurysm in distal descending thoracic aorta. Adjacent mediastinal hematoma and large right hemothorax are signs of aortic rupture. (d) Conventional aortogram in left anterior oblique projection shows aneurysm only. Because only the lumen is evaluated with conventional aortography, intramural hematoma is not visible.

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in 1986. Because of the relatively recent recognition of penetrating atherosclerotic ulcer, the literature defining its natural history and correlating imaging and pathologic findings is limited. Patients may present with the acute aortic syndrome or may be asymptomatic. Penetrating atherosclerotic ulcer is defined as an atheromatous ulcer that violates the aortic intima and penetrates into the media (5). In most cases, the ulcer precipitates hemorrhage (intramural hematoma) within the aortic wall. Localized aortic dissection may occur but is limited to the area surrounding the ulcer because transmural inflammation associated with penetrating atherosclerotic ulcer fuses the layers of the aortic wall, which prevents dissection from extending much beyond the ulcer. Penetrating atherosclerotic ulcer may regress, may remain stable in size, may enlarge to form an aneurysm or pseudoaneurysm, or may rupture (21). When compared with acute aortic dissection, penetrating atherosclerotic ulcer occurs in older patients who have extensive atherosclerosis. Penetrating atherosclerotic ulcer occurs in the descending thoracic or abdominal aorta and is relatively uncommon in the ascending aorta. Because penetrating atherosclerotic ulcer is a marker of a severely diseased aorta, surgery is usually reserved for a penetrating atherosclerotic ulcer that has ruptured or one for which medical management has failed.

CT findings.—Calcified atheromatous plaques are readily identified on unenhanced CT images. Ulceration in the center of an atheromatous plaque frequently occurs in patients with advanced atherosclerosis. The diagnosis of penetrating atherosclerotic ulcer is reserved for those relatively rare instances in which a contrast material–filled outpouching extends beyond the plaque and into the wall of the aorta, and the penetrating ulcer is usually surrounded by intramural hematoma (Fig 6) (22).

Aortic Aneurysm Aortic aneurysm may occur anywhere along the aorta from the ascending aorta to the bifurcation. A true aortic aneurysm is defined as focal irreversible dilation of the aorta involving all three layers of the aortic wall. A false aortic aneurysm (pseudoaneurysm) is a focal irreversible dilation of the aorta that does not involve all three layers of the wall. Atherosclerotic aneurysm is the most common example of a true aneurysm. In contrast, traumatic pseudoaneurysm involves tearing of the intima with a focal bulging of the aortic wall contained by the adventitia and possibly a portion of the media. Aneurysms are described according to their shape (fusiform or saccular), location (ascending, descending, or abdominal), and relationship to important vessels (left subclavian, renal, and iliac arteries). Aneurysms are diagnosed when the luminal diameter of

Figure 6. Penetrating atherosclerotic ulcer in aortic arch. (a) Unenhanced and (b) contrast-enhanced transverse CT images at aortic arch show intramural hematoma with intimal calcifications on surface of lumen. If this were mural thrombus, intimal calcifications would have been external to thrombus. (b) Contrast-filled ulcer (arrow) penetrates into media and is surrounded by intramural hematoma.

Nontraumatic Aortic Emergencies

the abnormal segment exceeds the diameter of an adjacent normal segment by at least 50%. Focal dilation of the thoracic aorta to 5 cm or more and dilation of the abdominal aorta to 3 cm or more are the generally accepted criteria for diagnosing an aneurysm. Most atherosclerotic aneurysms are fusiform and often have a smooth contour. In contrast, most infected (mycotic) aneurysms are saccular, with a lobulated contour (23). The pathogenesis of atherosclerotic aortic aneurysms is speculative, but loss of elastin from the media and inner one-third of the adventitia probably plays an important role (24). The etiology of aortic aneurysm is multifactorial, with genetic, environmental, and physiologic factors each contributing (24). In the ascending aorta, congenital disorders such as the Marfan syndrome and the EhlersDanlos syndrome are the main causes. Chronic aortic dissection is another causative factor in the development of ascending aortic aneurysm. In the descending thoracic aorta and the abdominal aorta, hypertension and atherosclerosis are the main risk factors. Infection (mycotic aneurysm and syphilitic aneurysm) and inflammation are relatively uncommon causes. The typical thoracic aortic aneurysm occurs in the descending thoracic aorta, is fusiform in shape, and occurs in an elderly man with hypertension and atherosclerosis. The typical abdominal aortic aneurysm is infrarenal in location and fusiform in shape and occurs in the same type of patient. Many aortic aneurysms are asymptomatic and are discovered incidentally with imaging studies, with patient participation in a health screening program, or at physical examination. These asymptomatic aneurysms are often followed periodically with US, CT, or MR imaging to assess their size and rapidity of enlargement with time. Imaging of asymptomatic aneurysms is intended to identify risk factors for impending rupture so that surgical or endovascular repair may be undertaken just in time (ie, prior to rupture). That is, repair should be timed to occur before the aneurysm ruptures but sufficiently close to the anticipated time

of rupture that the risk of repair is less than the risk of rupture and resultant death (25). The diameter of the aneurysm is the easiest parameter to follow over time. In one large series, the median diameter at which rupture or dissection complicated an atherosclerotic thoracic aortic aneurysm was 6.0 cm in the ascending aorta and 7.2 cm in the descending thoracic aorta (26). Therefore, the authors of that series recommend preemptive surgical therapy for atherosclerotic aneurysms at a diameter of 5.5 cm for ascending aortic aneurysms and 6.5 cm for descending thoracic aneurysms (26). For patients with Marfan syndrome, the parameters are a diameter of 5.0 cm for ascending aortic aneurysms and 6.0 cm for descending thoracic aneurysms (26). In the abdominal aorta, 5.0 cm is a widely quoted threshold for elective repair. Other indications for surgical repair include rupture, acute aortic dissection, pain consistent with rupture, compression on adjacent organs (trachea, esophagus, bronchi), or development of aortic insufficiency (26). Growth of the aneurysm at a rate of 1 cm/y or more is also an indication for repair (26,27). More sophisticated morphologic parameters, such as CT estimation of wall stress, may provide better predictors of the risk of aneurysm rupture (28). This advanced technique requires substantial computing power and the thinner images routinely obtained with multi–detector row CT scanners. Patients with aortic aneurysm come to the emergency center when they have pain related to aortic aneurysm. Symptoms develop when the aortic aneurysm creates a mass effect on an adjacent structure, enlarges rapidly, or ruptures. In an emergency situation, CT scanning without intravenous contrast material may be used to establish the presence and measure the size of an aortic aneurysm. Unenhanced CT will also readily depict signs of aortic rupture or impending aortic rupture. The principal diagnostic sign of aortic rupture is periaortic hematoma (Fig 7). In the thorax, mediastinal hematoma or hemothorax and, in the abdomen, retroperitoneal

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West and Bhalla
Figure 7. Ruptured abdominal aortic aneurysm. (a, b) Unenhanced transverse CT images of abdominal aorta show contained hematoma in right retroperitoneum at 7 o’clock position. (c) Contrast-enhanced transverse CT image at same level as in b shows extensive mural thrombus within abdominal aortic aneurysm. Note intimal calcifications external to mural thrombus at 11, 1, and 5 o’clock positions. Figure 8. Leaking abdominal aortic aneurysm. (a, b) Contrast-enhanced transverse CT images. (a) Image obtained in midportion of abdomen demonstrates complete ring of intimal calcification. Large mural thrombus separates intima from contrastenhanced lumen. (b) More caudally, intimal calcifications are disrupted at 11 o’clock position, with hematoma extending from point of aortic rupture into right retroperitoneum.

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hematoma are easily recognized without intravenous contrast material administration. In the absence of periaortic hematoma, demonstration of a well-defined crescent-shaped area of increased attenuation within the aortic wall indicates impending rupture (29–33). This hyperattenuating crescent sign represents an acute intramural or mural thrombus hemorrhage and is a CT sign of acute or impending rupture. Demonstration of a focal defect in an otherwise calcified aortic wall is another sign of impending aortic rupture (Fig 8) (32). When the clinical situation permits, intravenous administration of contrast material permits detailed morphologic analysis of the aortic aneurysm, particularly when a multi–detector row CT scanner is used. CT angiography demonstrates the anatomic structures of complex aortic aneurysms and shows the relationship of the aneurysm to adjacent vessels (34). The presence and extent of mural thrombus are readily apparent when the aortic lumen is enhanced. In the abdomen, the number and location of renal arteries can be established to aid in planning treatment. CT angiography helps to determine whether or not an aneu-

rysm is suitable for treatment with endovascular stentgraft placement (35–37).

Aortic Occlusion Acute occlusion of the abdominal aorta causes pain, pallor, pulselessness, paresthesia, and paralysis of the lower extremities. Either embolism or in situ thrombosis may cause the occlusion. Paresthesia and paralysis indicate limb ischemia, requiring urgent embolectomy or revascularization (38). CT can be used to identify the level of aortic occlusion but is limited in its ability to show the extent of blockage, which is better assessed with conventional aortography (38).

CT TECHNIQUE
The CT scanning technique and contrast injection technique may be tailored to imaging of the aorta. The use of a general chest, abdomen, and pelvis protocol, which is helpful for evaluation of trauma, limits the spatial resolution and arterial enhancement that can be achieved by optimizing the parameters specifically for aortic imaging.

Figure 9. Motion artifact. Contrastenhanced transverse CT image shows linear band of low attenuation along anterolateral wall of aortic arch that might be mistaken for intimomedial flap.

Obtaining an unenhanced scan prior to the CT angiography is recommended by several authors (13,39,40). Others use only contrast-enhanced examinations (34,41). Advocates of unenhanced imaging emphasize its value for the detection of intramural hematoma and displaced or disrupted intimal calcifications, CT findings that are often obscured by high-attenuation contrast material in the aortic lumen. If unenhanced CT is to be performed, obtaining 5-mm images with a maximum gantry rotation speed, a radiation-efficient detector configuration (4 × 3.75 mm, 4 × 5 mm, 8 × 2.5 mm, or 16 × 1.25 mm), and relatively high table speed (pitch > 1.0:1), should limit radiation exposure while producing acceptable images. As discussed in the section on “Aortic Aneurysm,” a rapid unenhanced CT examination may be the first and only imaging procedure required if aortic rupture is suspected and if CT signs of rupture are unequivocally present. CT aortography may be performed by using standard protocols for contrast material injection, such as 150 mL of nonionic contrast material (300 mg of iodine per milliliter) injected at a rate of at 3.0 mL/sec after a 30-second delay. This standard injection protocol offers the advantage of simplicity. It is a one-sizefits-all approach that will yield adequate but clearly not optimal results. Such an approach is particularly valuable in busy emergency centers, where tailoring contrast material administration to specific clinical indications and patient factors may reduce efficiency or increase the likelihood of an error. Although we intuitively assume that production of the best-quality images results in the best diagnoses, we know of no scientific study that evaluates this hypothesis. In some settings, the one-size-fits-all approach may be preferable. For optimal aortic imaging, the technical details of contrast material administration are critical. In general, high iodine concentrations (300–400 mg of iodine per milliliter) and rapid injection rates (4–6 mL/ sec) are needed. The delay between onset of injection and onset of scanning should be customized to each patient by using either the test-bolus or automatic scantriggering techniques available on all multi–detector row CT scanners. The duration of contrast material in-

jection should be adjusted so that injection continues through the entire scan of the aorta but stops when scanning is completed. The use of a saline flush at the end of contrast material injection offers theoretical advantages in reducing the contrast dose but is not easy to implement in routine clinical practice. For a detailed discussion of techniques of contrast material injection, the reader should consult an excellent article by Fleischmann (42). CT scanner settings for CT angiography are necessarily specific to the vendor and model of the scanner. On single–detector row scanners, the fastest possible gantry rotation time (0.75–1.0 second), moderately thin collimation (3–5 mm), and high pitch (2.0:1) produce good results (43). On four–detector row scanners, the choice of detector configuration will depend on the length of the torso to be scanned. To image the entire thoracoabdominal aorta, including the origins of aortic branches and the iliac arteries, with a four–detector row CT scanner, the 4 × 2.5-mm mode with high pitch (1.5:1) is needed. For shorter scans, the 4 × 1.25-mm mode may be used. On eight– and 16–detector row scanners, the 8 × 1.25-mm or 16 × 1.25-mm mode, with a pitch of 1.35:1 on both eight– and 16–detector row scanners or a pitch of 0.67:1 on 16–detector row scanners, should produce excellent results. Obtaining thinner images in the 16 × 0.625-mm mode is possible, but no published literature is available regarding the utility of submillimeter imaging for aortic abnormalities. Diagnosis may be made from 5-mm transverse CT images. Thinner 2.5-mm images may be useful in selected areas, if finer detail is needed for equivocal findings. Routine review of thin, noisy transverse CT images (0.625–2.5 mm) of the entire aorta is both tedious and impractical. Transverse CT images are sufficient for diagnosis of aortic abnormalities and are probably the only images the emergency radiologist needs to establish the diagnosis. Treatment planning may be aided by analysis of postprocessed images. Two- and three-dimensional maximum intensity projections, curved planar reformations, and multiplanar volume-rendered images depict the gross morphologic structure of the diseased aorta and the relationship to nearby vessels. If these postprocessing techniques are used, obtaining overlapping transverse images improves image quality. A 2:1 overlap is frequently recommended, but the applicability of this degree of overlap to submillimeter images has not been established.

Nontraumatic Aortic Emergencies

PITFALLS
One of the most problematic artifacts encountered in aortic imaging is pulsation of the ascending aorta, which may simulate the appearance of acute aortic dissection or intramural hematoma (Fig 9). Alternatively, aortic pulsations may mask real pathologic

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findings. To some extent, the experienced radiologist can learn to read around these artifacts, but a more definitive solution is needed. The current generation of 16–detector row (or higher) CT scanners with gantry rotation times of 500 msec or less may allow routine use of electrocardiographic gating to substantially reduce aortic pulsation artifacts (44). Technical problems often degrade image quality. Bolus timing errors may be reduced by using test injection or automated scan-triggering tools. Streak artifacts may be reduced, but not eliminated, by moving the upper extremities above the head and by minimizing metal hardware on the torso of the patient. Radiologists become adept at recognizing streak artifacts as linear low-attenuation bands on one or a few adjacent images, usually emanating from an adjacent high-attenuation structure. Streaks from the contrast-enhanced superior vena cava or left brachiocephalic vein are familiar sources of image degradation. To a limited extent, streak artifacts may be reduced by using strategies to dilute contrast material, to add a saline chaser, to inject the right rather than the left arm, or to inject the lower rather than the upper extremity. Normal periaortic anatomic structures may be mistaken for aortic dissection. The origins of the aortic arch branches and the left brachiocephalic, superior intercostal, or pulmonary veins may mimic the appearance of a double lumen (45). The thymus, superior pericardial recess, atelectatic lung, enlarged lymph nodes, pleural thickening, or pleural effusion may lead the unwary into a false diagnosis of aortic abnormalities. In conclusion, CT, particularly multi–detector row helical CT, is an excellent tool for evaluating the aorta for dissection, intramural hematoma, penetrating atherosclerotic ulcer, or aortic aneurysm. Patients with aortic abnormalities often present to the emergency center with the acute aortic syndrome, which is characterized by severe, intense, acute searing or tearing, throbbing, and migratory chest pain. An understanding of the pathology of aortic emergencies, particularly the understanding that failure of the aortic media is common to all of these entities, helps the radiologist to make sense of imaging findings. Unenhanced CT is often valuable and may be the only imaging study required for diagnosis. Contrast-enhanced CT studies performed during peak aortic enhancement allow excellent transverse images of the aorta and are usually sufficient to diagnose and fully characterize the aortic abnormalities. Many postprocessing techniques are available and may aid in treatment planning, but they have not replaced transverse CT images as the primary diagnostic tool for the emergency radiologist.

References
1. Sommer T, Fehske W, Holzknecht N, et al. Aortic dissection: a comparative study of diagnosis with spiral CT, multiplanar transesophageal echocardiography, and MR imaging. Radiology 1996; 199:347–352.

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2. Vilacosta I, Roman JA. Acute aortic syndrome. Heart 2001; 85:365–368. 3. Wooley CF, Sparks EH, Boudoulas H. Aortic pain. Prog Cardiovasc Dis 1998; 40:563–589. 4. Klompas M. Does this patient have an acute thoracic aortic dissection? JAMA 2002; 287:2262–2272. 5. Coady MA, Rizzo JA, Elefteriades JA. Pathologic variants of thoracic aortic dissections: penetrating atherosclerotic ulcers and intramural hematomas. Cardiol Clin 1999; 17:637– 657. 6. Hirst AE Jr, Johns VJ Jr, Kime SW Jr. Dissecting aneurysm of the aorta: a review of 505 cases. Medicine (Baltimore) 1958; 37:217–279. 7. Larson EW, Edwards WD. Risk factors for aortic dissection: a necropsy study of 161 cases. Am J Cardiol 1984; 53:849– 855. 8. Farber A, Wagner WH, Cossman DV, et al. Isolated dissection of the abdominal aorta: clinical presentation and therapeutic options. J Vasc Surg 2002; 36:205–210. 9. Daily PO, Trueblood HW, Stinson EB, Wuerflein RD, Shumway NE. Management of acute aortic dissections. Ann Thorac Surg 1970; 10:237–247. 10. DeBakey ME, Henly WS, Cooley DA, Morris GC Jr, Crawford ES, Beall AC Jr. Surgical management of dissecting aneurysms of the aorta. J Thorac Cardiovasc Surg 1965; 49:130–149. 11. Quint LE, Platt JF, Sonnad SS, Deeb GM, Williams DM. Aortic intimal tears: detection with spiral computed tomography. J Endovasc Ther 2003; 10:505–510. 12. Yoshida S, Akiba H, Tamakawa M, et al. Thoracic involvement of type A aortic dissection and intramural hematoma: diagnostic accuracy—comparison of emergency helical CT and surgical findings. Radiology 2003; 228:430–435. 13. Ledbetter S, Stuk JL, Kaufman JA. Helical (spiral) CT in the evaluation of emergent thoracic aortic syndromes: traumatic aortic rupture, aortic aneurysm, aortic dissection, intramural hematoma, and penetrating atherosclerotic ulcer. Radiol Clin North Am 1999; 37:575–589. 14. LePage MA, Quint LE, Sonnad SS, Deeb GM, Williams DM. Aortic dissection: CT features that distinguish true lumen from false lumen. AJR Am J Roentgenol 2001; 177:207– 211. 15. Kapoor V, Ferris JV, Fuhrman CR. Intimomedial rupture: a new CT finding to distinguish true from false lumen in aortic dissection. AJR Am J Roentgenol 2004; 183:109–112. 16. Krukenburg E. Baitrage zur frage des aneurysma dissecans. Beitr Pathol Anat 1920; 67:329–351. 17. Alfonso F, Goicolea J, Aragoncillo P, Hernandez R, Macaya C. Diagnosis of aortic intramural hematoma by intravascular ultrasound imaging. Am J Cardiol 1995; 76:735–738. 18. Choi SH, Choi SJ, Kim JH, et al. Useful CT findings for predicting the progression of aortic intramural hematoma to overt aortic dissection. J Comput Assist Tomogr 2001; 25: 295–299. 19. Shennan T. Dissecting aneurysms. Medical Research Council Special Report series. London, United Kingdom: Medical Research Council, 1934. 20. Stanson AW, Kazmier FJ, Hollier LH, et al. Penetrating atherosclerotic ulcers of the thoracic aorta: natural history and clinicopathologic correlations. Ann Vasc Surg 1986; 1:15–23. 21. Cho KR, Stanson AW, Potter DD, Cherry KJ, Schaff HV, Sundt TM. Penetrating atherosclerotic ulcer of the descending thoracic aorta and arch. J Thorac Cardiovasc Surg 2004; 127:1393–1401. 22. Macura KJ, Corl FM, Fishman EK, Bluemke DA. Pathogenesis in acute aortic syndromes: aortic dissection, intramural hematoma, and penetrating atherosclerotic aortic ulcer. AJR Am J Roentgenol 2003; 181:309–316.

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23. Macedo TA, Stanson AW, Oderich GS, Johnson CM, Panneton JM, Tie ML. Infected aortic aneurysms: imaging findings. Radiology 2004; 231:250–257. 24. Coady MA, Rizzo JA, Goldstein LJ, Elefteriades JA. Natural history, pathogenesis, and etiology of thoracic aortic aneurysms and dissections. Cardiol Clin 1999; 17:615–635; vii. 25. Juvonen T, Ergin MA, Galla JD, et al. Prospective study of the natural history of thoracic aortic aneurysms. Ann Thorac Surg 1997; 63:1533–1545. 26. Coady MA, Rizzo JA, Elefteriades JA. Developing surgical intervention criteria for thoracic aortic aneurysms. Cardiol Clin 1999; 17:827–839. 27. Scott RA, Tisi PV, Ashton HA, Allen DR. Abdominal aortic aneurysm rupture rates: a 7-year follow-up of the entire abdominal aortic aneurysm population detected by screening. J Vasc Surg 1998; 28:124–128. 28. Fillinger MF, Marra SP, Raghavan ML, Kennedy FE. Prediction of rupture risk in abdominal aortic aneurysm during observation: wall stress versus diameter. J Vasc Surg 2003; 37:724–732. 29. Pillari G, Chang JB, Zito J, et al. Computed tomography of abdominal aortic aneurysm: an in vivo pathological report with a note on dynamic predictors. Arch Surg 1988; 123: 727–732. 30. Posniak HV, Olson MC, Demos TC, Benjoya RA, Marsan RE. CT of thoracic aortic aneurysms. RadioGraphics 1990; 10:839–855. 31. Mehard WB, Heiken JP, Sicard GA. High-attenuating crescent in abdominal aortic aneurysm wall at CT: a sign of acute or impending rupture. Radiology 1994; 192:359–362. 32. Siegel CL, Cohan RH, Korobkin M, Alpern MB, Courneya DL, Leder RA. Abdominal aortic aneurysm morphology: CT features in patients with ruptured and nonruptured aneurysms. AJR Am J Roentgenol 1994; 163:1123–1129. 33. Gonsalves CF. The hyperattenuating crescent sign. Radiology 1999; 211:37–38.

34. Hartnell GG. Imaging of aortic aneurysms and dissection: CT and MRI. J Thorac Imaging 2001; 16:35–46. 35. Thurnher SA, Grabenwoger M. Endovascular treatment of thoracic aortic aneurysms: a review. Eur Radiol 2002; 12: 1370–1387. 36. Fattori R, Napoli G, Lovato L, et al. Descending thoracic aortic diseases: stent-graft repair. Radiology 2003; 229: 176–183. 37. Schoder M, Cartes-Zumelzu F, Grabenwoger M, et al. Elective endovascular stent-graft repair of atherosclerotic thoracic aortic aneurysms: clinical results and midterm followup. AJR Am J Roentgenol 2003; 180:709–715. 38. Surowiec SM, Isiklar H, Sreeram S, Weiss VJ, Lumsden AB. Acute occlusion of the abdominal aorta. Am J Surg 1998; 176:193–197. 39. Bhalla S, Menias CO, Heiken JP. CT of acute abdominal aortic disorders. Radiol Clin North Am 2003; 41:1153–1169. 40. Castaner E, Andreu M, Gallardo X, Mata JM, Cabezuelo MA, Pallardo Y. CT in nontraumatic acute thoracic aortic disease: typical and atypical features and complications. RadioGraphics 2003; 23(special issue):S93–S110. 41. Rubin GD. MDCT imaging of the aorta and peripheral vessels. Eur J Radiol 2003; 45(suppl 1):S42–S49. 42. Fleischmann D. Use of high concentration contrast media: principles and rationale—vascular district. Eur J Radiol 2003; 45(suppl 1):S88–S93. 43. Rubin GD, Shiau MC, Leung AN, Kee ST, Logan LJ, Sofilos MC. Aorta and iliac arteries: single versus multiple detectorrow helical CT angiography. Radiology 2000; 215:670–676. 44. Roos JE, Willmann JK, Weishaupt D, Lachat M, Marincek B, Hilfiker PR. Thoracic aorta: motion artifact reduction with retrospective and prospective electrocardiography-assisted multi–detector row CT. Radiology 2002; 222:271–277. 45. Batra P, Bigoni B, Manning J, et al. Pitfalls in the diagnosis of thoracic aortic dissection at CT angiography. RadioGraphics 2000; 20:309–320.

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Nontraumatic Aortic Emergencies

NOTES

Udo Hoffmann, MD, Ricardo C. Cury, MD, Maros Ferencik, MD, PhD, Fabian Moselewski, BS, Suhny Abbara, MD, and Thomas J. Brady, MD

Cardiac Applications for Multi–Detector Row CT in the Emergency Department1
Although more than 6 million patients present with acute chest pain to emergency departments in the United States each year and roughly a third of them are admitted to the hospital, only a fraction (∼10%) are subsequently diagnosed with acute coronary syndrome. This practice can be attributed to the low sensitivity of early biomarkers (troponin) and changes in the electrocardiogram (ECG) for acute coronary syndrome. In addition, missed acute myocardial infarctions are still responsible for 20% of emergency department malpractice dollar losses (1,2), and the number of missed myocardial infarctions remains relatively high (1%–3%), albeit decreased from approximately 6% many years ago (1,3,4). Despite the fact that significant coronary artery disease (>50% coronary stenosis) is the leading cause of acute coronary syndrome (90%) in patients with acute chest pain, current strategies to diagnose acute coronary syndrome in the emergency department do not include morphologic information on the presence and severity of coronary artery disease. Although cardiac multi–detector row computed tomography (CT) is not a part of the usual clinical care in patients with chest pain, it is conceivable that the fast and noninvasive detection of the presence or absence of significant coronary artery stenosis constitutes an attractive approach to substantially improve the clinical care of patients with acute chest pain.

DIAGNOSTIC STRATEGY FOR PATIENTS WITH ACUTE CHEST PAIN
Patients who present with typical clinical symptoms without initial elevation of enzyme levels who have a nondiagnostic ECG are observed for 6–12 hours while repeat ECG and biomarker tests are performed. Patients may stay in the hospital for 24 hours or longer until a negative stress test has been obtained to exclude acute coronary syndrome. Stress testing is routinely used in clinical practice to assess patients for inducible ischemia, but such testing has limitations. In a population with a 20% prevalence of significant coronary artery disease, exercise tolerance tests and scintigraphic myocardial studies (technetium Tc 99m sestamibi nuclear perfusion imaging or stress [exercise or dobutamine] echocardiography) have good sensitivity for the detection of significant underlying coronary artery disease (sensitivity of 76% for the exercise tolerance test, 83% for technetium Tc 99m sestamibi nuclear perfusion imaging, and 85% for stress echocardiography). With the exception of stress echocardiography, these same three

RSNA Categorical Course in Diagnostic Radiology: Emergency Radiology 2004; pp 59–69.
1From the Department of Radiology, Massachusetts General Hospital, 100 Charles River Plaza, Suite 400, Boston, MA 02114 (e-mail: [email protected]).

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tests have relatively poor specificity (60%, 64%, and 77%, respectively) for the detection of significant underlying coronary artery disease (5–7). In addition, stress tests can only be performed after acute myocardial infarction has been excluded (usually excluded by negative results on two sets of serum troponin assays), and stress tests are complex procedures, requiring time (ie, approximately 150 minutes for stress single photon emission CT) and expertise, which is not usually available 24 hours per day and 7 days per week. Thus, accurate noninvasive detection of significant coronary artery stenosis in the emergency department setting would have an incremental value to current procedures: (a) Patients with chest pain and hemodynamically significant underlying coronary artery disease could be identified more quickly and treated earlier and thus have potentially improved clinical outcomes. (b) The number of unnecessary hospital admissions could be reduced, and the efficacy and cost-effectiveness of the care of patients with chest pain could be improved.

MULTI–DETECTOR ROW CT TECHNIQUE AND PROTOCOLS
With short examination times and robust image quality, cardiac CT imaging constitutes a highly attractive approach for patient work-up in the setting of the emergency department. In addition, most CT scanners now provide easy handling of the large number of CT images, including image reconstruction at different phases of the cardiac cycle and postprocessing. Thus, diagnostic evaluation of the findings from an examination can usually be completed within minutes of completion of the scanning procedure. However, proper selection and preparation of patients are required to optimize diagnostic image quality.

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Patient Selection and Preparation In candidates for CT coronary angiography, relative contraindications are (a) a previous severe reaction to an iodinated contrast agent or (b) renal failure (serum creatinine level, >1.5 mg/dL [>133 µmol/L]). To ensure diagnostic image quality, the heart of the patient should be in sinus rhythm, and a target heart rate of less than 65 beats per minute should be achieved with intravenous administration of short-acting β-adrenergic blocking agents (ie, 5 mg of metoprolol). In most patients in whom the target heart rate cannot be achieved, image quality is suboptimal, and the diagnostic value of the CT scan is limited. In addition, patients should be able to perform a breath hold of 15–25 seconds. A heart rate of less than 65 beats per minute is almost imperative for diagnostic image quality. In our institution, patients receive a short-acting β-adrenergic blocking agent intravenously immediately prior to the examination unless their heart rate is less than 60 beats per minute or contraindications are present (eg, congestive

heart failure, asthma, bradycardia, atrioventricular block). The necessity for β-adrenergic blocking agent administration can be assessed during a test breath hold. Usually, the heart rate drops 5–10 beats per minute during the first 30 seconds of an inspirational breath hold. The patient is placed in the supine position in the scanner, and three ECG leads are attached. An appropriately sized intravenous line is placed into the antecubital vein, although most patients from the emergency department already have intravenous access established. The level of monitoring of those patients typically includes blood pressure, heart rate, ECG, and oxygen saturation, which should be maintained throughout the transport and imaging procedure. The multi–detector row CT imaging protocol for coronary angiography consists of three steps: 1. Localization.—The heart position is localized in a topographic scan of the chest. 2. Determination of contrast agent transit time.—Ten milliliters of a contrast agent (eg, iodixanol [320 mg of iodine per milliliter]), immediately followed by 40 mL of saline (optional), is injected at a flow rate of 4 mL/sec. Ten seconds after initiation of the contrast agent injection, axial images are acquired at the level of the aortic root (3.0-mm collimation), followed by subsequent images acquired at the same level at intervals of 2 seconds. Images are instantly displayed, and imaging is terminated when sufficient contrast enhancement of the aortic lumen is detected. The time interval from initiation of injection to the peak opacification of the ascending aorta represents the transit time of the contrast agent. 3. Data acquisition.—Images are acquired in a spiral mode during injection of 80–100 mL of contrast agent, according to the scan duration, followed by 40 mL of saline solution (optional), at a rate of 4 mL/sec. The start of the image acquisition is delayed according to the previously determined contrast agent transit time. Images are acquired with a pitch of 2.8–3.4 mm per rotation. Typically, images are reconstructed with a 1-mm section thickness and a 0.5-mm overlap (16section multi–detector row CT). Retrospectively, ECGgated half-scan reconstruction is performed. Raw CT data may be archived on a magneto-optical drive or a DVD. However, retrospective reconstruction of data sets can be performed online immediately after the scanning procedure on the console of the CT scanner.

Hoffmann et al

Image Reconstruction and Postprocessing To minimize motion artifacts, the image reconstruction algorithm retrospectively synchronizes the image information with the ECG tracing that is recorded simultaneously. Usually, images are reconstructed at different phases of the cardiac cycle. In many cases, images reconstructed in diastole (between 55% and 65% of the R-R interval) have the fewest motion artifacts, while in some cases, the right coronary artery is better depicted between 35% and 50% of the R-R interval.

Figure 1. Images obtained with different techniques in a patient with significant stenosis of proximal LAD depicted with multi–detector row CT and selective coronary angiography. (a) Axial thin-section (5-mm) MIP multi–detector row CT image shows significant narrowing of vessel lumen, with residual contrast agent filling in presence of eccentric noncalcified plaque (arrow). (b) Curved multiplanar reconstruction along centerline of LAD demonstrates contrast enhancement of mid and distal segments of artery. Arrow indicates noncalcified atherosclerotic plaque. (c) Volume-rendered three-dimensional image (surface shadowing display) of heart demonstrates tomographic view of lesion (arrow). (d) Invasive selective coronary angiographic image demonstrates eccentric stenosis of proximal LAD, with residual filiform lumen (arrow). Quantitative coronary angiography determined 94% luminal obstruction.

Cardiac Applications for Multi–Detector Row CT

To achieve adequate temporal resolution, only information for 180° plus the fan angle is used for image reconstruction, which results in a temporal resolution of 210 msec in the center of rotation (gantry rotation time [Trot] is 0.42 second). A linear interpolation is performed between the data of those two detectors that are closest to the chosen image plane. At heart rates less than 65 beats per minute, only one heart cycle is used to generate an image, and the temporal resolution is Trot/2, assuming that the patient is positioned in the center of the gantry. At higher heart rates, information from different detectors obtained during subsequent heart cycles (M) (as many as three) are used for image reconstruction, which improves the temporal resolution to Trot/(M 2). However, this algorithm requires an extremely stable heart rate. In most cases, beat-to-beat variation causes spatial blurring and impaired image quality. The 16 central rows of the scanner detector define 12 detectors or 16 detectors with 0.75-mm collimated section width (12 × 0.75-mm or 16 × 0.75-mm, respectively), depending on the software version. To limit image noise, images may be reconstructed by using a section thickness of 1 mm and an overlap of 0.5 mm.
•

The resulting data set primarily consists of overlapping axial two-dimensional images. Because of a nearly isotropic resolution and voxel size (0.6 mm × 0.5 mm × 0.5 mm), any arbitrary plane can be calculated without a substantial loss of image information. Depending on the application software, many options are available to depict and display the acquired data. To depict specific regions of interest (such as the origin of the left coronary artery), anatomically adjacent structures including the pulmonary trunk, the bones of the thorax, and the left atrial appendix, have to be digitally removed. Several functions permit moving and cropping or punching of the volume data set to most clearly show the important region and the anatomic structures of interest (Fig 1). Here are some typical postprocessing techniques to illustrate findings. Multiplanar reformations.—The image plane can be chosen arbitrarily. Multiplanar reformations are most often used to generate cross-sectional images of coronary arteries or typical views, such as short- or long-axis views. Curved multiplanar reconstructions.—This algorithm creates a single image that displays the course of a coronary artery (section follows the centerline of the vessel). This display is most useful to demonstrate the course of

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a coronary artery from the ostium to its distal end. Curved multiplanar reconstructions have been shown to be useful in the evaluation of contrast agent–enhanced electron-beam CT scans of coronary arteries (8). Maximal intensity projection.—Reconstructions can be displayed as a single image or as a stack of images summarizing the information from adjacent sections. This results in a loss of spatial detail but improvement in image contrast and a decrease in image noise. Images are similar to conventional angiograms. Maximum intensity projections (MIPs) allow depiction of a longer length of coronary artery lumen and have been shown to be more accurate for the depiction of significant coronary artery lesions than multiplanar reconstructions and three-dimensional displays (9). MIPs are also useful for demonstration purposes. Volume rendering.—Volume rendering includes the entire volume of data, sums the contributions of each voxel along a line from the eye of the viewer through the data set, and displays the resultant composite for each pixel of the display. By using crop and punch functions of modern workstations, three-dimensional images of the heart can be generated within minutes. The volume-rendered display has been shown to be useful in showing the anatomic structures and the spatial relationships of the heart and its surrounding vascular system and may be useful for surgical planning (9,10).

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Figure 2. Axial CT image obtained at level of left main coronary artery (LM ) ostium. Left main coronary artery arises from left sinus of Valsalva and runs posterior to pulmonary artery. Left main coronary artery divides into LAD (LAD ) and left circumflex coronary artery (LCX ). In this image, trifurcation is present. Ramus intermedius (RI ) arises from left main coronary artery. RVOT = right ventricular outflow tract.

Radiation Exposure in CT Coronary Angiography The effective radiation exposure varies from 7.6 to 6.7 mSv in male subjects and from 9.2 to 8.1 mSv in female subjects and is comparable to that from routine CT of the thorax. By using an ECG-controlled dose modulation that reduces the tube current during systole, exposure can be reduced effectively to approximately 4.3 mSv. However, studies to demonstrate the feasibility of this technique are warranted. In comparison, diagnostic selective conventional coronary angiography has a mean effective radiation dose of approximately 5 mSv. Depiction of Coronary Artery Calcification: CT Scanning Protocol The established imaging protocol for coronary calcification uses sequential image acquisition with prospective ECG triggering. Considerations with respect to heart rate and image quality are similar to those for retrospective imaging. However, the literature lacks studies demonstrating the effect of β-adrenergic blocking agents. Scanning is performed by using prospective ECG triggering during a single breath hold (12 seconds) and sequential data acquisition. Scans are prospectively initiated at 50% of the R-R interval. The scan typically results in 48 consecutive nonoverlapped 2.5mm-thick sections (120–140 kVp, 150 mAs, temporal resolution of nearly 330 msec for a gantry rotation time of 500 msec [240° partial scan]). The effective

patient dose is 1.0 mSv. Nonenhanced spiral retrospectively ECG-gated protocols for the depiction of coronary calcium are also available. With less than 3mm collimation and the possibility of multiple reconstructions within the R-R interval, these protocols may yield better sensitivity and reproducibility but at the cost of higher radiation dose.

IMAGE ANALYSIS: DETECTION OF SIGNIFICANT CORONARY STENOSIS
Usually, axial and multiplanar reformatted cross-sectional images reconstructed perpendicular to the vessel centerline and MIPs are used to assess the presence of significant luminal obstruction. The presence of significant luminal obstruction is visually assessed. In our experience, significant stenosis is rarely present as long as some intraluminal contrast enhancement can be detected within the segment in question. Assessment tends to be more accurate in the absence of motion artifacts and calcification. Calcification especially may lead to overestimation of luminal narrowing. The question of whether quantitative measurements are helpful in increasing diagnostic accuracy has yet to be answered.

FINDINGS
Coronary Anatomy A thorough understanding of the coronary artery anatomy is a prerequisite for the correct diagnostic interpreta-

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Figure 3. Axial CT image. Mid and distal segments of LAD (LAD ) are located in interventricular groove. Left circumflex coronary artery (LCX ) runs in left atrioventricular groove close to great cardiac vein (GCV ). RCA = right coronary artery.

tion of CT coronary angiographic findings. Major coronary arteries are well delineated and easy to evaluate on good-quality CT coronary angiograms obtained with the current CT technology (16-section multi–detector row CT, submillimeter collimation, temporal resolution of 210 msec). For a better understanding of the coronary anatomic structures, the appearance of the major coronary arteries in contiguous axial CT images is described. Typically, the American Heart Association’s 16-segment model of the coronary arteries is used to describe the anatomic structures. Two coronary arteries originate from the aorta. The left main coronary artery arises from the left sinus of Valsalva and courses to the left and posterior to the main pulmonary artery. On the left side, the left main coronary artery divides into the left anterior descending coronary artery (LAD) and left circumflex coronary artery (Fig 2). The LAD runs anteriorly in the anterior interventricular groove and gives off diagonal and septal branches (Fig 3). The LAD can be followed to the apex of the heart. The left circumflex coronary artery runs in the left atrioventricular groove close to the great cardiac vein (Fig 3). The left circumflex coronary artery gives off obtuse marginal branches, which supply the lateral wall of the left ventricle. The right coronary artery originates from the right sinus of Valsalva. The ostium of the right coronary artery is typically caudal to the origin of the left main coronary artery in the axial sections. The right coronary artery has a short horizontal proximal segment that runs anteriorly and to the right. More distally, the right coronary artery courses caudally in the right atrioventricular groove. The mid segment of the right

coronary artery is commonly shown in cross section in axial images (Fig 3). The distal segment of the right coronary artery is located in the atrioventricular groove on the inferior surface of the heart and reaches the posterior crux of the heart. The posterior descending coronary artery arises from the right coronary artery in 70% of people (ie, right dominance) and runs in the posterior interventricular groove parallel to the middle cardiac vein. In 10% of people, the left circumflex coronary artery reaches the crux of the heart and continues as the posterior descending coronary artery (ie, left dominance). In 20% of people, the right coronary artery gives rise to the posterior descending coronary artery, but the left circumflex coronary artery gives rise to branches, which supply the inferior wall of the left ventricle (ie, balanced system or codominance). For identification of coronary artery calcification, coronary anatomy is more difficult because the lumen of the coronary vessels is not enhanced. Quantification of coronary artery calcium is performed for the left main coronary artery, the LAD, the left circumflex coronary artery, the right coronary artery, and the posterior descending coronary artery. There are common pitfalls in the evaluation of CT coronary angiographic findings. The LAD may extend above the level of the left main artery ostium. Coronary veins may be confused with coronary arteries or may overlay coronary arteries; specifically, the great cardiac vein frequently overlaps the proximal LAD, ramus intermedius, and proximal left circumflex coronary artery. However, scrolling through the axial sections of the data set, where vascular structures can typically be followed, allows the separation of veins and arteries. In addition, specifically for coronary calcium scoring, artifacts (eg, beam hardening, pacemaker leads, intracoronary stents, valve replacements, bypass clips) may be falsely scored. Also, mitral valve annulus or leaflet calcifications may be confused with midsegment left circumflex coronary artery calcifications. The diagnostic evaluation of coronary CT angiographic findings may be further enhanced with postprocessing of the original data set by using techniques discussed previously (eg, MIPS, volume rendering).

Cardiac Applications for Multi–Detector Row CT

Pathologic Findings Typical pathologic findings in patients referred for cardiac CT in the emergency department include disease of the coronary arteries, myocardium, and paracardiac structures. The diagnostic implications of such findings are discussed in the following paragraphs. The cause of chest pain includes more than 50 different diagnostic possibilities. The most important differential diagnoses include aortic dissection and pulmonary embolism, which are discussed extensively elsewhere in this syllabus. For a complete overview of differential diagnoses, we refer the reader to Gibbons et al (11).

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Figure 4. Images of a patient with unstable angina. (a) Fivemillimeter thin-slab MIP multi– detector row CT image shows stenosis (arrow) in right coronary artery. (b) Invasive selective coronary angiographic image confirms presence of significant stenosis (arrow) at identical location.

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Figure 5. Images of a patient with acute myocardial infarction who underwent successful thrombolysis. (a) Coronary angiographic image shows occlusion (arrow) of LAD (LAD) just distal to second diagonal branch (2DIAG). 1DIAG = first diagonal branch. (b) Multi–detector row CT image demonstrates perfusion deficit (area between white arrows) in same region supplied by distal LAD, in anteroseptal segment of mid and apical portions of left ventricular myocardium, representing area of acute myocardial infarction. Note large thrombus (arrowhead) within left ventricular cavity. LA = left atrium, LV = left ventricle, RV = right ventricle. (c) Volume-rendered multi–detector row CT image obtained after successful thrombolysis during invasive coronary angiography demonstrates patent distal LAD (arrow) after second diagonal branch (2DIAG). LAD = left anterior descending coronary artery, LCX = left circumflex artery, 1DIAG = first diagonal branch.

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Cardiac CT imaging is unlikely to be performed in patients with known myocardial infarction, ongoing angina, or hemodynamic instability. However, patients with a typical clinical manifestation, nonspecific ECG changes (ST-segment depression < 1 mm, T-wave

inversion), and negative initial serum cardiac markers or patients with unstable angina may profit from detection or exclusion of significant coronary artery stenosis (Fig 4). The nature of the occlusion may be identified in some patients (eg, thrombotic occlusion

Figure 6. Multi–detector row CT images of acute thrombotic occlusion of left circumflex artery in a patient with recent myocardial infarction. (a) Curved multiplanar reformation image of left circumflex artery shows proximal stenosis (arrowhead) and midthrombotic occlusion (arrow). (b) Cross-sectional multiplanar reformation image of left circumflex artery shows typical appearance of thrombotic occlusion (arrow).

Cardiac Applications for Multi–Detector Row CT

Figure 7. Images of a patient obtained after coronary artery bypass surgery. (a) Volume-rendered multi–detector row CT image shows patent left internal mammary artery graft to LAD (arrows) and saphenous vein graft to first obtuse marginal branch (arrowheads). (b) Volume-rendered multi–detector row CT image demonstrates patent saphenous vein graft (arrows) to posterior descending coronary artery.

Figure 8. Image of a patient with atypical chest pain. Thinslab MIP reconstruction demonstrates two nonstenotic calcified and noncalcified plaques (arrows) of mid right coronary artery.

of long segments of the artery) (Fig 5). In patients with acute myocardial infarction who receive systemic thrombolysis without percutaneous intervention, cardiac multi–detector row CT may be used to demonstrate the success of thrombolysis (Fig 6). Because the acquired CT data permit the assessment of left ventricular function, the assessment of global and regional wall motion abnormities, myocardial thinning consistent with scar tissue, and previous myocardial infarction may be possible. CT may also be used to depict thrombi (Fig 6) typically found in the presence of left ventricular aneurysms and impaired left ventricular function. The findings in some cases suggest that CT may be able to be used to depict perfusion deficits in acute myocardial infarction. In patients with coronary artery bypass grafts, graft patency can be assessed (Fig 7). In patients who have a history of chest pain or atypical chest pain, nonobstructive calcified and noncalcified coronary atherosclerotic plaques may be detected (Figs 8, 9). In addition, although the condition

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Figure 9. Images demonstrating positive remodeling in left main coronary artery of a patient with a history of chest pain. (a) Curved reconstruction of left main coronary artery and LAD demonstrates positive remodeling with small calcified and noncalcified plaque (arrow) in left main coronary artery. (b) Cross-sectional image at level of the left main coronary artery shows mixed plaque (arrow) with calcified and noncalcified components. Figure 10. Images showing anomalous right coronary artery of a patient with syncope and exertional chest pain. (a) Thinslab MIP shows anomalous origin of right coronary artery (arrow) from left sinus of Valsalva, with narrowing of proximal right coronary artery segment when it travels between main pulmonary artery (MPA) and ascending aorta (AO). Note normal origin of left main coronary artery (arrowhead). (b) Volume-rendered image also demonstrates anomalous origin of right coronary artery (arrow) from left sinus of Valsalva, adjacent to origin of left main coronary artery (arrowhead).

is rare, anomalous origin of a coronary artery may be detected (Fig 10).

DIAGNOSTIC VALUE OF MULTI–DETECTOR ROW CT
Detection of Significant Coronary Artery Stenosis in Patients with Stable Angina Although the examples in the preceding paragraphs suggest that multi–detector row CT may be used to improve the diagnosis of acute coronary syndrome in patients with acute chest pain, no systematic analysis

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of the diagnostic value of cardiac multi–detector row CT in the emergency department has been reported. We summarize here the results of available studies that have been conducted in patients with stable angina. Considerable selection bias is prevalent throughout the individual case series because only patients who were highly suspected of having significant coronary artery disease were included. Early studies with electron-beam CT and early versions of multi–detector row CT scanners (equipped with four detectors and a temporal resolution of 250–

Table 1 Pooled Measures of Accuracy from a Meta-analysis of the Current Literature Regarding CT for the Detection of Significant Coronary Artery Stenosis Multi–Detector Row CT Electron-beam CT Simple Method Assessable segments only Weighted mean sensitivity Weighted mean specificity All segments Weighted mean sensitivity Weighted mean specificity Per patient Weighted mean sensitivity Weighted mean specificity Mean LL 95% UL 95% 4 Detector Rows Mean LL 95% UL 95% 16 Detector Rows Mean LL 95% UL 95%

Cardiac Applications for Multi–Detector Row CT

(%) (%) (%) (%) (%) (%)

82 87 69 67 81 54

79 84 66 64 78 51

85 89 72 71 84 57

84 93 67 77 86 80

81 91 63 74 83 77

88 96 71 81 89 84

92 93 83 85 91 82

87 89 76 79 87 76

97 97 89 91 96 89

Note.—LL = lower limit, UL = upper limit.

330 msec) showed that cardiac CT could be used to detect significant coronary stenosis with high sensitivity and excellent specificity: For electron-beam CT, the sensitivity was 82% ± 6.4, and the specificity 87% ± 0.6, and for multi–detector row CT, the values were 81% ± 7.2 and 91% ± 0.9, respectively, when compared with selective conventional coronary angiography in segments that could be evaluated. However, the clinical applicability of these methods was limited by incomplete CT evaluation of coronary anatomic structures: Roughly one-third of all coronary artery segments could not be evaluated because of stair-step and motion artifacts and the presence of calcification. If all coronary segments were included, diagnostic accuracy substantially decreased for electron-beam CT and for multi–detector row CT (sensitivity, 68% ± 4.3 and 63% ± 2.9, respectively; specificity, 68% ± 0.2 and 71% ± 0.2, respectively) (12−18). Initial reports of 16-section technology are promising. Results show improved diagnostic accuracy for the depiction of significant stenosis in assessable segments (92% sensitivity, 93% specificity) compared with elective conventional coronary angiography. Improved image quality achieved with better spatial and temporal resolution led to a substantial decrease of the number of segments that could not be evaluated in coronary vessels more than 1.5 mm in diameter (12%). Subsequently, sensitivity and specificity with the inclusion of all segments increased considerably (84% and 85%, respectively) (19,20). Results from a recent meta-analysis are summarized in Table 1. In addition to the detection of coronary artery stenoses and occlusions, CT imaging provides other information of potential value in patients with acute chest pain. Global and regional left ventricular function can be assessed with high accuracy. The depiction

of myocardial perfusion deficits has been demonstrated, and the results of preclinical studies have illustrated the potential to assess microvascular function.

Comparison with Magnetic Resonance Imaging Magnetic resonance (MR) imaging is being intensively explored because of its potential for coronary vessel depiction (21−24). In spite of impressive advances, MR still requires temporally prolonged acquisitions and data averaging during several (as many as 40) heart beats to generate one image, which substantially limits image quality. In addition, a sufficient signal-to-noise ratio relies on relatively thick (1.5-mm) sections that importantly limit spatial resolution. In a recent multicenter study of 109 patients, MR imaging demonstrated moderate accuracy (72%) for the detection of significant coronary artery stenosis (25). In one study, investigators assessed the value of MR imaging in 161 patients with chest pain who had a nondiagnostic ECG for acute myocardial infarction and found a significant benefit compared with the usual clinical care and diagnostic tests; the benefit was derived predominantly from accurate assessment of left ventricular function at rest (26). Despite the natural advantage of MR for soft-tissue imaging, artifacts caused by cardiac and respiratory motion and the relatively low spatial resolution remain challenges for coronary MR imaging. More important, long imaging times limit its applicability in the setting of evaluating patients in the emergency department. Consequently, coronary MR imaging is rarely available in emergency departments and currently would be less feasible to incorporate into the rapid evaluation of patients with chest pain, compared with multi–detector row CT.

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Table 2 Predictive Value of the Presence or Absence of Coronary Artery Calcification for Coronary Events in Patients with Acute Chest Pain and Uncertain Myocardial Infarction Positive Predictive Value NA 0.08 0.26 Negative Predictive Value 1.00 0.98 1.00

Reference Laudon et al (27) McLaughlin et al (28) Georgiou et al (29) Note.—NA = not available.

Year 1999 1999 2001

Modality Electron-beam CT Electron-beam CT Electron-beam CT

No. of Patients 105 134 192

Sensitivity 1.00 0.88 1.00

Specificity NA 0.37 0.47

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Coronary Artery Calcification in Patients with Acute Chest Pain The only experience with cardiac CT in patients with acute chest pain comes from the results of a few studies in which electron-beam CT depiction of coronary artery calcification was used to predict the likelihood of acute coronary syndrome in patients with acute chest pain (Table 2) (27−29). In those studies, investigators demonstrated that the absence of coronary calcifications had a high negative predictive value for acute coronary syndrome. Although these results are promising, imaging of coronary calcification is not routinely used in the diagnostic work-up of patients with acute chest pain. Indeed, the role of coronary calcification is controversially discussed. Among individuals dying of sudden cardiac death, calcium was found in only 50% of the coronary artery “culprit” lesions. In addition, the absence of coronary calcification does not imply the absence of any coronary atherosclerotic plaque, especially in young patients. Moreover, noncalcified plaque may be more prone to rupture and cause symptoms and events than calcified plaque because noncalcified plaque consists of a lipid core and a thin “unstable” fibrous cap. In summary, diagnostic tools that permit the reliable and rapid triage of patients with acute coronary syndrome are urgently needed. Imaging may play a prominent role in that work-up if it provides accurate information in an economically reasonable way. CT imaging with multi–detector row CT (16 sections or more) has matured to a stage that permits reliable depiction of the coronary arteries after intravenous injection of a contrast agent. Currently available data suggest a high negative predictive value of multi–detector CT in the assessment of hemodynamically relevant coronary artery lesions in the absence of calcifications and motion artifacts. Although no study has specifically investigated the usefulness of cardiac CT in the setting of acute chest pain, the ability of multi–detector row CT to provide additional information on coronary atherosclerotic plaque burden and left ventricular function makes cardiac CT likely to be beneficially integrated into the work-up of patients with acute chest pain. However, dedicated trials have not been

completed, and we must await their results before recommendations for use can be made.

References
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Cardiac Applications for Multi–Detector Row CT

NOTES

Nisa Thoongsuwan, MD, Jeffrey P. Kanne, MD, and Eric J. Stern, MD

Imaging of Blunt Chest Trauma1

Trauma is the leading cause of death in Americans younger than 45 years of age (1). Blunt chest trauma is the second most common cause of death in trauma patients, following injury to the central nervous system. This chapter will discuss the imaging findings of chest trauma, organized by specific organ or structure, including lung parenchyma, pleura, airway, and chest wall. Injury to the aorta and great vessels will be discussed elsewhere.

MECHANISM OF INJURY IN BLUNT CHEST TRAUMA
Three main mechanisms of injury are associated with blunt chest trauma: (a) rapid acceleration and/or deceleration, (b) direct impact, and (c) thoracic compression (2,3). Acceleration/deceleration injuries are often caused by a motor vehicle accident or a fall from a height (4), leading to shearing forces on tissues, organs, and blood vessels that can result in tissue disruption. The most lethal shearing injury is aortic rupture, which can be fatal within seconds (3). Direct-impact injuries result from a motor vehicle accident, a fall, or a direct blow from a moving object, leading to localized chest wall injury, such as fractures of the ribs, sternum, and scapulae and soft-tissue hematoma. Direct-impact forces can also injure the lungs and heart because kinetic energy is transmitted through the chest wall into the deeper tissues. Secondary penetrating injuries may also be seen. Compression injuries often occur in the setting of rapid deceleration as tissues strike a fixed object such as the chest wall or spine, leading to organ rupture, contusion, or hemorrhage (5).

IMAGING FOR BLUNT CHEST TRAUMA
Supine anteroposterior chest radiography is the initial, as well as the most common, imaging examination used for evaluating the condition of a patient who is suspected of having blunt chest injury. Many common injuries are identified with the chest radiograph alone. However, in severely injured patients, the ideal upright full-inspiratory posteroanterior chest radiograph cannot be obtained, and suboptimal supine radiographs, often with poor positioning, poor inspiration, and underlying backboard and overlying monitoring equipment, are generally the rule, rather than the exception. These factors can easily hinder depiction of injuries.

RSNA Categorical Course in Diagnostic Radiology: Emergency Radiology 2004; pp 71–79.
1From the Department of Radiology, Harborview Medical Center, 325 Ninth Ave, Box 359728, Seattle, WA 98104-2499 (e-mail: [email protected]).

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Computed tomography (CT) of the chest, particularly in the era of multi–detector row CT technology, has become a common examination for imaging the trauma patient with known or suspected thoracic injury because CT scanners are available in almost all trauma centers and because scan times have markedly decreased. The clear advantage of chest CT over radiography is the ability of chest CT to depict occult injuries that may not be evident on a supine chest radiograph, such as mediastinal hematoma, pneumothorax, or hemopericardium (6). Transesophageal echocardiography may have a role in evaluating patients with blunt chest trauma. Despite its dependence on the skill of the operator, transesophageal echocardiography has been found to be particularly useful in assessing the descending thoracic aorta for injury, as well as cardiac structure and function in selected cases (7). These imaging studies are an essential component of evaluating the trauma patient after assessing and stabilizing the airway and respiratory and cardiac function. It is essential to identify life-threatening conditions on the chest radiograph, such as pneumothorax, hemothorax, abnormal mediastinum (possibly suggestive of aortic or other great vessel injury), and thoracic spine fracture, as well as malpositioned life-support devices. The technical limitations of a chest radiograph should be declared when it is difficult or impossible to exclude a life-threatening injury, and alternative imaging studies should be suggested (8).

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Figure 1. Supine chest radiograph of a 12-year-old boy injured in high-speed motor vehicle accident shows peripheral parenchymal opacity of left lung, compatible with pulmonary contusion. Also note soft-tissue swelling of left chest wall (arrows).

LUNG PARENCHYMA
Pulmonary Contusion Pulmonary contusion (Fig 1) is a term that describes interstitial and alveolar injury without substantial laceration. Pulmonary contusion is the most common pulmonary injury resulting from blunt chest trauma (9). Pathologically, both hemorrhage and transudate fill the alveolar interstitium following loss of alveolar capillary integrity without accompanying major parenchymal disruption (10). The mechanism for this injury involves local compressive and recoil forces within the lung (9,11–14). Although the radiographic findings of pulmonary contusion are nonspecific, ranging from irregular confluent or discrete nodular opacities to large opacities, the time course of the development and evolution of the opacity is the key to identifying this injury (12). Pulmonary contusions typically appear within hours of injury and clear within 7 days (12). Moreover, the pulmonary opacities found in pulmonary contusion occur in a nonanatomic distribution, in contrast to opacities resulting from pneumonia or aspiration (15), because the energy absorbed has no respect for bronchovascular segmental anatomic structures.

Figure 2. CT scan of a 36-year-old woman injured in highspeed motor vehicle accident shows round air-containing lesion in right lung, consistent with type 1 pulmonary laceration.

CT is highly sensitive and is more specific than chest radiography for identifying pulmonary contusion (16). Pulmonary contusion appears as an illdefined area of peripheral consolidation at CT. Although chest radiographs are useful, they may not depict a contusion early in its course (1) because the contusion may be obscured by comorbidities.

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Pulmonary Laceration Pulmonary laceration is a tear in the lung parenchyma. The mechanism of injury centers on either shearing forces from blunt trauma or direct puncture from a penetrating injury (9,12–14). As a result

Imaging of Blunt Chest Trauma

Figure 3. (a) Supine chest radiograph of a 15-year-old girl involved in high-speed motor vehicle accident shows elliptical air-fluid lesion at right cardiophrenic sulcus (arrow), representing type 2 pulmonary laceration. (b) Transverse CT scan better defines pulmonary laceration (arrow).

Figure 4. Transverse CT scan of a 25-year-old man injured in high-speed motor vehicle accident shows round air-containing lesion (white arrow) in right lung adjacent to fractured rib (black arrow), consistent with type 3 pulmonary laceration.

of the recoil properties of the adjacent lung, the initial linear parenchymal tear rapidly becomes an ovoid or round space (9,12). When the laceration fills with blood, it can be called a hematoma. If the space fills with air, it can be referred to as a traumatic pneumatocele. Frequently, both blood and air are present; therefore we prefer to use the term pulmonary laceration to cover all scenarios. The typical radiographic appearance of pulmonary laceration is a round lesion containing either air or both air and fluid. Pulmonary lacerations commonly are seen as isolated lesions but may be multiple. Most pulmonary lacerations are 2–5 cm in diameter, but they can occasionally be extremely large, as much as 14 cm in diameter. Pulmonary lacerations are present at the time of injury but may

be obscured by surrounding pulmonary contusion, hemothorax, and pneumothorax (9,17). Pulmonary lacerations can be categorized into four types on the basis of the mechanism of injury, as described by Wagner et al (12). A type 1 pulmonary laceration (Fig 2) is typically a large (2–8-cm) cavity filled with a variable amount of air and blood occurring deep within the pulmonary parenchyma. Type 1 pulmonary laceration results from sudden compression of the pliable chest wall against the closed glottis, which causes the air-containing parenchyma to rupture. Type 2 pulmonary laceration (Fig 3) also results from rapid compression of the chest wall. In this case, however, lung injury occurs from shearing forces as the lung is squeezed over the vertebral bodies. The resulting laceration typically occurs in the paraspinal lung parenchyma. These lacerations can be long and tubular, rather than spherical. A type 3 pulmonary laceration (Fig 4) typically appears as a small peripheral area of low attenuation intimately associated with an adjacent rib fracture and is caused by puncture with a fractured rib. Type 3 pulmonary lacerations are often multiple. Type 4 pulmonary laceration is the result of a previously formed, firm pleuropulmonary adhesion causing the lung to tear when the overlying chest wall is violently compressed inward or is fractured. This type of pulmonary laceration is almost always and only identified at surgery or autopsy. The findings from one study showed that the most common type of pulmonary laceration is type 1, followed by type 3 and type 2. Type 4 pulmonary lacerations were rare (12).

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Figure 5. Supine anteroposterior chest radiograph of a 54year-old man who fell 20 ft (6 m) shows increased lucency of right hemithorax and deep sulcus sign (arrows), indicative of right pneumothorax.

Figure 6. Nonenhanced transverse CT scan of an 83-year-old woman who fell shows bilateral pleural collections. The fluidfluid level in right pleural space (arrow) is referred to as hematocrit sign and is indicative of hemothorax.

PLEURA
Pneumothorax Pneumothorax (Fig 5) is a collection of gas in the pleural space. Pneumothorax occurs in 15%–38% of the patients with blunt chest trauma (18,19). Because pneumothorax is usually associated with rib fracture, the mechanism of injury is generally a direct puncture of the visceral pleura, with subsequent air leakage into the pleural space (20). Although the clinical importance of the pneumothorax is not dependent on its size, but rather on the underlying cardiopulmonary function of the patient, almost all pneumothoraces in victims of trauma should be considered clinically important, given that pneumothoraces can rapidly become life threatening when patients receive general anesthesia or are treated with positive pressure mechanical ventilation (21,22). As previously mentioned, in the setting of trauma, the chest radiograph is usually obtained with the patient supine. When the patient is supine, free intrapleural gas preferentially collects in the nondependent anteromedial and inferior aspect of the pleural space. Consequently, the radiographic findings of pneumothorax on supine radiographs are different from those seen on upright radiographs. Radiographic features of pneumothorax on the supine radiograph include the deep sulcus sign (prominence of the costophrenic angle), basilar hyperlucency, unusual sharp delineation of the mediastinal or cardiac contour, and clear depiction of the apical pericardial fat pad (8,14,23). When an upright chest radiograph cannot be obtained and in the appropriate clinical setting, lateral decubitus or cross-table lateral radiographs may demonstrate a pneumothorax.

CT is the most accurate method for detecting pneumothorax (24). The advantages of CT over radiography are (a) CT is performed with the patient supine, and (b) CT can be used to distinguish pneumothorax from gas in the overlying soft tissues (8). Because the smallest pneumothorax can develop into a life-threatening tension pneumothorax, chest CT should be considered in patients with no evidence of pneumothorax on the supine radiograph who are at risk for pneumothorax and who will receive positive pressure ventilation (8,9,14). Some trauma centers also routinely obtain CT images through the lung bases as a part of an abdominal trauma CT protocol, potentially identifying radiographically occult pneumothoraces (24). When carefully sought, pneumothoraces can also be depicted on cervical or thoracic spine CT scans. Tension pneumothorax is one of the most common life-threatening intrathoracic injures caused by blunt trauma (25). The diagnosis in most cases is made from clinical signs and symptoms, which include dyspnea, hypoperfusion, jugular venous distention, diminished breath sounds on the affected side, hyperresonance to percussion, and tracheal shift to the unaffected side (1). The radiographic findings resulting from tension pneumothorax include (a) increased lucency of the affected hemithorax with contralateral displacement of the mediastinum and trachea and (b) flattening or even inversion of the ipsilateral hemidiaphragm (20).

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Hemothorax Hemothorax is a collection of blood within the pleural space. Bleeding from low-pressure vessels may subside spontaneously or following placement of a pleural drain (8). However, massive hemotho-

Imaging of Blunt Chest Trauma

Figure 7. Images of an 18-year-old man injured in motor vehicle accident. (a) Supine radiograph shows right pneumomediastinum and right pneumothorax. (b) Transverse CT scan demonstrates tracheal laceration (arrow). Note the collapsed lung (∗) has fallen away from the hilum inferiorly and laterally, which is also called the fallen lung sign.

rax is a life-threatening condition because of potential mass effect on the heart and great vessels from the accumulated blood, acute hypovolemic shock, and hypoxia from lung collapse (2). The findings of hemothorax on the supine chest radiograph are often indirect. They include (a) diffusely increased opacity through the affected hemithorax, (b) a homogeneous crescent-shaped opacity interposed between the inner margin of the ribs and the lung, or (c) an apical cap (a crescent opacity over the lung apices on the supine radiograph) (8). At CT, particularly in the acute setting, blood products in the pleural space may have increased attenuation, and when active bleeding is present, layering of fluids with different attenuation may occur. This layering is referred to as a hematocrit layer or the hematocrit sign (Fig 6).

AIRWAY
Tracheobronchial Laceration Among patients sustaining blunt chest injury, the occurrence of tracheobronchial laceration is rare. In this group, tracheal rupture accounts for approximately 15%–27% of all tracheobronchial lacerations and is associated with higher overall morbidity and mortality (26–28). The diagnosis of tracheal rupture may be delayed because of its rarity and its often nonspecific clinical and radiographic manifestations. In addition, other more common associated injuries, such as the rupture of the great vessels, may mask underlying tracheobronchial laceration (27,29). The injuries to the tracheobronchial tree can be divided into intrathoracic and extrathoracic types. We will discuss only the intrathoracic type. Mecha-

nisms of intrathoracic tracheobronchial laceration include a sudden increase in intra-airway pressure against a closed glottis at the time of impact. This increase can cause a tear across the lower tracheocarinal junction from anteroposterior chest compression forcing the lungs apart laterally. Other mechanisms include hyperextension of the neck, direct crush injury of the trachea between the sternum and thoracic spine, and sudden and rapid deceleration with shearing force applied to the relatively fixed cricoid cartilage and carina (26,28,30). The most common radiographic manifestations of tracheobronchial laceration are pneumomediastinum and pneumothorax, occurring in approximately 70% of patients (31). The “fallen lung” sign, while diagnostic, rarely occurs and represents complete disruption of all anchoring attachment of the lung to the hilum. The transected lung falls against the posterolateral chest wall or hemidiaphragm (32–34), and there is a dramatic hydropneumothorax. This sign is more readily apparent at CT than on the chest radiograph (35) (Fig 7). CT of the chest with an appropriate window setting can frequently show the exact site of a tear, manifesting as a focal defect in or a circumferential absence of the tracheal or bronchial wall, a central airway wall contour deformity, abnormal communication of the central airway with other mediastinal structures (36–39), overdistention of the endotracheal tube balloon, herniation of the deformed endotracheal balloon beyond the trachea, or extraluminal location of the endotracheal tube (40). Indirect signs, such as deep cervical emphysema and pneumomediastinum, should raise suspicion for tracheobronchial injury in the appropriate clinical setting (28,41–43).

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Diaphragmatic Injury Diaphragmatic injury (Fig 8) occurs in as many as 8% of the patients with blunt trauma injuries (44), occurring most often in young men injured in motor vehicle accidents (11,45). Diaphragmatic injury can be a diagnostic challenge because of occasional subtle imaging findings or the presence of associated and more apparent injuries, such as pelvic fracture (40%–55%), splenic injury (60%), and renal injury (46), which may receive more clinical attention. Failure to identify diaphragmatic injury may lead to intrathoracic visceral herniation and subsequent strangulation, with mortality and morbidity rates as high as 50% (47). The mechanisms of injury include (a) lateral impact, which distorts the chest wall and tears the diaphragm, and (b) a direct blow to the abdomen, leading to increased intraabdominal pressure and subsequent diaphragmatic rupture (46). In contrast to penetrating injuries, injury sustained from blunt chest trauma usually produces a long tear, generally longer than 10 cm, and occurs in the posterolateral aspect of the hemidiaphragm between its intercostal attachment and the lumbar spine (44). Chest radiographic findings specific for diaphragmatic rupture include intrathoracic herniation of a hollow viscus and depiction of the nasogastric tube above the left hemidiaphragm (44). Other radiographic findings that are suggestive of but not specific for diaphragmatic injury include apparent elevation of the hemidiaphragm, distortion or obliteration of the diaphragmatic outline, and a contralateral shift of the mediastinum (48). Even though chest radiographs are recommended in all patients with major trauma, chest radiographs are insensitive for identifying diaphragmatic rupture (sensitivity of 46% for the left and 17% for the right) (48). Delayed rupture of the diaphragm has been reported in intubated patients as positive pressure ventilation is withdrawn (49). With the advent of helical and now multi–detector row CT technology, the diagnostic accuracy of CT for diaphragmatic injury has improved (50). CT has a reported sensitivity and specificity of 61%–71% and 87%–100%, respectively, for acute traumatic diaphragmatic rupture (51,52). CT findings suggestive of hemidiaphragm rupture include discontinuity of the hemidiaphragm (73% sensitivity and 90% specificity) (52,53), intrathoracic herniation of abdominal contents (55% sensitivity and 100% specificity) (52), the collar sign (a waistlike constriction of the herniating hollow viscus at the site of diaphragmatic tear, with 63% sensitivity and 100% specificity) (51), and the dependent viscera sign (herniated viscera layering dependently in the hemithorax against the posterior ribs). In one series, investigators reported a positive dependent viscera sign with 100% of left and 83% of right hemidiaphragmatic injuries (45).

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Figure 8. Chest radiograph of a 20-year-old man involved in motor vehicle accident shows nasogastric tube (arrow) coursing into left hemithorax above the expected position of diaphragm, indicating diaphragmatic rupture and herniation of stomach into chest.

Even though CT has a higher sensitivity and specificity than chest radiography for diaphragmatic injury, several pitfalls must be avoided so as not to misdiagnose diaphragmatic injury. A Bochdalek hernia, a congenital posterolateral diaphragmatic defect occurring predominantly on the left and occurring in approximately 6% of asymptomatic adults, can mimic diaphragmatic rupture (54). Diaphragmatic eventration can also mimic diaphragmatic tear; however, coronal and sagittal reformations are helpful in demonstrating the isolated focal elevation of the hemidiaphragm without discontinuity (44). When diaphragmatic rupture manifests with pleural effusion, the underlying defect may be obscured, particularly with small tears without associated herniation of intraabdominal contents (44). Magnetic resonance (MR) imaging is not ideal for the initial evaluation of diaphragmatic injury and should be reserved for patients with equivocal findings at CT or delayed signs and symptoms of a diaphragmatic tear (44).

CHEST WALL INJURY
Rib Fractures Rib fractures are the most common injury following blunt chest trauma (13,55). The most common sites of rib fractures are ribs 4–9 laterally, where there is less overlying musculature (3,25). However, fracture of the first and/or second rib is a hallmark of high-energy trauma because these ribs are short, thick, and relatively well protected by the thoracic muscles (3). Injuries associated with first and second rib fractures

Sternal Fracture Sternal fracture (Fig 9) occurs in about 8% of the patients admitted for blunt chest injury (59), and the majority of such fractures occur in elderly patients. Motor vehicle accidents are the cause of about 80% of sternal fractures (20). Sternal fracture is generally a marker for high-energy trauma and is associated with injuries to mediastinal structures, such as the heart, great vessels, and tracheobronchial tree. Sternal fractures cannot be seen on frontal chest radiographs. A lateral view may help to identify a sternal fracture, but CT is the examination of choice, especially because it can show associated mediastinal injuries (13). Sternoclavicular Dislocation The mechanism of injury is generally a lateral compression force to the shoulder, with the force transmitted through the clavicle, or a direct blow to the medial aspect of the clavicle. The epiphysis usually remains attached to the sternum, but the medial aspect of the clavicular shaft may be displaced anteriorly or posteriorly. Anterior dislocation of the medial head of the clavicle is more common than posterior dislocation. However, posterior sternoclavicular dislocation is far more serious because of the risk of great vessel injury (60). Chest radiographs provide somewhat limited depiction of the sternoclavicular joints because of overlying structures. Again, CT is superior to radiography in evaluating the presence and complications of sternoclavicular dislocation. However, the key to recognizing this injury is clinical evaluation, with imaging used to confirm the presence of the injury (14). Scapular Fracture The scapula is a well-protected structure, and, therefore, a scapular fracture is a marker of high-energy trauma. On the chest radiograph, scapular fracture is overlooked in as many as 43% of the patients. Moreover, 72% of these unobserved fractures are visible in retrospect on the initial radiograph (61). CT is more sensitive than radiography for depicting the fracture site and its associated injuries, which include rib fractures, pneumothorax, hemothorax, and pulmonary contusion (13). Thoracic Spine Fracture Fracture of the thoracic spine accounts for approximately 25%–30% of all spine fractures (62). It usually occurs with motor vehicle accidents or with a fall from great height. The mechanism of injury includes hyperflexion and/or axial loading (63). Thoracic spine fractures or dislocations have the highest incidence of associated neurologic deficits, compared with fractures elsewhere in the spine (11).

Imaging of Blunt Chest Trauma

Figure 9. The posteroanterior chest radiograph (not shown) of a 20-year-old man with chest pain following motor vehicle accident had appeared normal. This lateral chest radiograph obtained on same day shows segmental fracture of lower segment of sternum (arrow).

include pulmonary and cardiac contusion, neck injuries, and severe abdominal injuries (3,5). Isolated first rib fractures are also associated with whiplash injuries (56). Lacerations of the liver, spleen, and kidney are associated with fractures of ribs 9–12 (3). Although rib fracture is a common injury, not all rib fractures are identified on the initial chest radiograph, particularly when they are not displaced (57). CT has proved to be useful in the setting of rib fractures, not only because it can show nondisplaced fractures, but also because it can help to identify injuries associated with rib fractures, such as pulmonary laceration or abdominal visceral injuries. Flail chest deformity is a serious manifestation of rib fracture and is defined as five or more adjacent rib fractures or more than three segmental rib fractures (9,24,55,58). Flail chest deformity can lead to respiratory failure from the direct effect of lung and pleural injury, as well as impaired ventilation caused by dysfunction of normal chest wall mechanics. Although the normal hemithorax expands during inhalation, the flail hemithorax will paradoxically retract, leading to hypoventilation of the affected lung, with rebreathing of stagnant air (9,24,55,58).

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Chest radiography is not an adequate study to completely evaluate the thoracic spine. Dedicated frontal and lateral radiographs centered on and collimated to the thoracic spine are necessary to provide the minimally acceptable radiologic evaluation. Radiographic signs of thoracic spine fracture include cortical disruption, vertebral body height loss or deformity, abnormal vertebral alignment, focal mediastinal contour abnormality, and focal lateral displacement of the paravertebral stripe from paraspinal hematoma (8,63). CT is the imaging modality of choice for evaluating spinal fracture because of its high sensitivity and the ability to reformat images in multiple planes, particularly with multi–detector row CT (64). MR imaging is a useful adjunct imaging modality to evaluate spinal soft tissues, including the intervertebral disks, spinal ligaments, paravertebral soft tissues, spinal cord, and nerve roots. However, MR imaging does not demonstrate actual fractures as well as conventional radiography or CT does (65–67), and because of the imaging time and the difficulty with life-support equipment, MR is not generally used in the primary imaging evaluation. In conclusion, chest imaging plays an important role in the diagnosis of blunt chest trauma, because the history and the findings from physical examination are often unreliable. However, each imaging modality has its limitations. Selecting the appropriate study for the suspected diagnosis is very important. Finally, the radiologist should be aware of the limitations of the supine chest radiograph, to minimize overdiagnosis or underdiagnosis.

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Imaging of Blunt Chest Trauma

NOTES

Stuart E. Mirvis, MD

Imaging Diagnosis of Thoracic Aorta and Great Vessel Injuries1
The rapid diagnosis of traumatic injury to the aorta and its major branches following major blunt trauma is both extremely urgent and potentially challenging. The combination of the relative rarity of the injury (<0.5% of major trauma admissions) and the high lethality when not treated (40% mortality at 24 hours after injury) creates this demanding clinical situation (1). The newer imaging modalities, including multi–detector row helical computed tomography (CT), intravascular and transesophageal ultrasonography (US), and, occasionally, magnetic resonance imaging, have been key factors in establishing the diagnosis with higher accuracy and in less time than had been true prior to application of these techniques. Still, in most centers, the chest radiograph continues to serve as the initial diagnostic study for detecting injury within the mediastinum. This study remains sensitive for the detection of mediastinal hemorrhage and potential aortic injury but is impaired by low specificity (2). Multi–detector row CT has rapidly become the secondary study performed in patients with abnormalities of the mediastinal contour (3–6) and in many institutions has replaced the previous reference standard of thoracic angiography. As described in this chapter, the high sensitivity of multi–detector row CT has increased the recognized spectrum of injuries to the aorta and great vessels and has opened the door for selective nonsurgical management of some injuries.

HOW TO USE THE CHEST RADIOGRAPH
Most patients who have undergone acute blunt trauma whose condition is hemodynamically stable will undergo chest radiography among several routine studies performed at admission. The chest radiograph can be used to detect a number of immediately life-threatening traumatic pathologic conditions, including gross hemothorax, tension pneumothorax, tension pneumopericardium, and ruptured diaphragm with massive herniation of abdominal viscera. Careful inspection of the mediastinum is required to detect contour abnormalities that suggest hemorrhage. During the past decades, many radiologic findings have been described to indicate a high likelihood of mediastinal hematoma (7–10). A mediastinal diameter at the level of the aortic arch of greater than 8 cm (widened mediastinum) and a mediastinal–to–chest-width ratio of more than 0.25% at the same level have been popular, though unreliable, indicators for further investigation for potential aortic injury (11).

RSNA Categorical Course in Diagnostic Radiology: Emergency Radiology 2004; pp 81–89.
1From the Department of Radiology and the Maryland Shock-Trauma Center, University of Maryland School of Medicine, 22 S Greene St, Baltimore, MD 21201-1544 (e-mail: [email protected]).

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Figure 1. Normal mediastinal contours. Anteroposterior view of chest obtained at time of admission of a patient with blunt trauma shows a well-defined aortic arch and descending aorta, no soft tissue in right paratracheal region, no evidence of widening of paraspinal stripes, and a midline trachea. These findings together have a greater than 98% negative predictive value for major mediastinal arterial injury.

Figure 2. Mediastinal hemorrhage. Anteroposterior chest radiograph of patient with blunt trauma shows abnormal contour of aortic arch and tracheal deviation to right (arrow). Findings indicate mediastinal hemorrhage in this setting and were associated with aortic injury in this case.

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The disturbance of the normal shadows of the mediastinal contour, such as an obscured aortic arch or descending aorta or an abnormal contour of the arch, the loss of the aortopulmonary window, widening of the left paraspinal stripe or its extension to the left extrapleural apex, and right paratracheal soft-tissue density accurately indicate potential mediastinal hematoma (12,13) (Figs 1, 2). Unfortunately, this approach requires a well-established knowledge of radiographic anatomic structures, experience in interpreting a large number of chest radiographs, and specific experience with radiographs of patients with mediastinal hemorrhage. The results of large series have verified the limited utility of simple quantitative measures of the mediastinal diameter to guide management (11,14). The presence of a mediastinal contour abnormality is still a nonspecific finding for major thoracic arterial injury. A number of reasons account for this limitation, among them the following: (a) limited quality of portable radiographs, (b) suboptimal or lack of patient cooperation, (c) magnification and distortion of mediastinal silhouettes related to the supine view, and (d) nontraumatic causes of mediastinal contour abnormality, such as lymphadenopathy, mediastinal lipomatosis, vascular ectasia, and aberrant vascular branching (15). In many cases, the mediastinal contour is effaced by both traumatic and nontraumatic entities. In trauma, common sources of obscuration of the mediastinal margins include atelectasis, medial pleural effusions, and lung contusions and hematomas. Another serious limitation of chest radiography in the diagnosis of traumatic aortic injury is the fact

that most patients (approximately 80%) with mediastinal blood do not actually have a major thoracic arterial injury (12). Thus, even if all patients with true mediastinal hemorrhage could be selected with radiography, the true-positive rate for vascular injury would only approach 20% (12). The use of the erect or true erect (leaning forward 15°) view can improve the specificity of the chest radiograph and can often show a normal mediastinal contour when the supine view appears abnormal (16). A chest radiograph with a normal mediastinal contour for age has at least a 98% negative predictive value for traumatic aortic injury (2,12). Again, the accurate interpretation of the chest radiograph and the decision to accept it as showing a normal mediastinum or to go on to further imaging is vitally important and requires both experience and confidence.

EMERGENCE OF THORACIC CT IN DIAGNOSIS OF MAJOR VASCULAR INJURY
Beginning in 1983, investigators in numerous studies have described the use of CT to diagnose aortic injury. Of course, in the earliest studies, the investigators studied relatively small series and used the relatively slow, low-resolution conventional CT systems of the mid-1980s (17–19). Naturally, these early attempts at “CT angiography” with an 8–10-mm section thickness were limited but still clearly showed that aortic injuries could be diagnosed with CT. The issue of sensitivity was still open to question. During the next 15 years, debate raged among surgeons and cross-sectional imagers about the true accu-

Figure 3. Traumatic aortic injury with peridiaphragmatic hemorrhage. (a) Supine chest radiograph obtained at admission demonstrates wide mediastinal shadow with no depiction of aortic arch or descending aorta, a right paratracheal density, and tracheal deviation to right, indicating mediastinal blood. (b) Axial multi–detector row CT image through aortic hiatus shows hemorrhage around aorta at this level. (c) Axial CT image through proximal descending aorta shows diffuse mediastinal hemorrhage, displacement of carina to right, and aortic pseudoaneurysm arising from medial aspect of aorta.

Thoracic Aorta and Great Vessel Injuries

racy of CT and whether high accuracy could be achieved routinely or only in specialized trauma centers (20–23). The time-honored reference standard of thoracic angiography remained firmly in place in many institutions. A number of issues crystallized as this debate continued. It was obvious that angiography was invasive, costly, and difficult to perform quickly. In most polytrauma cases, CT scans were indicated for assessment of other body regions. Finally, it became clear with careful review that thoracic angiography for aortic injury was often challenging to interpret and occasionally incorrect diagnostically (24,25). With the advent of multi-detector row CT and the potential to create angiogram-like images of the aorta and its major branches, the pendulum for most trauma centers swung toward multi–detector row CT as the test of choice in stable patients with blunt trauma who do not have a clearly normal mediastinal contour at chest radiography.

CT IN AORTIC AND MAJOR BRANCH VESSEL INJURY
The diagnostic accuracy of CT for thoracic aortic and major branch vessel injury steadily improves as one moves from single-section helical to 4–detector row CT and, subsequently, 16–detector row CT. At each step, image quality is improved both with the use of thinner axial sections and with decreased motion artifact. The quality of multiplanar reformations in any orthogonal axis or in the curved axis of the aorta and its first-order branches improves similarly with the use of thin (1–2-mm) and overlapping axial sections.

In my practice, thoracic CT is performed with a 16– detector row CT scanner with a 16 × 1.5-mm detector array, a 0.75-second scan time, and pitch varying from 1 to 1.2. Axial images are usually viewed with fusion of three 1.5-mm images, which are subsequently saved to the picture archiving and communications system. If needed, the axial 1.5-mm images are available for 3 days online. All reformations are acquired by using the original 1.5-mm axial images. All thoracic studies are performed with intravenous contrast material enhancement with automated bolus triggering. The chest images are routinely viewed in softtissue, lung, and bone windows. For general cases of blunt trauma, reformations are not obtained unless the study is positive and further elucidation of the injury is needed. Almost all traumatic aortic injuries are associated with hemorrhage around the aorta or its proximal branches. The quantity of blood can range from minimal and focal to abundant and diffuse. Often, periaortic hemorrhage will track along the vessel inferiorly through the aortic hiatus and along the abdominal aorta (Fig 3). This is one sign seen at abdominal CT that should initiate a mandatory evaluation of the thoracic aorta. A number of direct signs of aortic and proximal branch vessel injury can be observed at contrast material–enhanced multi–detector row CT (3–5,25–27). In the most typical case, a pseudoaneurysm or contained partial aortic wall tear is seen projecting anteriorly at the level of the left main stem bronchus and left pulmonary artery (Figs 3–5). This region is believed to be prone to injury through shearing effects and stretching, compression, and torsion (28,29). In addition, the relative disorganization of the elastic lamina at the level of the remnant ductus arteriosus may create a local weakness in the wall at this level. The pseudoaneurysm is usually delineated by intimal flaps on either side and may be larger in size than the true aortic lumen (Fig 6). The pseudoaneurysm is usually relatively small in longitudinal extent and diameter (1–3 cm), forming an acute angle with the aortic wall and with a smooth exterior surface (Figs 3, 5).

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Figure 4. Aortic pseudoaneurysm. Axial multi–detector row CT image of 42-year-old woman who was injured in a highspeed motor vehicular crash shows pseudoaneurysm arising from anterior aspect of proximal descending aorta (arrow) at left of left main pulmonary artery. Note moderate surrounding mediastinal hemorrhage. Pseudoaneurysm is larger than aortic lumen and compresses it.

Figure 5. Aortic pseudoaneurysm. Axial CT image of another patient with blunt chest trauma shows typical pseudoaneurysm (arrow) arising from anterior proximal descending aorta at level of left main stem bronchus.

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The second most common site of injury is the ascending aorta just above the valve ring (Fig 7). Injury at this site is seldom seen clinically because of its high early mortality. Other sites of potential injury include the aortic arch, arch–branch vessel origins, and the descending aorta (Figs 5, 6). In my experience, injuries to the arch itself are relatively more common in elderly individuals with ectatic aortas than in a younger population. When the aortic pseudoaneurysm is large, it may indent the lumen of the aorta and produce a pseudocoarctation, leading to decreased perfusion below the level of injury. This finding is manifest as a sudden decrease in the diameter of the aorta along a segment without major branches. The descending and abdominal aorta will appear smaller in caliber than would be expected (Figs 8, 9). Clinically, there will be a decrease in blood pressure and pulse strength in the lower extremity. A small abdominal aorta is another CT sign that should prompt assessment of the thorax in a patient with blunt trauma. Other signs of direct aortic injury at CT include an irregularly shaped lumen, one or more linear filling defects due to intimal flaps, intraluminal blood clot, sudden narrowing of the luminal caliber as noted previously, and, rarely, extravasation of intravenous contrast material into the periaortic hematoma (Figs 3–6, 9, 10). In most cases, these injuries are apparent on highquality multi–detector row systems. If there are no direct findings on the axial images but there is blood around the aorta or great vessels, then thin-section multiplanar reformations along the aortic and great vessel axes should be obtained because these can enhance appreciation of injuries that may be subtle findings on axial views alone (Fig 11). When there are direct findings of aortic and branch vessel injury, further assessment with multiplanar reformations along the major vascular axes is also valuable to demonstrate the injury in relation to other vessels. On occasion, I have

Figure 6. Large aortic pseudoaneurysm and intimal flap. Axial CT image of a 66year-old man struck by a car shows huge pseudoaneurysm (P) arising from anterior proximal descending aorta. Flap of disrupted intima (arrow) divides pseudoaneurysm from native aortic lumen. Note diffuse mediastinal blood.

Figure 8. Pseudocoarctation of injured aorta. Axial CT image through upper abdomen of same patient as in Figure 4 shows small-caliber aorta secondary to compression of aortic lumen by thoracic aortic pseudoaneurysm.

found endoluminal (“angioscopic”) views helpful in verifying subtle injuries (Fig 12). The term traumatic aortic dissection is not appropriate for most aortic injuries. These injuries may contain a short interval when blood under pressure dissects a short distance into an otherwise normal aortic media, but this is not a principal feature of the injury. In rare cases, I have seen long medial or subadventitial dissections within a normal aorta, resulting from blunt trauma, that extend from the thoracic aortic tear into the abdominal aorta (Fig 13), but these are exceptional injuries. To be of true value, the multi–detector row CT study of the aorta should not only demonstrate the presence of an injury, but also characterize its severity, size, and extent. A small intimal irregularity may be managed ef-

Thoracic Aorta and Great Vessel Injuries

Figure 7. Ascending aortic pseudoaneurysm. (a) Axial multi–detector row CT image shows three lumina arising from the base of the heart. Middle "lumen" is pseudoaneurysm (P) arising from proximal ascending aorta. (b) Coronal multiplanar reformation shows relation of pseudoaneurysm (arrow) to proximal aorta and pulmonary artery. Injury was successfully repaired. (c) Angiographic image shows ascending aortic pseudoaneurysm. (Parts a and b: Reprinted, with permission, from reference 38.).

Figure 9. Pseudocoarctation of injured aorta. (a) Axial CT image through aortic injury in a 34-year-old man injured in motorcycle crash shows area of soft-tissue attenuation across the aorta, consistent with thrombus. (b) Axial CT image of upper portion of abdomen shows small aortic luminal diameter secondary to decreased flow through the injured area in the proximal thoracic aorta. Note well-defined low-attenuation areas in spleen, most likely representing infarcts from embolization from aortic thrombus.

Figure 10. Aortic injury. Axial CT image through aortic injury shows slightly irregular aortic lumen, periaortic mediastinal hemorrhage, and thrombus in lumen. Note displacement of nasogastric tube to right.

istence of more than one site of injury. Although a typical repair of the proximal descending aorta will be performed through a left posterior thoracotomy, an arch or proximal branch vessel injury requires a median sternotomy for adequate exposure, but would be suboptimal for the typical injury site in the proximal descending thoracic aorta. Multiplanar reformation, surface contour, and volumetric images are usually best to display the relationship of an aortic or branch vessel injury to the surrounding vascular and nonvascular structures. The precise distance from the edges of the injury to adjacent arterial branches is helpful in planning endovascular stent placement, when appropriate.

SHOULD AORTOGRAPHY BE PERFORMED?
fectively with blood pressure control and observation, whereas large pseudoaneurysms will typically be managed surgically or, in some centers, with endovascular stent placement (30,31). It is vital to show the relationship of the injury to adjacent branches, the branching pattern that will be encountered at surgery, and the exThe use of aortography has diminished with the ascent of multi–detector row CT for trauma imaging. Still, aortography can play important selective roles. If a goodquality multi–detector row CT study shows normal vasculature without hemorrhage around the major thoracic arteries, no further studies are required. In cases in which perivascular blood and normal vessels are seen

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Figure 11. Subtle CT findings of traumatic aortic injury. (a, b) Two axial CT images across descending aorta show marked difference in caliber and aortic contour abnormality in a. Note periaortic hemorrhage. (c) Volume-rendered image shows slight enlargement of aorta in proximal descending portion and intimal flaps (arrowheads). Findings of aortic injury are subtle in this case. (Part c: Reprinted, with permission, from reference 38.)

at multi–detector row CT, the decision of how to proceed is based on experience. Individuals with experience in chest CT interpretation for trauma may confidently consider the study normal for the vessels and not proceed to further investigation. Those with lesser experience may opt to perform other studies, such as aortography or intravascular or transesophageal US (32). The decision of which study to perform should be made on the basis of the experience of the examiner and the availability of the study. It should rarely be necessary to perform an “exploratory thoracotomy,” given current diagnostic capabilities. In patients with studies that are unequivocally positive for one or more injuries, it should not be necessary to perform aortography, which may introduce potentially long delays in initiating surgical care. Blood pressure control should be an immediate step in management, once a possible aortic injury is seen, but this method is not a foolproof way to avoid a sudden complete tear, free hemorrhage, and rapid exsanguination. If there is any question of active bleeding from the aorta into the mediastinal hematoma, immediate thoracic surgery should be performed because this situation can rapidly become fatal (33). It seems prudent that the urgency for a definitive diagnosis of major intrathoracic branch vessel injury should be the same as that for injury of the thoracic aorta, although the natural history of these injuries is less well known.

contrast-enhanced thoracic CT will limit the utility of the study, but even with a complete lack of intravenous contrast material, this study should allow the diagnosis or exclusion of mediastinal hemorrhage and thus lead to the correct next step. A number of situations can confound interpretation of even well-performed multi–detector row CT studies. Among these are (a) subtle injuries, (b) a background of severe atherosclerotic disease with ulceration, (c) variants in vascular branching (Fig 14), and (d) diverticular bronchial artery origin, as well as (e) the ductus diverticulum (24,25). Similarly, a diverticular origin of the bronchial artery can mimic an injured aorta. A traumatic pseudoaneurysm and penetrating aortic ulceration could appear similar, although the former is typically in the proximal descending aorta and the latter in the midportion of the descending aorta. Penetrating aortic ulceration is uniformly associated with severe aortic arteriosclerosis and calcification and is essentially a disease of the 7th, 8th, and 9th decades of life (34). Thoracic angiographic studies can also be difficult to interpret with some of these entities and may entirely miss an injury that is not shown in profile. Again, multi–detector row CT is complementary with angiography and US, and these studies can be helpful if the multi–detector row CT is equivocal.

HOW WILL IMAGING AFFECT THE FUTURE OF TREATMENT?
Just as the diagnostic capabilities for major thoracic arterial injuries have grown markedly in the past decade, so has the range of treatment options. Traditionally, most centers will urgently undertake surgical repair of these arterial injuries, with partial or complete bypass, to

PITFALLS OF MULTI–DETECTOR ROW CT IN AORTIC INJURY
As in all diagnostic studies, the combination of increased use and familiarity with the method uncovers new difficulties. Technical problems in performing

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Figure 12. Use of endoluminal view to diagnose aortic injury. (a, b) Axial CT images through proximal descending aorta demonstrate periaortic mediastinal hemorrhage and possible wall irregularity of anterior aorta in b. (c) Endoluminal rendering shows clear intimal flap (arrow) projecting into lumen. H = oriented toward head. (d) Aortogram confirms aortic pseudoaneurysm in typical location.

Figure 13. Dissection associated with aortic injury. (a) Axial CT image of young woman with blunt trauma shows ring of hemorrhage surrounding opacified lumen, with small amount of contrast material (arrow) projecting into hematoma. (b) Axial CT image at more caudal level shows an apparent thrombosis of false lumen and narrowed true lumen. (c) Abdominal aortogram shows irregularity of posterior aortic wall, narrowed distal abdominal aortic lumen, and small amount of bleeding into distal false channel (arrow).

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Figure 14. Traumatic aortic injury with dissection. (a) Axial CT image of patient with blunt trauma shows large pseudoaneurysm arising from anterior aspect of aortic isthmus region, with surrounding periaortic hemorrhage. (b) Axial CT image shows that aberrant right subclavian artery (arrow) crosses behind trachea at more rostral level. (c) Posterior volumetric view of aortic arch shows relationship between pseudoaneurysm (Ps) and aberrant artery above it. RSC = right subclavian artery.

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avoid sudden complete vessel wall rupture. More recently, nonsurgical management with blood pressure control and serial observation has been shown to be a possible alternative (35,36). In addition, endovascular stent placement, to protect the injured area while maintaining major branch perfusion, has been used with increasing frequency, either as a temporizing or definitive treatment (30,31). Although several clinical factors affect the decision as to what approach to use, as do the local facilities and expertise, this decision is also influenced by the nature and extent of the injury. In the future, the precise grading of major arterial injuries with multi–detector row CT, as has been proposed previously (37), should be performed in an effort to scale management of a given injury to an appropriate level of intervention to achieve successful long-term treatment.

References
1. Parmley LF, Marion WC, Jahnke EJ. Nonpenetrating traumatic injury of the aorta. Circulation 1958; 17:1086–1092. 2. Mirvis SE, Bidwell JK, Buddemeyer EU, et al. Value of chest radiography in excluding traumatic aortic rupture. Radiology 1987; 163:487–493. 3. Wintermark M, Wicky S, Schnyder P. Imaging of acute traumatic injuries of the thoracic aorta. Eur Radiol 2002; 12: 431–442. 4. Melton SM, Kerby JD, McGiffin D, et al. The evolution of chest computed tomography for the definitive diagnosis of blunt aortic injury: a single-center experience. J Trauma 2004; 56:243–250. 5. Mirvis SE, Shanmuganathan K, Buell J, Rodriguez A. Use of spiral computed tomography for the assessment of blunt trauma patients with potential aortic injury. J Trauma 1998; 45:922–930. 6. Dyer DS, Moore EE, Mestek MF, et al. Can chest CT be used to exclude aortic injury? Radiology 1999; 213:195– 202. 7. Simeone JF, Minagi H, Putman CE. Traumatic disruption of the thoracic aorta: significance of the left apical extrapleural cap. Radiology 1975; 117:265–268. 8. Wales LR, Morishima MS, Reay D, Johansen K. Nasogastric tube displacement in acute traumatic rupture of the thoracic aorta: a postmortem study. AJR Am J Roentgenol 1982; 138:821–823.

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9. Peters DR, Gamsu G. Displacement of the right paraspinous interface: a radiographic sign of acute traumatic rupture of the thoracic aorta. Radiology 1980; 134:599– 603. 10. Marnocha KE, Maglinte DD. Plain-film criteria for excluding aortic rupture in blunt chest trauma. AJR Am J Roentgenol 1985; 144:19–21. 11. Marnocha KE, Maglinte DD, Woods J, Goodman M, Peterson P. Mediastinal-width/chest-width ratio in blunt chest trauma: a reappraisal. AJR Am J Roentgenol 1984; 142:275–277. 12. Mirvis SE, Bidwell JK, Buddemeyer EU. Imaging diagnosis of traumatic aortic rupture: a review and experience at a major trauma center. Invest Radiol 1987; 22:187–196. 13. Marnocha KE, Maglinte DD, Woods J. Blunt chest trauma and suspected aortic rupture: reliability of chest radiograph findings. Ann Emerg Med 1985; 14:644–649. 14. Woodring JH, Dillon ML. Radiographic manifestations of mediastinal hemorrhage from blunt chest trauma. Ann Thorac Surg 1984; 37:171–178. 15. Schwab CW, Lawson RB, Lind JF, Garland LW. Aortic injury: comparison of supine and upright portable chest films to evaluate the widened mediastinum. Ann Emerg Med 1984; 13:896–899.

16. Ayella RJ, Hankins JR, Turney SZ, Cowley RA. Ruptured thoracic aorta due to blunt trauma. J Trauma 1977; 17:199– 205. 17. Kubota RT, Tripp MD, Tisnado J, Cho SR. Evaluation of traumatic rupture of descending aorta by aortography and computed tomography: case report with follow-up. J Comput Tomogr 1985; 9:237–240. 18. Heiberg E, Wolverson MK, Sundaram M, Shields JB. CT in aortic trauma. AJR Am J Roentgenol 1983; 140:1119–1124. 19. Mirvis SE, Kostrubiak I, Whitley NO, Goldstein LD, Rodriguez A. Role of CT in excluding major arterial injury after blunt thoracic trauma. AJR Am J Roentgenol 1987; 149:601–605. 20. Durham RM, Zuckerman D, Wolverson M, et al. Computed tomography as a screening exam in patients with suspected blunt aortic injury. Ann Surg 1994; 220:699–704. 21. Miller FB, Richardson JD, Thomas HA, Cryer HM, Willing SJ. Role of CT in diagnosis of major arterial injury after blunt thoracic trauma. Surgery 1989; 106:596–602. 22. Fenner MN, Fisher KS, Sergel NL, Porter DB, Metzmaker CO. Evaluation of possible traumatic thoracic aortic injury using aortography and CT. Am Surg 1990; 56:497–499. 23. Raptopoulos V, Sheiman RG, Phillips DA, Davidoff A, Silva WE. Traumatic aortic tear: screening with chest CT. Radiology 1992; 182:667–673. 24. Mirvis SE, Pais SO, Shanmuganathan K. Atypical results of thoracic aortography performed to exclude aortic rupture. Emerg Radiol 1998; 1:42–46. 25. Fisher RG, Sanchez-Torres M, Wingham CJ, et al. "Lumps" and “bumps” that mimic acute aortic and brachiocephalic vessel injury. RadioGraphics 1997; 17:825–834. 26. Cleverley JR, Barrie JR, Raymond GS, Primack SL, Mayo JR. Direct findings of aortic injury on contrast-enhanced CT in surgically proven traumatic aortic injury: a multi-centre review. Clin Radiol 2002; 57:281–286. 27. Scaglione M, Pinto A, Pinto F, et al. Role of contrast-enhanced helical CT in the evaluation of acute thoracic aortic

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injuries after blunt chest trauma. Eur Radiol 2001; 11:2444– 2448. Feczko JD, Lynch L, Pless JE, et al. An autopsy case review of 142 nonpenetrating (blunt) injuries of the aorta. J Trauma 1992; 33:846–849. Shkrum MJ, McClafferty KJ, Green RN, Nowak ES, Young JG. Mechanisms of aortic injury in fatalities occurring in motor vehicle collisions. J Forensic Sci 1999; 44:44–56. Fujikawa T, Yukioka T, Ishimaru S, et al. Endovascular stent grafting for the treatment of blunt thoracic aortic injury. J Trauma 2001; 50:223–229. Karmy-Jones R, Hoffer E, Meissner MH, Nicholls S, Mattos M. Endovascular stent grafts and aortic rupture: a case series. J Trauma 2003; 55:805–810. Kearney PA, Smith DW, Johnson SB, et al. Use of transesophageal echocardiography in the evaluation of traumatic aortic injury. J Trauma 1993; 34:696–701. Shiau YW, Wong YC, Ng CJ, Chen JC, Chiu TF. Periaortic contrast medium extravasation on chest CT in traumatic aortic injury: a sign for immediate thoracotomy. Am J Emerg Med 2001; 19:229–231. Coady MA, Rizzo JA, Elefteriades JA. Pathologic variants of thoracic aortic dissections: penetrating atherosclerotic ulcers and intramural hematomas. Cardiol Clin 1999; 17:637– 657. Kepros J, Angood P, Jaffe CC, Rabinovici R. Aortic intimal injuries from blunt trauma: resolution profile in nonoperative management. J Trauma 2002; 52:475–478. Holmes JH, Bloch RD, Hall RA, et al. Natural history of traumatic rupture of the thoracic aorta managed nonoperatively: a longitudinal analysis. Ann Thorac Surg 2002; 73:1149– 1154. Gavant ML. Helical CT grading of traumatic aortic injuries: impact on clinical guidelines for medical and surgical management. Radiol Clin North Am 1999; 37:553–574. Mirvis SE. Diagnostic imaging of acute thoracic injury. Semin Ultrasound CT MR 2004; 25:156–179.

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NOTES

James T. Rhea, MD

CT of Abdominal Trauma: Part I1

Trauma is the leading cause of death in individuals younger than 5 years old and ranks third or fourth as the cause of death in the whole population of the United States and western Europe (1). About 10% of all trauma deaths are due to abdominal injuries. Both compressive and deceleration mechanisms are at work with blunt trauma. Compression may injure the solid organs or the vessels, resulting in lacerations, hematomas, and thrombosis, and may injure the hollow viscera, resulting in rupture. Deceleration forces cause stretching and shearing, especially of vessels between the relatively fixed origin of the vessel and the relatively mobile viscera. Figures 1–10 illustrate and exemplify the range of findings shown with computed tomography (CT) in patients with blunt-force trauma to the abdomen and pelvis.

EVOLUTION OF TRAUMA MANAGEMENT
In the early 1900s, mortality from trauma was noted to be high without surgery; and aggressive diagnosis, with laparotomy and surgical treatment when possible, was undertaken (2). In 1965, diagnostic peritoneal lavage was shown to be useful for depicting the presence of large volumes of intraperitoneal fluid and for determining the type of fluid (3). In the 1970s, ultrasonography (US) was applied to diagnosis in the patient with multiple trauma and was useful in depicting not only large volumes of intraperitoneal fluid but also certain visceral injuries. US was, and continues to be, limited in the characterization of injuries, the depiction of small volumes of intraperitoneal fluid, the differentiation of blood from other fluid, and the depiction of specific injuries that would require immediate surgery. Exploratory laparotomy remained the mainstay of diagnosis in the patient with multiple trauma. Problems with aggressive surgery became evident. In the early 1950s, mortality from infection was noted in infants after splenectomy. Hepatic surgery following traumatic injury was complicated by uncontrollable hemorrhage. Lengthy surgery had its own complications, especially when accompanied by loss of large volumes of blood. The rate of nontherapeutic laparotomy for trauma shows variation from one institution to another, but the rate has been about 20%. Morbidity has been seen at a rate of 10%– 20% in trauma patients after “negative” (nontherapeutic) laparotomy (4). Thus, there was a desire within the surgical community to select those patients for whom surgery would be the indicated therapy if diagnosis could be improved (2).
RSNA Categorical Course in Diagnostic Radiology: Emergency Radiology 2004; pp 91–100.
1From the Departments of Radiology, Harvard Medical School and Massachusetts General Hospital, FH 210, 55 Fruit St, Boston, MA 02114 (e-mail: [email protected]).

J.T.R. holds stock in General Electric Co (purchased on open market).

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The use of CT in the patient with multiple trauma began in the 1980s. With improved CT technology and improved accuracy, CT has become the diagnostic method of choice, replacing exploratory laparotomy. In addition, the development of interventional radiologic techniques of therapeutic embolization has made it possible, in patients who have certain intraabdominal injuries, to treat active bleeding with less morbidity and mortality than was possible previously (4). Today, the indications for surgery include uncontrollable hypotension, signs of peritonitis, and specific life-threatening injuries. CT can be used to detect active arterial extravasation and the specific type and grade of injury, allowing the selective use of surgical or other interventional therapy. Incorporation of CT into the early evaluation of the patient with multiple trauma has allowed nonsurgical management and has been shown to decrease the mortality rate of these patients (5). With nonsurgical management, patients must be closely observed because the rate of failure of nonsurgical management has been found to be 10%–20%, depending on the organ that has been injured (6,7). Predictors of failure of nonsurgical management have been defined, and many of these findings can be seen at CT. These findings include a higher grade of injury to the spleen, active arterial extravasation, hypotension at manifestation, and a large volume (>300 mL) of free blood within the abdomen (6). Because of its accuracy, CT has facilitated the change to nonsurgical management of many cases of multiple trauma. CT can be used to define specific injuries that are indications for immediate intervention. In addition, CT can be used to define those findings that, as predictors of failure of nonsurgical management, require closer observation of the patient.

CT TECHNIQUES
Evaluation of the Abdomen To optimize the accuracy of CT, both orally and intravenously administered contrast materials are widely used. One dose of oral contrast material may consist of ¼ oz (7.5 mL) of diatrizoate meglumine in 10 oz (300 mL) of fluid. Usually, scanning is not delayed for complete opacification of the bowel, but the presence of oral contrast material in even the proximal portion of the bowel allows better assessment of the duodenum and the pancreas. Extravasation of oral contrast material, although not sensitive, would be 100% specific for bowel injury. Oral contrast material may be given in the trauma bay after placement of a nasogastric tube and again just prior to scanning. If time permits, a full dose regimen of oral contrast material would consist of three 10-oz (300-mL) portions given at 30-minute intervals. Intravenous contrast material administration consists of power injection of 135 mL of a nonionic agent that is approximately 60% iodine at a rate of at least 2.5

mL/sec. The use of intravenous contrast material is necessary to identify debilitating vascular injuries and active arterial bleeding and to better characterize the type of organ injuries that occur. Both oral and intravenous contrast materials carry a small risk. Aspiration of oral contrast material may occur, although the frequency of aspiration is low. Investigators have found that between 1 in 500 and 1 in 1000 patients will aspirate oral contrast material (8,9). The use of oral contrast material continues to be the subject of recent investigations, with mixed conclusions about the necessity of its use (10). Intravenous contrast material carries the usual low risk of an adverse reaction to the contrast material. The benefit of improved identification of life-threatening injury would appear to outweigh the relatively low risk associated with contrast material. CT scan parameters for four–detector row helical CT scanning include the following: (a) 75-second delay after intravenous injection of 135 mL of nonionic contrast material (300 mg of iodine per milliliter) at 2.5 mL/sec; (b) scan from above the dome of the diaphragm to sacral vertebra S1; (c) additional 120-second delay to allow enhancement of the distal portion of the ureters and the bladder; (d) scan from S1 to the ischial tuberosities; (e) detector configuration, 4 × 1.25 mm; (f) 5-mm section thickness and image spacing; (g) table speed, 15 mm/sec; and (h) standard algorithm. CT scan parameters for 16–detector row helical CT scanning are undergoing revision to reduce dosage and currently include the following: (a) 75-second delay after intravenous injection of 135 mL of nonionic contrast material (300 mg of iodine per milliliter) at 3.0 mL/sec; (b) scan from above the dome of the diaphragm to vertebra S1; (c) additional 120-second delay to allow enhancement of the distal portion of the ureters and the bladder; (d) scan from S1 to the ischial tuberosities; (e) detector configuration, 16 × 1.25 mm; (f) 5-mm section thickness and image spacing; (g) table speed, 18.75 mm/sec; (h) pitch, 0.938; (i) tube rotation time, 0.5 second; and (j) standard algorithm. Prior to scanning of the abdomen, the arms of the patient should be placed up near the head to minimize artifacts, the Foley catheter should be clamped, and the cardiac leads should be removed, if possible, to minimize artifacts. After the initial complete scan, delayed scanning should be performed through any suspected pancreatic, renal, or bowel injury. This delayed scanning allows better characterization of the injury. In addition, CT data should be reformatted for evaluation of the spine. Sagittal and coronal reformations of the entire abdomen are made with a detail algorithm from the primarily acquired 1.25-mm image data used to reconstruct an axial image set.

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Evaluation of the Spine One to two percent of the patients with blunt trauma have a spine fracture, including Chance and

burst fractures. Attention may be diverted from the spine because about half of the trauma patients with spine fractures have associated injuries, about half of which are intraabdominal. Investigators have shown that “screening” the lumbar spine for injury is more accurate with use of the data from the abdominal CT examination than with the use of separate conventional radiographic imaging of the spine (11–13). To evaluate the spine, the 5-mm axial CT images are reconstructed to at least contiguous 2.5-mm axial images. These thinner axial images are then used to make sagittal and coronal reformations of the spine. Viewing the axial CT images and the sagittal and coronal reformations with the bone window allows assessment of the spine. It is advisable to leave the field of view on the sagittal and coronal images open to include the soft tissues of the abdomen. At times, the diagnosis of vascular and visceral injuries is improved if these injuries are viewed in the sagittal or coronal plane.

mesentery. The frequency of extravasation varies from rates of 20%–24% for kidney, mesentery, and pelvic injuries to less than 10% for liver and adrenal injuries.

CT of Abdominal Trauma: Part I

Evaluation of the Urinary Bladder: CT Cystogram With the Foley catheter clamped, extravasation of urine leads to the diagnosis of urinary bladder rupture. However, a full-appearing bladder without extravasation does not exclude bladder rupture. To confidently exclude bladder rupture, CT cystography is necessary. The technique for CT cystography is as follows: (a) Unclamp the Foley catheter, and drain the bladder. (b) Then instill 300–400 mL of bladder contrast material through the Foley catheter. This contrast material consists of 40 mL of diatrizoate meglumine in 1 L of normal saline. (c) Rescan the pelvis from above the iliac crests to the symphysis pubis.

Hypotension Hypotension results in specific findings that can be noted at CT (Fig 3) (18–22). These findings include the following: (a) flat inferior vena cava (3-cm-long segment of the inferior vena cava with a transverse-toanteroposterior diameter ≤3:1); (b) small aorta (<6mm diameter below the superior mesenteric artery), especially in children; (c) hyperemic bowel mucosa; (d) bowel wall thickening; (e) bowel dilatation with fluid; (f) hyperemic kidneys and adrenal glands; and (g) hypoperfusion of the spleen. The hyperemic bowel mucosa is due to two factors, which have been demonstrated experimentally. With hypotension, blood flow shifts to the mucosa of the bowel, and the transit time of the blood through the bowel wall is prolonged. The small aorta and hypoperfusion of the spleen are thought to be due to arterial constriction; such constriction is more likely in children than in adults with some degree of arteriosclerosis. Free Fluid Isolated free fluid may occur without any explanatory injury being found. The frequency of isolated free fluid in patients with multiple trauma is 2%–3% (23,24). This isolated free fluid may be the result of rapid fluid resuscitation, in which case the finding is totally benign, except for a possible contribution to abdominal compartment syndrome. However, other more important causes of isolated free fluid are possible, and the finding may present a diagnostic dilemma. The options for management when isolated free fluid is seen include observation, diagnostic peritoneal lavage, laparotomy, or repeat CT. Free fluid is seen in about 75% of the patients with intraabdominal injury (25). If free fluid is seen in the patient with multiple trauma, the location, type, and volume of the fluid should be assessed. The location of free fluid can be either intraperitoneal or extraperitoneal. The type of fluid could be blood, urine, bowel content, bile, ascites, or diagnostic peritoneal lavage fluid. The volume may be characterized as minor, moderate, or major. Location.—The intraperitoneal compartments include the perisplenic and perihepatic spaces, the Morison pouch between the right kidney and the tip of the liver, the pericolic gutters, the inframesocolic space, the lesser peritoneal sac, and the pelvis. In addition, small amounts of free fluid may be seen as triangular collections between the leaves of the mesentery. The extraperitoneal compartments include the anterior pararenal, perirenal, posterior pararenal, perivesicle, anterior prevesicle, and pericholecystic spaces. The anterior pararenal space contains the pancreas

MULTITRAUMA ABDOMINAL CT: WHAT TO LOOK FOR
Active Arterial Extravasation Active arterial extravasation correlates with a failure of conservative management of the patient and is seen in 10%–20% of the patients with blunt trauma (14–17). The results of investigations have shown that about 78% of the patients who demonstrate active arterial extravasation at CT will require surgery or therapeutic embolization to attain hemodynamic stability. This contrasts with the fact that only 28% of the patients without extravasation require surgery (15,16). Thus, it is important to note and inform our clinical colleagues of any active arterial extravasation that is seen. Extravasation has been described as a “vascular blush.” The finding evident at CT is the presence of extravascular contrast material adjacent to or within the injured structure. Delayed scanning may demonstrate an increased volume of extravasation of contrast material. The sources of active extravasation may frequently be identified at CT and include the viscera, vessels, and

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Figure 1. Intraperitoneal versus extraperitoneal blood. (a) Axial CT image shows blood between the liver and kidney. Note that blood does not wrap around the tip of the liver (arrow) and is in the anterior pararenal space from a laceration of the bare area of the liver. (b) In contrast, this axial CT image shows that the blood in this patient wraps around the tip of the liver (arrows) and is in the peritoneal space from a spleen laceration.

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and duodenum. The perirenal space contains the kidneys, adrenal glands, inferior vena cava, and aorta. The posterior pararenal, perivesicle, and anterior prevesicle spaces contain fat. The location of blood in a particular compartment correlates with an injury to a structure within that compartment. In two areas, the location may appear confusing at CT. One area is the space between the liver and kidney. Blood in both the intraperitoneal space (Morison pouch) and the retroperitoneal anterior pararenal space will appear between the liver and kidney. To differentiate which location is involved, you must determine whether the blood wraps around the inferior tip of the liver. The anterior pararenal fascia tightly adheres to the lateroconal fascia, and blood in the retroperitoneal anterior pararenal space will not wrap around the tip of the liver (Fig 1a). In contrast, blood in the Morison pouch will wrap around the inferior tip of the liver (Fig 1b). The second area that may present problems in interpretation is the pelvic intraperitoneal space and the fat-containing extraperitoneal spaces around the urinary bladder. One such extraperitoneal space is the anterior prevesicle space (Fig 2b). This is a potential space extending deep to the rectus muscles along the anterior abdominal wall from the level of the urinary bladder to the umbilicus. The fat around the bladder is also continuous with the pelvic sidewalls and the presacral spaces. The definitive finding of intraperitoneal urine or blood or contrast material is that the fluid surrounds bowel loops (Fig 2a). Type.—The type of fluid is assessed by measuring the attenuation of the fluid in Hounsfield units. The following CT attenuation values are characteristic: (a) blood, more than 25 HU, with unclotted blood measuring 25–50 HU and clotted blood measuring 40–75 HU; and (b) ascites, bile, urine, bowel contents, and lavage fluid, 5–10 HU.

A mixture of blood with other fluid will be of intermediate attenuation, and the cause of the fluid cannot be specified. Because the finding of free bile, urine, or bowel contents is serious, peritoneal lavage should only be performed after CT scanning, not prior to scanning. Peritoneal lavage after scanning may be useful in distinguishing the type of low-attenuation fluid that is present. Volume.—The volume of fluid is of less importance than the hemodynamic status of the patient. However, a large volume of blood within the peritoneum is more likely to lead to pyrexia and correlates with failure of nonsurgical management if the volume is greater than 300 mL (6). The volume may be estimated by the number of intraperitoneal compartments in which fluid is seen. Volume may be characterized as minor (100 mL to <200 mL) when fluid occupies one compartment. Moderate volume (200– 500 mL) tends to occupy two compartments. Major volume (>500 mL) tends to be seen in three or more compartments. A small amount of fluid may be important and may be the only indication of bowel or other injury. CT has been shown to depict as little as 10 mL of free fluid (26). US is not reliable in depicting small amounts of fluid. The results of experimental work with cadavers have shown that a volume of 100 mL is necessary for US to reliably depict free fluid (27).

Associated Injuries Multiple injuries tend to occur together. Focusing on a dramatic injury may lead to overlooking other less obvious injuries. Two phrases are useful as reminders to keep looking until a thorough search of the images has been completed: the “seat-belt syndrome“ and “packages of injury.“ To our knowledge, the seat-belt syndrome was first described by Garrett and Braunstein (28) in 1962, and

CT of Abdominal Trauma: Part I

Figure 2. Intraperitoneal versus extraperitoneal contrast material. (a) Axial CT image shows contrast material from a bladder rupture surrounding bowel loops (arrows). This indicates that there has been an intraperitoneal rupture. (b) This axial CT image shows that contrast material (arrows) from a bladder rupture is anterior to the bowel and deep to the rectus muscles. This indicates that the rupture is extraperitoneal, with contrast material in the anterior prevesicle space.

Figure 3. Axial CT images demonstrating signs of hypotension. (a) CT image shows hyperemic bowel mucosa (black arrow) and a narrow inferior vena cava (white arrow), which are indications of hypotension. (b) Hypotension may also result in hypoperfusion of the spleen (black arrow) and a hyperattenuating kidney (white arrow).

the term refers to the simultaneous occurrence of bruising of the abdominal wall, bowel or mesenteric injury, solid organ injury, and spine fracture. Major vessels may also be injured, as the term seat-belt aorta indicates (29,30). The mechanism of the seat-belt syndrome is thought to be compression of intraabdominal structures between the spine and the anterior abdominal wall by a lap belt during a motor vehicle collision. The packages of injury include the left, middle, and right packages (31). An injury in a given region is likely to be accompanied by other injuries nearby. The left package would include combinations of simultaneous injuries to the left lobe of the liver, the spleen, the left kidney or adrenal gland, the distal portion of the pancreas, and/or left-sided thoracic injuries. The right package would include similar injuries on the right. The midline injuries include combinations of injuries to the liver, transverse colon, small bowel, mesentery, pancreas anterior to the spine, duodenum,

aorta, inferior vena cava, and/or spine and midline thoracic injuries.

INJURIES TO SPECIFIC ORGANS
Gallbladder Injury Injury to the gallbladder occurs in 2%–8% of the patients with blunt abdominal trauma (32). Associated injuries are frequent, with liver injury occurring in about 80% and duodenal injury in about 50% of such patients. Injury to the extrahepatic bile duct occurs about one-fourth as often as gallbladder injury. Rupture may be extraperitoneal, around the gallbladder fossa, or may be intraperitoneal. If the rupture is intraperitoneal, a bile-induced peritonitis may occur. If the rupture is extraperitoneal, peritoneal signs will be absent, and pericholecystic fluid will be seen at CT (Fig 4). The types of gallbladder injury seen include wall contusion, rupture, and avulsion of the gallbladder

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Figure 4. Gallbladder rupture. Axial CT image of patient with rupture of the gallbladder shows blood in the pericholecystic space and areas of active arterial extravasation (arrows). Between the arrows, the wall of the gallbladder is not depicted, which is consistent with rupture.

Figure 5. Pancreatic contusion. Axial CT image shows an area in the tail of the pancreas (arrows) in which the subtle septa seen elsewhere are absent. This represents an area of pancreatic contusion. The patient had transient elevation of the serum amylase level.

from its fossa. CT findings to look for with gallbladder injury include the following: (a) irregular ill-defined wall contour, (b) wall thickening, (c) wall discontinuity, (d) intraluminal (high-attenuation) blood, (e) collapsed lumen, (f) mucosal flap, and (g) blood or lowattenuation bile adjacent to the gallbladder.

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Pancreatic Injury Injury to the pancreas has been reported in from less than 1% to 3% of the patients with multiple trauma and most often results from compression of the pancreas against the spine (32,33). Associated injuries occur in about 70% of the adult cases but only 15%–30% of the pediatric cases, with duodenal and liver injuries being the most frequent. Early diagnosis is important because delay in diagnosis correlates with increased morbidity (34). Unfortunately, the diagnostic accuracy of CT has not been as great in acute pancreatic injury as in most other injuries. Recent advances in technology offer possible improvement, but the findings from earlier investigations indicated that the sensitivity of CT for diagnosing pancreatic injury was 68%–80% (35,36). The difficulty in diagnosis is compounded by the fact that the serum amylase level is neither sensitive nor specific for pancreatic injury in the acute setting (34). However, 1–2 days after injury, the amylase level will be increased in 80%–90% of the patients with pancreatic injury. Pancreatic injuries include contusion (Fig 5), laceration, and fracture (Fig 6). Contusion may be focal or diffuse and may be seen as a hypoattenuating or isoattenuating area within the pancreas. One clue for identification of isoattenuating contusion is asymme-

Figure 6. Pancreatic fracture. Axial CT image shows that the head of the pancreas (white arrow) is separated from the body (black arrow) by a pancreatic fracture. Abundant blood is seen around the pancreas, superior mesenteric vein, and superior mesenteric artery. The pancreatic duct, though not seen, would be torn when a fracture or laceration crosses more than 50% of the width of the pancreas.

try of the pancreatic septa. The appearance of the septa is variable from patient to patient. Younger patients may have no apparent septa, and older patients may have prominent septa. If septa are seen, look for an area in which the septa are less evident than elsewhere within the pancreas. Lacerations are more easily recognizable, except for possible confusion with a normal cleft that may occur in the anterior aspect of the pancreatic body anterior to the spine. Lacerations are usually perpendicular to the

Figure 7. Adrenal hematoma. (a) Axial CT image shows a right adrenal hematoma with points of active arterial extravasation (arrows). (b) Two weeks later, repeat axial CT image shows an increase in size of the adrenal hematoma (arrows).

CT of Abdominal Trauma: Part I

axis of the pancreas and most frequently occur in the neck. Fractures of the pancreas do not present much diagnostic difficulty because of the separation of the fragments and the abundant blood in the anterior pararenal space. Injury to the pancreatic duct occurs in about 15% of the patients with pancreatic injury (33) and is not directly seen during the acutely performed abdominal CT examination. Pancreatic duct injury may be implied if a laceration is larger than one-half the thickness of the pancreas. Duct injury is a surgical emergency, and if there is evidence of injury in the anterior pararenal space, other methods of evaluating the duct, such as endoscopic retrograde cholangiopancreatography or magnetic resonance cholangiopancreatography, may be considered (34,37,38). Blood in the anterior pararenal space may be seen in various locations. One place to look is between the pancreas and the splenic vein. Normally, the splenic vein is closely applied to the body of the pancreas without intervening fluid or fat. Blood may be located around the superior mesenteric artery, in the transverse mesocolon, or in the lesser sac and may appear as thickening of the margins of the left anterior pararenal fascia. If fluid is seen in the anterior pararenal space, always measure the attenuation to determine if the fluid is simple lowattenuation fluid rather than blood. If rapid resuscitative administration of fluids leads to intra- or extraperitoneal accumulations, the most frequent location of such fluid is in the anterior pararenal space. If pancreatic injury is seen, grading the injury is useful because the difficulty of surgery increases with the grade of injury. The classification of the American Association for the Surgery of Trauma (AAST) (39) includes the following classes: (a) class I, minor contusion, superficial laceration, intact duct; (b) class II, major contusion, major laceration, intact duct; (c) class III, duct injury, distal transection; (d) class IV, proximal transection, ampullary injury; and (e) class V, massive disruption of pancreatic head.

In addition to the AAST classification, Lucas (40) developed the following classification that includes associated injury to the duodenum: (a) class I, contusion, minor peripheral laceration, duct intact; (b) class II, deep laceration, transection of the body or tail, duct may be damaged; (c) class III, severe injury to the head of the pancreas, duct may be damaged, duodenum intact; and (d) class IV, combined pancreatic and duodenal injuries.

Adrenal Injury Adrenal injury is seen in about 2% of the patients with blunt abdominal trauma (41). Because the adrenal glands are well protected in the retroperitoneum, other associated injuries are frequent in patients with adrenal injury from blunt abdominal trauma and are seen in more than 90% of these patients. The right adrenal gland is injured more frequently than the left, and injury is usually unilateral. Bilateral adrenal injury may cause acute adrenal crisis, with hypotension, hypokalemia, hyponatremia, and acidosis (42). CT findings of adrenal injury may be grouped into (a) findings that involve the adrenal gland itself and (b) secondary findings (43). The adrenal gland may contain a round or oval mass, or hematoma (Fig 7); and this is the most common manifestation, seen in about 80% of injured adrenal glands. Diffuse hemorrhage will obscure the adrenal gland in about 10% of injured adrenal glands. A uniformly enlarged and indistinct adrenal gland will be seen in about 10% of injured adrenal glands. Active arterial extravasation may be demonstrated, and delayed hemorrhage may occur (44). Secondary findings of adrenal injury include fat stranding around the adrenal gland, thickening of the crus of the diaphragm, thickening of the adjacent fascia, and frank retroperitoneal hemorrhage. As seen on the trauma CT image, the shape and attenuation of an adrenal hematoma may be the same as those of an adrenal neoplasm. If follow-up CT images are obtained, the hematoma may increase in

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Figure 8. Combined intraperitoneal and extraperitoneal bladder rupture. (a) Axial CT image through the bladder obtained before CT cystography shows the point of rupture of the bladder (black arrow) and unopacified urine, which is hypoattenuating, in the perivesicle space anteriorly, which is continuous with the anterior prevesicle space (white arrows) seen in b. (b) Axial CT image obtained after CT cystography shows contrast material around a loop of bowel (arrow), consistent with the intraperitoneal component of the rupture, which was confirmed at surgery. The contrast material just deep to the rectus muscles is in the anterior prevesicle space.

size during the next few days and decrease in attenuation. A hematoma should have decreased in size at 6 months after injury, and adrenal atrophy may be seen at 12 months.

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Urinary Bladder Injury Bladder rupture (Fig 8) is seen in 5%–10% of the trauma patients with pelvic fracture and in about 10% of the trauma patients with gross hematuria (45,46). Rarely, bladder rupture may occur without hematuria. Associated injuries are seen in about 90% of such bladder injuries because the bladder is well protected by the bones of the pelvis. The mechanism of injury is either pressure on a full bladder or penetration by a bone fragment. On the initial CT examination, a “full-appearing bladder” with the Foley catheter clamped does not exclude bladder rupture, and CT cystography is indicated if there is a suspicion of bladder injury. Investigators have shown that the sensitivity of abdominal CT without cystography is only about 60% (47,48). The sensitivities of the retrograde fluoroscopic cystogram (85%– 100%) and the CT cystogram (95%–100%) are similar (49–51). Details of the technique for CT cystography are given in the section, “Evaluation of the Urinary Bladder: CT Cystogram.” The types of bladder injury include contusion or interstitial injury, in which hematoma or contrast material is noted in the bladder wall, and rupture. If rupture is present, urine or contrast material will be seen in the intraperitoneal space, the extraperitoneal spaces, or both locations. It is important to distinguish intraperitoneal from extraperitoneal rupture because the treatment is different. Intraperitoneal rupture,

Figure 9. Portal vein laceration. Axial CT image shows that the contour of the portal vein is irregular (arrow), and there is adjacent hemorrhage. Extrahepatic portal vein laceration was found at surgery.

which occurs in 10%–20% of the cases of bladder rupture, requires surgery. Extraperitoneal rupture, which occurs in about 80%–90% of the cases of bladder rupture, requires only decompression with a Foley catheter until healing takes place. Rupture into both spaces occurs in 5%–10% of the patients with bladder rupture and also requires surgery. To differentiate intraperitoneal from extraperitoneal rupture of the bladder, look for urine or contrast material accumulating around bowel loops, in the peritoneal recesses, or between the leaves of the mesentery. Fluid between bowel loops in the mesentery will appear as small triangular areas of soft-tissue density; bowel does not usually have this triangular appearance. The location of the extraperitoneal spaces around the bladder is noted in the section, “Free Fluid.”

Figure 10. Aortic injury with thrombosis. (a) Axial CT image from patient who was in a motor vehicle collision shows that the lumen of the aorta is narrowed, with contrast material centrally (arrow) and thrombus peripherally. (b) Coronal reformation of the abdominal CT data shows the short segment of almost complete thrombosis of the aorta (arrow). This patient also had a Chance fracture of the adjacent lumbar vertebra (not shown).

CT of Abdominal Trauma: Part I

Major Vascular Injury The major vessels may be injured in the trauma patient, and the CT appearance may be subtle. Associated injuries are frequent and can distract attention from evaluation of the vascular structures. The findings to look for with any vascular injury include the following: (a) irregular contour of vessel (Fig 9), (b) indistinct edge of vessel, (c) narrowing of lumen, (d) abrupt cutoff of vessel, (e) arterial pseudoaneurysm or flap, (f) extravasation of contrast material, and (g) hemorrhage with vessel at the center (52–55). Injury to the inferior vena cava may demonstrate additional findings, including a liver laceration extending into the porta hepatis and, rarely, fat herniating into the lumen. The location of the injury to the inferior vena cava is important to specify because surgery becomes more difficult with the more proximal injuries. Location may be specified as (a) infrarenal, (b) suprarenal and infrahepatic, (c) retrohepatic, or (d) suprahepatic. The extrahepatic portion of the portal vein and the hepatic veins are subject to shearing injury with thrombosis. The dual blood supply of the liver may result in continued perfusion with portal vein injury. Thus, portal vein thrombosis may result in an absence of depiction of the normally contrast material– enhanced intrahepatic portal veins but with parenchymal enhancement via the hepatic artery. If there is thrombosis of the hepatic veins, an absence of perfusion with hypoattenuating segments of the liver may be seen because contrast-enhanced blood can enter the liver from neither the portal vein nor the hepatic artery. Injuries to the abdominal aorta are rare (56). The most common site of aortic injury is near the inferior mesenteric artery, presumably related to a seat-belt

mechanism; the second most common site is near the renal arteries. The types of aortic injury that may be seen include partial thrombosis (Fig 10) or occlusion, intramural hematoma, pseudoaneurysm, late true aneurysm, rupture, or intimal injury resulting in a flap or dissection (54). The major aortic branches may also be injured and should be carefully assessed.

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33. Patel SV, Spencer JA, el-Hasani S, Sheridan MB. Imaging of pancreatic trauma. Br J Radiol 1998; 71:985–990. 34. Cirillo RL Jr, Koniaris LG. Detecting blunt pancreatic injuries. J Gastrointest Surg 2002; 6:587–598. 35. Ilahi O, Bochicchio GV, Scalea TM. Efficacy of computed tomography in the diagnosis of pancreatic injury in adult blunt trauma patients: a single-institutional study. Am Surg 2002; 68:704–707. 36. Wales PW, Shuckett B, Kim PC. Long-term outcome after nonoperative management of complete traumatic pancreatic transection in children. J Pediatr Surg 2001; 36:823–827. 37. Canty TG Sr, Weinman D. Management of major pancreatic duct injuries in children. J Trauma 2001; 50:1001–1007. 38. Dondelinger RF, Boverie JH, Cornet O. Diagnosis of pancreatic injury: a need to improve performance. JBR-BTR 2000; 83:160–166. 39. American Association for the Surgery of Trauma. Injury scoring tables: Table 10—pancreas injury scale. Available at: www.aast.org. Accessed May 19, 2004. 40. Lucas CE. Diagnosis and treatment of pancreatic and duodenal injury. Surg Clin North Am 1977; 57:49–65. 41. Iuchtman M, Breitgand A. Traumatic adrenal hemorrhage in children: an indicator of visceral injury. Pediatr Surg Int 2000; 16:586–588. 42. Udobi KF, Childs EW. Adrenal crisis after traumatic bilateral adrenal hemorrhage. J Trauma 2001; 51:597–600. 43. Burks DW, Mirvis SE, Shanmuganathan K. Acute adrenal injury after blunt abdominal trauma: CT findings. AJR Am J Roentgenol 1992; 158:503–507. 44. Oto A, Ozgen B, Akhan O, Besim A. Delayed posttraumatic adrenal hematoma. Eur Radiol 2000; 10:903–905. 45. Morey AF, Iverson AJ, Swan A, et al. Bladder rupture after blunt trauma: guidelines for diagnostic imaging. J Trauma 2001; 51:683–686. 46. Morgan DE, Nallamala LK, Kenney PJ, Mayo MS, Rue LW III. CT cystography: radiographic and clinical predictors of bladder rupture. AJR Am J Roentgenol 2000; 174:89–95. 47. Haas CA, Brown SL, Spirnak JP. Limitations of routine spiral computerized tomography in the evaluation of bladder trauma. J Urol 1999; 162:51–52. 48. Hsieh C, Chen R, Fang J, et al. Diagnosis and management of bladder injury by trauma surgeons. Am J Surg 2002; 184: 143–147. 49. Peng MY, Parisky YR, Cornwell EE III, Radin R, Bragin S. CT cystography versus conventional cystography in evaluation of bladder injury. AJR Am J Roentgenol 1999; 173:1269–1272. 50. Deck AJ, Shaves S, Talner L, Porter JR. Computerized tomography cystography for the diagnosis of traumatic bladder rupture. J Urol 2000; 164:43–46. 51. Vaccaro JP, Brody JM. CT cystography in the evaluation of major bladder trauma. RadioGraphics 2000; 20:1373–1381. 52. Hewett JJ, Freed KS, Sheafor DH, Vaslef SN, Kliewer MA. The spectrum of abdominal venous CT findings in blunt trauma. AJR Am J Roentgenol 2001; 176:955–958. 53. Kimoto T, Kohno H, Uchida M, et al. Inferior vena caval thrombosis after traumatic liver injury. HPB Surg 1998; 11: 111–116. 54. Berthet JP, Marty-Ane CH, Veerapen R, Picard E, Mary H, Alric P. Dissection of the abdominal aorta in blunt trauma: endovascular or conventional surgical management? J Vasc Surg 2003; 38:997–1003. 55. Lin PH, Barr V, Bush RL, Velez DA, Lumsden AB, Ricketts J. Isolated abdominal aortic rupture in a child due to all-terrain vehicle accident: a case report. Vasc Endovascular Surg 2003; 37:289–292. 56. Safriel YI, Sclafani SJ, Kurtz RS. Preoperative diagnosis of right hepatic vein injury by CT scan and venography. J Trauma 2001; 51:149–152.

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Kathirkamanathan Shanmuganathan, MD

CT of Abdominal Trauma: Part II1

Diagnosis and treatment of patients admitted to a trauma center with potential blunt abdominal injury has been a difficult and challenging task for the trauma surgeon and emergency radiologist (1–4). Computed tomography (CT) is the imaging modality of choice to evaluate hemodynamically stable patients who have sustained blunt abdominal trauma. During the past 5 years, single–detector row helical CT has been replaced by multi–detector row CT. This change has revolutionized cross-sectional imaging in trauma radiology. Volumetric imaging with helical CT has been a major factor for nonsurgical management of solid-organ injuries. The ability to obtain high-resolution images during optimal contrast enhancement at unparalleled speed has made multi– detector row CT the primary imaging modality of choice in evaluating hemodynamically stable patients with abdominal pain, tenderness, or positive ultrasonographic findings for free intraperitoneal fluid. Currently, a 16–detector row CT scanner can image the neck, chest, abdomen, and pelvis (from the circle of Willis to the symphysis pubis) in less than 60 seconds (5). This chapter will discuss the role of multi–detector row CT in the diagnosis and management of splenic, liver, renal, bowel, and mesenteric injuries.

TECHNIQUE
At our trauma center, multi–detector row CT examinations of the abdomen and pelvis of blunt trauma patients are performed (a) as part of a “whole-body” CT examination, which includes the neck, chest, abdomen, and pelvis, or (b) from the lower portion of the chest to the symphysis pubis. Contrast material (150 mL containing 300 mg of iodine per milliliter) is routinely administered intravenously with a power injector (biphasic injection: 90 mL at 6 mL/sec, followed by 60 mL at 4 mL/sec) unless there is (a) a known history of a major allergic reaction to iodinated contrast material or (b) renal insufficiency. Delayed images are obtained routinely about 2–3 minutes following intravenous injection of the contrast material to evaluate the renal collecting system for injuries. The CT parameters used at our institution for single–detector row helical and multi–detector row CT and for intravenous administration of contrast material are shown in the Table. Currently, studies are under way at our institution to optimize the whole-body multi–detector row CT scanning parameters and the rate, concentration, and volume of intravenous contrast material to obtain high-resolution images at peak contrast enhancement.

RSNA Categorical Course in Diagnostic Radiology: Emergency Radiology 2004; pp 101–112.
1From the Department of Radiology, University of Maryland School of Medicine, 22 S Greene St, Baltimore, MD 21201 (e-mail: [email protected]).

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CT Protocols

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Type of Spiral CT Single–detector row CT Sixteen–detector row CT Four–detector row CT

Intravenous Contrast Material (mL) 150.0 90.0 60.0 90.0 60.0

Delay (sec)* 60 70 70

Injection Rate (mL/sec) 3 6 4 6 4

Collimation (mm) 8. 16 × 1.5† 4 × 2.5†

Table Speed (mm) 8 37.4 10

Pitch 1.0 1.2 1.0

* Delay in initiation of scan from beginning of intravenous bolus. † Detector configuration: number of sections (detectors) × section thickness (in millimeters). Number of sections is number obtained per rotation (0.75 or 0.8 second).

Figure 1. Splenic lacerations and active bleeding. Multi–detector row axial CT images obtained during (a) portal venous phase and (b) renal excretory phase show areas of active bleeding (arrowheads) and lacerations (straight arrows) seen within a grade V splenic injury. A large perisplenic hematoma (curved arrows) is also seen. Delayed image shows the active bleeding increases in extent. (c) Maximum intensity projection coronal image obtained in portal venous phase demonstrates active bleeding (arrowheads) and hematoma and hemoperitoneum (curved arrows) displacing the peritoneal content inferiorly and to the right side.

Although oral administration of contrast material remains controversial in trauma centers, we routinely administer a total volume of 600 mL of 2% sodium diatrizoate orally or through a naso- or orogastric tube at 30 minutes before and immediately before the scan. Patients who require urgent CT scanning on arrival at the admitting area may be scanned immediately following oral administration of one dose of contrast material. Rectal contrast material is not routinely used to evaluate blunt trauma patients.

played by the spleen in the immune defense system been fully appreciated, and this understanding has led to a more conservative (nonsurgical) approach to the management of splenic injury, both in adults and children (6–11).

SPLENIC INJURY
The spleen is the solid abdominal organ most commonly injured with blunt trauma. During the past 2 decades, CT has had an important effect in supporting nonsurgical approaches to management of blunt splenic trauma (6–8). Only recently has the vital role

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Splenic Injury CT Grading Systems Although contrast material–enhanced CT is highly accurate in the diagnosis of splenic injury, CT grading systems have been generally unreliable in predicting outcome following blunt splenic injury in adults (12– 14). Many systems have been proposed to grade splenic injury following trauma. The grades of splenic injury may be based on the extent of injury seen at laparotomy, CT, or autopsy (12,14). None of the current surgical or CT-based splenic injury grading systems have incorporated select predictive CT findings commonly seen on contrast-enhanced studies, including active

splenic bleeding, pseudoaneurysms, or posttraumatic arteriovenous fistulas. In the recent radiologic and surgical literature, investigators have suggested that these three CT findings have a high association with failed nonsurgical management (7,8,15,16).

CT Appearances of Splenic Injury Contrast-enhanced CT can be used to accurately diagnose the four principal types of splenic injury: hematoma, laceration (Fig 1), active hemorrhage (Figs 1, 2) (17), and vascular injuries, including pseudoaneurysm and posttraumatic arteriovenous fistula (Fig 3) (7,8,15,16,18). High-resolution overlapping thin axial images generated with multi– detector row CT can be used by sophisticated multiplanar postprocessing programs to generate highquality isotropic images. These images are used to detect and depict the relationship between the parenchymal lesions and vascular structures and to differentiate the spectrum of splenic injuries seen following blunt trauma (Figs 1c, 2e, 3g). Hematomas and laceration.—Splenic hematomas may be intraparenchymal (Figs 2b, 3a) or subcapsular (Fig 2). Single or multiple hematomas may be seen following blunt trauma. On contrast-enhanced CT images, acute hematomas appear as irregular high- or low-attenuation areas within the parenchyma. On contrast-enhanced CT images, subcapsular hematomas are typically seen as low-attenuation collections of blood between the splenic capsule and the enhancing splenic parenchyma. On nonenhanced CT images, subcapsular hematoma is hyperattenuating relative to normal splenic parenchyma. Subcapsular hematomas often compress the underlying splenic parenchyma, and this CT finding helps to differentiate subcapsular hematomas from small amounts of blood or fluid in the perisplenic space. Attenuation values of uncomplicated subcapsular hematomas typically decrease with time and resolve within 4–6 weeks. Acute splenic lacerations have sharp or jagged margins and appear as linear or branching low-attenuation areas on contrast-enhanced CT images (Fig 1b). With time, the margins of splenic lacerations and hematomas become less well defined, and the lesions decrease in size until the area becomes isoattenuating compared with normal splenic parenchyma. Complete healing, as determined from the CT appearance, may take weeks to months, depending on the initial size of the injury. Enlargement or development of a new lesion at follow-up CT should raise the possibility of injury progression and warrants close clinical observation, further follow-up CT, or arteriography. Active hemorrhage.—On contrast-enhanced CT images, active hemorrhage in the spleen is seen as an irregular or linear area of contrast material extravasation (Figs 1, 2). The difference between the attenuation value of extravasated contrast material (range,

85–350 HU; mean, 132 HU) and hematoma (range, 40–70 HU; mean, 51 HU) is helpful in distinguishing active bleeding from clotted blood (18,19). Active splenic hemorrhage may be seen within the splenic parenchyma (Fig 2), subcapsular space (Fig 2), or intraperitoneally (Fig 1b). On multi–detector row CT images, ongoing hemorrhage may be seen as an increase over time in the amount of extravasation of intravenous contrast material in the identical anatomic region by comparing the arterial and delayed renal excretory phases of the CT examination (Figs 1, 2). Splenic vascular injuries.—The appearances of posttraumatic splenic pseudoaneurysms (Fig 3) and arteriovenous fistulas are similar on contrast-enhanced multi–detector row CT images; these lesions can only be differentiated with splenic angiography (8). On multi–detector row CT images, both of these lesions appear as well-circumscribed focal areas of increased attenuation compared with the normal enhanced splenic parenchyma (attenuation within extravasations typically measures within 10 HU of the attenuation of an adjacent major artery) (8,18). On images obtained in the delayed renal excretory phase, these lesions become minimally hyperattenuating or isoattenuating compared with the normal splenic parenchyma (Fig 3) (5). With multi–detector row CT, the ability to scan during peak contrast enhancement in the early arterial or portal venous phase and during the excretory phase aids in differentiating active bleeding from posttraumatic splenic pseudoaneurysms or arteriovenous fistulas (Figs 1–3). Usually, posttraumatic vascular injuries are similar in attenuation value to active hemorrhage in the arterial phase but “wash out” in the excretory phase to become minimally hyperattenuating or isoattenuating compared with normal splenic parenchyma (Fig 3). Good correlation between the multi–detector row CT findings of active splenic hemorrhage and the need for angiographic or surgical intervention to treat hemorrhage has led to an aggressive diagnostic and therapeutic pursuit of splenic vascular injury with splenic angiography at our trauma center. Patients with CT evidence of splenic vascular contrast material extravasation and without vascular injury at splenic arteriography undergo prophylactic proximal main splenic artery embolization, which potentially increases the number of patients with blunt splenic injuries who can be treated successfully without surgery. Posttraumatic splenic infarction.—Segmental splenic infarction is a rare manifestation of blunt trauma to the spleen (20). On contrast-enhanced CT images, posttraumatic splenic infarcts are seen as well-demarcated segmental wedge-shaped low-attenuation areas, with the base of the wedge toward the periphery of the splenic parenchyma (Fig 4). These infarcts can be the only CT finding of blunt splenic trauma and may occur without any adjacent free fluid. Splenic infarcts

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Figure 2. Active bleeding from grade IV splenic injury in a patient admitted following motor vehicle collision. (a, b) Multi– detector row axial CT images obtained in portal venous phase show a well-defined rounded pseudoaneurysm (black arrowhead) and linear areas of active bleeding within splenic parenchymal hematoma (white arrowhead) and subcapsular space (curved arrow). Active bleeding and pseudoaneurysms were similar in attenuation to intravenous contrast material seen in splenic vessels (not shown). Large hematoma (straight arrows) is seen around spleen. (c, d) Delayed multi– detector row axial CT images obtained in same region during renal excretory phase show washout of contrast material in splenic pseudoaneurysm and increase in parenchymal (arrowhead) and subcapsular (curved arrow) hemorrhage. (e) Multiplanar curved coronal reformation shows splenic injury (white arrowheads), subcapsular active bleeding (curved arrow), perisplenic clot (straight arrows), and hemoperitoneum (black arrowheads) adjacent to liver. (f) Early splenic arteriogram shows an actively bleeding pseudoaneurysm (arrow). (g) Delayed splenic arteriogram confirms intraparenchymal bleeding (straight arrow) and subcapsular bleeding (curved arrows) seen on multi–detector row CT images. (Reprinted, with permission, from reference 17.)

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CT of Abdominal Trauma: Part II
Figure 3. Multiple posttraumatic splenic pseudoaneurysms. (a–c) Multi–detector row axial CT images obtained in portal venous phase show multiple splenic pseudoaneurysms (curved arrows) with hemoperitoneum (black arrowheads). Splenic lacerations (straight arrow) and a parenchymal hematoma (white arrowheads) are seen. (d–f) Delayed axial images obtained in same region during renal excretory phase. Pseudoaneurysms (arrow) wash out and become minimally hyperattenuating or isoattenuating compared with normal splenic parenchyma. (g) Coronal maximum intensity projection image shows three pseudoaneurysms (arrowheads). (h) Splenic arteriogram shows three pseudoaneurysms (arrowheads), which were embolized. (Reprinted, with permission, from reference 17.)

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Figure 4. Posttraumatic splenic infarction. (a) Axial multi–detector row CT image and (b) coronal multiplanar reformation show wedge-shaped low-attenuation area (arrows) of splenic infarction. No perisplenic fluid is seen.

may also be seen in association with splenic lacerations and segmental infarcts in the kidney. Injury to the intima of splenic artery branches caused by sudden deceleration at the time of impact can lead to thrombosis and infarction of the splenic parenchyma because of a lack of parenchymal perfusion distal to the intimal injury. Similar injuries have been observed at CT of the kidneys following blunt trauma (5,20). Although the exact natural history of this injury is not known, most of these lesions usually heal without need for surgical or angiographic intervention. Delayed complications following posttraumatic splenic infarction are rare and include splenic abscess formation or delayed rupture of the spleen (20).

Figure 5. Intraparenchymal hepatic hematoma. Multi–detector row CT axial image obtained on admission shows large intraparenchymal hematoma (arrows) in the right lobe, with perihepatic blood (arrowhead).

LIVER INJURY
The liver is the second most commonly injured solid organ following blunt trauma. From 70% to 90% of hepatic injuries are minor and either do not require surgery or have stopped bleeding at the time of celiotomy (21,22). Because the right lobe constitutes 80% of the hepatic volume, it is the most frequently injured region. Mortality rates may exceed 50% in patients with complex liver injuries who present with hemodynamic instability caused by active bleeding (23–26). Isolated injuries of the liver occur in less than 50% of the patients with blunt liver injury.

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Hepatic Injury Grading System Radiologic and surgical injury severity scores are based on the anatomic disruption of the liver, including the depth and number of lacerations and the surface area involved by subcapsular or intraparenchymal hematomas seen at laparotomy (12,27,28). These injury scales have helped to standardize reporting of liver injuries over a period of time and to compare outcomes and treatment protocols within the same trauma center or among different centers.

Multi–Detector Row CT Appearance of Liver Injury The four principal types of parenchymal liver injury shown with CT are hematoma, laceration, vascular injury, and active hemorrhage. The results of numerous studies have shown that CT can be used to accurately diagnose these four types of injuries and to guide care of blunt trauma patients with liver injury (27–30). Hematoma.—Hepatic hematomas may be intraparenchymal (Fig 5) or subcapsular. On contrastenhanced CT images, most subcapsular hematomas are seen along the anterolateral aspect of the right lobe of the liver as a low-attenuation lens-shaped collection of blood between Glisson capsule and the enhancing liver parenchyma. Subcapsular hematomas cause direct compression of underlying liver parenchyma, and this CT sign is helpful in differentiating subcapsular hematoma from small amounts of

CT of Abdominal Trauma: Part II

Figure 6. Hepatic lacerations extending into hepatic vein and porta hepatis. (a) Axial multi–detector row CT image and (b, c) coronal maximum intensity projection images show hepatic lacerations (straight arrows) extending into region of hepatic vein (curved black arrow) and porta hepatis (curved white arrow). Hemoperitoneum (arrowheads) is also seen around liver.

free intraperitoneal blood or fluid seen adjacent to the liver (perihepatic spaces). Follow-up CT images typically show resolution of uncomplicated subcapsular hematomas within 6–8 weeks (31). Contusion.—Parenchymal contusions of the liver appear as irregular areas of low attenuation on contrastenhanced CT images, with possible intermixed highattenuation blood. On nonenhanced CT images, acute hematomas appear as irregular high-attenuation regions of clotted blood surrounded by lower-attenuation nonclotted blood or bile. With early healing, the contusion may initially expand in size slightly and develop smoother, more regular margins, which should not be taken as a sign of worsening injury. With further resolution, the lesion demonstrates a gradual decrease in the attenuation and size of the hematoma until there is blending with the background parenchyma. Laceration.—On contrast-enhanced multi–detector row CT images, liver lacerations appear as irregular linear or branching low-attenuation areas (Fig 6). The location of a laceration and its relationship to the hepatic veins may be important in predicting the likelihood of hemorrhage. Poletti et al (29) reported highgrade liver lacerations (grades III to V) involving the portal veins (Fig 6b) and the region of the major branches of the hepatic veins (Fig 6c); with active bleeding, such lacerations have an increased likelihood for major vascular injury and should prompt hepatic arteriography in patients with clinical signs of hemorrhage. Prior knowledge of lacerations extending into the region of the intrahepatic inferior vena cava or the three major hepatic veins indicates a high likelihood of inferior vena cava or hepatic vein disruption. Hepatic lacerations with a branching pattern could mimic the appearance of unopacified portal or he-

patic veins or dilated bile ducts and may require careful evaluation of serial images to differentiate among these various structures. Acute liver lacerations have sharp or jagged margins. As the lesion heals, it enlarges, its margins become smoother, and it assumes a round to oval configuration on follow-up CT images. These lesions may gradually decrease in size with time or remain as well-defined hepatic cysts. Active hemorrhage.—Multi–detector row CT can often be used to distinguish a pseudoaneurysm from intraparenchymal extravasation by comparing the appearance of the lesion during peak arterial enhancement and delayed “washout” imaging (delayed renal collecting system phase). Pseudoaneurysms will show a more or less complete washout of contrast material, whereas parenchymal contrast enhancement from local tissue extravasation will persist and may be seen to increase on the delayed images. Liver lesions that could mimic active bleeding at CT, other than retained extravasated arteriographic contrast material, include contrast enhancement seen in hepatic hemangiomas or other vascular tumors. Other signs of hepatic trauma essentially always accompany bleeding of traumatic origin, but trauma-induced hemorrhage from hypervascular hepatic tumors should also be considered. Vascular injuries.—Retrohepatic vena cava injuries are typically associated with high mortality (90%–100%) (23–25,32,33). Retrohepatic vena cava injuries are suspected at CT when (a) liver lacerations extend to the major hepatic veins or inferior vena cava or (b) profuse hemorrhage is present behind the right lobe of the liver, extends into the lesser sac, or collects adjacent to the diaphragm. On contrast-enhanced CT images, devascularized segments may appear as wedge-shaped

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Figure 8. Full-thickness bowel injury with subtle free intraperitoneal air. (a, b) Multi–detector row axial CT images show free intraperitoneal fluid (arrowheads) in pelvis and upper portion of abdomen adjacent to spleen and liver. (c, d) Axial CT images show proximal smallbowel wall thickening (black arrows), mesenteric infiltration (arrowheads), and bubble of free intraperitoneal air (white arrow). At celiotomy, full-thickness jejunal and mesenteric injuries were repaired. (Reprinted, with permission, from reference 17.)

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regions extending to the periphery that fail to enhance with the normally perfused liver. Pseudoaneurysms or injury of the hepatic artery and its branches may result from lacerations extending across the course of these vessels, as well as from shearing forces. Arteriovenous or arterioportal fistulas may mimic the contrast-enhanced CT appearance of hepatic pseudoaneurysms. The findings from a retrospective review of patients sustaining blunt hepatic injury who had undergone both contrast-enhanced single–detector row spiral CT and hepatic arteriography showed that single–detector row contrastenhanced helical CT had a sensitivity of 65% and a specificity of 85% for detecting hepatic arterial injury for all CT injury grades when arteriography was the reference standard (29). Periportal low attenuation.—Periportal low attenuation refers to regions of low attenuation that parallel the portal vein and its branches at CT (Fig 7). This CT finding has been noted in several nontraumatic clinical conditions, including acute transplant rejection, malignant neoplasm of the liver, liver transplantation, cardiac failure, and cardiac tamponade and is usually attributed to dilatation of the intrahepatic lymph channels caused by obstruction of the normal hepatic

Figure 7. Periportal low attenuation from vigorous volume resuscitation. Multi–detector row CT image shows diffuse lowattenuation areas (arrowheads) paralleling portal vein and its branches, compatible with periportal edema. No liver injury was seen. Inferior vena cava (curved arrow) is markedly distended and larger than aorta from raised central venous pressure.

lymphatic drainage. In trauma patients, periportal areas of low attenuation on CT images are often the consequence of (a) vigorous intravenous fluid adminis-

CT of Abdominal Trauma: Part II

Figure 9. Active mesenteric hemorrhage. (a, b) Axial multi–detector row CT and (c) coronal multiplanar CT images show large mesenteric hematoma (arrows) with active bleeding (black arrowheads) within center of hematoma. Hemoperitoneum (white arrowheads) is also seen. At surgery, mesenteric hemorrhage and hematoma were confirmed. Segment of ischemic small bowel was also resected.

tration prior to performing CT or (b) other trauma-related causes of elevated central venous pressure (such as tension pneumothorax or pericardial tamponade) that result in distention of the periportal lymphatic vessels (34,35). Periportal low attenuation seen on CT images without evidence of parenchymal liver injury is not considered to represent hepatic injury and does not warrant hospitalization for observation or follow-up CT.

BOWEL AND MESENTERIC INJURIES
Bowel and mesenteric injuries are found in approximately 5% of the patients sustaining blunt abdominal trauma (36,37). The classic symptoms of rigidity, tenderness, and decreased or absent bowel sounds may be present in only one-third of the patients (38). In more recent studies with helical CT, investigators have reported sensitivities ranging from 84% to 94%, with accuracy from 84% to 99% in diagnosing hollow viscus injury (39,40). CT can be used to differentiate between surgical bowel injury (full-thickness bowel injury) and nonsurgical bowel injury (serosal tear or bowel wall contusion) with a reported accuracy of 75%–86%. CT was found to be less reliable in determining the need for surgical intervention for mesenteric injuries, with an accuracy of 54%–75% (40,41). Active bleeding and bowel wall thickening associated with mesenteric hematoma are

the most specific signs for surgically important mesenteric injury. CT findings of a full-thickness bowel injury include extraluminal gas (Fig 8) (17), intramural air, extraluminal oral contrast material or intestinal content, and discontinuity of bowel wall. Focal bowel wall thickening (Fig 8) (>4 mm) and isolated free peritoneal fluid are nonspecific CT findings of bowel injury (42,43). CT findings of mesenteric injury include active extravasation of intravenous contrast material into the mesentery (Fig 9), bowel wall thickening associated with mesenteric hematoma, focal mesenteric hematoma (Fig 9), or mesenteric infiltration (Fig 8). Radiologists should be familiar with abnormalities observed in the bowel of patients with “hypoperfusion complex” and fluid overresuscitation (44,45). These two entities can mask the diagnosis of bowel injury (44,45). On CT images, small-bowel injury usually appears as a segmental focal abnormality, in contrast to the diffuse abnormality involving the entire small bowel associated with both hypoperfusion complex and fluid overresuscitation. The bowel wall changes seen following vigorous fluid overresuscitation may result in diffuse edema of the bowel wall, particularly the small bowel (45). Other CT findings of intravenous volume expansion include periportal low attenuation, distention of the inferior vena cava, retroperitoneal fluid attenuation, and occasionally ascites, and these CT findings usually accompany bowel wall thickening. The CT findings of shock bowel or diffuse smallbowel ischemia in hypotensive adult patients with blunt trauma include diffuse thickening of the smallbowel wall (range, 7–15 mm), fluid-filled dilated smallbowel loops, increased contrast enhancement of the

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Figure 10. Renal laceration and contusion. (a) Multi– detector row axial CT image obtained at admission shows renal laceration (straight arrow) in mid anterior portion of kidney; laceration does not extend into collecting system. Small perinephric hematoma (curved white arrow) and stranding (curved black arrow) of fat around renal hilum are also seen. Followup (b) axial nonenhanced multi–detector row CT image and (c) coronal multiplanar reformation obtained 4 hours after admission show collections of parenchymal extravasation (curved arrows) in areas of renal contusion that were not seen on CT images obtained at admission.

Figure 11. Catastrophic renal injury. (a, b) Multi– detector row axial CT images show large perinephric hematoma (straight arrows) with fragmentation of renal parenchyma (curved arrows). Perinephric hematoma displaces peritoneal organs anteriorly and to the left. (c) Coronal maximum intensity projection image shows fragmented renal parenchyma (straight arrows) and renal artery branch (curved arrow) that supplies lower pole.

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small-bowel wall from slow perfusion and interstitial leakage of intravenous contrast material, and a flattened inferior vena cava. The large bowel usually appears normal. Usually, follow-up CT performed after adequate treatment of the cause of hypoperfusion shows complete resolution of the small-bowel changes (44).

RENAL INJURY
CT provides information valuable to the diagnosis and staging of blunt-force renal trauma in hemodynamically stable patients (46–48). An intravenous pyelogram can be obtained in the admitting area or the operating room to depict both kidneys in hemodynamically unstable patients taken directly to surgery. Controversy still exists regarding the strength of the relationship between hematuria and renal injury (46). CT aids the accurate assessment of parenchymal disruption, the integrity of the renal collecting sys-

tems, excretion of urine, the extent of perinephric hematoma, and active hemorrhage. Management of renal injuries can be based on these CT findings and the overall status of the patient.

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CT of Minor Renal Injuries Most renal injuries (75%–98%) are minor and are treated without surgical intervention (49–51). Contu-

Figure 12. Renal artery occlusion. (a) Axial multi–detector row CT image and (b) coronal multiplanar reformation show no contrast enhancement of right kidney (straight white arrows). Right renal artery is completely occluded (black arrow) at junction of proximal and middle segments of vessel. Hematoma (curved white arrows) is seen around renal pedicle.

CT of Abdominal Trauma: Part II

sions may appear as ill-defined low-attenuation areas or discretely limited regions of a striated nephrographic pattern from parenchymal extravasation on delayed postcontrast CT images (Fig 10). Subcapsular hematomas are rare, assume a convex shape, compress the renal parenchyma, and are limited by the renal capsule. Lacerations are seen on contrast-enhanced CT images as linear low-attenuation areas (Fig 10a). In most cases, these injuries will resolve without intervention. Segmental renal infarcts are relatively common following blunt trauma and occur at the upper or lower pole of the kidney. The infarcts appear as wedgeshaped, sharply demarcated low-attenuation areas. Isolated segmental renal infarcts do not warrant renal arteriography for confirmation or treatment.

be used to confirm the diagnosis by demonstrating a lack of renal enhancement (Fig 12) and diminished kidney size. Peripheral subcapsular cortical enhancement may be seen from collateral vessels but is not typically present in the acute setting. Angiography is not required to establish the diagnosis and may delay definitive treatment. CT findings of renal pelvis disruption include limited or no parenchymal disruption and urinary contrast extravasation adjacent to the ureteropelvic junction and anterior pararenal space. The injury may be missed at helical CT unless delayed images are obtained with urinary contrast material within the renal pelvis. In the presence of proximal urine extravasation, depiction of the distal ureter indicates a partial disruption.

References
1. Fabian TC, Mangiante EC, White TJ, et al. A prospective study of 91 patients undergoing computed tomography and peritoneal lavage following blunt abdominal trauma. J Trauma 1986; 26: 602–608. 2. Jones TK, Walsh JW, Maull KI. Diagnostic imaging in blunt trauma of the abdomen. Surg Gynecol Obstet 1983; 157:389– 398. 3. Bain IM, Kirby RM, Tiwari P, et al. Survey of abdominal ultrasound and diagnostic peritoneal lavage for suspected intraabdominal injury following blunt trauma. Injury 1998; 29:65–71. 4. Peitzman AB, Makaroun MS, Slasky BS, et al. Prospective study of computed tomography in initial management of blunt abdominal trauma. J Trauma 1986; 26:585–592. 5. Shanmuganathan K, Killeen KL. Imaging of abdominal trauma. In: Mirvis SE, Shanmuganathan K, eds. Imaging in trauma and critical care. 2nd ed. Philadelphia, Pa: Saunders, 2003; 369– 482. 6. Pachter HL, Guth AA, Hofstetter SR, Spencer FC. Changing patterns in the management of splenic trauma: the impact on nonoperative management. Ann Surg 1998; 227:708–719. 7. Davis KA, Fabian TC, Corce MA, et al. Improved success in nonoperative management of blunt splenic injury: embolization of splenic artery pseudoaneurysm. J Trauma 1998; 44:1008– 1015. 8. Shanmuganathan K, Mirvis SE, Boyd-Kranis R, Takada T, Scalea TM. Nonsurgical management of blunt splenic injury: use of CT criteria to select patients for splenic arteriography and potential endovascular therapy. Radiology 2000; 217:75– 82. 9. Meguid AA, Bair HA, Howells GA, Bendick PJ, Kerr HH, Villalba MR. Prospective evaluation of criteria for the nonoperative management of blunt splenic trauma. Am Surg 2003; 69:238–242; discussion 242–243.

CT of Major Renal Injuries Major renal injuries include lacerations extending into the collecting system with urinary extravasation, large perinephric hematomas, renal lacerations disrupting more than 50% of the renal parenchyma, and subcapsular hematomas causing delay in excretion (46). These lesions may or may not require surgical or angiographic intervention. Collecting system injuries with persistent urine leakage may be treated with percutaneous nephrostomy or double-J ureteral catheterization. Angiographic embolization or surgical intervention may be required to treat expanding or large perinephric or parenchymal hematomas. CT of Catastrophic Renal Injuries Catastrophic renal injuries warrant surgical or angiographic intervention. Evidence of these injuries include CT findings of (a) fragmentation of renal parenchyma with associated large perinephric or pararenal hematoma (Fig 11), (b) major renal pedicle injuries (renal artery or vein) (Fig 12), (c) renal arterial bleeding or pseudoaneurysm, (d) renal pelvis disruption, and (e) urinary leak into the peritoneal space. Renal artery occlusion results from an intimal injury at the junction of the proximal and middle one-third of the renal artery. Contrast-enhanced CT can usually

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10. Hartnett KL, Winchell RJ, Clark DE. Management of adult splenic injury: a 20-year perspective. Am Surg 2003; 69:608–611. 11. Pimpl W, Dapunt O, Kaindl H, Thalhamer J. Incidence of septic and thromboembolic-related deaths after splenectomy in adults. Br J Surg 1989; 76:517–521. 12. Moore EE, Cogbill TH, Jurkovich GJ, et al. Organ injury scaling: spleen and liver (1994 revision). J Trauma 1995; 38:323–324. 13. Mirvis SE, Whitley NO, Vainwright JR, Gens DR. Blunt splenic trauma in adults: CT-based classification and correlation with prognosis and treatment. Radiology 1989; 171:33–39. 14. Starnes S, Klein P, Magagna L, et al. Computed tomographic grading is useful in the selection of patients for nonoperative management of blunt injury to the spleen. Am Surg 1998; 64:743–748; discussion 748–749. 15. Federle MP, Courcoulas AP, Powell M, Ferris JV, Petizman AB. Blunt splenic injury in adults: clinical and CT criteria for management, with emphasis on active extravasation. Radiology 1998; 206:137–142. 16. Gavant ML, Schurr M, Flick PA, Croce MA, Fabian TC, Gold RE. Predicting clinical outcome of nonsurgical management of blunt splenic injury: using CT to reveal abnormalities in the splenic vasculature. AJR Am J Roentgenol 1997; 168:207–212. 17. Shanmuganathan K. Multi-detector row CT imaging of blunt abdominal trauma. Semin Ultrasound CT MR 2004; 25:180–204. 18. Shanmuganathan K, Mirvis SE, Sover ER. Value of contrastenhanced CT in detecting active hemorrhage in patients with blunt abdominal or pelvic trauma. AJR Am J Roentgenol 1993; 161:65–69. 19. Jeffrey RB Jr, Cardoza JD, Olcott EW. Detection of active abdominal arterial hemorrhage: value of dynamic contrast-enhanced CT. AJR Am J Roentgenol 1991; 156:725–729. 20. Miller LA, Mirvis SE, Shanmuganathan K. CT diagnosis of splenic infarction in blunt trauma: imaging features, clinical significance and complications. Clin Radiol 2004; 59:342–348. 21. Matthes G, Stengel D, Seifert J, et al. Blunt liver injuries in polytrauma: results from a cohort study with the regular use of whole-body helical computed tomography. World J Surg 2003; 27:1124–1130. 22. Feliciano DV, Mattox KL, Jordan GL Jr, Burch JM, Bitondo CG, Cruse PA. Management of 1000 consecutive cases of hepatic trauma (1979-1984). Ann Surg 1986; 204:438–445. 23. Asensio JA, Demetriades D, Chahwan S, et al. Approach to the management of complex hepatic injuries. J Trauma 2000; 48: 66–69. 24. Gao JM, Du DY, Zhao XJ. Liver trauma: experience in 348 cases. World J Surg 2003; 27:703–708. 25. Asensio JA, Roldan G, Petrone P, et al. Operative management and outcomes in 103 AAST-OIS grades IV and V complex hepatic injuries: trauma surgeons still need to operate, but angioembolization helps. J Trauma 2003; 54:647–653; discussion 653–654. 26. Pachter HL, Feliciano DV. Complex hepatic injuries. Surg Clin North Am 1996; 76:763–782. 27. Mirvis SE, Whitley NO, Vainwright JR, Gen DR. Blunt hepatic trauma in adults: CT-based classification and correlation with prognosis and treatment. Radiology 1989; 171:27–32. 28. Becker CD, Gal I, Baer HU, Vock P. Blunt hepatic trauma in adults: correlation of CT injury grading with outcome. Radiology 1996; 201:215–220. 29. Poletti PA, Mirvis SE, Shanmuganathan K, et al. CT criteria for management of blunt liver trauma: correlation with angiographic and surgical findings. Radiology 2000; 216:418–427. 30. Hagiwara A, Yukioka T, Ohta S, et al. Nonsurgical management of patients with blunt hepatic injury: efficacy of transcatheter arterial embolization. AJR Am J Roentgenol 1997; 169:1151–1156.

31. Savolaine ER, Grecos GP, Howard J, et al. Evolution of CT findings in hepatic hematoma. J Comput Assist Tomogr 1985; 9:1090–1096. 32. Denton JR, Moore EE, Coldwell DM. Multimodality treatment for grade V hepatic injuries: perihepatic packing, arterial embolization, and venous stenting. J Trauma 1997; 42:964–967; discussion 967–968. 33. Buckman RF Jr, Miraliakbari R, Badellino MM. Juxtahepatic venous injuries: a critical review of reported management strategies. J Trauma 2000; 48:978–984. 34. Yokota J, Sugimoto T. Clinical significance of periportal tracking on computed tomographic scan in patients with blunt liver trauma. Am J Surg 1994; 168:247–250. 35. Shanmuganathan K, Mirvis SE, Amerosa M. Periportal low density on CT in patients with blunt trauma: association with elevated venous pressure. AJR Am J Roentgenol 1993; 160: 279–283. 36. Williams MD, Watts D, Fakhry S. Colon injury after blunt abdominal trauma: results of the EAST Multi-Institutional Hollow Viscus Injury Study. J Trauma 2003; 55:906–912. 37. Rizzo MJ, Federle MP, Griffiths BG. Bowel and mesenteric injury following blunt abdominal trauma: evaluation with CT. Radiology 1989; 173:143–148. 38. Donohue J, Crass R, Trunkey D. Management of duodenal and small intestinal injury. World J Surg 1985; 9:904–913. 39. Malhotra AK, Fabian TC, Katsis SB, et al. Blunt bowel and mesenteric injuries: the role of screening computed tomography. J Trauma 2000; 48:991–998. 40. Killeen KL, Shanmuganathan K, Poletti PA, Cooper C, Mirvis SE. Helical computed tomography of bowel and mesenteric injuries. J Trauma 2001; 51:26–36. 41. Dowe MF, Shanmuganathan K, Mirvis SE, et al. CT findings of mesenteric injury after blunt trauma: implications for surgical intervention. AJR Am J Roentgenol 1997; 168:425–428. 42. Hanks PW, Brody JM. Blunt injury to mesentery and small bowel: CT evaluation. Radiol Clin North Am 2003; 41:1171– 1182. 43. Hawkins AE, Mirvis SE. Evaluation of bowel and mesenteric injury: role of multidetector CT. Abdom Imaging 2003; 28:505–514. 44. Mirvis SE, Shanmuganathan K, Erb R. Diffuse small-bowel ischemia in hypotensive adults after blunt trauma (shock bowel): CT findings and clinical significance. AJR Am J Roentgenol 1994; 163:1375–1379. 45. Chamrova Z, Shanmuganathan K, Mirvis SE, et al. Retroperitoneal fluid resulting from rapid intravascular resuscitation in trauma: CT mimic of retroperitoneal injury. Emerg Radiol 1994; 1:85–88. 46. Mirvis SE. Injuries to the urinary system and retroperitoneum. In: Mirvis SE, Shanmuganathan K, eds. Imaging in trauma and critical care. 2nd ed. Philadelphia, Pa: Saunders, 2003; 483–518. 47. Stein JP, Kaji DM, Eastham J, Freeman JA, Esrig D, Hardy BE. Blunt renal trauma in the pediatric population: indications for radiographic evaluation. Urology 1994; 44:406–410. 48. Smith JK, Kenney PJ. Imaging of renal trauma. Radiol Clin North Am 2003; 41:1019–1035. 49. Toutouzas KG, Karaiskakis M, Kaminski A, et al. Nonoperative management of blunt renal trauma: a prospective study. Am Surg 2002; 68:1097–1103. 50. Matthews LA, Smith EM, Spirnak JP. Nonoperative treatment of major renal lacerations with urinary extravasation. J Urol 1997; 157:2056–2058. 51. Robert M, Drianno, Muir G, et al. Management of major blunt renal lacerations: surgical or nonoperative approach? Eur Urol 1996; 30:335–339.

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Carlos J. Sivit, MD

Imaging the Pediatric Patient with Acute Abdominal Disease1
The most frequent nontraumatic conditions resulting in an acute abdomen in children are midgut malrotation, intestinal intussusception, and acute appendicitis. The imaging evaluation of these conditions strongly affects diagnosis and management. Therefore, selection of an appropriate imaging strategy is essential to ensure prompt treatment. This chapter focuses on the important imaging features of these three conditions.

MIDGUT MALROTATION
Midgut malrotation is the most important cause of upper intestinal obstruction in newborns. The malfixated bowel is associated with a narrow mesentery that is prone to twisting, which results in occlusion of mesenteric vessels and secondary bowel necrosis. The twisting is labeled a midgut volvulus. In addition, aberrant peritoneal bands are frequently present. These are called Ladd bands and can lead to duodenal obstruction. The clinical manifestation of midgut malrotation is usually characterized by vomiting, which is often bilious. Note that the majority of patients with bilious vomiting do not have malrotation (1). Symptoms may occur at any age, but most patients present in the 1st month of life. Evaluation of infants and children who are suspected of having midgut malrotation typically begins with abdominal radiography. However, the radiographic findings associated with malrotation are nonspecific. The abdominal radiograph may demonstrate a proximal obstruction caused by Ladd bands or a distal small-bowel obstruction caused by a midgut volvulus (2). However, the abdominal radiograph may show normal findings. Therefore, radiography should not be used to exclude the diagnosis of malrotation. The examination of choice for the diagnosis of malrotation is the upper gastrointestinal examination. Midgut malrotation with malfixation of the intestines is inferred from malposition of the duodenojejunal junction. The normal location of the duodenojejunal junction is to the left of the spine (to the left of the left pedicles) and at the level of the duodenal bulb (3). Patients with malrotation have an abnormally positioned duodenojejunal junction located to the right or inferior to the normal position (Fig 1). In a child without obstruction, the abnormally located duodenojejunal junction may be the only finding. One diagnostic pitfall to avoid is the fact that an overdistended stomach may inferiorly displace the normal duodenojejunal junction

RSNA Categorical Course in Diagnostic Radiology: Emergency Radiology 2004; pp 113–117.
1 From

the Departments of Radiology and Pediatrics, Rainbow Babies and Children’s Hospital of the University Hospitals of Cleveland and Case Western Reserve University School of Medicine, 11100 Euclid Ave, Cleveland, OH 44106-5056 (e-mail: [email protected]).

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Figure 1. Midgut malrotation. Spot radiograph from an upper gastrointestinal examination demonstrates the duodenojejunal junction in an abnormal location to the right of the spine and below the duodenal bulb. This finding is diagnostic for malrotation.

Figure 2. Midgut malrotation. Transverse sonogram through the middle of the abdomen of a child with malrotation shows inversion of the mesenteric vessels, with the superior mesenteric vein (V) to the left of the superior mesenteric artery (A).

below its normal location. In such circumstances, repeating the upper gastrointestinal examination by administering a small amount of contrast material (10– 15 mL) through a nasoenteric tube can help to confirm the diagnosis. The diagnosis of midgut malrotation can also be made at ultrasonography (US) and computed tomography (CT). Most patients with malrotation have inversion of the normal relationship between the mesenteric vessels (4). Thus, the superior mesenteric vein lies to the left of the superior mesenteric artery (Fig 2). However, this finding is neither as sensitive nor as specific as the identification of the duodenojejunal junction on images from the upper gastrointestinal series (4). Therefore, the diagnosis should always be confirmed with an upper gastrointestinal examination.

INTUSSUSCEPTION
Intestinal intussusception occurs when a segment of bowel, the intussusceptum, telescopes into a more distal segment, the intussuscipiens. Intussusception occurs more frequently in boys than in girls. It is rare in infants younger than 3 months and in children older than 3 years of age. The peak incidence is between 5 and 9 months of age. The most common type of intussusception is ileocolic, followed by ileoileocolic. Approximately 95% of all pediatric intussusceptions have no pathologic lead point and result from hypertrophy of lymphoid tissues, typically following a recent viral infection. In 5% of the patients, recognizable causes for the intussusception are found, including Meckel diverticulum, intestinal polyp, enteric duplication, intramural hematoma, and lymphoma. The clinical manifestation is usually characterized by intermittent colicky abdominal pain. Vomiting is

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also commonly noted. Lethargy and somnolence may develop later. Stool containing blood and mucus, otherwise described as currant jelly stool, may be noted in approximately two-thirds of the patients. Abdominal distention and tenderness may develop if the disorder is complicated by bowel obstruction. Evaluation of children suspected of having intussusception has traditionally begun with abdominal radiography. The role of abdominal radiography is to serve as a screening examination for the detection of intussusception and to assess for possible complications related to the condition, such as bowel obstruction or perforation. Radiographic findings of intussusception include (a) a soft-tissue mass or (b) no depiction of an air-filled right colon. A distal small-bowel obstruction and extraluminal air may also be noted, caused by complications of the condition. Abdominal radiographs may be normal in nearly one-half of all children with intussusception (5). Therefore, the diagnosis cannot be excluded on the basis of the radiographic findings. US is being used with increasing frequency for the diagnosis of intussusception. A technique of graded compression is used, with pressure slowly applied with the transducer during the examination. The results of numerous studies have shown that US has a high sensitivity and specificity for this diagnosis. Therefore, it may be confidently used as the primary screening examination (6–8). At our hospital, US has replaced radiography as the primary screening modality for children suspected of having intussusception. The US appearance of an intussusception is an outer hypoechoic ring with a hyperechoic center or multiple concentric rings. On the transverse view, the appearance has been likened to a doughnut (Fig 3), whereas on longitudinal section, the appearance has been likened to a “pseudokidney.”

Pediatric Acute Abdominal Disease
Figure 4. Intussusception. Spot radiograph from an air-contrast enema study shows a focal mass representing an intussusception in the left upper quadrant.

Figure 3. Intussusception. Transverse sonogram through the middle of the abdomen demonstrates a focal rounded mass representing an intussusception.

The therapeutic study of choice for intussusception is a contrast enema study. Rates of reduction of intussusception range from 60% to 90% (9,10). Perforation is reported in approximately 1% of the attempts at reduction. The only absolute contraindication to attempting to reduce an intussusception with imaging guidance is perforation. Successful reduction of intussusception is marked by the free flow of contrast material into the distal ileum, associated with disappearance of the softtissue mass. Controversy exists about the optimal choice of the contrast material to use for the treatment of intussusception: Air (Fig 4), water-soluble contrast material (Fig 5), or barium may be used. Proposed advantages of intussusception reduction with air include decreased cost, decreased fluoroscopy time and radiation dose, ability to monitor the intraluminal pressure generated, and less fecal spillage if perforation occurs. Proposed advantages of reduction with liquid contrast material include improved depiction of the intussusception and of contrast material refluxing into the small intestine and earlier depiction of perforation. If water-soluble liquid contrast material is used, a dilute meglumine–sodium diatrizoate mixture is preferred. A 1:3 or 1:4 dilution with water results in a relatively iso-osmolar concentration.

ACUTE APPENDICITIS
Figure 5. Intussusception. Spot radiograph from a watersoluble contrast enema study demonstrates an intussusception in the ascending colon.

Acute appendicitis is the most common condition requiring emergency abdominal surgery in the pediatric population (11). The condition typically develops in older children and young adults. The incidence in the

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Figure 6. Acute appendicitis. Contrast material–enhanced CT scan through the lower part of the abdomen of a child with appendicitis shows an enlarged appendix. Note the appendiceal wall enhancement and surrounding stranding of periappendiceal fat.

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pediatric population is highest in male patients between the ages of 10 and 14 years, while in female patients, the incidence is highest between the ages of 15 and 19 years (12). Acute appendicitis presents a challenging problem to caregivers because it must be differentiated from a variety of other conditions that result in acute abdominal pain in childhood. The classic constellation of periumbilical pain migrating to the right lower quadrant, nausea, vomiting, and fever is present in less than one-third of the patients (13). The diagnosis is even more challenging in younger children because they are not able to clearly describe their symptoms. Between one-third and one-half of the children with appendicitis who undergo surgery have an uncertain preoperative diagnosis (13). Often, many of these children are initially admitted for observation prior to undergoing surgery. Abdominal radiography has been shown to be a relatively insensitive and nonspecific means to evaluate appendicitis (14). In nonperforated appendicitis, the abdominal radiograph is usually normal or demonstrates nonspecific findings such as diffuse air-fluid levels or mild bowel dilatation. Therefore, the routine use of abdominal radiography has little value unless bowel obstruction or perforation is suspected. There has been a great deal of variability in the use of cross-sectional imaging for the diagnosis of acute appendicitis in children. In the period since its introduction by Puylaert (15) in 1986 up until the mid1990s, graded-compression US has been the principal imaging technique for evaluating children suspected of having appendicitis (13,16). Operator skill is an important factor in the diagnostic accuracy of US, as evidenced by the great variability in the reported diagnostic sensitivity and specificity of the examination.

Figure 7. Acute appendicitis. Contrast-enhanced CT scan through the lower part of the abdomen in a child with appendicitis shows a distended appendix with an appendicolith.

The reported sensitivity of US in children has ranged from 44% to 100%, and the specificity has ranged from 47% to 95%. The inflamed appendix appears at US as a fluidfilled noncompressible blind-ending structure measuring greater than 6 mm in maximal diameter. Other findings of appendicitis include (a) an appendicolith, which appears as a hyperechoic focus with acoustic shadowing, (b) pericecal or periappendiceal fluid, and (c) increased periappendiceal echogenicity, representing fat infiltration. The characteristic US findings associated with perforated appendicitis include (a) focal periappendiceal or pelvic fluid collections or (b) a complex mass, representing intraperitoneal abscess. CT has become the modality of choice in the evaluation of children suspected of having appendicitis. CT has been shown to be a highly sensitive and specific examination for the diagnosis of acute appendicitis in children. CT is less dependent on the operator than is US, and thus, higher diagnostic accuracies have been achieved. The reported sensitivity of CT for the diagnosis of acute appendicitis in children has ranged from 87% to 100%, and the specificity has ranged from 89% to 98% (17–20). CT is also more useful than US for evaluating complications of acute appendicitis, such as phlegmon and abscess formation. A variety of CT techniques have been used in the performance of appendiceal CT. These techniques include (a) full abdominopelvic scanning after intravenous and oral administration of contrast material, (b) imaging limited to the lower portion of the abdomen and pelvis without any contrast material, (c) imaging limited to

References
Pediatric Acute Abdominal Disease
1. Lilien L, Srinivasan G, Pyatt S, et al. Green vomiting in the first 72 hours in normal infants. Am J Dis Child 1986; 140: 662–664. 2. Berdon WE, Baker DH, Bull S, Santulli TV. Midgut malrotation and volvulus: which films are most helpful? Radiology 1970; 96:375–384. 3. Long FR, Kramer SS, Markowitz RI, Taylor GE, Liacouras CA. Intestinal malrotation in children: tutorial on radiographic diagnosis in difficult cases. Radiology 1996; 198:775–780. 4. Zerin JM, DiPietro MA. Superior mesenteric vascular anatomy at US in patients with surgically proved malrotation of the midgut. Radiology 1992; 183:693–694. 5. Sargent MA, Babyn P, Alton DJ. Plain abdominal radiography in suspected intussusception: a reassessment. Pediatr Radiol 1994; 24:17–20. 6. Lim HK, Bae SH, Lee KH, Seo GS, Yoon GS. Assessment of reducibility of ileocolic intussusception in children: usefulness of color Doppler sonography. Radiology 1994; 191: 781–785. 7. Verschelden P, Filiatrault D, Garel L, et al. Intussusception in children: reliability of US in diagnosis—a prospective study. Radiology 1992; 184:741–744. 8. Weinberger E, Winters WD. Intussusception in children: the role of sonography. Radiology 1992; 184:601–602. 9. Eklof OA, Johanson L, Lohr G. Childhood intussusception: hydrostatic reducibility and incidence of leading points in different age groups. Pediatr Radiol 1980; 10:83–86. 10. Gu L, Alton DJ, Daneman A, et al. John Caffey Award: intussusception reduction in children by rectal insufflation of air. AJR Am J Roentgenol 1988; 150:1345–1348. 11. Janik JS, Firor HV. Pediatric appendicitis: a 20-year study of 1,640 children at Cook County (Illinois) Hospital. Arch Surg 1979; 114:717–719. 12. Bell MJ, Bower RJ, Ternberg JL. Appendectomy in childhood: analysis of 105 negative explorations. Am J Surg 1982; 144:335–337. 13. Sivit CJ, Newman KD, Boenning DA, et al. Appendicitis: usefulness of US in diagnosis in a pediatric population. Radiology 1992; 185:549–552. 14. Campbell JP, Gunn AA. Plain abdominal radiographs and acute abdominal pain. Br J Surg 1988; 75:554–556. 15. Puylaert JB. Acute appendicitis: US evaluation using graded compression. Radiology 1986; 158:355–360. 16. Vignault F, Filiatrault D, Brandt ML, Garel L, Grignon A, Ouimet A. Acute appendicitis in children: evaluation with US. Radiology 1990; 176:501–504. 17. Garcia-Pena BM, Mandl KD, Kraus SJ, et al. Ultrasonography and limited computed tomography in the diagnosis and management of appendicitis in children. JAMA 1999; 282: 1041–1046. 18. Lowe LH, Penney MW, Stein SM, et al. Unenhanced limited CT of the abdomen in the diagnosis of appendicitis in children: comparison with sonography. AJR Am J Roentgenol 2001; 176:31–35. 19. Sivit CJ, Applegate KE, Stallion A, et al. Imaging evaluation of suspected appendicitis in a pediatric population: effectiveness of sonography versus CT. AJR Am J Roentgenol 2000; 175:977–980. 20. Sivit CJ, Siegel MJ, Applegate KE, Newman KD. When appendicitis is suspected in children. RadioGraphics 2001; 21: 247–262.

Figure 8. Acute appendicitis. Contrast-enhanced CT scan through the lower part of the abdomen of a child with a ruptured appendix demonstrates multiple intraloop fluid collections.

the lower portion of the abdomen and pelvis with the use of orally and rectally administered contrast material, and (d) imaging of the lower portion of the abdomen and pelvis with the use of only rectally administered contrast material. The goals in using rectally administered contrast material are to (a) distend the sigmoid colon and cecum, (b) delineate the cecal wall and identify wall thickening, and (c) opacify the appendix if it is not obstructed. A 3% diatrizoate meglumine solution is administered intracolonically through a rectal catheter. The administered volume of fluid ranges from 500 mL in small children to 1000 mL in adolescents. Intravenous administration of contrast material can also aid in the diagnosis of appendicitis by permitting the identification of the inflamed appendix and allowing differentiation of the appendix from the adjacent iliac vessels. CT signs of acute appendicitis include a distended appendix greater than 7 mm in maximal diameter (Fig 6), appendiceal wall thickening and enhancement (Fig 6), an appendicolith (Fig 7), circumferential or focal apical cecal thickening, pericecal fat stranding, adjacent bowel wall thickening, focal or free peritoneal fluid, mesenteric lymphadenopathy, intraperitoneal phlegmon, or abscess (Fig 8). The identification of cecal apical thickening is particularly useful in allowing a confident diagnosis of acute appendicitis if there is difficulty in identifying an enlarged appendix.

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Dean D. T. Maglinte, MD, James T. Rhea, MD, and M. Stephen Ledbetter, MD

The Role of CT in Acute Abdominal Disease: Pitfalls and Their Lessons1
Learn from the mistakes of others. You can’t live long enough to make them all yourself. —Eleanor Roosevelt (1) Since the introduction of the first commercial computed tomographic (CT) scanner in 1973, the ability of single-section CT to help in the diagnosis of nontraumatic acute gastrointestinal disease, such as the different causes of intestinal obstruction, appendicitis, diverticulitis, and mesenteric ischemia, has emerged. The introduction of helical CT in 1989, the twin detector in 1991, and, subsequently, multi–detector row helical CT technology in 1998 began to further change the way radiologists looked at the intestinal tract. In addition to looking at solid organs, even more attention is now given to the intestines, mesentery, and visceral blood supply. The ability of CT to help diagnose acute nontraumatic and trauma-related intestinal disorders and how CT has changed clinical management are no longer in question (2). CT is now the dominant method in the investigation of the patient with acute abdominal pain in the United States. The radiology literature is replete with reports on the relevance, the high accuracy, and the role of CT in the diagnosis of causes of the acute abdomen and its management. Little, if any, emphasis, however, is placed on the limitations and pitfalls of CT. This chapter reviews our observations on these issues and addresses pitfalls and limitations relevant to the diagnosis of small-bowel diseases, appendicitis, colonic diverticulitis, and intestinal ischemia. Recommendations on how to decrease or avoid these shortcomings are discussed.

CLASSIFICATION OF ERRORS
The classification of radiologic errors is considered in the framework suggested in prior reports (3,4). This classification includes the following: 1. Perceptive error.—The abnormality is obvious in retrospect, and purely technical deficiencies of the examination were not thought to contribute to the error. 2. Interpretive error.—The lesion was observed at the time of the study, but the diagnosis was not considered in the differential diagnosis, or the observation was thought to be insignificant or a normal variant.

RSNA Categorical Course in Diagnostic Radiology: Emergency Radiology 2004; pp 119–131.
1From the Departments of Radiology, Indiana University School of Medicine, UH0279, Indiana University Hospital, 550 N University Blvd, Indianapolis, IN 46202-5253 (D.D.T.M.); Massachusetts General Hospital, Harvard Medical School, Boston, Mass (J.T.R.); and Brigham and Women’s Hospital, Harvard Medical School, Boston, Mass (M.S.L.) (e-mail: [email protected]).

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Figure 1. Perceptive and interpretive error secondary to inherent limitation of method of examination. (a, b) Axial CT scans of lower portion of abdomen of a 38-year-old patient with chronic renal failure who presented to emergency department with severe abdominal pain, nausea, and vomiting. Three previous abdominal CT scans (not shown) obtained in past 2 years because of similar symptoms were unremarkable, as were results of small-bowel follow-through examination performed electively. Note oral contrast material in small bowel and colon. Obliteration of fat plane in right paramedian region posterior to rectus muscle between anterior small-bowel loops and anterior parietal peritoneum is difficult to appreciate, in absence of a transition point suggestive of smallbowel obstruction. (c, d) CT enteroclysis scans at same level as in a and b, obtained electively after conventional CT, show transition point (arrow) and collapsed loops distally. Cause of obstruction is clearly defined. Right lower abdominal anterior enteroparietal peritoneal adhesions were evidenced by fixation noted on fluoroscopic phase of CT enteroclysis examination (not shown) and by loss of fat plane between anterior wall of flattened small bowel and adjacent parietal peritoneal lining (arrow). Compare with convex anterior margin of small bowel on left side. Also note enteroenteric adhesions posterior to peritoneal adhesion in d. (e) Coronal CT reformation obtained at same level shows precise level of transition point in anterior portion of abdomen (information of value to laparoscopic surgeons). Laparoscopic adhesiolysis confirmed findings after CT enteroclysis.

3. Combined perceptive and technical error.—An abnormality was seen on review, and technical inadequacy was thought to be contributory. 4. Technical limitation.—Lesions not visible in retrospect were regarded as a technical limitation or “missed” lesion beyond the capability of the method to demonstrate.

INTERRELATIONSHIPS OF ABDOMINAL VISCERAL ORGANS AND THE INFLUENCE OF PERITONEAL FLUID DYNAMICS
Errors in the diagnosis of abdominal abnormalities at CT examination can be ascribed to inherent limitations of the method, failure to optimize technique, failure to appreciate normal anatomic structures, and congenital anatomic and postoperative alterations resulting in interpretive and perceptive errors. An understanding of peritoneal fluid dynamics and anatomic structures of the small bowel, the colon and its mesentery, blood supply, and peritoneal reflections, and the variations in position and size of the appendix are important in understanding the limitations and pitfalls in the imaging

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of the patient who presents with acute abdominal pain. Awareness of these interrelationships prevents misdiagnosis and misleading false-negative and false-positive interpretations. A small amount of serous fluid (50–100 mL) is usually found in the peritoneum. This fluid circulates within the peritoneal cavity cephalad to caudad and back cephalad. Flow is governed by gravity (downward) and respiration (upward). During inspiration, the negative intrathoracic pressure is released, and fluid travels downward by gravity (5). Negative pressure under the diaphragm during expiration causes peritoneal fluid to move superiorly. Bowel peristalsis and the peritoneal reflections and mesentery direct the fluid paths. These peritoneal reflections and recesses provide watersheds and a drainage basin for the spread and localization of fluid (6). Thus, inflammatory processes involving any segment of the alimentary tube may localize elsewhere in the peritoneal cavity and be mistaken for a primary abnormality unless these interrelationships and fluid dynamics are understood. Unrecognized rotational anomalies of the small bowel and colon and variations in the size and position of the appendix, as

Figure 2. Interpretive error secondary to admixture defect simulating small-bowel mass. (a) Axial CT scan of abdomen of middle-aged patient with nausea, vomiting, and abdominal pain shows incompletely opacified lumen with presumed mass and narrowed bowel lumen (arrow). Also note unopacified proximal loops. (b) Radiograph obtained at enteroclysis shows no small-bowel mass. The patient was receiving narcotics for pain caused by chronic pancreatitis.

well as nonspecific imaging findings, contribute to both perceptive and interpretive errors.

PITFALLS IN DIAGNOSIS
Small-Bowel Diseases Symptoms of small-bowel disease can be mimicked by diseases of other organs. Because of the dimensions and anatomic location of the small bowel, diseases of adjacent organs may mimic intrinsic smallbowel disease (7). Lack of understanding of the normal physiologic function of the mesenteric small intestine can lead to misinterpretations. Filling and distention of the small bowel are dependent on gastric emptying and the smooth muscle of the intestinal wall to move intestinal contents along the length of the bowel. The volume ingested, the rate of gastric emptying, and diminished small-bowel peristalsis may result in underfilling of the small intestine or stasis of orally ingested fluid. This is an acknowledged inherent limitation of examinations performed without enteral volume challenge, such as conventional radiography, the oral small-bowel examination, or abdominal CT, in the diagnosis of lower grades of mechanical small-bowel obstruction (8,9).

Intestinal obstruction remains a difficult entity to diagnose accurately and treat (8). Radiologists assume a critical role in the clinical decision making for patients with suspected or known small-bowel obstruction because imaging can provide answers to specific questions that have a major effect on clinical management (10). Pitfalls are primarily combined perceptive and interpretive errors secondary to this inherent limitation of the methods of examination (Fig 1). Because of the serpentine course of the intestine in a limited space, lesions may not be apparent when viewed in a single plane. Multiplanar reformatting should be used. Simple mechanical obstruction cannot be reliably differentiated clinically from strangulated obstruction on the basis of the findings at physical examination, laboratory results, or abdominal conventional radiographic findings (11). A prompt and precise CT diagnosis allows triage of these patients into a surgical or nonsurgical management category and decreases the number of subsequent diagnostic examinations, the morbidity, and the cost of patient care. When small-bowel stasis occurs, admixture defects result, especially when inadequate amounts of radiopaque oral contrast material (water-soluble contrast material or dilute barium) are ingested or when contrast material is vomited by a nauseated patient. Abnormal images are produced (Fig 2). Because CT does not allow real-time assessment (static imaging), normal physiologic features or enteric debris may simulate pathologic findings. In addition to pseudomasses, admixture defects from stasis can also result in pseudo–bowel wall thickening. These defects result in interpretive errors and may result in unnecessary work-up for inflammatory bowel diseases (Fig 3). Medication-related hypoperistalsis or functional motility abnormalities from prior surgery may simulate acute small-bowel obstruction. To avoid these errors, appropriate clinical correlation of the CT findings to the medication history or prior surgery is necessary. Congenital anatomic and postoperative alterations may result in perceptive and interpretive errors. An understanding of midgut rotational anomalies and knowledge of the surgical history are important in avoiding these pitfalls (Fig 4). Not infrequently, perforated appendicitis is misdiagnosed as inflammatory bowel disease, ileus, or acute small-bowel obstruction because of the effects of peritoneal irritation (Fig 5). Therefore, appendicitis should be taken into consideration when acute findings of enteritis or acute small-bowel obstruction are seen in patients without a clinical prodrome of Crohn disease. Extraappendiceal abscess in the subacute phase may simulate an intrinsic small-bowel mass. The combination of a nonspecific clinical manifestation of many small-bowel diseases, a misleading clinical history, and suboptimal bowel opacification results in these interpretive errors (Fig 6).

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Figure 3. Interpretive error secondary to abnormal peristalsis and admixture defects. (a, b) Axial CT scans of mid and lower portions of abdomen of middle-aged woman with previous distal small-bowel resection and partial colectomy for Crohn disease who presented with severe abdominal pain. Findings of thickened walls of distal small-bowel loops and colon were interpreted as consistent with recurrent Crohn disease. (c, d) Selected radiographs of a barium enteroclysis performed following CT. No evidence of recurrence was seen. Note fluid and debris in dilated small-bowel loop (arrow in c) diluting contrast material. (d) Double-contrast barium enteroclysis image shows normal-sized folds. Results of colonoscopy and ileoscopy were also normal. The patient was also addicted to narcotics.

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Figure 4. Perceptive and interpretive error secondary to congenital anatomic abnormality (ie, unusual course of appendix). (a) Axial CT scan obtained without oral contrast material in patient with severe abdominal pain shows mesenteric stranding and area of soft-tissue attenuation in midportion of abdomen. Presumed normal appendix is seen to the right of area of soft-tissue attenuation. Appendicolith within area of soft-tissue attenuation was not appreciated. Preliminary diagnosis was inflammatory bowel disease. (b) CT scan obtained after opacification of small bowel with oral contrast material shows appendicolith surrounded by soft-tissue attenuation and mesenteric stranding away from cecum. Surgery revealed abscess with fecalith at appendiceal tip, located in midportion of abdomen. (Images courtesy of Bernard Birnbaum, MD, New York, NY.)

Figure 5. Interpretive error secondary to peritoneal irritation and anatomic interrelationships in patient with abdominal pain and constipation. Axial CT scans obtained with intravenous contrast material show mild thickening of distal small-bowel loops, mucosal hyperemia, and perienteric and mesenteric stranding. Patient vomited oral contrast material. Diagnosis was inflammatory bowel disease. Because of peritoneal signs and symptoms, surgery was performed, which revealed a perforated appendix with peritonitis.

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Figure 6. Interpretive error influenced by misleading clinical history, nonspecific clinical manifestation, paucity of abdominal fat, and effects of peritoneal irritation on distal small bowel from pus from perforated appendix. (a, b) Initial axial CT scans of teenage male patient with severe abdominal pain and family history of Crohn disease show extensive mesenteric stranding without evidence of pericecal inflammatory changes (not shown). There is paucity of mesenteric fat and no contrast material filling of pelvic small-bowel loops. (c, d) Delayed axial CT scans show increased mesenteric attenuation and poorly opacified pelvic loops with markedly thickened loops of pelvic ileum. Oral contrast material was vomited. Examination was interpreted as worrisome for active Crohn disease, and enteroclysis was recommended. Patient was referred to gastroenterologist, who instead performed colonoscopy, which yielded unremarkable findings. Worsening of symptoms and a follow-up CT scan (not shown) that revealed pelvic abscesses prompted surgery. Surgery confirmed pelvic abscesses from a perforated appendix.

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Appendicitis CT has had an important effect on the management of patients suspected of having appendicitis (12,13). Perceptive and interpretive errors may result from secondary involvement of small bowel by perforative appendicitis. Such secondary involvement mimics primary small-bowel disorders because of peritoneal dynamics and anatomic interrelationships. Among the specific problems encountered in the diagnosis of appendicitis is a failure to opacify the cecum and appendix. These common technical pitfalls and limitations result in no depiction of the normal appendix, which increases falsenegative or false-positive diagnoses (Figs 5, 6) and lowers the diagnostic certainty of a normal examination. Such failure also results in the inability to depict the findings that are 100% specific for appendicitis: focal cecal apical thickening, the “arrowhead” sign, and the cecal bar adjacent to an appendicolith (14–17). Inadequate familiarity with the findings of appendicitis results in perceptive error. Nonspecific features may be considered conclusive and specific findings and can be misapplied if the cecal apex is not identified. A learning curve exists in recognizing either the abnormal or the normal appendix (15,16). Lack of intraabdominal fat, especially in children, the elderly, and cachectic patients, increases the difficulty of finding the normal or abnormal appendix. Sonography, when expertise is available, is an impor-

tant examination in this subset of patients, particularly in children. The CT technique should always include the intravenous administration of contrast material in these patients because of the resulting enhancement of the abnormal appendiceal wall and the demonstration of skip areas in the enhancement when the appendix is focally necrotic (14–17). A failure to monitor the examination and administer additional contrast material or to obtain different projections if needed to help clarify initially indeterminate findings is a pitfall that can be avoided. Volume averaging associated with CT section thickness greater than 5 mm can limit the ability to distinguish the appendix from adjacent structures. Failure to use appropriate CT window settings, especially if free fluid is present, may obscure the appendix and result in interpretive errors. Interpretive errors also result when the diagnostic threshold is too low for the CT diagnosis of acute appendicitis (Fig 7). Variation in the position of the cecum or appendix may cause difficulty in interpretation (Fig 4). The transverse cecum, cecal bascule, or malposition of the colon makes it imperative to identify the position of the cecum and terminal ileum before attempting to identify the appendix. Other interpretive problems include misidentification of an opacified vessel for the normal appendix or misidentification of a loop of unopacified small bowel for the abnormal appendix. Tip appendicitis, stump appendicitis, and secondary appendicitis may all present interpretive problems. As discussed in the section on the

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Figure 7. Interpretive error caused by setting threshold too low in CT diagnosis of acute appendicitis. Axial CT scans at level of cecum of patient with acute abdominal pain show 8-mm-wide appendix without periappendiceal stranding but with adjacent enlarged nodes. CT findings were interpreted as indeterminate. Surgery and pathologic evaluation of specimen showed acute appendicitis. Figure 8. Interpretive pitfall: misinterpretation of secondary finding caused by appendicitis as the principal diagnosis. (a) Axial CT scan of upper portion of abdomen of patient presenting with diffuse abdominal pain shows thrombosis of superior mesenteric vein (arrow). (b, c) Axial CT scans show slightly thickened appendix (arrow) with periappendiceal stranding, without contrast material extravasation. Stopping the search for other abnormalities after finding superior mesenteric vein thrombosis (seen in a) could have been a pitfall in the diagnosis of appendicitis. (d, e) Axial CT scans obtained more cephalad show mild periappendiceal stranding (arrow) where thrombosis of superior mesenteric vein is intimately related.

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small bowel, findings secondary to appendicitis are often attributed to primary small-bowel diseases (Fig 8). There are a variety of alternative diagnoses (or mimics), which should be sought because of the nonspecific clinical findings in appendicitis. Indeterminate CT examinations should be resolved by opacification of the cecum and appendix in the emergency department. A misleading clinical history also results in an interpretive pitfall (Fig 9).

Diverticulitis Diverticulitis eventually complicates approximately 20% of the cases of colonic diverticulosis. Diverticular inflammation with perforation results in an intramural or a localized pericolic abscess. Complications include bowel obstruction, bleeding, peritonitis, and sinus tract and fistula formation. Interpretive errors occur secondary to a nonspecific clinical manifestation, subtle findings early in the manifestation, or limita-

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Figure 9. Interpretive pitfall from misleading clinical history in patient suspected of having infection of aortoiliac graft. (a) Axial CT scan obtained at level of graft shows round area of soft-tissue attenuation (arrow). Perigraft thickening with small amount of gas is suggestive of graft infection. (b–e) Successive axial CT scans obtained inferior to scan in a show gas-filled appendix (arrow). At surgery, tip appendicitis localized to lateral graft limb was found. Findings from pathologic examination confirmed appendix adjacent to graft, with extensive transmural inflammation, mucosal ulceration, and fat necrosis in mesoappendix.

Figure 10. Interpretive error in differential diagnosis of diverticulitis versus colon cancer. (a, b) Axial CT scans of pelvis in middle-aged patient with anemia and lower abdominal pain show stranding in sigmoid mesocolon and (b) eccentric thickening of inferior margin of sigmoid suggestive of carcinoma. Colonoscopy performed after 2 weeks of antibiotic treatment revealed multiple diverticula in sigmoid, without evidence of mass.

tions of the method of examination. Most diverticular abscesses are quickly walled off and confined, but free perforation, with pus and air in the peritoneal cavity, may occur. Diffuse peritonitis also occurs because of peritoneal fluid dynamics and the interrelationships of the abdominal viscera. Diverticular abscess may be mistaken for a mass (Fig 10) or an unopacified segment of colon (18–20). Colonic underfilling, spasm, and intraluminal content can make it difficult to determine if the colonic wall is greater than 4 mm thick. Unfamiliarity with the appearance of inflamed bowel wall from various conditions and the noninflammatory causes of thickening, such as submucosal fat, may cause perceptive errors. Identification of the inflamed diverticulum and asso-

ciated inflammatory stranding increases the specificity of imaging diagnosis. Difficulty in the differentiation of diverticulitis from colon carcinoma is a major interpretive limitation (21–24). Colon carcinoma will perforate in about 5% of the patients, resulting in inflammatory changes usually characteristic of diverticulitis. The combination of a length of involved colonic segment greater than 10 cm and the presence of mesenteric vascular engorgement favors a diagnosis of diverticulitis. The presence of adenopathy and a shelflike margin of the colonic thickening favors a diagnosis of colon carcinoma. However, no single finding is 100% specific (21–24). In a group of examinations with similar numbers of patients with diverticulitis and patients

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Figure 11. Interpretive pitfall secondary to indeterminate CT scan. Axial CT scans of patient with right lower abdominal pain show stranding and mildly thickened small-bowel wall. Appendix or diverticula are not seen. CT scans were interpreted as equivocal for appendicitis or right-sided diverticulitis. At surgery, omental torsion was found. Appendix showed lymphoid hyperplasia.

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Figure 12. Interpretive and perceptive error in diagnosis of intestinal ischemia. (a) Axial CT scan of elderly patient with acute abdominal pain. Note dilated loops of small bowel (arrows). Diagnosis was ileus. (b) The clinical significance of extensive atherosclerotic calcification of superior mesenteric artery (arrows) was not appreciated. Infarcted small bowel was found at surgery.

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with colon carcinoma, combined findings were shown to allow a confident diagnosis of diverticulitis in only about 40% of the patients with diverticulitis and 66% of the patients with colon carcinoma (21). In at least 10% of the patients coming to the emergency department, a confident diagnosis cannot be made. Failure to note colonic wall thickening in a collapsed colon and difficulty in differentiating muscular wall hypertrophy from colonic wall edema are interpretive pitfalls and may result in diagnostic misclassification. Diverticulitis is a less common cause of colon obstruction than is colon carcinoma. Recognition of an alternative diagnosis is particularly important in diverticulitis because these patients tend to be older than patients with appendicitis and have a greater variety of alternative diagnoses. Radiologists should be familiar with the CT findings of primary epiploic appendagitis, or omental torsion, which can mimic diverticulitis (Fig 11). Secondary epiploic appendagitis may complicate diverticulitis. The techniques for evaluation of patients suspected of having diverticulitis are variable. However, the usual technique consists of using both oral and intravenous contrast materials. Sometimes an iodinated rectal contrast material or air is added in puzzling cases, and the colon has to be filled to assess colonic wall thickness. CT section thickness greater than 5 mm may obscure the subtle fat stranding seen in mild diverticulitis. Use of thick CT sections may account for the high falsenegative rate reported by early investigators. The use of

neutral (water) colonic contrast material with intravenous contrast enhancement needs to be investigated.

Intestinal Ischemia Mesenteric ischemia or infarction occurs in a variety of conditions that result in interruption or reduction of the blood supply of the intestine. Regardless of the causes of the ischemic insult, the end results are similar and range from transient alteration of bowel activity to transmural hemorrhagic necrosis. Mesenteric ischemia is classified into four categories that are distinct conditions with different causes, clinical manifestations, therapy, and prognoses. These four categories are (a) acute mesenteric ischemia, an acute ischemia of the small bowel with or without colonic involvement; (b) focal mesenteric ischemia, an acute ischemia of localized segments of small intestine exemplified by strangulating small-bowel obstruction; (c) chronic mesenteric ischemia, or ischemia without loss of tissue viability; and (d) colonic ischemia. Early diagnosis is crucial because critical intestinal ischemia progresses to fatal infarction unless promptly diagnosed and treated. The initial signs and symptoms of acute mesenteric ischemia are often nonspecific. Patients at risk include those with the following: a history of prior mesenteric ischemia, vasculopathy, atrial fibrillation, nontherapeutic anticoagulation therapy, hypotension (trauma, sepsis, cardiogenic shock), a history of recent myocardial infarction, congestive heart failure, or hypercoagulable states (cancer, etc) (25). Intestinal infarction ac-

Figure 13. Interpretive errors secondary to nonspecific imaging findings. (a) Diffuse thickening of long segments of pelvic loops of ileum in patient with acute abdominal pain simulates CT findings of small-bowel Crohn disease. Colonoscopy revealed changes consistent with ischemia. (b) Pelvic CT scan obtained in another patient with severe lower abdominal pain shows rectal wall thickening (arrows) and perirectal stranding (arrowheads), which were ascribed to inflammatory disease. Focal ischemia seen at proctoscopy was not considered.

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counts for 1% of the patients presenting with an acute abdomen. Acute mesenteric ischemia is a life-threatening condition, with mortality rates that range from 59% to 93% (26). Findings from studies have shown that early diagnosis and treatment have a substantial effect on the outcome in a patient. Abdominal CT has been considered of limited use in the diagnosis of acute mesenteric ischemia, except in patients suspected of having superior mesenteric vein thrombosis (26). Perceptive errors in the diagnosis of venous thrombosis result from focusing on a more common abnormality that explains the clinical manifestation. Specific findings of bowel ischemia are relatively uncommon in patients evaluated with CT. As such, radiologists are most often required to rely on secondary CT findings, such as bowel wall thickening, pneumatosis intestinalis, portomesenteric venous gas, or ascites, as indirect signs of bowel ischemia. Any of these findings alone or in combination may raise suspicion for this diagnosis, but they can be subtle and lack specificity, particularly in the absence of a clinical manifestation suggestive of ischemia (27–31). These findings result in interpretive errors (Fig 12). Although these secondary findings are important in the CT evaluation and clinical management of acute abdominal pain, the pitfalls of CT imaging merit special consideration. Bowel ischemia remains one the most difficult diagnoses to establish with CT imaging criteria alone. Unlike many other diagnoses for which CT findings can be pathognomonic, considerable emphasis must be placed on the need for appropriate clinical correlation of CT findings to establish a diagnosis of bowel ischemia and guide appropriate further workup and management. The nonspecificity of clinical findings, the constellation of nonspecific CT findings, and the limitation of CT technology prior to the use of multi–detector row CT technology account for most of the errors reported in the literature in the diagnosis of early intestinal ischemia (Fig 13). Lack of optimization (timing, rate)

of the intravenous contrast material bolus, thick collimation, single-phase acquisition, and the failure to achieve adequate intestinal opacification contribute to technical pitfalls in the diagnosis of intestinal ischemia. Findings noted at angiography involving small vessels were difficult to depict with single-detector helical CT technology. In addition, patients are rarely brought to the radiology department during an acute episode of ischemia, so nonspecific CT findings of mucosal enhancement from reperfusion are shown, rather than the more specific finding of intestinal ischemia: lack of mucosal enhancement from arterial insufficiency (32). Lack of familiarity with mesenteric vascular anatomic structures on cross-sectional imaging results in perceptive errors. In patients with intestinal obstruction, the recognition of complicating ischemia in the absence of a recognizable closed-loop configuration may be difficult. Mesenteric fat stranding and ascites have a low sensitivity. The presence of interloop mesenteric fluid increases both sensitivity and specificity. When two or three of these findings are present, the CT specificity for strangulated obstruction is high (94%). Although the imaging features of intestinal ischemia are relatively nonspecific, an understanding of the pathophysiologic function and clinical features of this disease in various conditions and the radiologic findings allow the radiologist to consider ischemic bowel disease and its differential diagnosis and arrive at a correct diagnosis (Fig 14). For every complex problem, there is a simple solution. And it’s always wrong. —H. L. Mencken (33)

COMMENTS AND RECOMMENDATIONS
Precise categorization of errors in the performance and interpretation of CT of the acute abdomen is difficult because of the contribution of many factors.

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Figure 14. Interpretive error secondary to nonspecific findings. (a) Axial CT scan of upper portion of abdomen of elderly man with known metastatic prostatic cancer who presented with acute abdominal pain. Portal venous gas is seen. Also note metastatic foci in liver. (b) Axial CT scan at level of gallbladder shows gas in portal vein. (c) Axial CT scan at level of midportion of abdomen shows dilated small bowel and "misty" mesentery. (d) Axial CT scan at level of kidneys shows dilated small bowel displacing collapsed ascending colon. Note atherosclerotic plaque in abdominal aorta. At surgery, there was no evidence of intestinal infarction. Small-bowel obstruction was from adhesions, which were lysed. Patient had an uneventful postoperative course. (Images courtesy of Stefania Romano, MD, Naples, Italy.)

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However, errors can be decreased by understanding common pitfalls, optimizing CT technique, and performing additional maneuvers to increase the accuracy of interpretation. Acknowledged inherent limitations should be recognized, and more sensitive methods of examination in the further work-up of patients should be recommended to prevent repeated performance of examinations with low sensitivity. Indeterminate scans caused by unfilled loops of small bowel, appendix, or colon can be eliminated by administering oral or rectal contrast material. Errors secondary to technical limitation or “missed” lesions that are beyond the capability of the imaging examination to demonstrate as clinical pathologic findings are often related to lack of distention or an absence of enteral volume challenge, which results in a lower sensitivity of CT for lower grades of small-bowel obstruction and precludes exclusion of small-bowel obstruction in the appropriate clinical setting. These patients often come to the emergency department. The results of a critical analysis of the accuracy of CT in the diagnosis of small-bowel obstruction have shown an overall accuracy of 65% (9). With high-grade partial or complete obstruction, however, the accuracy increases to 81%. Unfortunately, with low-grade obstruction, the accuracy is only 48%. You need to look for subtle clues to justify recommending more sensitive methods of examination. Findings of enteroparietal peritoneal adhesions are often present at conventional CT but are not perceived because of the lack of a transition zone in the absence of adequate enteral volume–challenged examinations for low-grade obstruction. Distortion of the convex anterior margin of the bowel with loss of the fat

plane or thickening of the soft-tissue density between the small bowel wall and the anterior parietal or posterior parietal peritoneum can be recognized, although no intraluminal pressure gradient may be present. Thus, in the setting of a history of prior abdominal surgery, clinical correlation for recurrent small-bowel obstruction can be suggested, and more sensitive enteral volume–challenged examination of the small bowel can be performed electively (Fig 1). Factors that influence nonfilling of small-bowel loops and postoperative and congenital anatomic alterations should be recognized. An understanding of the influence of peristalsis and retained fluid and digestive secretions in producing pseudo–bowel wall thickening and pseudomasses should lead to suggesting more appropriate methods of investigation. Recognizing normal structures, such as the right colic artery, that can mimic a normal appendix will decrease false-negative interpretations. A failure to opacify or recognize the appearance of a normal cecum and appendix results in perceptive and interpretive errors that can be avoided by optimizing CT technique. Although there is now consensus that appendiceal CT should include thin-section scanning of the right lower quadrant of the abdomen, disagreement still persists regarding the need for intravenous, oral, or rectal contrast material (34–36). The most conservative and conventional approach is to perform helical CT of the abdomen and pelvis with both intravenous and oral contrast material. This is the most popular method and has allowed alternative diagnosis of appendicitis. Intravenous contrast material has been shown to aid the diagnosis of appendicitis by facilitating identification of the in-

Figure 15. Abdominal/pelvic CT protocol that uses water as oral contrast material. Instead of water, commercially prepared bottled flavored drinks (or such drinks diluted in water) or verylow-density oral contrast material may be substituted.

flamed appendix in those who have mild forms of appendicitis, in whom the diagnosis may rest solely on identification of luminal dilatation and pathologic appendiceal wall enhancement (13,37–39). Use of nonenhanced helical CT of the abdomen and pelvis without intravenous, oral, or rectal contrast material has been proposed because it can be done faster without exposing patients to iodinated contrast material (40,41). This technique may be effective in patients with large body habitus. Proponents of oral contrast material advocate its use to limit misinterpretation of mimics of appendicitis and to allow diagnosis of smallbowel diseases (34). Because of the length of time needed to opacify the ileocecal region, a focused appendiceal CT protocol has been proposed (42,43). This protocol entails administration of colonic contrast material and acquisition of a limited helical CT study of the right lower quadrant. This technique has been shown to be as accurate as other protocols, and it increases the negative predictive value of CT in the diagnosis of acute appendicitis and can be completed within 15 minutes in the majority of patients. Clearly, agreement has not been reached on an optimized technique to address all of the pitfalls discussed. The interested reader can look at the technical details of these different methods. Because there is controversy in the radiology literature with regard to the use of oral contrast material, some radiologists are now exploring the use of water or a lower-density iodinated or barium contrast material as the oral contrast material, along with intravenous contrast enhancement, to use the capabilities of multi– detector row CT technology to show mucosal enhancement, which can be masked by the intraluminal opacity of currently used oral radiopaque contrast material (44). Early experience has shown that a high volume of water as oral contrast material, coupled with intravenous contrast enhancement, appears to offer a feasible

substitute for radiopaque oral contrast material for evaluating the small bowel (45). The use of neutral oral contrast material (water) with intravenous contrast material, instead of radiopaque oral contrast material, may prevent admixture defects and pseudo–bowel wall thickening and allows recognition of subtle mucosal hyperemia and submucosal edema. Mucosal hyperemia may be isoattenuating relative to the attenuation of the currently used radiopaque oral contrast material in the lumen of the small bowel but can be seen with neutral (water) or a lower-density radiopaque contrast material. Not infrequently, patients presenting with acute abdominal pain have nausea and vomiting, which could be aggravated by the bad taste of the currently used radiopaque oral contrast materials. On the basis of personal clinical experience performing CT enteroclysis with neutral (water or methylcellulose) enteral contrast materials combined with intravenous contrast enhancement, an abdominalpelvic CT protocol is suggested (Fig 15). With this protocol, the study should be carefully monitored, and multi–detector row CT parameters should be properly selected to tailor the examination to the clinical query, particularly if mesenteric ischemia is a leading clinical possibility. This protocol should be augmented with a focused appendiceal CT protocol when imaging findings are equivocal or anatomic limitations (no fat planes) exist for reliable diagnosis of acute appendicitis in a patient in whom appendicitis was not the primary diagnostic consideration. In the imaging of the true acute abdomen, appendicitis is not ruled out if the normal appendix is not depicted or filled with contrast material from its base to the tip. The unfounded fear that water does not distend distal small-bowel loops is due to administration of inadequate amounts of water and the lack of administration of a hypotonic agent prior to scanning. Furthermore, the initial use of a peristaltic agent ensures filling of distal small-bowel loops and colon. The diagnosis of early intestinal ischemia will require close communication between emergency physicians and radiologists. In patients who present with an acute abdomen and a clinical history of one or more of the high-risk factors for acute mesenteric ischemia, the findings from early experience indicate that biphasic CT with mesenteric CT angiography with the use of multi–detector row CT technology appears to be effective in the diagnosis of acute mesenteric ischemia (32). Further experience is needed with this method of examination. Optimizing CT technique to address all pitfalls described will undoubtedly decrease errors in the CT diagnosis of the acute abdomen. No single technique can address all of the pitfalls and limitations. Local practice will influence how the CT technique will be optimized. To take advantage of multi–detector row CT technology, a method that results in luminal distention and opacification of the entire small bowel and

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colon, combined with intravenous contrast enhancement, should be adopted. A bowel-focused technique has been described, a minor variation to the routine abdominal scanning, geared toward a more substantial bowel filling with oral contrast material and use of multiplanar reformatting. This technique has been termed “CT enterography” by Raptopoulos et al (46,47). CT enterography also addresses more than small-bowel abnormalities. In CT enterography, approximately 1000–1500 mL of a 2% barium-based or 2%–2.5% water-soluble iodine-based oral contrast material is administered during a period of 1–2 hours before scanning. A high dose of intravenous contrast material and a biphasic injection regimen have been recommended. First, 30–50 mL of contrast material is administered at 2 mL/sec without CT acquisition. After a delay of 2–3 minutes, the remainder of the 150 mL of solution containing 300 mg of iodine per milliliter is given. Eighty to one hundred milliliters is infused at 2–3 mL/sec. Scanning starts 60– 70 seconds after the second dose. This method results in vascular opacification, parenchymal enhancement, and combined renal parenchymal and excretory phase scanning (46). CT parameters will depend on the vendor and model of multi–detector row CT scanner. Reformatting may be done on a dedicated workstation. Another bowel-focused method that has been described uses a neutral enteral contrast material, polyethylene glycol and whole milk, as well as an isotonic oral solution (48,49). The volumes of oral contrast material required in these alternative methods may not be feasible to use in a nauseated patient, and the length of time needed to ingest the recommended volume may be impractical in a busy emergency department, where speed is required in the performance of these examinations. These methods can be readily used if a patient has a nasogastric tube. The methods that use neutral enteral contrast material (water, polyethylene glycol with milk) together with biphasic CT acquisition should be of value in patients suspected of having intestinal ischemia. The techniques that use neutral oral and enteral contrast material need to be supplemented with a focused appendiceal CT examination when appendicitis as a possibility has not been ruled out. None of these newer alternative methods have been validated in a large group of emergency department patients. The use of a large volume of water with initial use of a propulsive medication (metoclopramide) can shorten the lag time of some of the proposed methods. Use of a hypotonic agent allows partial distention of smallbowel loops. Admixture defects and pseudomasses will be prevented by the use of a neutral enteral contrast material, which also allows depiction of mucosal enhancement. Obtaining more clinical information than the usual complaint of “abdominal pain” or “acute abdomen”

enhances the diagnostic utility of CT because the clinical information provided on the imaging requests is frequently inadequate. In most imaging requests for emergent CT for acute abdomen indications, the condition is rarely a true acute abdomen. Current advances in information technology allow radiologists to immediately retrieve the clinical background data of a patient. In conclusion, the past several years have spanned an ongoing revolution in CT technology. Improvement in technology led to the development of singledetector scanning, followed by multi–detector row CT scanning. Advanced computer workstations with special hardware are now available to process the large volumes of data that the newest multi–detector row scanners produce (44). Optimizing the protocol for abdominal CT will be the key to addressing diagnostic pitfalls and limitations but may not be possible with a single imaging method. Emergency radiologists must use the advantages of multi–detector row CT technology and understand the reasons for the various pitfalls and limitations. Careful monitoring of the CT examination and the use of additional techniques to opacify the appendix when it is not completely depicted will diminish errors in the diagnosis of acute appendicitis. Peritonitis from perforated appendicitis is a great mimic of small-bowel disease. Misdiagnosis of appendicitis tends to occur in patients with paucity of intraabdominal fat. Pseudoobstruction from acute appendiceal perforation, ileus from peritoneal irritation, or hypoperistalsis from medication can lead to a false-positive diagnosis of small-bowel obstruction. The attention of the radiologist should not be diverted by a misleading clinical history or atypical clinical manifestation. Retrieval of patient information, which is available with advances in information technology, should be used more often. The best allies of the radiologist are experienced emergency physicians and general surgeons who examine their patients first before sending them to the radiology department for abdominal CT. Close clinical communication with these physicians will allow radiologists to tailor abdominal CT protocols by using multi–detector row CT technology to address the precise clinical query. It’s what you learn after you know it all that counts. —John Wooden, Hall of Fame basketball coach (50)

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5. Sitting KM, Korr MS, McDonald JC. Abdominal wall, umbilicus, peritoneum, mesenteries, omentum, and retroperitoneum. In: Sabiston DC Jr. Textbook of surgery: the biological basis of modern surgical practice. 15th ed. Philadelphia, Pa: Saunders, 1996; 809–823. 6. Meyers M. Dynamic radiology of the abdomen: normal and pathologic anatomy. 4th ed. New York, NY: Springer, 1994. 7. Maglinte DD, Kelvin FM, O’Connor K, Lappas JC, Chernish SM. Current status of small bowel radiography. Abdom Imaging 1996; 21:247–257. 8. Maglinte DD, Balthazar EJ, Kelvin FM, Megibow AJ. The role of radiology in the diagnosis of small-bowel obstruction. AJR Am J Roentgenol 1997; 168:1171–1180. 9. Maglinte DD, Gage SN, Harmon BH, et al. Obstruction of the small intestine: accuracy and role of CT in diagnosis. Radiology 1993; 188:61–64. 10. Herlinger H, Maglinte DD. Small bowel obstruction. In: Herlinger H, Maglinte DD, eds. Clinical radiology of the small intestine. Philadelphia, Pa: Saunders, 1989; 479–507. 11. Sarr MG, Bulkley GB, Zuidema GK. Preoperative recognition of intestinal strangulation: prospective evaluation of diagnostic capability. Am J Surg 1983; 145:176–182. 12. Bendeck SE, Nino-Murcia M, Berry GJ, Jeffrey RB Jr. Imaging for suspected appendicitis: negative appendectomy and perforation rates. Radiology 2002; 225:131–136. 13. Raptopoulos V, Katsou G, Rosen MP, Siewert B, Goldberg SN, Kruskal JB. Acute appendicitis: effect of increased use of CT on selecting patients earlier. Radiology 2003; 226:521–526. 14. Rao PM. Technical and interpretative pitfalls of appendiceal CT imaging. AJR Am J Roentgenol 1998; 171:419–425. 15. Callahan MJ, Rodriguez DP, Taylor GA. CT of appendicitis in children. Radiology 2002; 224:325–332. 16. Urban BA, Fishman EK. Targeted helical CT of the acute abdomen: appendicitis, diverticulitis, and small bowel obstruction. Semin Ultrasound CT MR 2000; 21:20–39. 17. Rhea JT. CT evaluation of appendicitis and diverticulitis. I. Appendicitis. II. Diverticulitis. Emerg Radiol 2000; 7:237–244. 18. Akbar SA, Shirkhoda A, Jafre SZ. Pictorial essay: normal variants and pitfalls in CT of the gastrointestinal and genitourinary tracts. Abdom Imaging 2003; 28:115–128. 19. Macari M, Balthazar EJ. CT of bowel wall thickening: significance and pitfalls of interpretation. AJR Am J Roentgenol 2001; 176:1105–1116. 20. Wittenberg J, Harisinghani MG, Jhaveri K, Varghese J, Mueller PR. Algorithmic approach to CT diagnosis of the abnormal bowel wall. RadioGraphics 2002; 22:1093–1109. 21. Chintapalli KN, Chopra S, Ghiatas AA, Esola CC, Fields SF, Dodd GD III. Diverticulitis versus colon cancer: differentiation with helical CT findings. Radiology 1999; 210:429–435. 22. Balthazar EJ, Megibow A. Schninella RA, et al. Limitations in the CT diagnosis of acute diverticulitis: comparison of CT, contrast enema, and pathologic findings in 16 patients. AJR Am J Roentgenol 1990; 154:281–285. 23. Hulnick DH, Megibow AJ, Balthazar EJ, Gordon RB, Surapenini R, Bosniak MA. Perforated colorectal neoplasms: correlation of clinical, contrast enema, and CT examinations. Radiology 1987; 164:611–615. 24. Van Breda Vriesman AC, Puylaert JB. Pictorial essay: epiploic appendagitis and omental infarction: pitfalls and look-alikes. Abdom Imaging 2002; 27:20–28. 25. Wiesner W, Khurana B, Ji H, Ros PR. CT of acute bowel ischemia. Radiology 2003; 226:635–650. 26. Brandt LJ, Boley SJ. AGA technical review on intestinal ischemia: American Gastrointestinal Association. Gastroenterology 2000; 118:954–968. 27. Bartnicke BJ, Balfe DM. CT appearance of intestinal ischemia and intramural hemorrhage. Radiol Clin North Am 1994; 32: 845–860. 28. Frager D, Baer JW, Medwid SW, et al. Detection of intestinal ischemia in patients with acute small bowel obstruction due

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CT in Acute Abdominal Disease

NOTES

Stephen R. Baker, MD

The Contemporary Role of Conventional Radiographs in Evaluating the Acute Abdomen1
The last RSNA Categorical Course in Emergency Radiology took place at the RSNA scientific assembly in 1995. In the past 9 years, the imaging approach to the emergently ill patient with abdominal discomfort has changed radically. The capabilities of ultrasonography (US) were clearly recognized back then, but its current role has really not expanded much. Developments in magnetic resonance imaging, both instrumental and interpretive, offer promise, yet this technique still remains on the periphery. The revolution in emergent abdominal imaging—and it has been a revolution—is encompassed largely by developments in computed tomographic (CT) technology and its rapid and largely uncritical embrace by emergency physicians, surgeons, internists, and radiologists alike. A dependence on CT has caused CT findings to displace, to a large degree, the clinical history, the findings from physical examination, and even laboratory data as the first data to be assessed in the quest for a diagnosis in patients with acute abdominal disease. Where does this dependence on CT leave the conventional radiograph? Is it just a venerable, but limited, image characterized as a relic of a bygone era? Is the conventional radiograph maintained as an exercise only because of the impress of tradition, obtained as a matter of course but considered fundamentally irrelevant as our attention is promptly and inevitably directed to CT? Should we term the performance of conventional radiography merely a vestigial ritual having really no place in our armamentarium that provides any value to the patient? The answer to this challenge, I believe, is tripartite: (a) At present, for two common acute conditions, conventional radiography does have an essential role. (b) In the medium term, a synthesis of conventional radiography and CT may occur, if reimbursement incentives are recast. (c) In the long run, a renewal of interest will likely occur as the issue of excessive radiation dose, especially in children and young adults, takes its place on the national agenda, where not only physicians but also health policy makers and the public at large all lend their strident voices to the debate about risk, cost, and benefit.

LIMITATIONS OF USE
First things first! The conventional radiograph is important today for only two categories of nontraumatic acute disease evaluated at an emergency facility: pneumoperitoneum and intestinal obstruction. For both, the nonenhanced supine radiograph can
RSNA Categorical Course in Diagnostic Radiology: Emergency Radiology 2004; pp 133–141.
1From the Department of Radiology, University Hospital, New Jersey Medical School, PO Box 1709, Room C318, 150 Bergen St, Newark, NJ 07101 (e-mail: [email protected]).

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often provide the definitive diagnostic information with a sensitivity equal to that of CT. Although the nonenhanced spine radiograph cannot reveal the welter of additional spatial relationships that are the hallmark of a CT study, it can demonstrate the key finding requiring undelayed medical therapy or surgical intervention. Almost always, the observation of bowel obstruction on conventional radiographs should engender an undelayed clinical response. Likewise, the recognition of free air cannot be ignored. In most instances of these two emergencies, supplementary findings discernible with CT will most often not be crucial for the initiation or modification of immediate therapy. Conventional abdominal radiographs can sometimes allow detection of a tumefaction, if the mass is large enough to displace stomach or bowel gas or to obliterate fat planes. Yet the plain films cannot delineate detailed information about the precise location, exact size, and particularities of tumor contour with any degree of precision. Conventional radiography can be used to discern the small bubbles of pus collections, but a comprehensive display of the extent, configuration, and multiplicity of abscesses is beyond its capabilities. Most abdominal calcifications are observable on conventional radiographs, and the differential diagnosis can almost always be limited to no more than two or three entities with an evaluation of the multiplicity, size, shape, internal architecture, location, and movement of such calcifications on successive images. However, the effect of the calcification on the lumen in which is contained or on the structures that the calcification abuts requires further investigation with contrast agent–enhanced radiography, US, or CT. It is important, then, to know much about the conventional radiographic appearances of free air and bowel obstruction because even today, conventional radiography may be the only study available to detect these conditions in certain facilities and at certain times of the day. Moreover, it is critical for radiologists to maintain an interest in the intricacies of conventional radiographic interpretation because it is likely that in the future, CT use will be regulated more closely and is apt to be restricted in utilization to minimize dose accumulation—a practice that exists today in many countries in the European Union.

Baker

Figure 1. Simulation of bowel obstruction by mesenteric ischemia. Radiograph shows dilated small bowel and nondilated colon, caused by acute vascular insufficiency. There was no luminal occlusion.

RELATIVE VALUE OF HISTORY
It is a given that knowledge of the clinical history is vital, not just for emergency patients but for all manifestations, before a diagnosis that is based on imaging studies can be made. That having been said, once it has been made clear that the possible presence of pneumoperitoneum is not related to a recent abdominal operation or biopsy and is not a consequence of the rare situations in which air has been introduced into the peritoneal space by purposeful human activ-

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ity, then the history is actually not so important and, in fact, can be misleading. Most patients who have a perforated ulcer experience immediate and severe pain. On the other hand, perforation of the colon may exhibit a slower tempo in its generation of symptoms. Consequently, the radiographic signs of pneumoperitoneum may appear before substantial patient discomfort supervenes. For the elderly and for demented individuals or those receiving steroids, perforation of a hollow viscus, especially if it is the stomach or duodenum, is often associated with no sensation of distress or pain and can be accompanied by normal findings at physical examination. Hence, the emergency radiologist should examine every conventional radiograph of the abdomen with a high index of suspicion, searching for the subtle manifestations of free air even though no corroborating information is available to him or her. On the contrary, the diagnosis of bowel obstruction unequivocally depends on the correlation of clinical and radiographic findings. The radiologist who has attempted to render this diagnosis when no accompanying clinical information is available, either from the history, physical examination, or the acquisition of laboratory data, will be inevitably placing the patient in jeopardy and placing himself or herself and the referring physician at risk for a malpractice suit. The reason is that the conventional radiographic manifestations of luminal occlusion can (a) often be simulated by an adynamic ileus, (b) sometimes be mimicked by mesenteric ischemia without intestinal obstruction

Figure 2. Anterior bubble sign (arrows), a manifestation of free air from a perforated anterior distal stomach ulcer. Radiograph shows that the air is situated anterior to liver, well above right kidney.

beyond the superior margin of the KUB radiograph, out of sight and, consequently, out of mind (Fig 2). The remedy for the deficiency of the KUB radiograph was to obtain upright radiographs of the chest or abdomen and/or right-side-elevated decubitus views to assess the uppermost peritoneal cavity for signs of perforation or obstruction. The assumption of an upright position is difficult for the inebriated patient, for the patient with dementia, and especially for the weak patient with obtundation. Moreover, the upright position is not necessary when CT is contemplated as the imminently available follow-up examination. Nonetheless, a horizontal-beam erect radiograph or a decubitus erect radiograph, or both, remain as part of the customary abdominal series in many centers. However, the results of a recent investigation have shown that upright and decubitus views are unnecessary and should be replaced with a protocol involving two slightly overlapping recumbent supine images, one of the upper part of the abdomen and the other of the middle part of the abdomen and pelvis (1).

Conventional Radiographs of the Acute Abdomen

MINIMAL DETECTABLE AMOUNT OF FREE AIR
In the early 1970s, Miller and co-workers (2,3), in their landmark reports on detection of pneumoperitoneum, observed that as little as 1–2 mL of free air could be seen on conventional radiographs when the subject was placed in the upright or decubitus position. Miller made that observation by injecting aliquots of air of varying volume into his own peritoneal cavity. However, these investigations were constrained by the same dogma that enabled the KUB radiograph to gain ascendancy. These investigators presumed that the supine view was not sensitive for the detection of free air, inasmuch as it did not encompass the subdiaphragmatic space. Today, with the presence of CT, we have reexamined those observations. By analogy alone, we know that a nonenhanced radiograph is exquisitely able to depict gas bubbles anywhere in the abdomen, as evidenced by the almost ubiquitous observation of tiny bubbles of gas within intraluminal fecal deposits. Bubbles with diameters as small as 2 mm (giving them a volume of approximately 0.004 mL) are routinely seen in the colonic shadow (Fig 3). If bubbles of gas can be discerned in the large bowel, then liberated gas should also be recognizable in the right upper quadrant overlying the homogeneous gray shadow of the liver (1). More recent attempts to determine the sensitivity of various imaging approaches in addition to CT have included investigations of the upright abdomen, the lateral chest (4), the upright chest (5), US (6), and others. All of these approaches have two problems: (a) When a patient is repositioned from the supine orientation, bubbles of free air will move. (b) If the CT study is not done simultaneously or at least contemporaneously

(Fig 1), and (c) occasionally be imitated by air swallowing alone. Thus, the radiographic finding of dilatation of bowel segments proximal to the point of a putative intestinal blockage must be considered within a particular clinical context, not in isolation from the history, physical findings, and laboratory data.

THE FALLACY OF THE KIDNEY-URETERBLADDER RADIOGRAPH
Early in the 20th century, the term KUB (for kidneyureter-bladder radiograph) gained prominence and then dominance as both an appellation and as the accepted standard image for a full assessment of the abdomen and pelvis. There are compelling reasons why this limited projection with its prescriptive initials became the surrogate for a comprehensive radiographic inspection of the contents of that part of the body situated below the diaphragm and down to the perineum. KUB was a name congruent with the particular interests of urologists because it encompassed the span of the urinary tract. The KUB radiograph provided a suitable frame within which calculi could be detected. Furthermore, the acceptance of the KUB radiograph was based on denial of an important photographic fact. For most American adults, with the use of a standard 40-inch (102-cm) source-to-film distance for a supine radiograph, the entirety of the peritoneal cavity extending from the uppermost hemidiaphragm rostrally to the obturator foramina caudally cannot be encompassed on a single radiograph. This fact has often left the upper reaches of the abdomen, which are situated

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Baker
Figure 3. Minimal pneumoperitoneum. (a) Digital scout view shows a sliver of free air (arrows) obliquely oriented above distal portion of stomach. (b) Corresponding transverse CT image shows a collection of free air (arrow) anterior to liver, conforming in site and orientation to the bubble seen on preliminary radiograph.

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with the performance of either conventional radiography or US, the CT image cannot be used as the reference standard because more gas may be either liberated or absorbed in the interval between the two imaging studies. However, the simple digital scout view, which is a part of almost every CT study of the abdomen, provides the opportunity to determine the smallest amount of free air that could be seen on supine projections, if that projection includes the uppermost part of the abdomen to encompass the otherwise featureless gray background of the hepatic shadow (Fig 4). The digital scout view is obtained at the same time as the cross-sectional images, and the patient does not change position when both are obtained. We have evaluated this issue with both phantoms and clinical examples. Our results indicate that in the upper part of the abdomen, the supine radiograph is just as sensitive as the CT image for the detection of small bubbles of free air (7,8). Consequently, we insist that an appropriately focused series consisting of overlapping supine radiographs be obtained to interrogate the entire abdomen. With such a protocol, any lucency in the right upper quadrant that is lateral and superior to the duodenal bulb and superior to the hepatic flexure must be explained before being dismissed (Fig 5). Such an emphasis on the right upper quadrant has allowed us to recognize subtle signs of free air that otherwise would be missed with a routine supine study consisting of only a KUB radiograph (9). Moreover, the presence of free air in specific locations over the liver shadow can enable an inference to be drawn as to the likely location of the perforation from which the free air is derived. It takes approximately 6–12 hours after perforation before a perito-

neal insult results in a generalized ileus (10). As mentioned before, perforated ulcers in the stomach or duodenal bulb in a steroid-free, alert patient are generally accompanied by the experience of immediate pain. On the other hand, colonic perforations are more insidious in the development of signs and symptoms. Therefore, in someone suspected of having spontaneous pneumoperitoneum, the absence of an adynamic ileus is suggestive that the free air involves the stomach or duodenum, whereas the presence of an adynamic ileus makes one look for a more distal perforation. Furthermore, free air in the right upper quadrant situated below the hemidiaphragm indicates an anterior perforation, whereas the confinement of air below the right 11th rib, while still intraperitoneal, is suggestive of localization in the Morison pouch, a posterior-superior intraperitoneal recess intimately related to the posterior wall of the duodenal bulb.

MISCONCEPTIONS: CONVENTIONAL RADIOGRAPHIC DIAGNOSIS OF INTESTINAL OBSTRUCTION
In the 1950s, Dr Frimann-Dahl, an influential Norwegian radiologist, made a series of observations that were, in short order, widely accepted. His claims have influenced pathophysiologic conceptions among surgeons and radiologists for many decades now. The reports by Frimann-Dahl, which were based on fluoroscopic examination of the abdomen, led to the notion of differential fluid levels as being a finding crucial to the distinction of intestinal obstruction from adynamic ileus. He stated that differing fluid levels in one loop indicate obstruction, whereas fluid levels at the

Conventional Radiographs of the Acute Abdomen

Figure 5. Intraperitoneal air. Radiograph shows bubbles (arrows) scattered over the liver, well above the colon and the duodenal bulb.

Figure 4. Inhomogeneity of the liver shadow caused by free air. (a) Conventional radiograph shows areas of lucency (arrow) scattered over the hepatic shadow. (b) Transverse CT image shows anterior free-air bubble (outlined in white).

same height in a single bowel segment were evidence of adynamic distention or ileus (11). Frimann-Dahl made several assumptions that are not correct. First, he stated that “at equilibrium,” such findings would be noted. However, there is no

such thing as equilibrium in the intestines because the peristaltic movement of air and liquid through the tubular gastrointestinal tract is never in a steady state. The passive rising and falling of gas-liquid interfaces and the progression or reversal of peristalsis proximal to an obstruction mandate that luminal contents are always in flux with respect to volume and position. There is no quiet interval allowing fluid levels to equilibrate because fluid is constantly being introduced from above or returned above by muscular contraction. Furthermore, liquid and gas will sporadically pass through an intermittent obstruction or will merely fill up an arm of one loop and start to drip into another arm of that same loop at any point in time. Thus, the equilibrium propounded so compellingly by Frimann-Dahl does not exist in real life. Moreover, Frimann-Dahl was making his observations with fluoroscopic examination of a patient. In essence, he was producing movies, while we take snapshots either with CT or conventional radiography. CT has demonstrated clearly that interfaces of differing heights can be observed in one loop, and at the same time, fluid levels of the same height may be seen in either that same loop or an adjacent loop in patients who have either mechanical obstruction or adynamic ileus. Therefore, the recognition of fluid levels with horizontal-based radiographs, either with decubitus or upright projections, does not advance our understanding of intestinal obstruction (Fig 6). In addition, there is really no need to make patients stand or lie on their side if the conventional radiographs are not diagnostic and if CT is contemplated. In corroboration of this skepticism, the findings from a number of studies have shown the nonutility of upright radiographs, in the presence of supine radiographs, for the determination of obstruction (11,12).

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Baker
Figure 6. In the appropriate clinical context, the diagnosis of intestinal obstruction can often be made equally well with conventional radiography and CT. (a) Supine conventional radiograph shows dilated small bowel and nondilated ascending colon. (b) Transverse CT image shows mostly fluid-filled distended small-bowel loops and nondilated ascending colon.

BOWEL OBSTRUCTION: QUESTIONABLE ASSUMPTIONS
A variety of false notions attend and confound a correct conventional radiographic diagnosis of bowel obstruction. Some have become fiercely held tenets that are still readily accepted or at least acknowledged, yet they fail to hold up with careful scrutiny. Before proceeding with this list, some important points of conventional radiographic interpretation should be established. A guide to the location of the large bowel and, from that, to the observation of the stomach and small bowel depends on recognition of the appearance and position of the transverse colon. This intestinal segment is almost always available for depiction because the colon almost always contains some gas. On supine views, the transverse colon is the least dependent segment of the large bowel. Therefore, the transverse colon is most apt to be the place where flatus will collect. Of course, the transverse colon (a) could have been removed in a prior operation, (b) could be displaced upward or downward, depending on body habitus, and (c) may never have formed if the patient had a malrotated large bowel. However, in most cases, the transverse colon is readily observable. After identifying the transverse colon, which is distinguishable by the presence of intraluminal feces, by the bordering haustral outpouchings, and by the infoldings of the plicae semilunares, one should attempt to determine the location and the degree of dilatation of the cecum (13). A colonic landmark often sought, but rarely involved in the determination of obstruction, is the rectal gas

shadow. In the presence of obstruction, the rectum may still contain gas because the obstruction may be recent or intermittent or because an extensive amount of feces beyond the point of luminal occlusion may continue to ferment and produce flatus even when the obstruction is total and unremitting. Thus, the presence of rectal gas does not mean that there is no obstruction. Conversely, the absence of rectal gas does not mean that there is an obstruction. The rectum is the most dependent colonic segment, and therefore it is least apt to contain flatus. Hence, a flatus-free rectum is not indicative of a proximal luminal blockage.

MEASUREMENT OF DILATATION
Many radiologists and surgeons believe that a smallbowel loop measuring greater than 2.5 cm in diameter is indicative of distention and is often associated with luminal blockage. However, the reliance on this measurement is based on a fallacy. Remember that a conventional x-ray emanates from a point source, and the resultant image is displayed on the flat surface of an imaging plate placed behind the patient. Thus, magnification is always a factor. Also, one cannot determine on a single supine view whether a loop of bowel that may be distended is in fact close to the film, and therefore far from the point source, or if it is more ventrally situated. Moreover, one also does not know how thick the patient is to determine how far anteriorly the ventral bowel loop may be situated. For example, in an obese patient measuring 20 inches (51 cm) from front to back at the umbilicus, an anteriorly situated bowel loop will be magnified by at least a fac-

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of obstruction cannot be determined or even suggested. It is just as conceivable that what is being observed is persistent intermittent obstruction rather than an obstruction seen early in its course (Fig 7).

Conventional Radiographs of the Acute Abdomen

PARTIAL OR INTERMITTENT OBSTRUCTION
The term partial obstruction is one long favored by surgeons. However, the surgical literature provides no definition of partial obstruction in the setting of an acute clinical situation. The term presupposes that somehow the lumen is narrowed but not completely blocked, thereby not completely hindering the passage of gas distally. This notion may be rational in conception, but it has no empiric verification. It is entirely likely that what is deemed “partial obstruction” may be a complete but intermittent obstruction caused by the reversible sharp bending of the bowel near the point of occlusion as a result of peristalsis. However, although the dynamic of complete but intermittent obstruction seems plausible, it, too, has yet to be proved. Thus, because partial, incomplete, or intermittent blockages are not amenable to confirmation, these terms should not be used to further characterize an intestinal occlusion. It is enough to say that an obstruction exists.

Figure 7. Early obstruction versus intermittent obstruction. Radiograph shows dilated small bowel and nondistention of colon 1 day after admission. From these findings, it was thought that the bowel recently became obstructed. A more complete history revealed that the obstructive symptoms had persisted over several days.

tor of two and will appear to be dilated even when it is actually of normal caliber (14).

TUBE IN PLACE: RELIEF OF DILATATION
The determination of bowel obstruction on conventional radiographs depends on the differential distention of gas in loops proximal to the point of occlusion and a lack of distention in loops distal to it. Thus, the contrast agent used for the determination of bowel obstruction at conventional radiography is primarily swallowed air. An effective treatment in many cases of bowel obstruction before or in lieu of surgery is to place a nasogastric tube into the stomach or more distally into the proximal duodenum. The function of the tube is to remove accumulations of intraluminal gas. With such removal, the patient may feel better, and the resulting radiograph could show a decrease in the distention of the bowel proximal to the obstruction. However, the relief of obstruction is occasioned by the passage of gas through the anus. It is not determined by a decrease in the amount of gas proximal to the occlusion even if a tube is in place and even if the treatment makes the patient feel better. Thus, it is fair to say that the dilatation has been ameliorated but not that the obstruction has necessarily been resolved when a tube is in place.

POINT OF OBSTRUCTION
With conventional radiographs, one cannot determine the actual point of luminal occlusion. Almost always, many liquid-filled loops are interposed between the site of blockage and the most distal gas-filled loop that can be detected radiographically. Consequently, a single loop of dilated jejunum may be associated with a jejunal obstruction, but it is also possible that the dilated jejunal loop is a concomitant of an ileal or colonic obstruction. Hence, except for rare cases in which an additional pathognomonic finding is present, determination of the actual site of bowel occlusion on a conventional radiograph should not be attempted. Here, too, it is enough to recognize the presence of bowel occlusion (Fig 8).

SENSITIVITY OF THE CONVENTIONAL ABDOMINAL RADIOGRAPH AND EVALUATION OF OBSTRUCTION
Clearly, CT is more versatile than conventional radiography in assessing some of the important characteristics of a bowel obstruction. CT can be used to determine the presence and, at times, to find the site and the cause of obstruction; whereas, some rare exceptions withstanding, conventional radiography can only distinguish the presence of an obstruction. Nonetheless, the results of two studies have shown a conventional radiographic sensitivity of 66% in one

EARLY OBSTRUCTION
When the conventional radiograph reveals gas in a nondilated loop distal to an obstruction in association with proximal distended loops, the temptation often is to claim that the luminal occlusion is early or recent. One cannot make this statement with any validity because on one radiograph, the temporal course

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study and 68.8% in the other (15,16). The latter study also assessed contemporaneous CT. The findings revealed that CT had a sensitivity of only 64% for the recognition of bowel obstruction (16). Of course, CT is more specific, but its overall accuracy was similar to that of conventional radiography. Therefore, even in this present era of abundant and steadily increasing use of multi–detector row CT, which will soon include standard coronal reformation in addition to sagittal and transverse views, the conventional radiograph stands up well with respect to the crucial issue of the recognition of the presence of bowel blockage.

Baker

PROGRESSION OF PATIENTS THROUGH EMERGENCY DEPARTMENT EVALUATION
The customary progression of a patient with acute abdomen, as practiced in many medical centers, begins with conventional radiographs of the abdomen. The images may be assessed separately, yet often they are obtained but not immediately interpreted. The patient is then transported from the standard radiography room to a separate suite in which a CT examination is performed, sometimes after contrast agents are administered orally and intravenously. As part of the CT examination, a digital view of the abdomen is obtained in most instances prior to the generation of CT sections. Several issues in this ritual should be assessed to provide optimal care at reasonable dose accumulation. In actual practice, the CT scout view is superior to standard radiographs of the abdomen for several reasons. Some have complained that this examination does not reveal subtle findings of calcification or lucency. However, in our studies comparing the supine radiograph to CT images for free-air detection, we have used the digital scout view as the plain radiographic examination of choice because the CT examination could not be delayed, nor could the patient be moved. We have found that the conventional radiograph equals CT images for the recognition of pneumoperitoneum. Furthermore, the CT scout view encompasses the entire abdomen, overcoming the problem intrinsic with abdominal radiographs obtained with a 40-inch source-to-film distance. Therefore, we believe that the stand-alone abdominal series should be bypassed and that the CT scout view is an integral part of the radiographic work-up. For intestinal obstruction, the next most important view obtained after a supine radiograph was shown by Bryk in the 1970s to be successive supine radiographs (17). Most of the time, we can make the diagnosis of the presence of obstruction, if it was in doubt in the first radiograph, by looking at the CT scout view. It is often more revealing than the initial radiograph because in the interval between the two, the patient has had time to become more anxious and thus has had the opportunity to swallow air to a greater ex-

Figure 8. Dilated gas-filled colon to the sigmoid. Radiograph shows that in actuality, the obstruction was in the rectum, more distal than the distribution of gas shadows would seem to indicate.

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tent, enabling the successive supine radiograph to be more revealing. The problem with this scenario is that reimbursement is provided for the supine radiographic studies obtained in a standard radiography room and also for the CT examination that encompasses the digital scout view. If the digital scout view is obtained as part of the CT examination and yet considered as a separate examination, it will not be reimbursed. Nonetheless, that is precisely the stepwise way that we proceed in our imaging evaluation: We assess the digital scout view before the cross-sectional views are inspected. Consequently, we propose that the digital scout view be looked at as a separate examination for billing purposes, if it was done alone and if it determined the presence of obstruction or perforation. If the digital scout view was part of a subsequent CT study, it should not be billed separately but encompassed in the charge for the entire study. If separate reimbursement is established for the digital scout view, this change in payment may give impetus to reduce the rate of CT utilization. However, there is probably little enthusiasm for such an alteration of professional compensation today because it is counterproductive to the accustomed means of generation of the income of radiologists. When the debate about CT use becomes more intense, especially when focused studies in young patients reveal a relationship between exposure and later

malignancy, radiologists will need to make behavioral changes in acknowledgment of the implication of dose accumulation with CT. We have recently witnessed an effort by manufacturers to reduce x-ray exposure in pediatric patients in response to the publicity recently directed at the dose from CT machines. However, no real change has occurred in the activity of radiologists or in initiatives with respect to the restriction of unindicated studies. The next phase of the discussion about dose will inevitably be disquieting to those who favor the status quo. A new approach to reimbursement for the CT scout view (the modern conventional radiograph) may be a consideration in the upcoming debate.

References
1. Baker SR, Hirschorn D, Jacobs AF. The recognition of miniscule intra abdominal gas bubbles: comparison of supine radiographs, CT scouts and CT sections (abstr). Radiology 1999; 213(P):252–253. 2. Miller RE. The technical approach to the acute abdomen. Semin Roentgenol 1973; 8:267–279. 3. Miller RE, Becker GJ, Slabaugh RA. Detection of pneumoperitoneum: optimum body position and respiratory phase. AJR Am J Roentgenol 1980; 135:487–490. 4. Woodring JH, Heiser MJ. Detection of pneumoperitoneum on chest radiographs: comparison of upright lateral posterior-anterior projections. AJR Am J Roentgenol 1995; 165: 45–47. 5. Stapakis JC, Thickman D. Diagnosis of pneumoperitoneum: abdominal CT vs upright chest film. J Comput Assist Tomogr 1992; 16:713–716.

6. Nirapathpongporn S, Osatavanichvong K, Udompanich O, Pakanan P. Pneumoperitoneum detected by ultrasound. Radiology 1984; 150:831–832. 7. Levine MS, Scheiner JD, Rubesin SE, Laufer I, Herlinger H. Diagnosis of pneumoperitoneum on supine abdominal radiographs. AJR Am J Roentgenol 1991; 156:731–735. 8. Baker SR. Imaging of pneumoperitoneum. Abdom Imaging 1996; 21:413–414. 9. Cho KC, Baker SR. Extraluminal air: diagnosis and significance. Radiol Clin North Am 1994; 32:829–844. 10. Keeffe EJ, Gagliarki RA, Pfister RC. The roentgenographic evaluation of ascites. Am J Roentgenol Radium Ther Nucl Med 1967; 101:388–396. 11. Frimann-Dahl J. Roentgen examinations in acute abdominal diseases. 2nd ed. Springfield, Ill: Thomas, 1960. 12. Bryk D. Functional evaluation of small bowel obstruction by successive abdominal roentgenograms. Am J Roentgenol Radium Ther Nucl Med 1972; 116:262–275. 13. Mindelzun RE, McCort JJ. Questions and answers. AJR Am J Roentgenol 1996; 166:716–718. 14. Baker SR. Unenhanced helical CT versus plain abdominal radiography: a dissenting opinion. Radiology 1997; 205: 45–47. 15. Wittenberg J. The diagnosis of colonic obstruction on plain abdominal radiographs: start with the cecum, leave the rectum to last. AJR Am J Roentgenol 1993; 161:443–444. 16. Maglinte DD, Reyes BL, Harmon BH, et al. Reliability and role of plain film radiography and CT in the diagnosis of small-bowel obstruction. AJR Am J Roentgenol 1996; 167: 1451–1455. 17. Maglinte DD, Balthazar EJ, Kelvin FM, et al. The role of radiology in the diagnosis of small-bowel obstruction. AJR Am J Roentgenol 1997; 168:1171–1180.

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Conventional Radiographs of the Acute Abdomen

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C. Craig Blackmore, MD, MPH

Imaging of Cervical Spine Trauma1

The objective of this chapter is to introduce an evidence-based approach to imaging of the cervical spine in blunt trauma. In particular, I will focus on the role of computed tomography (CT) and on the reasons that we elect to use either CT or radiography in different patients. I will also discuss injury patterns in the cervical spine, dividing the cervical spine into upper and lower components and identifying several problem areas where there are challenges to the interpretation of CT or radiographic studies.

SELECTION OF APPROPRIATE IMAGING APPROACH
Trauma victims who come to the emergency department need to have their cervical spines evaluated to exclude the presence of an unstable fracture that could progress to neurologic compromise. In some cases, tools such as the National Emergency X-Radiography Utilization Study (NEXUS) (1) or the Canadian cervical spine rule (2) can be used to identify patients who do not require imaging but instead might have their cervical spines cleared purely on clinical grounds. However, most patients will require imaging with either CT or radiography. For decades, the standard method of clearing the cervical spine has been with radiography. A series of radiographs consisting of anteroposterior (including open-mouth odontoid) and lateral (including swimmer) views that show the spine from the base of the skull to the junction of the seventh cervical vertebra with the first thoracic vertebra can be used to exclude the presence of cervical spine fracture. Radiography has many advantages. It is relatively inexpensive, is available essentially everywhere that there is an emergency department, and has been around sufficiently long that there is interpretation expertise at nearly all centers. However, radiography struggles in patients who are at the highest risk of fracture. In patients who have sustained major trauma, the presence of spine immobilization backboards, other injuries that prevent optimal positioning (including upper extremity fractures and head injury), and lifesupport apparatus (such as endotracheal tubes) makes obtaining adequate evaluation of the cervical spine with radiography challenging (3). In addition, patients with major trauma may be uncooperative because of hypoxia, intoxication, or head injury. In patients with major trauma, radiography, instead of requiring 10 minutes to complete, may require an hour and may still lead to incomplete or inadequate imaging studies (4).

RSNA Categorical Course in Diagnostic Radiology: Emergency Radiology 2004; pp 143–149.
1From the Department of Radiology, Harborview Medical Center, Harborview Injury Prevention and Research Center, University of Washington, Box 359960, 325 Ninth Ave, Seattle, WA 98104 (e-mail: [email protected]).

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In the mid-1990s, CT was promoted as an alternative to radiography for clearing the cervical spine in trauma patients (5). CT offers several advantages. It is more sensitive for fracture (6–8), is more specific in patients with major trauma, and is fast, particularly in subjects who are already positioned on the CT gantry for head CT (5). Although the amount of collective experience with CT is less than that with radiography, most fractures fortunately are readily apparent on CT. In addition, the use of coronal and sagittal reformations, particularly after multi–detector row CT scanning, can enable adequate evaluation of the cervical spine, even in the presence of other injuries, life-support devices, and preexisting conditions such as osteopenia and kyphosis. Obviously, there is a trade-off between CT and radiography. CT is more sensitive, more specific, and faster but does have a higher cost, especially when one considers the direct cost of the imaging involved. However, CT becomes cost-effective if subjects are identified who are at high (>4%) probability of fracture (9). The costeffectiveness of CT is due to the frequency of inadequate radiographs, the extreme cost of a missed fracture (even though only a small percentage of patients will develop neurologic deficit, such as paralysis), and the higher cost of radiography in high-risk subjects that is caused by the requirement for multiple repeat views. It is possible to identify subjects who are at high risk by using the Harborview CT screening criteria (10), a validated clinical prediction rule that is based on the presence of focal neurologic deficit, severe head injury, or a high-energy trauma mechanism. Thus, CT is accurate, rapid, and effective as a screening strategy for the cervical spine in trauma patients and becomes cost-effective when criteria, such as the Harborview cervical spine screening criteria, are used to identify appropriate high-probability patients. Radiography remains optimal (a) for subjects at low risk or (b) if rapid (helical) CT is not available (11).

Figure 1. (a) Axial CT image and (b) coronal reformation show fracture (arrow) of left occipital condyle from avulsion of alar ligament.

Blackmore

UPPER CERVICAL SPINE
The upper portion of the cervical spine, particularly the craniocervical junction, is one of the most frequently injured areas of the cervical spine. Further, this region is difficult to depict with radiography. With the introduction of CT screening, injuries to this region are being diagnosed more frequently. Therefore, radiologists need to be aware of the injury patterns and osseous and ligamentous anatomic structures. Many of the fractures of the craniocervical junction are avulsion-type injuries, emphasizing the importance of the ligamentous structures. The major ligaments of the craniocervical junction include the occipital condylar articulation capsular ligaments, the apical ligament from basion to dens, the alar ligaments from occipital condyles to dens, the

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cruciate ligaments, including both the transverse and horizontal components, and the tectorial membrane, representing the extension of the posterior longitudinal ligament cephalad. Occipital condyle fractures are classically divided into three types. The first type is a burst fracture. These burst fractures result from axial load with compression of the condyle but generally involve intact atlanto-occipital capsular ligaments and are therefore stable. Type 2 occipital fractures represent extension of an occipital bone fracture into the condyle. Type 3 occipital condyle fractures are the most common (Fig 1). These are avulsions from the alar ligament (12). Stability of occipital condyle fractures remains a controversial topic (13). There are no good data on the natural history of these injuries to define which are stable. This problem is exacerbated by the fact that until the past several years, occipital condyle fractures were thought to be rare. With CT screening, such fractures have become one of the more commonly identified injuries of the craniocervical region. Current definitions of stability are related to the extent of displacement of avulsion injuries, with displacement of less than 5 mm considered stable. In addition, any evidence of disruption of the capsular ligaments is a criterion for instability, and in general, bilateral injuries are considered unstable. Treatment for these injuries remains controversial. Instability at the atlanto-occipital joint may be subtle. However, sagittal reformations and coronal reformations of the CT scan data provide a side-to-side comparison that can facilitate identification of subtle atlanto-occipital injury. Magnetic resonance (MR) imaging may also be indicated to evaluate these injuries.

Figure 2. Axial CT image shows burst fracture (arrows) of cervical vertebra C1. Stability and integrity of transverse ligament are inferred from absence of widening of lateral masses with respect to dens.

Figure 3. Sagittal CT reformation demonstrates type 2 fracture of dens, with nearly 100% posterior displacement of dens.

Fractures of the first cervical vertebra ring (Fig 2) are generally related to axial loading and commonly occur in association with other injuries, including those of the occipital condyle and the axis. Neurologic compromise is relatively infrequent with fractures of the cervical vertebra C1 ring, presumably because the axial compression mechanism results in a burst configuration with expansion of the spinal canal. Burst fractures are defined as stable if the transverse component of the cruciate ligaments, which is also referred to as the transverse atlanto-axial ligament, is intact. Integrity of the transverse ligament is inferred from the displacement of the lateral masses at cervical vertebra C1. Greater than 7 mm of displacement or an avulsion fracture of the cervical vertebra C1 tubercle is considered ligamentous injury. Displacement is assessed by evaluating the overlap of the lateral masses of the cervical vertebra C1 upon the lateral masses at cervical vertebra C2. Fractures of the atlas are divided into two major groups: (a) fractures isolated to the dens and (b) frac-

tures involving the posterior elements. Dens fractures are frequent, although the mechanism of injury is complex and not well understood. Dens fractures are commonly broken down into three types. Type 1 injuries are avulsion fractures of the tip of the dens, either from alar or apical ligament avulsion. These injuries tend to be stable, although like occipital condyle fractures, bilaterality connotes instability. There is an association between type 1 dens fractures and cervical vertebra C1 ring fractures. Type 2 dens fractures are fractures across the base of the dens (Fig 3) and are particularly common and problematic in the elderly. Type 3 dens fractures involve some portion of the body of the dens and may include the articular facet but do not involve the posterior elements (14). Avulsion fractures can also occur from the attachment of the anterior longitudinal ligaments on the anterior inferior corner of cervical vertebra C2. These hyperextension teardrop injuries may be subtle, and they are generally stable. It is important, however, to differentiate the stable anterior longitudinal ligament avulsion from the potentially unstable anulus fibrosus avulsion with disk dislocation. The differentiating factor between these two is that the stable anterior longitudinal ligament hyperextension teardrop avulsion fracture will have normal alignment at the C2–3 disk space. Any evidence of abnormal alignment at this disk space should raise suspicion for C2–3 dislocation and should be considered unstable. Detection of cervical vertebra C2 hyperextension teardrop fractures is a potential pitfall for CT scanning. When these injuries are subtle and nondisplaced, they may occasionally be difficult to depict with CT scanning. Fractures involving the posterior elements of cervical vertebra C2 generally fall into the category of the C2 traumatic spondylolisthesis, also called the hangman fracture (Fig 4). These fractures tend to occur from a hyperextension mechanism, although this, too, is controversial. In general, the canal is enlarged with hangman fractures, and neurologic compromise is uncommon. Sometimes the fracture will involve a portion of the posterior vertebral body. In these variant hangman fractures, the involved component of the posterior vertebral body may undergo retropulsion and may contribute to cord injury.

Cervical Spine Trauma

LOWER CERVICAL SPINE
The anatomic structures and injury patterns from cervical vertebra C3 to cervical vertebra C7 are relatively stereotypical. Anatomically, the lower portion of the cervical spine can be divided into anterior and posterior columns. Biomechanical stability is defined as involvement of all of the osseous elements of one column plus one element of the other column. Instability may also be defined by (a) olisthesis of 3.5 mm or more or (b) focal kyphosis at a single level of 11° or more (15).

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Figure 4. (a) Axial and (b) sagittal CT images show traumatic spondylolisthesis of cervical vertebra C2. Involvement of posterior margin of vertebral body (arrow) increases probability of neurologic compromise.

Blackmore

Figure 5. (a) Axial and (b) sagittal CT images show anterior end-plate fracture (arrow) with preserved alignment. Usually, these injuries are stable and are managed conservatively.

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There is no universal classification system for the lower portion of the cervical spine. Several systems have been proposed, which are based both on the direction of force and the resultant injury patterns. The system that will be used in this discussion is based on management practices at our institution (16). We will divide injuries of the lower portion of the cervical spine into minor stable fractures, facet fractures with normal alignment, facet dislocations, burst fractures, and extension injuries. Minor stable fractures include spinous process fractures, extraforaminal transverse process fractures, and fractures isolated to the anterior column. Anterior column fractures (Fig 5) generally involve only the end plate, with little or no anterior vertebral body height loss, and are generally treated conservatively with a cervical collar. Spinous process fractures, particularly at cervical vertebrae C6 and C7, may occur in isolation from forces applied by the interspinous or nuchal ligaments. These stable injuries are generally treated conservatively. Management of fractures of the transverse process (Fig 6) is more controversial, although the fracture itself, if isolated to the transverse process, will be biomechanically stable; however, the proximity of the vertebral arteries to these injuries raises the specter of

vertebral artery injury and heightens the risk of vertebral basilar system stroke. Some investigators advocate vascular imaging in all transverse process fractures, an approach that remains controversial (17–19). Fractures through the articular facets occur as a consequence of lateral bending or rotation. These fractures may be isolated but with disruption of the capsular ligaments may still be potentially unstable and are often treated with halo external-fixation devices. Facet fractures are often difficult to depict with radiography and represent an area where CT has higher sensitivity. Dislocations at the facet joint, by definition, involve disruption of the capsular ligaments and therefore are potentially unstable. Dislocations include “jumped” facets, where the inferior articular surface of the upper vertebral body is dislocated anterior to the superior articular facet of the lower vertebral body. Such dislocations may or may not be accompanied by fracture. “Perched” facets occur when the apex of the articular facets of adjacent vertebral levels are in apposition. Injuries with such large displacements of the articular facet usually lead to olisthesis. In general, unilateral facet dislocation (Fig 7) will lead to canal compromise of approximately 25% of the diameter, and bilateral

Figure 6. (a) Lateral radiograph shows soft-tissue swelling (arrows) that is the only radiographic evidence for fracture. (b) Axial CT image shows subtle fracture through left transverse process at cervical vertebra C2. Although stable and not requiring specific treatment, fractures through transverse foramen raise suspicion for vertebral artery injury.

Cervical Spine Trauma

Figure 7. (a) Axial and (b) sagittal CT reformations show unilateral facet dislocation (perch) (arrow).

facet dislocation will lead to canal compromise of 50% (Fig 8). Because of the potential for cord ischemia in such high degrees of canal compromise, immediate reduction is advocated. In general, we do not perform definitive imaging (eg, CT, MR imaging) in these patients until fluoroscopy-guided reduction has been performed by the physicians of our spine service. Burst fractures are a consequence of axial load, typically with an element of flexion, and these fractures result in crushing and expansion of the vertebral body (Fig 9). Canal compromise often occurs, and there may be an additional distraction component to the injury in the posterior elements. Often burst fractures will result in a triangular bone fragment from the anterior vertebral body. This fragment bears some resemblance to a teardrop; hence, the common term flexion teardrop fracture is applied to these cases. The probability of neurologic deficit with such injuries is high. MR imaging may be indicated to evaluate the neural elements and to evaluate for associated distraction injuries of the posterior ligaments.

Finally, extension injuries can occur in the cervical spine. As in other portions of the spine, extension injuries are more common and more severe in subjects with abnormal fusion of the spine. The classic example is ankylosing spondylitis, in which the syndesmophytes bridging the disk space and the ankylosis of the facet articulations lead to a rigid spine. Failure of energy diffusion across multiple vertebral levels leads to fracture at lower energy in such subjects. Hyperextension fractures tend to be severely displaced, and neurologic compromise is common. A subcategory of extension injuries includes those that occur without fracture. These injuries are the so-called SCIWORA (Spinal Cord Injury Without Radiologic Abnormality) injuries. These injuries tend to occur in two groups of patients. The first group is children, in whom hypermobility of the cervical spine related to immaturity can allow cord injury without fracture or ligamentous disruption. The second category is patients with spinal stenosis, as in ossification of the posterior longitudinal ligament. In these patients, the narrowing of the canal

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Figure 8. (a) Axial CT image shows bilateral facet dislocation with olisthesis. (b) Sagittal reformation demonstrates canal compromise. Reduction is usually performed prior to CT. However, interfacet osseous fragments can prevent adequate closed reduction, as in this case.

Figure 9. (a) Axial and (b) sagittal CT images show burst fracture of cervical vertebra C6, with retropulsion of osseous fragments and canal compromise.

Blackmore

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is exacerbated by physiologic motion, and cord injury can result. In conclusion, the intent of this chapter was twofold. The first purpose was to introduce an evidencebased imaging approach to the cervical spine and trauma patients. CT is the preferred imaging modality in subjects at high risk of injury because of the higher sensitivity and specificity of CT. However, radiography is still preferred in low-risk subjects because it is more cost-effective and because the radiation dose is lower. The second purpose was to discuss injury patterns in the upper and lower portions of the cervical spine, calling attention to challenging areas in the interpretation of both CT and radiographic studies.

References
1. Hoffman J, Mower W, Wolfson A, Todd K, Zucker M. Validity of a set of clinical criteria to rule out injury to the cervical spine in patients with blunt trauma. N Engl J Med 2000; 343: 94–99. Stiell I, Wells G, Vandemheen K, et al. The Canadian C-spine rule for radiography in alert and stable trauma patients. JAMA 2001; 286:1841–1848. Blackmore CC, Deyo RA. Specificity of cervical spine radiography: importance of clinical scenario. Emerg Radiol 1997; 4:283–286. Blackmore CC, Zelman WN, Glick ND. Resource cost analysis of cervical spine trauma radiography. Radiology 2001; 220:581–587. Nunez DB, Ahmad AA, Coin CG, et al. Clearing the cervical spine in multiple trauma victims: a time-effective protocol

2.

3.

4.

5.

using helical computed tomography. Emerg Radiol 1994; 1:273–278. 6. Nunez DB, Quencer RM. The role of helical CT in the assessment of cervical spine injuries. AJR Am J Roentgenol 1998; 171:951–957. 7. Ptak T, Kihiczak D, Lawrason J, et al. Screening for cervical spine trauma with helical CT: experience with 676 cases. Emerg Radiol 2001; 8:315–319. 8. Hanson JA, Blackmore CC, Mann FA, Wilson AJ. Cervical spine injury: accuracy of helical CT as a screening technique. Emerg Radiol 2000; 7:31–35. 9. Blackmore CC, Ramsey SD, Mann FA, Deyo RA. Cervical spine screening with CT in trauma patients: a cost-effectiveness analysis. Radiology 1999; 212:117–125. 10. Hanson J, Blackmore CC, Mann FA, Wilson AJ. Cervical spine injury: a clinical decision rule to identify high-risk patients for helical CT screening. AJR Am J Roentgenol 2000; 174:713–717. 11. Blackmore CC, Mann FA, Wilson AJ. Helical CT in the primary trauma evaluation of the cervical spine: an evidencebased approach. Skeletal Radiol 2000; 29:632–639. 12. Anderson PA, Montesano PX. Morphology and treatment of occipital condyle fractures. Spine 1988; 13:731–736.

13. Hanson J, Deliganis A, Baxter A, et al. Radiologic and clinical spectrum of occipital condyle fractures: retrospective review of 107 consecutive fractures in 95 patients. AJR Am J Roentgenol 2002; 178:1261–1268. 14. Anderson LD, D’Alonzo RT. Fractures of the odontoid process of the axis. J Bone Joint Surg Am 1974; 56:1663–1674. 15. White AA, Southwick WO, Panjabi MM. Clinical instability in the lower cervical spine. Spine 1976; 1:15–27. 16. Anderson P. Spine. In: Hansen S, Swiontkowski M, eds. Orthopaedic trauma protocols. New York, NY: Raven, 1993; 211–216. 17. Biffl WL, Moore EE, Elliott JP, et al. The devastating potential of blunt vertebral arterial injuries. Ann Surg 2000; 231: 672–681. 18. Biffl WL, Ray CE Jr, Moore EE, et al. Treatment-related outcomes from blunt cerebrovascular injuries: importance of routine follow-up arteriography. Ann Surg 2002; 235:699– 706; discussion 706–707. 19. Azuaje R, Jacobson L, Glover J, et al. Reliability of physical examination as a predictor of vascular injury after penetrating neck trauma. Am Surg 2003; 69:804–807.

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Cervical Spine Trauma

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Friedrich M. Lomoschitz, MD, C. Craig Blackmore, MD, MPH, and Frederick A. Mann, MD

Imaging Spine Trauma in the Elderly1

National demographics show an increasingly larger number of older individuals in industrialized societies. In general, older individuals may be considered as “elderly” (aged ≥65 years) on physiologic and epidemiologic bases that reflect observed differences in functional decline, trauma mortality rates, and osteoporosis (1–4). During the past century, the number of persons in the United States older than age 65 increased 10-fold, and rapid growth is forecast with the baby-boom generation reaching retirement age starting in the year 2011 (5). In general, spine fractures and resultant spinal cord injuries are an important source of morbidity and mortality. In 1993, spinal cord injuries occurred at a rate of approximately 30 per 1 million person-years and cost society an estimated $3.4 billion (6,7). The elderly experience these injuries disproportionately. The results of a prospective survey in Taiwan revealed that spinal cord injuries occurred at a rate of approximately 48 per 1 million person-years in patients older than 65 years, compared to 19 per 1 million person-years in patients younger than 65 years (8). Moreover, injury patterns in elderly patients may differ from those in younger patients because of differences in bone density and injury mechanisms and because of the presence of degenerative changes (9). The purpose of our review is to (a) describe individual patient and mechanism factors that may affect spine injury in the elderly population, (b) discuss the influence of senescent changes on biomechanics and fracture patterns in the elderly spine, (c) illustrate common patterns of spine injury in elderly patients, and (d) analyze current imaging techniques for evaluation of spine injury with respect to elderly patients.

INDIVIDUAL PATIENT AND MECHANISM FACTORS
In the United States, almost 3 million individuals are admitted to the hospital for trauma annually (3). Among these admitted trauma patients, approximately 10.000 cervical spine fractures (incidence, approximately 15–30 per 1 million individuals per year) and 4000 thoracolumbar spine fractures (incidence, approximately 10–20 per 1 million individuals per year) are diagnosed. Within these groups of patients, approximately one-third and one-quarter, respectively, sustain neurologic injury (10). Thus, spinal cord injury is relatively rare. With the exception of the elderly, traumatic spinal cord injury results from high-energy mechanisms (eg, motor vehicle accidents, falls from heights greater than 3–4 m).

RSNA Categorical Course in Diagnostic Radiology: Emergency Radiology 2004; pp 151–158.
1From the Department of Radiology, Vienna Medical School, University of Vienna, Waehringer Guertel 18-20, A-1090 Vienna, Austria (F.M.L.); and the Department of Radiology, Harborview Medical Center, Seattle, Wash (C.C.B., F.A.M.) (e-mail: [email protected]).

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Among the elderly, lower-energy impacts, such as falls from seated or standing heights, are a common cause of clinically unstable spine injuries (11). Cervical spine injuries in elderly patients tend to involve more than one level with consistent clinical instability, and these injuries commonly occur at the atlantoaxial complex (12). Compared with younger individuals, the elderly are 2–12 times more likely to be injured in domestic falls (13–15) and are 2–4 times more likely to sustain injuries of the upper portion of the cervical spine (cervical vertebrae C1 and C2) (13,14,16). Fractures occurring at the atlantoaxial complex in elderly patients almost always involve cervical vertebra C2, and an isolated fracture of cervical vertebra C1 is rare (17). Moreover, elderly patients also are more likely to have fractures overlooked at initial diagnosis (15%–40% vs 4% in younger individuals) (15,16). In combination with the thoracic cage, the thoracic spine is inherently stable, and traumatic thoracic spine fractures are less common than fractures of the cervical and lumbar regions, which is also true for the elderly population. In the general population, about every second patient with a thoracic spine fracture has accompanying neurologic findings. This rate is due to the fact that injuries that result in thoracic spine fracture are usually caused by high-energy trauma. As a result, particularly in the upper portion of the thoracic spine, fracture-dislocations are more common than compression fractures and burst fractures. Moreover, the size of the thoracic spinal cord is large relative to the small spinal canal, and the size of the spinal canal may even be decreased by accompanying degenerative changes in elderly patients (18). Falls are the major cause of fractures in the lower portion of the thoracic spine and the lumbar spine, with burst fractures being the most frequent type of fracture encountered. In patients who are injured in falling accidents, age seems to have no influence on the type and location of thoracolumbar spine fractures (19).

Lomoschitz et al

Figure 1. "High" (Anderson-D’Alonzo type II) odontoid fracture and incomplete spinal cord injury in an 80-year-old man injured as a restrained driver in high-speed motor vehicle accident, with endotracheal and orogastric intubation performed at scene of accident. Lateral radiograph shows type II dens fracture (arrow), with posterior angulation and displacement of dens (outlined by ■). In lower portion of cervical spine, severe degenerative changes (chronic degenerative disk disease and diffuse idiopathic skeletal hyperostosis) are present.

INFLUENCE OF SENESCENT CHANGES ON BIOMECHANICS AND FRACTURE PATTERNS
Age-related comorbidities, such as concurrent medical illness and dementia, may distract from an accurate and reliable clinical evaluation. Spondylosis or osteoporosis distorts vertebral anatomic structures and may render normal standard paradigms less useful in detecting injury, may create structures outside the standard paradigms usually used in pattern recognition, and may obscure radiographic signs of trauma. All of the fractures that occur in the elderly also are found in younger individuals. However, there is a striking change in the frequency of some specific fractures in the elderly. In older individuals, among both men and women, there is a dramatic increase in the frequency of fractures of the atlantoaxial complex (ie, cervical vertebrae C1 and C2).

Osteoporosis and senescent degenerative disorders appear to predict the apparently lower force threshold for fractures. The frequency of osteopenia increases with age, especially for postmenopausal women. In the presence of osteoporosis, bone loss is global and equally affects the whole spine. However, normal senescent cortical and trabecular bone losses are quantitatively less in the cervical spine compared with the thoracolumbar spine (20).

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Craniocervical Junction The biomechanical response of the elderly spine to blunt trauma is different from that of the spine in younger patients. In the cervical spine, senescent degenerative changes tend to occur in the mid and lower portions of the cervical spine, allowing a relatively greater degree of mobility (a) to the craniocervical junction, including the motion segments of the occipital condyles through cervical vertebra C2, and (b) particularly to the atlantoaxial complex, which is where fractures most often occur in the elderly (9).

Spine Trauma in the Elderly

Figure 2. Multilevel injury in cervicocranial region, including occipital condyle fracture and "low" (Anderson-D’Alonzo type III) odontoid fracture in a 65-year-old man who fell out of top bunk on a cruise ship. (a) Transverse CT scan obtained at skull base shows occipital condyle fracture (arrow), with fragment displaced medially from inferomedial aspect of right occipital condyle. (b) Transverse CT scan obtained at level of cervical vertebra C2 shows fracture line (arrows) from "low" (type III) odontoid fracture extending into body of axis.

Degenerative osseous changes are known to influence the site of cervical spine injuries and are assumed to be present in almost all patients older than 65 years. Normally, in the younger individual, the most mobile cervical motion segments are cervical vertebrae C4 through C7. Not surprisingly, most cervical fractures in younger patients occur at these levels (8). With degenerative changes, these same segments become less mobile, and the motion segment of cervical vertebrae C1 and C2 becomes the most mobile portion (9). The higher incidence of injury to the upper portion of the cervical spine in the elderly population may be due to the stiffening effect of aging on the vertebral column.

high frequency of injury of the upper portion of the cervical spine, particularly fractures involving the atlantoaxial complex (16,21,22), which may be expected on the basis of simple biomechanics.

Cervicocranial Region The elderly are particularly prone to injuries in the cervicocranial region. The high incidence of atlantoaxial fractures reflects senescent changes, such as osteopenia (especially to the base of the dens), spondylotic immobilization of segments of the lower portion of the spine, and alteration of supporting soft tissues (eg, ligaments, disks, muscles) (Fig 1). Occipital Condyles The occipital condyle, a developmental unit of the cervicocranial region, acts as a functional part of the upper portion of the cervical spine (and is often referred to as C0). Occipital condyle fractures are rare, being found at postmortem examination in 1%–5% of patients who had sustained trauma to the cervical spine and head (23). Clinical manifestations of occipital condyle fractures are highly variable, and such fractures are not typically shown with conventional radiography. Because as many as 30% of occipital condyle fractures are biomechanically unstable (displaced > 3 mm), their presence must be excluded in all symptomatic elderly patients who have experienced trauma to the head and neck. Computed tomography (CT) is the diagnostic standard for occipital condyle fractures, and the base of the skull should be included in all CT examinations of the upper portion of the cervical spine. In our experience, occipital condyle fractures in elderly patients are often part of multilevel fractures of the functional craniocervical unit (Fig 2). In fractures of cervical vertebra C1 or combined fractures of

Thoracolumbar Junction The transition from the thoracic spine to the upper portion of the lumbar spine is referred to as the thoracolumbar junction (ie, thoracic vertebra T10 through lumbar vertebra L2). This transition zone, in general, is exposed to injury because of several factors, including the absence of a protective rib cage, a change in the alignment from kyphosis to lordosis, and a change in the orientation of the facet joints from a coronal orientation in the thoracic spine to a more oblique to sagittal orientation in the lumbar spine. Senescent changes, including osteoporosis, may lower the force threshold for fractures in this region in the elderly population. However, also in the general population, wedge-compression fractures are the most common injury pattern in the thoracic and lumbar spine, usually occurring near the thoracolumbar junction.

COMMON PATTERNS OF SPINE INJURY IN THE ELDERLY
The leading cause of cervical injury in older patients is low-energy trauma, mainly as a result of falls from standing or seated height (8,11,14). The elderly have a

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cervical vertebrae C1 and C2, a direct search for associated fractures of the occipital condyle is indicated.

Atlas (Cervical Vertebra C1) Among the elderly, an isolated fracture of the atlas is rare (17). Approximately 90% of the fractures of cervical vertebra C1 occur in combination with C2 fractures, typically dens fractures (Fig 3). Because multilevel fractures (cervical vertebrae C1 and C2) are considered biomechanically unstable, a heightened bidirectional search for contiguous fractures is critical (find C1 and then look for C2, and vice versa). Axis (Cervical Vertebra C2) Epidemiologic comparisons between elderly and young populations of patients with blunt injury show striking differences in the incidence, type, and distribution of fractures. In elderly and young adult populations, cervical vertebra C2 is the most frequently injured vertebra. In the elderly, however, the incidence is nearly twice that in younger individuals (40%–48% vs 22%–28%) (12,21). Combined injuries of the motion segment of cervical vertebrae C1 and C2, which are usually regarded as clinically unstable, are even more common among the elderly (69% vs 36%) (16). In elderly patients with a history of "low-energy" injury mechanisms (fall from standing or seated height), the proportion of C2 fractures is even higher (as much as 80%) (12). Odontoid fractures are by far the most common fractures of cervical vertebra C2. Fractures of the dens account for two-thirds of all C2 fractures in the elderly and are evenly distributed between “high” odontoid fractures (Anderson-D’Alonzo fracture type II) and “low” odontoid fractures (Anderson-D’Alonzo fracture type III) (24) (Fig 4). Anderson-D’Alonzo type I odontoid fractures are extremely rare in elderly patients. Traumatic spondylolisthesis (hangman fractures) and vertebral body fractures, including hyperextension teardrop fractures (Fig 5), are also less commonly seen. Lower Cervical Spine (C3 through C7) Because of the morphologic similarities among the motion segments of cervical vertebrae C3 through C7, the fracture patterns are stereotypic. However, because of individual-specific degenerative conditions, including severity and in-segment degenerative transition physiology, there are differences in the distribution of fractures. The most frequently injured motion segment of the lower portion of the cervical spine is cervical vertebrae C5 and C6, for the elderly and young adults alike. The motion segment of C5 through C6 accounts for 20%–28% of the injuries among the elderly, compared with 40%-50% in younger adults (8,12,16). In comparison with the rate in the general population, cervicothoracic junction injuries are seen less frequently in the elderly (5%–10% vs 9%–18%)

Figure 3. Atlantoaxial injury in a 74-year-old man injured as an unrestrained passenger in motor vehicle accident. Lateral radiograph shows "low" (type II) odontoid fracture (short black arrow) and fracture through spinous process of cervical vertebra C2 (white arrow), as well as bilateral fracture through the posterior arch of atlas (long black arrows) caused by hyperextension mechanism. Note prevertebral soft-tissue swelling (arrowheads).

(16,25). In the elderly, adjacent-level injury patterns are frequent, and multilevel fractures are generally considered clinically unstable. Fractures of the lower portion of the cervical spine can be divided into (a) clinically stable and relatively unimportant fractures (including transverse or isolated spinous process fractures, laminar fractures, avulsion fractures, and anterior compression fractures) and (b) clinically unstable and severe fractures (including burst fractures, hyperflexion teardrop fractures, and hyperextension-dislocations, which either [a] involve the facet joints with fracture and/or distraction or [b] are complex fractures) (Fig 6). Fractures seen in elderly patients tend to be severe and clinically unstable types (55%–75% of the cases) and seem to be independent of the causative mechanism of trauma (ie, low- vs high-energy injury mechanism) (16).

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Thoracic and Lumbar Spine Particularly in the elderly patient, the cause of a compression fracture of a thoracic or lumbar vertebra can be uncertain, and the question of metastatic replacement of the vertebra, with subsequent collapse, versus osteopenic compression fracture is often raised. In particular, elderly patients with a compression fracture of a thoracic or lumbar vertebra may present without a history of substantial trauma. Besides comparison with remote radiographs (that are often not available), certain other features may be used as reliable predictors of a benign cause. If the

Spine Trauma in the Elderly

Figure 4. "Low" (type III) odontoid fracture in a 74-year-old woman injured in a fall from standing position. (a) Transverse CT scan shows "low" (type III) odontoid fracture with fracture line (arrowheads) crossing through superior portion of axis body caudad to the junction of base of dens and axis body. (b) Coronal and (c) sagittal CT reformations more clearly show orientation of fracture line (arrowheads) relative to (b) cervical vertebra C2 lateral mass articulations (arrows) and (c) vertebral body.

Figure 5. Hyperextension teardrop fracture of axis in a 69year-old woman injured as an unrestrained driver in motor vehicle accident. Lateral radiograph, obtained after placement of tongs, shows large triangular fragment (∗) comprising anterior inferior corner of axis avulsed by intact anterior longitudinal ligament during hyperextension.

the posterior vertebral body line (26). This line is normally mildly convex anteriorly. Nonvisualization or a posterior convexity of this line must raise the question of retropulsion of a fragment into the spinal canal. When there is concern that a fracture extends to the posterior longitudinal ligament or that retropulsion has resulted in a bony fragment in the canal, further evaluation becomes necessary, which is usually performed with CT (Fig 7). If there is a clinical suspicion of metastatic disease, further evaluation with bone scintigraphy or MR imaging may be useful. Bone scintigraphy may help to characterize other lesions, and MR imaging may help to define the morphologic structure of the fracture. Although in acute osteoporotic compression fractures, the vertebra may show signal intensity abnormality caused by bone marrow edema, there are certain distinctive features that imply a malignant cause, including complete replacement of the vertebral body by abnormal signal intensity, extension of abnormal signal intensity into the pedicle, epidural extension of abnormal signal intensity, and a paraspinal mass (27,28). Usually, bone marrow edema from an acute fracture resolves within 6 weeks, whereas changes caused by malignant disease persist or even progress.

patient has sustained trauma and the fracture has sharp margins, a benign cause is likely. Another radiographic feature that is a reliable predictor of a benign cause for a fracture is gas within the fracture or within the adjacent disk space. When conventional radiographs show that only the anterior column is involved in a compression fracture, no additional imaging studies are needed. Normally, the posterior edge of each vertebral body is noted as a vertical line, called

IMAGING TECHNIQUES TO EVALUATE SPINE INJURY IN ELDERLY PATIENTS
The optimal imaging strategy depends on the probability of injury in that individual. Indications for diagnostic imaging of elderly victims of spine trauma are widely agreed upon and include one or more of the following: (a) acute myelopathy or radiculopathy, (b) posterior midline tenderness, and (c) lack of a reliable clinical examination (inability to perform clinical examination because of preexisting or posttraumatic

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Figure 6. Hyperextension-dislocation of lower portion of cervical spine (cervical vertebra C6) and incomplete spinal cord injury in an 83-year-old woman injured as an unrestrained driver in high-speed motor vehicle accident. (a) Lateral radiograph shows severe degenerative changes, with skeletal hyperostosis and bridging anterior osteophytes. At C6 level, a broad lucent line represents fracture crossing osteopenic spine (arrowhead). (b) Sagittal CT reformation shows anterior widening of hyperextension fracture at C6 level (arrows). (c) Sagittal short inversion time inversion-recovery magnetic resonance (MR) image shows triangular area of abnormal high signal intensity (∗) at the C6 level, representing hyperextension injury and extensive soft-tissue swelling, with signal intensity alterations consistent with prevertebral hemorrhage (arrowheads). Figure 7. Back pain with no neurologic deficit in a 74-yearold man injured in a recent fall from flight of stairs. (a) Transverse CT scan obtained at level of lumbar vertebra L1 reveals two-column burst fracture with retropulsion of fragment of posterior vertebral cortex into spinal canal. Gas within vertebral body is suggestive of presence of Kümmel disease (posttraumatic osteonecrosis). (b) Sagittal CT reformation of thoracolumbar spine shows reduction of approximately 30% in vertebral height of L1.

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confusion or somnolence, intoxication, or distracting injury) (21). As in the general population, the role of imaging in acute spinal injuries in elderly patients is adjunctive to detection of clinical instability (9). Controversy exists, however, with regard to the optimal imaging modality in victims of blunt trauma who are suspected of having spine injury. The standard method for evaluating the spine in trauma is the conventional radiographic series, usually consisting of anterior, lateral, and odontoid views for the cervical spine and anterior and lateral views for the thoracic and lumbar spine. However, obtaining adequate views may be difficult in the acute trauma setting, particularly in elderly patients, and may lead to prolonged emergency department stays.

The results of a recent analysis revealed that 15%– 40% of cervical spine fractures in the elderly are overlooked in the initial survey, compared with 4% in patients younger than 65 years (11). Missed injuries were attributed to (a) difficulty in visualizing minimally displaced fractures in osteoporotic bone, (b) alterations in bone anatomic structures caused by spondylosis and spondylolisthesis, and (c) “satisfaction of search” because of the presence of multiple less important findings. Several authors have advocated CT “screening” for cervical spine fracture in high-risk patients, and such CT is now performed routinely at many trauma centers (15,25,29–31). The results of cost-effectiveness analysis demonstrate that CT of the cervical spine is cost-effective in patients undergoing head CT with a

greater than 4% probability of cervical spine fractures (32). Factors such as severe closed head injury, high-energy mechanism, and neurologic deficits have been associated with an increased risk of cervical spine fracture in the general population (25,30). In a recent study of a clinical prediction rule for cervical spine fracture applied to victims of blunt trauma aged 65 years and older, investigators identified predictors similar to those in the general adult population (30,33). However, because of the higher proportion of fractures from low-energy trauma, more fractures are missed with the prediction rule in the elderly than in the general adult population. To date, we are unaware of any validated clinical prediction rules to guide the selection of patients with blunt-force trauma for imaging of thoracolumbar spine injuries. However, it seems reasonable that the enunciated clinical prediction rules for cervical spine imaging may be extrapolated to the thoracic and lumbar spines, with inclusion of particular high-risk findings (eg, “lap-belt sign”) (34). CT is advocated for patients with a high probability of injury (30). Further, conventional radiographic evaluation alone may be inadequate in severely traumatized patients or for regions with incomplete radiologic assessment with conventional radiography (eg, cervicothoracic junction) (25,29). Senescent morphologic changes, such as spondylosis, skeletal hyperostosis, and paravertebral ligamentous ossification, may obscure radiographic signs of trauma on conventional radiographs. Therefore, in the elderly trauma patient with unremarkable radiographic findings, complaints about persistent pain in the posterior part of the neck, regardless of the injury mechanism, indicate that CT or MR imaging should be performed to exclude occult injuries of the cervical spine. The superiority of MR imaging in soft-tissue depiction makes it the diagnostic standard for evaluation of spinal cord injury. In addition, MR imaging shows prevertebral hemorrhage and traumatic disk and facet-joint abnormalities, as well as injury to the paravertebral ligaments, which may be subtle or even occult radiographically (35). In a manner analogous to young children, many more elderly individuals sustain acute neurologic compromise without acute conventional or CT imaging abnormalities, an adult variant of spinal cord injury without radiographic abnormality that is associated with acquired narrowing of the spinal canal and spondylosis (14,16,36). MR imaging is performed to evaluate the spinal cord and the musculoskeletal axis, particularly the posterior ligament complex. Further, epidural processes, such as hematomas, may be readily assessed and may guide surgical decompression. Spinal cord imaging is best performed with a T1-weighted MR sequence to evaluate the size of the cord and a T2-weighted MR sequence to evaluate areas of edema and hemorrhage within the cord. In addition, particularly in the assess-

ment of trauma patients, T2-weighted MR sequences with elimination of fat signal intensity (ie, either a T2weighted sequence with a chemical fat saturation pulse applied or a short inversion time inversion-recovery sequence) are a highly accurate method of evaluating ligamentous destabilizing injury (36). In conclusion, factors that may contribute to missed injuries in the elderly (a) include failure to identify elderly trauma patients at risk of injury and subsequent failure to obtain diagnostically adequate imaging studies, (b) difficulty in interpreting radiographic images of osteopenic and senescent anatomic structures, and (c) failure to appreciate the spectrum of injury among the elderly. The elderly are particularly prone to injuries at the atlantoaxial complex. Compared with younger patients, the elderly experience injuries in the lower portion of the cervical spine less often. When present, fractures are often severe and highly unstable and usually involve more than one level. Age, in and of itself, is not an indication for spine radiography. However, injuries to the spine, particularly fractures of the atlantoaxial complex, must be excluded in older patients with neck or back pain after even minor injury.

Spine Trauma in the Elderly

References
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13. Sterling DA, O’Connor JA, Bonadies J. Geriatric falls: injury severity is high and disproportionate to mechanism. J Trauma 2001; 50:116–119. 14. Spivak JM, Weiss MA, Cotler JM, Call M. Cervical spine injuries in patients 65 and older. Spine 1994; 19:2302–2306. 15. Hoffman JR, Wolfson AB, Todd K, Mower WR. Selective cervical spine radiography in blunt trauma: methodology of the National Emergency X-Radiography Utilization Study (NEXUS). Ann Emerg Med 1998; 32:461–469. 16. Daffner RH, Goldberg AL, Evans TC, Hanlon DP, Levy DB. Cervical vertebral injuries in the elderly: a 10-year study. Emerg Radiol 1998; 5:38–42. 17. Lomoschitz FM, Blackmore CC, Stadler A, Linau KF, Mann FA. Fractures of the atlantoaxial complex in the elderly: assessment of radiological spectrum of fractures and factors influencing imaging diagnosis. Rofo Fortschr Geb Rontgenstr Neuen Bildgeb Verfahr 2004; 176:222– 228. [German] 18. Brandser EA, El-Khoury GY. Thoracic and lumbar spine trauma. Radiol Clin North Am 1997; 35:533–557. 19. Bensch FV, Kiuru MJ, Koivikko MP, Koskinen SK. Spine fractures in falling accidents: analysis of multidetector CT findings. Eur Radiol 2004; 14:618–624. 20. Ritzel H, Amling M, Posl M, Hahn M, Delling G. The thickness of human vertebral cortical bone and its changes in aging and osteoporosis: a histomorphometric analysis of the complete spinal column from 37 autopsy specimens. J Bone Miner Res 1997; 12:89–95. 21. Ngo B, Hoffman JR, Mower WR. Cervical spine injury in the very elderly. Emerg Radiol 2000; 7:287–291. 22. Weller SJ, Malek AM, Rossitch E Jr. Cervical spine fractures in the elderly. Surg Neurol 1997; 47:274–280. 23. Leone A, Cerase A, Colosimo C, Lauro L, Puca A, Marano P. Occipital condylar fractures: a review. Radiology 2000; 216:635–644. 24. Anderson LD, D’Alonzo RT. Fractures of the odontoid process of the axis. J Bone Joint Surg Am 1974; 56:1663– 1674.

25. Hanson JA, Blackmore CC, Mann FA, Wilson AJ. Cervical spine injury: a clinical decision rule to identify high-risk patients for helical CT screening. AJR Am J Roentgenol 2000; 174:713–717. 26. Daffner RH, Deeb ZL, Rothfus WE. The posterior vertebral body line: importance in the detection of burst fractures. AJR Am J Roentgenol 1987; 148:93–96. 27. An HS, Andreshak TG, Nguyen C, et al. Can we distinguish between benign versus malignant compression fractures of the spine by magnetic resonance imaging? Spine 1995; 20: 1776–1782. 28. Jung HS, Jee WH, McCauley TR, Ha KY, Choi KH. Discrimination of metastatic from acute osteoporotic compression fractures with MR imaging. RadioGraphics 2003; 23: 179–187. 29. Nunez DB, Ahmad AA, Coin CG, et al. Clearing the cervical spine in multiple trauma victims: a time-effective protocol using helical computed tomography. Emerg Radiol 1994; 1: 273–278. 30. Blackmore CC, Emerson SS, Mann FA, Koepsell TD. Cervical spine imaging in patients with trauma: determination of fracture risk to optimize use. Radiology 1999; 211:759–765. 31. Stiell IG, Wells GA, Vandemheen KL, et al. The Canadian C-spine rule for radiography in alert and stable trauma patients. JAMA 2001; 286:1841–1848. 32. Blackmore CC, Zelman WN, Glick ND. Resource cost analysis of cervical spine trauma radiography. Radiology 2001; 220:581–587. 33. Bub LD, Blackmore CC, Mann FA, Lomoschitz FM. Cervical spine fractures in the elderly: a clinical prediction rule. Radiology (in press). 34. Mann FA, Cohen WA, Linnau KF, Hallam DK, Blackmore CC. Evidence-based approach to using CT in spinal trauma. Eur J Radiol 2003; 48:39–48. 35. Katzberg RW, Benedetti PF, Drake CM, et al. Acute cervical spine injuries: prospective MR imaging assessment at a level 1 trauma center. Radiology 1999; 213:203–212. 36. Cohen WA, Giauque AP, Hallam DK, Linnau KF, Mann FA. Evidence-based approach to use of MR imaging in acute spinal trauma. Eur J Radiol 2003; 48:49–60.

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Georges Y. El-Khoury, MD

Imaging of Thoracolumbar Spine Trauma1

More than 10.000 spinal cord injuries occur in the United States each year, and about one-third are complete, resulting in paraplegia or quadriplegia. These injuries are usually the result of motor vehicle accidents or falls from a height, and they often involve young individuals. The cost for treating spinal cord injuries in the United States is estimated to be around $2 billion annually. Because of the serious consequences of missing an unstable spinal fracture, the injured spine should ideally be “cleared” within the first few minutes after the patient is admitted to the emergency department (1). The introduction of the multi–detector row computed tomographic (CT) scanner into the emergency department has revolutionized imaging protocols for patients with multiple trauma, where time is of the essence. The advantages of multi–detector row CT include speed, increased coverage, isotropic imaging, and ease of image interpretation. Isotropic imaging provides uniform spatial resolution in all directions (x, y, and z), which allows the creation of two-dimensional multiplanar reformations in any arbitrary plane, as well as the creation of high-quality three-dimensional images. The results of a number of studies have shown that multi–detector row CT is superior to radiography in depicting fractures of the thoracolumbar spine and that multi–detector row CT can totally replace radiography in severely injured patients (1). Historically, injuries of the thoracic and lumbar spine have been lumped together. However, the anatomic structures and biomechanical properties of the different segments in the thoracic and lumbar spine vary markedly. On that basis, the thoracic and lumbar spine can be divided into three segments: (a) thoracic vertebrae T1 through T10, (b) thoracic vertebra T11 through lumbar vertebra L4, and (c) lumbar vertebra L5.

DISTINGUISHING FEATURES OF THE UPPER THORACIC SPINE (T1 THROUGH T10)
The upper portion of the thoracic spine is the largest segment of the spine and is where approximately 10%–20% of all spinal fractures occur. A distinguishing anatomic feature of the upper portion of the thoracic spine is the rib cage, which restricts motion and adds stiffness and stability to the spine (2). Some authors consider the rib cage as an integral part of the upper thoracic spine, calling it the fourth column, because of its capacity to absorb kinetic energy during accidents. These properties are lost after rib fractures or costovertebral fracture dislocations occur in the upper thoracic spine, and its inherent stability becomes questionable (2).

RSNA Categorical Course in Diagnostic Radiology: Emergency Radiology 2004; pp 159–167.
1From the Department of Radiology, University of Iowa Carver College of Medicine, University of Iowa Hospitals and Clinics, 200 Hawkins Dr, Iowa City, IA 52242 (e-mail: [email protected]).

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Another distinguishing feature of the upper portion of the thoracic spine relates to the considerable energy required to produce a fracture or fracture dislocations; therefore, the possibility of a noncontiguous spinal fracture should be kept in mind. The search for noncontiguous fractures requires imaging of the entire spine. Noncontiguous fractures are commonly underdiagnosed at conventional radiography. They are reported to occur in 5%–20% of the patients with spinal fractures (Fig 1). However, after the introduction of magnetic resonance (MR) imaging, it became obvious that both contiguous and noncontiguous injuries are much more common than previously thought. At MR imaging, bone bruises are counted as microtrabecular fractures; this creates problems for surgical planning because the importance of bone bruises is not yet settled. If only conservative therapy is considered, bone bruises have no clinical importance; however, if surgical stabilization is required, then it is not known whether bone bruises are a contraindication to instrumentation (3). Injuries of the upper portion of the thoracic spine are less common than those of the thoracolumbar junction, and they are more likely to cause neurologic deficits. Sixty-three percent of the patients with upper thoracic spine fractures present with a neurologic deficit, and the deficit is frequently complete (4). On the other hand, only 2% of the patients with lumbar spine injuries and 32% of the patients with cervical spine injuries have a complete neurologic deficit. Spinal cord damage in the upper thoracic spine is common because the ratio of the canal size to the cord size is small, and the blood supply to the midthoracic cord is tenuous (2).

El-Khoury

Figure 1. Noncontiguous thoracic spine fractures. Sagittal reformatted CT image shows two noncontiguous vertebral fractures at vertebrae T5 and T10 (arrows).

NORMAL ANATOMY AND MIMICS OF VERTEBRAL FRACTURES
Ribs articulate with vertebrae at two sites; each rib head articulates with two adjacent vertebrae at the intervertebral disk level, while the rib tubercle articulates with the transverse process at the costotransverse joint (5). In the upper thoracic spine, the facet joints are oriented in the coronal plane, providing marked resistance to anterior translation. The anteroposterior length of the vertebral bodies gradually increases from vertebrae T1 through T12, while the transverse diameter decreases from vertebrae T1 through T3 and then progressively increases from vertebrae T4 through T12. The height of the vertebral bodies is about 2–3 mm less anteriorly than posteriorly. In addition, some vertebral bodies show what it is known as physiologic wedging, which is most pronounced in the lower portion of the thoracic spine and is especially common in male patients. In the setting of trauma, physiologic wedging can be confused with compression fractures. The wedging ratio is measured by dividing the height of the anterior portion of the vertebral body by the height of the posterior por-

tion. Values of 0.80 in male patients and 0.87 in female patients at the level of vertebrae T8 through T12 are considered within normal limits (6) (Fig 2a). Another mimicker of vertebral fractures is Scheuermann disease, or adolescent kyphosis. In Scheuermann disease, an abnormality of the growth cartilage results in weakening of the vertebral endplates, formation of multiple Schmorl nodes, and narrowing of the intervertebral disks. Vertebral body growth in Scheuermann disease is impaired, causing anterior wedging that persists into adulthood. This deformity in adults may be easily confused with compression fractures (Fig 2b).

CLASSIFICATION OF UPPER THORACIC SPINE INJURIES
Fractures of the upper portion of the thoracic spine do not neatly fit into the Denis classification (7), which is intended for thoracolumbar junction injuries. Most injuries occur in flexion and axial loading because there is hardly any rotation in the upper thoracic spine (2). Bohlman (2) classified upper thoracic spine injuries

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Figure 2. (a) Physiologic wedging in a 21-year-old man who was in a motor vehicle accident. The anterior wedging in thoracic vertebra T12 was initially thought to represent a compression fracture. This sagittal reformatted CT image demonstrates no evidence of a fracture. (b) Scheuermann disease in a 42-year-old man admitted to the emergency department with history of a fall. Lateral radiograph of the thoracic spine shows Scheuermann disease resembling multiple fractures (arrows).

Thoracolumbar Spine Trauma

into five types: (a) wedge compression fracture, which is a common injury and is considered to be stable because of the support provided by the rib cage; (b) sagittal slice fracture dislocation is also a fairly common but unstable injury, the basic pattern in the sagittal slice injury consisting of anterior fracture dislocation with compression of the vertebral body below (Fig 3), and often this injury is associated with same-level facet joint fracture dislocations; (c) complete anterior dislocation, a rare but unstable injury; (d) posterior fracture dislocation, also known as lumberjack paraplegia, which accounts for about 3% of all upper thoracic spine fractures and is characterized by retrolisthesis of the upper segment; and (e) burst fractures, which are produced by severe axial loading. Spines that are fused as a result of ankylosing spondylitis, diffuse idiopathic skeletal hyperostosis, or severe degenerative disk disease with bridging osteophytes have a distinguishing injury pattern that is frequently associated with a neurologic deficit (Fig 4). The injury in this group is typically due to hyperextension and can be caused by relatively minor trauma. Two injury mechanisms are capable of producing a hyperextension fracture of the thoracic spine: (a) an anterior impact to the upper portion of the chest and neck, or (b) direct posterior impact to the thoracic spine. Fractures in this group always involve all three columns, and the spinal segments above and below the fracture act as long lever arms, rendering these injuries unstable (8). Conventional radiographs of hyperextension injury show disk space widening and retrolis-

thesis, which are hallmarks of this injury (Fig 4). During the subacute or chronic phase, these fractures are sometimes misdiagnosed as a neoplasm or infection, especially when the history of acute trauma is lacking. An entity that is often a source of confusion is known as delayed posttraumatic vertebral body collapse, or Kümmell disease. Patients are typically old or osteopenic or are receiving steroid therapy. Initially, they present with back pain; however, the initial radiographs and CT images are negative. A few days or weeks after the injury, the vertebral body collapses. Some evidence suggests avascular necrosis of the vertebral body as a mechanism for the delayed collapse. Radiographs and CT images obtained after the fracture develops show intradiskal and intravertebral vacuum phenomena. Disk herniation can occur in the upper portion of the thoracic spine following trauma, but compared to disk herniation in the cervical spine, it is rare. Posttraumatic disk herniations in the thoracic spine are usually associated with substantial neurologic deficit.

IMAGING
Although multi–detector row CT has been in use for about 6 years, radiography of the spine continues to be useful for “clearing” the upper thoracic spine in patients who are not severely injured. Upper thoracic spine fractures are difficult to detect on chest radiographs, and dedicated spine radiographs are recommended. Adequate lateral radiographs of the thoracic spine may be difficult to obtain in patients with

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Figure 3. Wide mediastinum and left-sided pleural effusion in a patient with sagittal slice fracture dislocation at the level of thoracic vertebrae T5 through T6. The patient presented with weakness in both lower extremities. (a) Supine anteroposterior radiograph of the chest shows a wide mediastinum (arrows) and left apical pleural capping (arrowheads). The nasogastric tube and trachea are in the midline. (b) Penetrated anteroposterior view of the thoracic spine shows the fractures in thoracic vertebrae T5 and T6 (arrow). (c) Midline sagittal T2-weighted MR image (2000/90 [repetition time msec/echo time msec]) shows the changes of a sagittal slice fracture dislocation. At the level of the injury, the cord is compressed. Figure 4. Paraplegia occurring after a motor vehicle accident in a patient known to have longstanding ankylosing spondylitis. (a) Lateral radiograph of the thoracic spine shows the fracture traversing the disk (arrow) in the midthoracic spine. The upper vertebral segment is displaced posteriorly. (b) Sagittal T2weighted MR image (2000/90) shows that all three columns are fractured, and the cord is compressed between the displaced fragments.

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multiple trauma because the shoulders are difficult to penetrate. A supine swimmer’s view of the upper thoracic spine is helpful in depicting the lower cervical and upper three thoracic vertebrae. For accurate counting, the C2 cervical vertebra should be included on the lateral supine swimmer’s view. However, when cervical vertebra C2 is not included, the sternal notch can be used as a landmark, and it is usually at the level of the T2 vertebral body. Lateral radiographs,

along with the anteroposterior view, are helpful in assessing the height of the vertebral bodies, disk spaces, endplates, and alignment of the spine. Of particular importance is the integrity of the posterior vertebral body line, which is normally concave anteriorly. The spinous processes are not depicted on the lateral view because the posterior ribs obscure them. Anteroposterior radiographs are helpful for the evaluation of the endplates, lateral vertebral body margins,

Thoracolumbar Spine Trauma
Figure 5. Paraspinal hematoma caused by a burst fracture of thoracic vertebra T8. (a) Anteroposterior radiograph of the thoracic spine reveals thickening of the paraspinal stripes (arrows) and collapse of the T8 vertebral body. (b) Coronal reformatted CT image shows the compressed T8 body and the thickened paraspinal stripes (arrows) to better advantage. (c) Sagittal reformatted CT image show a three-column burst fracture (arrows) with retropulsion of a posterior body fragment. The spinal canal at the level of the fracture is stenotic.

and pedicles. The posterior ribs, costovertebral joints, and costotransverse joints can also be depicted. The right paraspinal line should adhere closely to the vertebral column, and the left paraspinal line should follow the contour of the aorta from the aortic arch to the diaphragm, albeit just lateral to the lateral margins of the vertebral column (5). Thickening or focal bulging of the paraspinal lines is a good indication of a spinal fracture. The spinous processes in the thoracic spine normally project into the midline, and each spinous process tubercle (tip) extends slightly below the inferior endplate of its respective vertebral body. The double spinous process sign seen on the anteroposterior radiograph is a reliable indicator of a spinous process fracture. Because of the advantages mentioned previously, especially speed and increased coverage, multi–detector row CT has become an indispensable diagnostic tool in the emergency department. For the spine, multi–detector row CT is particularly helpful for depicting and assessing the severity of bone injuries. Sagittal reformations are particularly helpful in assessing the degree of retropulsion of bony fragments into the spinal canal (Fig 5). MR imaging is reserved for patients with a neurologic deficit (9) (Fig 3). In the acute phase, MR imaging is useful in looking for treatable causes of the neurologic deficit, such as bony fragments compressing the spinal cord, disk herniation, or epidural hematoma. The ability to depict cord edema and hemorrhage helps in predicting prognosis. Long segments of the cord in-

volved with edema or focal cord hemorrhage indicate worse prognosis (9). In the chronic phase, MR imaging can demonstrate the sequelae of cord injury, such as myelomalacia, syringomyelia, and cord atrophy. Ligamentous injuries can be indirectly inferred from conventional radiographs or CT images; however, MR imaging can directly show ligamentous disruption.

INDIRECT RADIOGRAPHIC SIGNS OF UPPER THORACIC SPINE INJURIES
Indirect radiographic signs of upper thoracic spine fractures have always been important because of the difficulty in diagnosing these fractures. These signs include mediastinal widening or paravertebral hematoma, pleural fluid, rib fractures and costovertebral dislocations, the double spinous process sign, and sternal fractures. Mediastinal widening and pleural fluid, which is usually blood, are also seen with traumatic aortic rupture. Mediastinal widening is seen in more than two-thirds of the patients with upper thoracic spine fractures above thoracic vertebra T5, and the question of differentiating a thoracic spine fracture from aortic rupture becomes a problem (10) (Fig 3). Because of the high mortality rate associated with aortic transection, it is recommended that an aortic injury should be ruled out first in patients with a wide mediastinum by using CT arteriography. In the meantime, the spine should be immobilized and protected

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Figure 6. Compression fracture of lumbar vertebra L1. (a) Axial CT image through the upper portion of vertebra L1 shows a fracture involving the anterior column. (b) Sagittal reformatted CT image shows compression of the superior endplate of vertebra L1.

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until it is cleared with CT (10). Spinal fractures are much more common than aortic ruptures, but occasionally the two injuries coexist. There are two types of sternal fractures, but only one type is associated with thoracic spinal injuries. A direct sternal fracture occurs when the force applied against the body of the sternum displaces it posterior to the manubrium. This occurs with car accidents in which sudden deceleration forces the anterior portion of the chest against the steering wheel. With the indirect sternal fracture, the excess energy from a fractured upper thoracic spine is transmitted through the ribs, displacing the manubrium posteriorly relative to the body of the sternum. Therefore a depressed, or posteriorly displaced, upper sternal segment indicates an indirect upper sternal fracture and should direct the attention to a fracture in the upper thoracic spine.

INSTABILITY
Criteria for instability in upper thoracic spine trauma are not well defined. However, most surgeons would surgically stabilize injuries associated with one or more of the following findings (2): (a) a fracture dislocation, (b) posttraumatic kyphosis greater than 40°, (c) indirect sternal fracture and associated rib fractures, and/or (d) costovertebral dislocations.

THORACOLUMBAR SPINE JUNCTION (T11 THROUGH L2) INJURIES
Fractures of the thoracolumbar junction are fairly common, accounting for about 40% of all spinal fractures. Fractures of the thoracolumbar junction are common because this is where the rigid upper thoracic spine transitions to the more freely mobile

lumbar spine. The majority of fractures occur between thoracic vertebra T11 and lumbar vertebra L2, while injuries below vertebra L2 are rare. In 1983, Denis proposed the three-column concept (7). The anterior column consists of the anterior longitudinal ligament and the anterior two-thirds of the vertebral body and disk. The middle column consists of the posterior third of the vertebral body, the posterior third of the disk, and posterior longitudinal ligament. The posterior column consists of the pedicles, laminae, facet joints, and the posterior ligamentous structures (facet joint capsules, ligamentum flavum, and interspinous and supraspinous ligaments). The reason for the enduring acceptance of the three-column concept lies in its simplicity and ability to provide a rationale for assessing fracture instability. The middle column is considered pivotal in maintaining spinal stability. The injured spine is unable to support physiologic loads when the anterior and middle or all three columns are compromised. The treatment of thoracolumbar fractures is still controversial. However, it is accepted that confirmed unstable injuries are treated with early fusion and instrumentation. On the basis of the three-column concept, Denis (7) described four basic types, each with subtypes, of thoracolumbar fractures. These types are compression fractures, burst fractures, flexion-distraction injuries (Chance fractures), and fracture dislocations (7).

COMPRESSION FRACTURE
A compression fracture is the most common type of fracture involving the thoracolumbar junction, and it accounts for about half of all of these fractures. Motor

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vehicle accidents and falls from a height are responsible for most compression fractures. Compression fracture represents failure of the anterior column while the middle column remains intact (Fig 6). The posterior column may remain intact, or it may fail in tension, depending on the magnitude of the force acting on the spine during the injury. The injury results from an axial load acting on a flexed spine. On the lateral view, a compression fracture typically involves the superior endplate of the vertebral body producing wedging of the vertebral body and disruption of the anterior cortex just inferior to the superior endplate. Minor compressions may be missed on axial CT sections, and sagittal reconstructions are always helpful in depicting these injuries. Initial imaging is performed with radiography and CT to rule out a potentially unstable burst fracture (Fig 6). Interruption of the posterior body line or retropulsion of a bony fragment on the lateral view should suggest a burst fracture. Widening of the interpediculate distance on the anteroposterior view is also a good sign of a burst fracture.

FLEXION-DISTRACTION INJURY (CHANCE FRACTURE)
The flexion-distraction injury accounts for about 5% of all major spinal injuries. It is produced by a hyperflexion force with the axis of rotation centered anterior to the middle column (12). The posterior and middle columns fail in tension, while the anterior column can fail in either tension or compression, depending on whether the axis of rotation is at or anterior to the anterior column. If only the bony elements of a single vertebra are involved, the injury is believed to represent the classic Chance fracture. Often, however, the injury involves both ligamentous and bony structures or could even extend to an adjacent vertebra. These are referred to as the Smith fractures. The Chance fracture horizontally splits the spinous process, laminae, and pedicles and extends into the posterior aspect of a single vertebral body (Fig 7); the anterior portion of the vertebral body may show mild compression. Radiographs frequently show the fracture lines in the spinous process, laminae, pedicles, and posterior body. On the lateral view, there is increased height of the posterior aspect of the involved vertebral body. Because the fracture runs in the axial plane, axial CT sections may not adequately demonstrate these fractures. The “disappearing laminae” sign on axial sections should tip off the observer to the presence of a Chance fracture. When the injury is purely ligamentous, the supraspinous and interspinous ligaments are disrupted, along with dislocation of the facet joints and disruption of the posterior longitudinal ligament and posterior portion of the disk. A high rate of intraabdominal injuries (45%) is associated with flexion-distraction injuries. Neurologic deficit is seen in as many as 15% of the patients with these injuries (12).

Thoracolumbar Spine Trauma

BURST FRACTURE
The burst fracture is a relatively common injury that makes up about 17% of all major spinal injuries. Nearly half of these fractures are associated with neurologic deficit. Burst fractures represent a failure of at least the anterior and middle columns, but many burst fractures also involve the posterior column. Most burst fractures are associated with retropulsion of a bony fragment, resulting in spinal canal stenosis. However, these injuries are often more serious than the initial images reveal. Burst fractures have been shown experimentally to represent a dynamic event in which the final position of the retropulsed fragment is not representative of the maximum canal stenosis occurring during the event. In fact, maximum stenosis and maximum cord compression occur at the moment of the impact (11). The lateral view shows disruption of the posterior vertebral body line and displacement of the retropulsed fragment into the spinal canal (Fig 5). In the majority of cases, the retropulsed fragment is situated at the posterior superior corner of the vertebral body, an area that is difficult to see on radiographs because of the overlying pedicles. The anteroposterior view may show the vertical fracture line through the lamina and a subtle increase in the interpediculate distance. Currently, CT images with sagittal reformations are routinely obtained for the evaluation of burst fractures (Fig 5); patients with neurologic deficit require MR imaging. Signs of burst fracture instability include a 50% or greater loss in vertebral body height, posterior column injury, progressive kyphosis, and progressive neurologic deficit.

FRACTURE DISLOCATION
Fracture dislocation is a fairly common injury, accounting for about 20% of all major spinal injuries, and has a high incidence of associated neurologic deficit (75%). Mechanisms implicated in producing a fracture dislocation include flexion-rotation, flexion-distraction, and shear forces. A fracture dislocation injury is characterized by displacement of one vertebral body with respect to an adjacent vertebral body, and therefore, any horizontal translation or rotation at the level of the injury should raise the suspicion of a fracture dislocation (Fig 8). All three columns fail, which results in an unstable injury. Radiographs demonstrate malalignment of the vertebral bodies and spinous processes at the affected level (Fig 8). Facet dislocation occurs with severe cases. Axial CT sections demonstrate (a) the malalignment of the vertebral bodies, which manifests as the

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Figure 7. Flexion-distraction (Chance) fracture. (a) Anteroposterior radiograph demonstrates the fracture traversing the vertebral body and pedicles (arrowheads). (b) Lateral radiograph from another patient shows a similar fracture (arrowheads).

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Figure 8. Fracture dislocation at the level of thoracic vertebrae T11 through T12 in a patient who presented with a complete neurologic deficit below vertebra T11. (a) Lateral radiograph of the thoracolumbar junction shows considerable anterior translation of vertebra T11 on vertebra T12. The T12 body is compressed. (b) Sagittal T2-weighted MR image (2000/90) shows the fracture dislocation, the cord hemorrhage (hypointense area), and cord edema (hyperintense area) at the conus. Also seen is the spinal stenosis at the site of the injury and a small extradural hematoma underneath the posterior longitudinal ligament. At the level of the injury, the ligamentum flavum, interspinous ligament, and supraspinous ligament are all disrupted.

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“double rim” sign, or (b) the dislocated facets, which are recognized by the presence of the “naked facets.” Sagittal, coronal, and three-dimensional reformations are now routinely obtained for thorough evaluation of fracture dislocation anywhere in the spine.

L5 VERTEBRAL FRACTURE
Fractures of lumbar vertebra L5 are rare and often have unique imaging features. The L5 vertebra is securely seated between the iliac wings and the sacrum,

and a common mechanism of injury is a high-energy axial load. Four injury patterns have been described: (a) compression fracture, (b) burst fracture, (c) fracture dislocation with facet “lock,” and (d) L5 vertebral fracture associated with a complex pelvic fracture, especially those that vertically split the sacrum. The latter two types of injury patterns are unstable and are frequently associated with neurologic deficit.

TRAUMATIC EPIDURAL HEMATOMA
Epidural hematomas were believed to be a rare complication of spinal fractures. They are reported to occur in 0.5%–7.5% of spinal fractures. MR imaging is the imaging technique of choice for detecting epidural blood collections (Fig 8b). Epidural hematomas typically originate from the epidural venous plexus and, therefore, are low-pressure collections. They were thought to represent a serious complication, causing cord compression and requiring emergent evacuation. The thinking is gradually changing, and epidural hematomas are now believed to run a fairly benign course, and they rarely require evacuation, especially in the lumbar spine.

References
1. Wintermark M, Mouhsine E, Theumann N, et al. Thoracolumbar spine fractures in patients who have sustained severe trauma: depiction with multi–detector row CT. Radiology 2003; 227:681–689.

2. Bohlman HH. Treatment of fractures and dislocations of the thoracic and lumbar spine. J Bone Joint Surg Am 1985; 67:165–169. 3. Qaiyum M, Tyrrell PN, McCall IW, Cassar-Pullicino VN. MRI detection of unsuspected vertebral injury in acute spinal trauma: incidence and significance. Skeletal Radiol 2001; 30:299–304. 4. Rogers LF, Thayer C, Weinberg PE, Kim KS. Acute injuries of the upper thoracic spine associated with paraplegia. AJR Am J Roentgenol 1980; 134:67–73. 5. El-Khoury GY, Whitten CG. Trauma to the upper thoracic spine: anatomy, biomechanics, and unique imaging features. AJR Am J Roentgenol 1993; 160:95–102. 6. Lauridsen KN, De Carvalho A, Andersen AH. Degree of vertebral wedging of the dorso-lumbar spine. Acta Radiol Diagn (Stockh) 1984; 25:29–32. 7. Denis F. The three column spine and its significance in the classification of acute thoracolumbar spinal injuries. Spine 1983; 8:817–831. 8. Weinstein PR, Karpman RR, Gall EP, et al. Spinal cord injury, spinal fracture, and spinal stenosis in ankylosing spondylitis. J Neurosurg 1982; 57:609–616. 9. Castillo M. Current use of MR imaging in spinal trauma. Emerg Radiol 1999; 6:121–123. 10. Bolesta MJ, Bohlman HH. Mediastinal widening associated with fractures of the upper thoracic spine. J Bone Joint Surg Am 1991; 73:447–450. 11. Wilcox RK, Boerger TO, Allen DJ, et al. A dynamic study of thoracolumbar burst fractures. J Bone Joint Surg Am 2003; 85:2184–2189. 12. Vaccaro AR, Kim DH, Brodke DS, et al. Diagnosis and management of thoracolumbar spine fractures. J Bone Joint Surg Am 2003; 85:2456–2470.

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NOTES

Diego Jaramillo, MD, MPH

Imaging of Upper Extremity Injuries in Children1

The upper extremity is the most common site of fractures in children. Several changing anatomic features predispose to these injuries. The junction between the dense lamellar bone of the diaphysis and the more porous bone of the metaphysis is a site of weakness, particularly in the distal portion of the radius. This weak transition is the site of most of the distal radial fractures. In the distal part of the humerus, the thin plate between the olecranon fossa and the coronoid fossa constitutes the origin of the supracondylar fractures. Finally, the transition from cartilage to bone results in increased susceptibility to injury. Epiphyseal separations in the distal humerus and proximal radius occur where the metaphyseal bone meets the physeal cartilage at the zone of provisional calcification. Salter-Harris–type fractures of several physes, particularly those of the proximal and distal humerus and proximal and distal radius, also arise in this region, although usually in older patients (1). Although it is likely that the activities in which children get involved are the main factors predisposing to extremity injury, recent evidence shows that decreased bone density may be a contributing factor in some pediatric fractures. In fact, in children, there is a dose-dependent association between wrist and forearm fractures and viewing television, the computer, and video games, presumably because of decreased bone density caused by inactivity, whereas light exercise is protective (2).

TECHNICAL CONSIDERATIONS
Radiographs of the elbow should include an anteroposterior radiograph in extension and a lateral radiograph obtained in 90° of flexion. An appropriate study can be performed only if the shoulder and elbow are at the same level and if the thumb is pointing toward the ceiling. A radiograph obtained in extension can make the posterior fat pad bulge out of the olecranon fossa and therefore can simulate an effusion (3). When confronted with findings on the radiographs that are suspicious for but not diagnostic of a fracture, bilateral shallow oblique radiographs can help in making the diagnosis. Comparison with contralateral radiographs can sometimes be useful, particularly when the diagnostic problem relates to whether a finding is a normal variant of ossification or a fracture. However, contralateral radiographs should be used sparingly because usually they are an unnecessary source of radiation. Ultrasonography (US) of the elbow can depict unossified structures with exquisite detail (Fig 1). US can also be useful (a) when the question is whether there is continuity

RSNA Categorical Course in Diagnostic Radiology: Emergency Radiology 2004; pp 169–174.
1From the Department of Radiology, Children’s Hospital of Philadelphia, 34th St and Civic Center Blvd, Philadelphia, PA 19104 (e-mail: [email protected]).

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Figure 1. Coronal US image of distal humeral epiphysis in a 1-year-old child suspected of having a dislocation of the elbow. Articular relationships between olecranon (o) and trochlea (t) are normal. There is early ossification of capitellum (c).

between the unossified epiphysis and metaphysis (such as would occur with a Salter-Harris fracture of the distal humerus in an infant), (b) when there is a question of dislocation of unossified structures, and (c) when it is important to detect whether the unossified epiphysis has been injured (4,5). Magnetic resonance (MR) imaging is useful for the evaluation of subtle injuries to unossified structures. This is true of the evaluation of sporadic cases of lateral condylar fractures, in which MR imaging can establish whether there is extension into the unossified epiphysis, or in avulsions of the medial epicondyle. MR imaging is also useful for the evaluation of injuries involving primarily ligamentous or muscular structures. In older children, as in adults, the evaluation of sequelae of anterior dislocation of the shoulder and the evaluation of wrist pathologic abnormalities of the triangular fibrocartilage complex and the carpal ligaments are done primarily with MR imaging. Computed tomography (CT) can help in the evaluation of subtle injuries. CT can also be used to depict the relationship between fracture fragments in cases of severely comminuted or complex displaced fractures.

Figure 2. Epiphyseal separation in a 6-month-old male infant who had suffered from child abuse. Radiograph shows that physis of proximal humerus (arrow) is wide, and humeral epiphysis is displaced medially with respect to shaft. There is periosteal calcification in this infant, who had an inflicted subperiosteal hemorrhage.

DEVELOPMENTAL PITFALLS THAT CAN RESEMBLE INJURIES
Most developmental pitfalls in the upper extremity are found in the elbow. The sequence of appearance of the multiple ossification centers of the elbow is as follows: capitellum, 0–2 years; radial head, 4–5 years; medial, or internal, epicondyle, 6–7 years; trochlea, 8–10 years; olecranon, 10 years; and lateral, or external, epicondyle, 11 years. This sequence can be summarized by the initials CRITOE, with “IT” being the

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most important; if the trochlea is present, the medial epicondyle should be visible. If the trochlea is not present, an avulsion of the medial epicondyle into the joint should be presumed. The fusion of the ossification centers follows a different sequence, with the capitellum, trochlea, and external epicondyle fusing together prior to becoming fused with the humeral metaphysis. The trochlea mineralizes in a fragmented fashion, with multiple ossification centers ultimately coalescing to form the trochlear epiphysis. The lateral and medial epicondyles are often slightly separated from the distal humeral metaphysis and can resemble an apophyseal separation (6). In the wrist, the scapholunate interval measured radiographically is wider in children than in adults. This spurious separation is due to the relatively late ossification of the lower pole of the scaphoid; on MR images, the scaphoid and lunate are never separated, regardless of age (7). On MR images, the preossification center (the hypertrophic changes developing in the unossified epiphysis prior to ossification) can result in a focal area of increased signal intensity on T2-weighted images (8). This is an issue particularly in the trochlea, where the ossification center is always fragmented, and initially only small fragments may be seen radiographically. It is also important to note that the

useful diagnostic modality. It is important to recognize that in younger children and adolescents, the glenoid may not be fully ossified, such that there is a band of high-signal-intensity cartilage between the low signal intensity of the glenoid fibrocartilage and the bony glenoid.

Upper Extremity Injuries in Children

ELBOW INJURIES
Most fractures of the elbow result from hyperextension-rotation with valgus or varus stress. The mechanism of injury separates elbow fractures into three main groups and explains the findings associated with some of these injuries: (a) Hyperextension with vertical stress results in supracondylar fractures, longitudinal linear ulnar fractures, and buckle fractures; (b) hyperextension with valgus stress results in impaction fractions of the radial head and neck, transverse olecranon fractures, and medial epicondylar fractures; and (c) varus stress produces Monteggia fractures, lateral condylar avulsion fractures, transverse olecranon fractures, and longitudinal linear ulnar fractures (10). Supracondylar fractures account for nearly 60% of the elbow injuries in children (11). When subtle, supracondylar injuries constitute a diagnostic challenge. The fracture occurs through an area of weakness in the metaphysis of the distal humerus, where the olecranon and coronoid fossae are separated by a thin, often porous bony plate. Almost invariably, the distal fragment is displaced posteriorly. Radiographic diagnosis of subtle supracondylar fractures is based on (a) the detection of an elbow effusion and (b) signs of posterior displacement of the distal fragment. The diagnosis of an elbow fracture is established by elevation of the anterior fat pad or by posterior displacement of the normally invisible posterior fat pad, which renders it detectable on the lateral radiograph. When the distal humerus is posteriorly displaced, a line through the anterior cortex of the humerus (the anterior humeral line) intersects the anterior third of the capitellum instead of bisecting the capitellum. The second most important injury, the lateral condylar fracture, accounts for 15% of pediatric elbow injuries. This fracture results from a varus stress on the elbow, and the fracture line extends from the most distal lateral humeral metaphysis, across the growth plate, and into the epiphyseal cartilage. In some cases, the fracture involves the articular surface, in which case the fracture is unstable. Otherwise, the fracture can stop in the epiphyseal cartilage. The diagnosis is difficult when only a small sliver of metaphyseal bone is separated from the parent bone; in this case, oblique radiographs can show the fragment to better advantage. MR imaging can be useful to determine whether the fracture involves the articular surface (Fig 3).

Figure 3. Lateral condylar fracture in a 4-year-old boy. Coronal fat-suppressed fast spin-echo T2-weighted MR image of distal humerus shows fracture extending along low-signal-intensity distal humeral epiphysis. Fracture stops before articular surface (arrow).

insertions of the flexor and pronator tendons often show high signal intensity on gradient-recalled echo MR images (9).

SHOULDER INJURIES
Physeal fractures and chronic physeal injuries of the proximal humerus are the most common injuries during childhood, whereas dislocations with glenoid labral injuries become more frequent in adolescence. In older children, physeal fractures do not constitute a diagnostic challenge and can be evaluated with radiographs. In infants and younger children, however, discontinuity between the proximal humeral metaphysis and the proximal ossification center can be subtle. With proximal epiphyseal injuries, the ossification center is usually displaced medially with respect to the shaft, and the physis appears unusually wide (Fig 2). This can be seen in the context of child abuse. It is important to recognize that in the absence of acute trauma, physeal widening can result from repeated physeal stress. This occurs most frequently with baseball players. Fractures of the humeral shaft can often be greatly displaced, but most such fractures remodel extremely well, regardless of the initial fragment separation. Disruptions of the glenoid labrum result from anterior dislocations. They are best evaluated with MR arthrography, but axial nonenhanced arthrography is a

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Jaramillo
Figure 4. Valgus injury of elbow in a 9-year-old boy. Frontal radiograph shows avulsion of medial epicondyle.

Figure 5. Monteggia fracture resulting in subtle dislocation in a 9-year-old boy. Radiocapitellar line is discontinuous because radial head is anteriorly dislocated with respect to capitellum.

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Other fractures of the elbow include epiphyseal separations of the distal humerus or the proximal radius. These lesions usually occur in infants or young children and are sometimes seen in the context of child abuse. Another important elbow injury is the avulsion of the medial epicondyle that occurs because of the forceful contraction of the pronators and flexors inserting on it (Fig 4). A separation greater than 5 mm indicates the need for surgery. At times, the distal fragment can be pulled into the joint, and the diagnosis can be difficult. Fractures that are not readily apparent generally are found to be supracondylar fractures or lateral condylar fractures. Fractures of the radial head, a common source of adult occult injuries, are extremely rare in children. A proximal elbow injury in a child is usually a Salter-Harris type 2 fracture of the radial neck. Elbow dislocations occur primarily as part of the complex of Monteggia injuries, in which an anterior dislocation of the proximal radius is associated with a middiaphyseal ulnar fracture (Fig 5). The isolated anterior dislocation of the radial head that occurs with hyperextension and rotation (nursemaid elbow) is usually reduced during the flexion and external rotation required for radiographic positioning, and hence this entity usually has a normal radiographic appearance. A line extending along the radial shaft proximal

to the radial tubercle should intersect the capitellum in every projection regardless of obliquity. Disruption of this radiocapitellar line is useful in diagnosing unsuspected anterior radial head dislocations. Imaging evaluation of elbow injuries relies primarily on anteroposterior and lateral radiographs. Additional imaging can include oblique radiographs. Controversy exists regarding the predictive value of elbow effusions in the context of trauma. Donnelly et al (12) have suggested that an elbow effusion is only seen in 17% of all elbow injuries, but if the effusion is persistent, a fracture is much more likely. On the basis of comparison with MR images, Major and Crawford (13) suggested that elbow effusions in children are associated with fractures in more than half of the cases. Our own experience with multi–detector row CT suggests that occult fractures are indeed prevalent in children with elbow effusions (unpublished data) (Fig 6). Comparison with the contralateral side is rarely helpful but may assist in the differentiation between a fracture and a normal developmental variant. CT helps in cases of subtle injuries or in severely displaced injuries by showing the separation of the fragments. US can be used for the evaluation of epiphyseal separations. MR imaging can assist in the determination of the extent of the cartilaginous injuries, as in some nondisplaced lateral condylar injuries (14,15).

Upper Extremity Injuries in Children
Figure 6. Images in a 5-year-old boy who was unable to move his elbow after falling on outstretched hand. (a) Lateral radiograph shows fat pads anteriorly (arrowhead) and posteriorly (arrows). (b) Sagittal reconstruction of elbow shows that anterior (arrowhead) and posterior (arrows) fat pads are displaced by elbow effusion. (c) Sagittal reconstruction at another level shows that there is subtle fracture (arrow) of anterior distal humeral metaphysis adjacent to capitellum, an occult Salter-Harris type 2 injury. An apparent fragment anterior to ulna corresponds to partial section of radial head.

FOREARM AND WRIST INJURIES
The radius and ulna are the most commonly fractured bones in childhood, accounting for 36% of all fractures before skeletal maturity (16). Fractures in the forearm usually involve both the radius and ulna. If only one bone is obviously fractured, it is important to search for subtle injury in the contralateral bone. For example, an ulnar fracture can be associated with a bowing (plastic) fracture of the radius. An ulnar fracture can also be associated with a subtle anterior dislocation of the proximal radius (Monteggia fracture). Conversely, an isolated fracture of the radius may be associated with a bowing fracture of the ulna or with a subtle distal ulnar dislocation (Galeazzi fracture). Monteggia injuries are

much more common in children than are Galeazzi fractures. Most injuries in the region of the wrist are buckle fractures of the distal radius. The fractures usually buckle one cortex, resulting in dorsal or volar angulation with minimal displacement. These fractures can be subtle, particularly on the frontal view. On the lateral radiograph, the fractures can be easily detected as an abrupt curvature in the metaphyseal cortex. Dorsal injuries occur more commonly than ventral ones. When the buckling of the cortex occurs circumferentially, the fracture is termed a torus fracture because it resembles the base (torus) of a column. Metaphyseal buckle fractures have little clinical importance and require no imaging beyond radiography. Displacement of the pronator quadratus fat pad can be a useful indirect sign of a distal forearm fracture. The distal radial physis is the site of 60% of all Salter-Harris–type fractures. Most injuries are type 1 and 2 fractures, and they seldom result in growth disturbance. The infrequent posttraumatic bony bridges usually occur in the central portion of the distal radial physis. This is in contrast to the bony bridges found in dyschondrosteosis (the genetic mesomelic dysplasia that accounts for most cases of Madelung deformity), in which the bony bridge is on the ulnar side of the physis. Repeated injury to the distal radial growth plate results in progressive widening and irregularity of the distal femoral physis that can resemble an acute

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fracture. This is most commonly seen in gymnasts and results in shortening of the radius. Injuries to the triangular fibrocartilage complex and the carpal bones and ligaments are common in adolescents, but the injuries are usually no different than those seen in adults. Fractures of the ulnar styloid process occur commonly in association with radius injuries but almost never as isolated injuries. For this reason, when a styloid process fracture is identified, a distal radial fracture should be sought (17).

References
1. Peterson HA. Physeal fractures of the elbow. In: Morrey BF, ed. The elbow and its disorders. 2nd ed. Philadelphia, Pa: Saunders, 1993; 248–265. 2. Ma D, Jones G. Television, computer, and video viewing; physical activity; and upper limb fracture risk in children: a population-based case control study. J Bone Miner Res 2003; 18:1970–1977. 3. Murphy WA, Siegel MJ. Elbow fat pads with new signs and extended differential diagnosis. Radiology 1977; 124:659– 665. 4. Davidson RS, Markowitz RI, Dormans J, Drummond DS. Ultrasonographic evaluation of the elbow in infants and young children after suspected trauma. J Bone Joint Surg Am 1994; 76:1804–1813. 5. Graif M, Stahl-Kent V, Ben-Ami T, Strauss S, Amit Y, Itzchak Y. Sonographic detection of occult bone fractures. Pediatr Radiol 1988; 18:383–385. 6. Silberstein MJ, Brodeur AE, Graviss ER, Luisiri A. Some vagaries of the medial epicondyle. J Bone Joint Surg Am 1981; 63:524–528. 7. Kaawach W, Ecklund K, Di Canzio J, Zurakowski D, Waters PM. Normal ranges of scapholunate distance in children 6 to 14 years old. J Pediatr Orthop 2001; 21:464–467. 8. Jaramillo D, Waters PM. MR imaging of the normal developmental anatomy of the elbow. Magn Reson Imaging Clin N Am 1997; 5:501–513. 9. Sugimoto H, Ohsawa T. Ulnar collateral ligament in the growing elbow: MR imaging of normal development and throwing injuries. Radiology 1994; 192:417–422. 10. John SD, Wherry K, Swischuk LE, Phillips WA. Improving detection of pediatric elbow fractures by understanding their mechanics. RadioGraphics 1996; 16:1443–1460; quiz 1463–1464. 11. Houshian S, Mehdi B, Larsen MS. The epidemiology of elbow fracture in children: analysis of 355 fractures, with special reference to supracondylar humerus fractures. J Orthop Sci 2001; 6:312–315. 12. Donnelly LF, Klostermeier TT, Klosterman LA. Traumatic elbow effusions in pediatric patients: are occult fractures the rule? AJR Am J Roentgenol 1998; 171:243–245. 13. Major NM, Crawford ST. Elbow effusions in trauma in adults and children: is there an occult fracture? AJR Am J Roentgenol 2002; 178:413–418. 14. Beltran J, Rosenberg ZS, Kawelblum M, Montes L, Bergman AG, Strongwater A. Pediatric elbow fractures: MRI evaluation. Skeletal Radiol 1994; 23:277–281. 15. Beltran J, Rosenberg ZS. MR imaging of pediatric elbow fractures. Magn Reson Imaging Clin N Am 1997; 5:567– 578. 16. Lyons RA, Delahunty AM, Kraus D, et al. Children’s fractures: a population based study. Inj Prev 1999; 5:129–132. 17. Stansberry SD, Swischuk LE, Swischuk JL, Midgett TA. Significance of ulnar styloid fractures in childhood. Pediatr Emerg Care 1990; 6:99–103. 18. Nimkin K, Spevak MR, Kleinman PK. Fractures of the hands and feet in child abuse: imaging and pathologic features. Radiology 1997; 203:233–236.

Jaramillo

HAND INJURIES
In infants, fractures of the hands are often seen in the context of child abuse. These injuries are best detected in the oblique projection and are primarily dorsal buckle fractures of the bases of the proximal phalanges (18). Older children can have similar injuries as the result of hyperextension of the fingers, often occurring during basketball or volleyball. The phalanges are also common sites of physeal injuries. These fractures are truly metaphyseal, rather than physeal, because typically a small sliver of bone can be seen adjacent to the physis. Volar plate injuries in children are less common than in adults, with a small sliver of bone being detached from the base of the middle phalanx. At the base of the thumb, a Salter-Harris type 2 injury of the physis in the proximal metacarpal is the counterpart of the Bennett fracture seen in adults. Injuries to the first metacarpophalangeal joint (the gamekeeper or skier thumb) are identical to those of the adult. In general, radiographs are sufficient to diagnose and define hand injuries. In the young, the evaluation of unossified epiphyseal separations of the phalanges can be subtle and may require MR imaging. In conclusion, imaging of injuries of the upper extremity in children is challenging because of multiple developmental variations that can simulate disease and because the patterns of injury are unique. Fractures involving the cartilaginous structures may be subtle on radiographs. Comparison radiography and US are used more frequently than in adults. MR imaging and CT can be extremely useful in certain injuries, but the roles of these modalities have not yet been fully determined.

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Thurman Gillespy III, MD

High-Energy Blunt-Force Injuries to the Upper Extremity1
UPPER EXTREMITY IMAGING IN THE SEVERELY INJURED PATIENT
Radiologic examination of the upper extremity in the severely injured patient begins, oddly enough, with the initial trauma chest radiograph. The radiograph should be carefully examined for injury to the clavicles and shoulders, in addition to the traditional evaluation of the heart, mediastinum, lungs, and ribs. Fractures of the clavicle, sternoclavicular Figure 1. Upper extremity injury on trauma chest radiograph. dislocation, acromioclavicular The left shoulder is dislocated anteriorly (arrow). separation, fractures of the scapula and shoulder joint, glenohumeral dislocation, and scapulothoracic dissociation are all injuries that can be diagnosed or suspected from the findings on the trauma chest radiograph. At Harborview Medical Center, we performed an internal quality assurance review of findings on the trauma chest radiograph that were missed by residents and fellows. We found that fractures of the clavicle and glenohumeral dislocation were by far the most frequently missed findings (Fig 1), which confirms the importance of examining the upper extremity on this study. Conventional radiographs of the upper extremity are obtained after the initial clinical examination. They are frequently suboptimal because of the injuries to the patient, and additional views are often obtained to further evaluate the region in question. If the condition of the patient is clinically stable, computed tomography (CT) of the upper extremity is used to assist the orthopedic surgeon in planning for fracture management and to clarify confusing or complex injuries. If a dislocation is present, CT is usually performed after closed reduction. Sagittal and coronal

RSNA Categorical Course in Diagnostic Radiology: Emergency Radiology 2004; pp 175–186.
1From the Department of Radiology, University of Washington, Harborview Medical Center, Box 359728, 325 Ninth Ave, Seattle, WA 98104-2499.

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Figure 2. Sternoclavicular dislocation. (a) Trauma chest radiograph shows widening of right superior mediastinum (arrowheads), consistent with mediastinal hematoma. (b) Axial CT image of chest shows widening of right sternoclavicular joint (arrow) and inferior displacement of right proximal clavicle. Small sliver of bone (arrowhead) at proximal right clavicle is proximal clavicle epiphysis. (c) CT angiogram shows hematoma in superior mediastinum (arrows). Filling defect in right brachiocephalic artery (arrowhead) indicates vascular injury. (d) Axial CT image of chest shows abnormal air collection (arrow) adjacent to trachea, which suggests tracheal laceration. (e) Angiogram shows dissection of right brachiocephalic artery (arrows).

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reformations are often helpful in demonstrating fracture fragment relationships. Three-dimensional reformations can be used for further clarification, but they are not a routine part of our practice. Magnetic resonance (MR) imaging is excellent in delineating soft-tissue structures, especially tendons and ligaments of the joint, but emergency MR imaging is usually reserved for the brain and spine. We seldom use MR for upper extremity imaging in the

severely injured patient because most displaced fractures require open reduction and internal fixation, where the joint in question can be directly inspected. Conventional angiography of the upper extremity is performed whenever the physical examination or a particular fracture pattern indicates that a vascular injury is likely. We do not use MR angiography for the evaluation of extremity trauma.

High-Energy Injuries to the Upper Extremity

Figure 3. Extraarticular scapula fracture. (a) AP view of shoulder shows that fracture through body of scapula (arrowhead) extends to neck of glenoid (arrow). (b) Scapula Y view shows scapula fracture (arrows) clearly. Glenoid is displaced anterior to body of scapula. (c) CT image of shoulder shows that fracture (arrowheads) does not involve glenohumeral joint.

BRACHIAL PLEXUS INJURY
Injury to the brachial plexus can cause devastating neurologic compromise to the upper extremity. The mechanism of injury includes direct trauma to the head and neck region (both blunt-force and penetrating injuries) and violent abduction of the neck and shoulder (often from motorcycle accidents). Clinical evaluation of the injury includes distinguishing between preganglionic injuries (which never heal) and postganglionic injury (which may heal). MR imaging of the neck and axilla is often used for staging brachial plexus injury.

STERNOCLAVICULAR DISLOCATION
Most injuries to the clavicle are not associated with serious complications, but sternoclavicular dislocation can cause life-threatening injuries in the mediastinum (Fig 2). Sternoclavicular dislocation is uncommon, accounting for perhaps 2%–3% of all shoulder girdle dislocations. The injury is important because of common complications, and delays in diagnosis are common. The clavicle is the only fixed attachment of the upper extremity to the trunk. With indirect anterior or posterior blows to the shoulder, the clavicle acts as a fulcrum through the coracoclavicular ligaments. Anterior force to the shoulder causes an anterior sternoclavicular dislocation, and posterior force to the shoulder causes posterior sternoclavicular dislocation. The classic mechanism is the “pile-on” injury in American football and rugby. Sternoclavicular dislocation most often occurs in late adolescence and young adulthood. Of interest, the epiphysis of the proximal clavicle is the last to form (age, 18–21 years) and the last to fuse (age, 25 years). Many sternoclavicular dislocations in young adults are probably epiphyseal injuries. Anterior sternoclavicular dislocation is more common but is not associated with mediastinal injury. Posterior dislocation, on the other hand, can cause injury

to the aorta, great vessels, trachea, esophagus, recurrent laryngeal nerve, jugular vein, and the superior vena cava. Sternoclavicular dislocation should be considered when there is evidence of hematoma in the upper mediastinum (Fig 2). Both injuries are famously difficult to diagnose, and delays in treatment are common. Sternoclavicular dislocation should be suspected whenever the medial clavicles are not at the same level on a trauma chest radiograph because the dislocations are often superior, in addition to anterior or posterior. Anteroposterior (AP) views of the sternum with 40° cephalad angulation (Rockwood view) can be used, but conventional radiographs are unreliable and difficult to interpret. CT is now the preferred imaging modality in patients suspected of having sternoclavicular dislocation. Not uncommonly, the dislocation is diagnosed when CT angiography is obtained for evaluation of mediastinal hematoma.

SCAPULA FRACTURE
The scapula is rarely injured except in patients with substantial trauma. Motor vehicle accidents probably cause about three-fourths of the cases, and 80% of scapula fractures are associated with other injuries, especially to the head and thorax. Scapula fractures can occur in association with acromioclavicular and glenohumeral dislocation, especially fractures of the spine, acromion, and glenoid. Fractures are often demonstrated on the chest radiograph or the AP view of the shoulder and can be further evaluated on the lateral (scapular Y) view (Fig 3). CT is used to determine if glenoid fractures are intraarticular (which may require internal fixation) and to assess more complex injures. Three-dimensional CT reconstructions also can be helpful for understanding more complex injuries (Fig 4).

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Figure 4. Intraarticular scapula fracture. (a) AP view of scapula shows fracture through upper scapula (arrowheads) extending toward glenoid. (b) Scapula Y view shows that fracture (arrows) extends through base of coracoid and into upper glenoid, but extent of glenoid involvement is unclear. (c) CT image of shoulder shows that coracoid and portion of superior glenoid are detached as separate fragment (arrow). (d, e) Three-dimensional CT reconstruction more clearly delineates size and position of coracoid-glenoid fracture fragment (arrow).

Gillespy

There are some noteworthy anatomic variants that should not be confused with a scapula fracture. These include os acromiale (nonunited acromion apophysis, often mistaken for acromion fractures), secondary ossification center of the inferior angle of the scapula, and nutrient foramina near the neck of the glenoid.

and to the brachial plexus. Both CT and angiography are used to assess skeletal, soft-tissue, and vascular damage. Scapulothoracic dissociation should be distinguished from the rare scapulothoracic dislocation, which is traumatic separation of the inferior scapulothoracic articulation without neurovascular injury.

SCAPULOTHORACIC DISSOCIATION
Scapulothoracic dissociation is a serious injury characterized by lateral displacement of the entire forequarter. This injury should be suspected clinically or radiographically whenever there is massive soft-tissue swelling in the shoulder region with no soft-tissue defect (Fig 5). The diagnosis can be made on the trauma chest radiograph by noting lateral displacement of the medial scapular border, compared with the other side, without a soft-tissue defect. Lateral scapular displacement with a soft-tissue defect indicates a partial amputation, a distinct and equally serious injury. Commonly associated injuries include (a) fractures of the scapula and clavicle and (b) acromioclavicular separation or sternoclavicular dislocation. Scapulothoracic dissociation indicates injury and disruption of the forequarter musculature, often associated with injury to the subclavian and brachial vessels

HUMERUS FRACTURE
Humerus fractures are uncommon in the 20–45-yearold age group and generally indicate severe trauma (Fig 6). Proximal humerus fractures in this age group are often associated with fracture-dislocations of the glenohumeral joint (Fig 7). The axillary neurovascular structures are at some risk from bone fragments from the proximal humeral shaft or humeral head. CT is often used to document fracture fragment position and to assess the articular surfaces of the humeral head and glenoid. In any age group, fractures at the junction of the proximal two-thirds and distal one-third of the humeral shaft can injure the radial nerve (Fig 8). As the radial nerve exits the axilla, it courses posterior and then lateral to the humeral shaft. Two-thirds of the way down the shaft of the humerus, the nerve is tethered lateral to the humerus in the lateral intermuscular septa

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High-Energy Injuries to the Upper Extremity

Figure 5. Scapulothoracic dissociation. (a) Trauma chest radiograph shows multiple left rib and scapula fractures (arrowheads) associated with massive soft-tissue swelling (S) over left shoulder. Medial border of right scapula (arrows) is in normal position, whereas left scapula is displaced lateral to chest wall. (b) CT image of chest shows multiple fractures (arrowheads) of left scapula, associated with massive soft-tissue swelling (S). (c) Presubtraction angiogram shows relationship of left subclavian and brachial arteries to fractures of scapula and ribs. (d) Subtraction angiogram shows no evidence of vascular injury.

and is at risk for laceration by a fracture fragment. The radial nerve can also become entrapped in the humerus fracture at this location during closed manipulation.

ELBOW INJURIES
Injuries to the elbow, including the distal portion of the humerus, are generally caused by force transmitted through the bones of the forearm. Elbow injuries in the young and elderly are commonly caused by a fall on the outstretched hand, but in young to middle-aged adults, more serious accidents involving automobiles, motorcycles, and falls from a height are common. In the adult, fractures of the distal portion of the humerus are typically intraarticular T- or Y-shaped transcondylar types or their more comminuted variants (Figs 9, 10). Distal humerus fractures are usually readily seen on the initial radiographs, but the images must be carefully examined for less obvious associated fractures to the olecranon, capitellum, or radial head and for any dislocation. Although uncommon, displaced or neglected fractures of the distal humerus can injure the brachial artery, which lies anterior to the joint. Injury to the brachial artery can lead to disabling ischemic injury to

Figure 6. Motor vehicle accident victim. (a) AP view of humerus shows displaced and angulated fracture in midportion of humerus. (b) AP view of forearm shows severity of trauma, with comminuted fractures of midportions of radius and ulna.

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Figure 7. Fracture-dislocation of right shoulder. (a) AP view of shoulder shows complex fracture-dislocation of glenohumeral joint. (b) Axial CT image show that large fragment is missing from humeral head (H). Glenoid is normal. (c) Oblique coronal and (d) oblique sagittal CT reformations show large portion of humeral epiphysis (arrowheads) displaced inferiorly and trapped beneath inferior rim of glenoid (G).

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the muscles of the forearm and hand, known as Volkmann contracture. In adults, fractures of the epicondyles are usually intraarticular. If the fracture of either the medial or lateral epicondyle includes the lateral aspect of the trochlea (Fig 11), the injury is considered mechanically unstable, and internal fixation is often warranted. Any injury to the medial epicondyle can injure the ulnar nerve, which passes through a groove on the posterior medial epicondyle, the cubital tunnel. Olecranon fractures are common in the elderly but also occur in more serious trauma at any age. These injuries are more likely to be open fractures, with gross contamination of the wound and elbow joint (Fig 12). Combined fractures of the humeral shaft and forearm are not uncommon, which result in the grossly unstable “floating elbow” (Fig 13). Elbow dislocations are common in both children and adults. In high-energy blunt-force trauma, elbow dislocations often occur in combination with dramatic fractures of the distal humerus or olecranon (Fig 14). In any elbow dislocation, the radiograph must be analyzed carefully for any associated fracture because dislocation without fracture is uncommon (Figs 15, 16). Soft-tissue injuries associated with elbow dislocation include injury to ligaments and tendon, injury to the brachial artery, and entrapment of the median nerve in the joint. It is useful to consider the spectrum of fractures and fracture-dislocations of the proximal ulna. Three patterns are common: (a) fracture of the mid to proximal portion of the olecranon without dislocation (Fig 12) (classic olecranon fracture), (b) fracture of the distal portion of the olecranon with radial head dislocation (Fig 16) (anterior fracture-dislocation of the elbow), and (c) extraarticular fracture of the proximal portion of the ulna with radial head dislocation (Fig 17) (Monteggia fracture-dislocation).

Figure 8. Humerus fracture. AP view of humerus shows fracture at junction of upper two-thirds and lower one-third of humerus. No radial nerve injury was present at physical examination.

CT is helpful for staging the more complex elbow fractures and fracture-dislocations. Depending on the severity of the initial injury, the CT examination is often performed after closed reduction.

Figure 9. Comminuted T-type transcondylar fracture of distal humerus. (a) AP view shows intraarticular extension (arrowhead) of fracture. (b) Lateral view.

High-Energy Injuries to the Upper Extremity

Figure 10. Combined T- and Y-type transcondylar fracture of distal humerus. (a) AP view. (b) Lateral view.

Figure 11. Epicondyle fracture. Intraarticular fracture (arrowheads) of lateral epicondyle involves lateral portion of trochlea (T).

Figure 12. Olecranon fracture. (a) Lateral view shows displaced fracture of olecranon with large soft-tissue wound. Gas and foreign material extend into elbow joint. (b) AP view shows gas (arrowheads) within elbow joint, which indicates joint contamination.

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Figure 13. Floating elbow. Radiograph shows fractures of humeral shaft and forearm.

Figure 14. Elbow fracture-dislocation. (a) AP and (b) lateral views show fractures of proximal ulna, coronoid process, and olecranon and posterior dislocation of radial head. Note impacted fracture of radial head (arrowhead).

HAND AND WRIST
Lunate and Perilunate Dislocation Approximately 10% of all carpal injuries are lunate or perilunate dislocations. Associated fractures and ligament injury are common and generally occur within the “zone of vulnerability” described by Gilula. Carpal dislocations are usually obvious on the lateral view, but important clues to carpal malalignment can be detected with careful analysis of the posteroanterior (PA) view. On the lateral view, no carpal bone should cross either the volar or dorsal radial line (Fig 18). The hallmark of most carpal dislocations is the dislocation of the capitate and the lunate on the lateral view. Perilunate dislocation is present when the capitate crosses the dorsal radial line and when the lunate lies behind the volar radial line (Fig 19). Volar tilting of the lunate is common and should not be confused with a lunate dislocation. Perilunate dislocations are two to three times more frequent than lunate dislocation. Roughly 75% of the cases are accompanied by a scaphoid waist fracture, which is then termed a transscaphoid perilunate dislocation. The dislocation is almost always volar. Lunate dislocation is present when the lunate crosses the volar radial line and when the capitate does not cross the dorsal radial line (Fig 20). The lunate is typically volar tilted, which results in the classic pie-shaped lunate on the PA view. Most lunate dislocations do not have an associated fracture. Not uncommonly, a mixed pattern of carpal dislocation is present, in which both the lunate and the capitate partially or completely cross the volar or dorsal radial lines, respectively. These injuries can be classified as midcarpal dislocations (Fig 21). Most

likely, lunate, midcarpal, and perilunate dislocations are a spectrum of the same carpal injury. Fractures associated with carpal dislocations are often easier to identify on the postreduction view. Ideally, a postreduction view should be obtained before a cast or splint is applied. CT can be helpful in clarifying more complex cases.

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Carpal-Metacarpal Dislocation Carpal-metacarpal dislocations are uncommon. However, every trauma hand radiograph should be carefully examined for this injury because it can be difficult to identify and is often missed. The dislocation is most often dorsal (Fig 22), although volar dislocation can also occur (Fig 23). The fifth metacarpal is involved in most cases, either alone or in combination with other metacarpals. Fifth and/or fourth metacarpal-carpal dislocations are often associated with fractures of the hamate, typically an avulsion fracture off the dorsal lip of the hamate.

High-Energy Injuries to the Upper Extremity

Figure 15. Posterior elbow fracture-dislocation. (a) AP and (b) lateral views show posterior dislocation of radius and ulna with displaced radial head fracture (arrow). (c) Postreduction view shows that elbow joint dislocation has been reduced, and severely comminuted fracture of radial head (arrow) is well demonstrated.

Figure 16. Anterior fracturedislocation of elbow. (a) Lateral view shows fracture through distal olecranon, with anterior dislocation of radial head and anterior displacement of adjacent proximal ulna. (b) Postreduction lateral view shows that olecranon fracture and radial head fracture have been nearly anatomically reduced. Radial head fracture (arrowhead) is partially obscured by coronoid process.

Figure 17. Monteggia fracture. (a) AP and (b) lateral views show extraarticular fracture of the proximal ulna with anterior dislocation of radial head.

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Figure 18. Normal wrist. (a) On this properly positioned PA view, there are parallel lines (arrowheads) at second through fifth metacarpal-carpal joints. (b) Lateral view. (c) Diagrammed lateral view shows that capitate articulates in fossa of lunate. Carpal bones should not cross volar radial line (V) or dorsal radial line (D).

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Figure 19. Perilunate dislocation. (a) PA view shows loss of normal congruency between articular surfaces of lunate and capitate, and proximal carpal row is disrupted. Ulnar styloid fracture is also seen. (b) Capitate (arrowheads) is dislocated dorsally and crosses dorsal radial line, while lunate is normally aligned with distal radius.

Figure 20. Lunate dislocation. (a) PA view shows that lunate is displaced laterally and is pie-shaped (arrowheads). There is also fracture of radial styloid. (b) Lateral view shows that lunate (arrow) crosses volar radial line, while capitate (arrowheads) and remainder of carpus are normally aligned with radius. Injury is classified as transradial lunate dislocation because of radial styloid fracture.

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Figure 21. Midcarpal dislocation. (a) PA view shows that articulation of lunate (arrowheads) and capitate (arrow) is disrupted, and there is gross malalignment of proximal carpal row. Lunate is displaced toward ulnar styloid and has pie-shaped configuration. (b) Lateral view shows volar subluxation of lunate (arrowhead), which touches volar radial line, and dorsal subluxation of capitate (arrow) and most of carpus, which touch dorsal radial line. In addition, small fractures off dorsal lip of distal radius or proximal pole of scaphoid are shown.

High-Energy Injuries to the Upper Extremity

Figure 22. Carpal-metacarpal dislocation. (a) PA view shows that normal parallel lines at metacarpal-carpal joints are missing at fourth and fifth metacarpals. White band (arrowhead) at base of fifth metacarpal indicates overlap of metacarpal and hamate, and dislocation. (b) Oblique and (c) lateral views show dorsal dislocation (arrow) of fourth and fifth metacarpals. Small bone fragments (arrowhead) are probably small fractures from dorsal lip of hamate.

On a properly positioned PA view of the hand or wrist, the bases of the second through fifth metacarpals form parallel lines with the adjacent carpal bones (Fig 18). Loss of these parallel lines suggests malalignment, especially if the metacarpal base and adjacent carpal bone overlap. Carpal-metacarpal dislocation should also be suspected whenever there is a fracture of a metacarpal base or adjacent carpal bone. However, the metacarpal-carpal joints are only clearly identified on the PA view if the palm is flat against the film cassette, and proper positioning is often not possible in the severely injured patient. The diagnosis of carpal-metacarpal dislocation is established on the lateral view, where one or more

metacarpal bases are not in proper alignment with the carpus. The lateral view of the hand can be challenging to the observer unfamiliar with this injury. The second through fifth metacarpal shafts are often not precisely parallel, so the analysis should focus on the metacarpal-carpal region. CT is helpful in clarifying cases with unclear findings on the conventional radiographs.

Axial Carpal Dislocation Axial dislocation of the carpus is a rare injury indicated by widening between the carpal bones and their associated metacarpals in the distal carpal row, typically seen in severe crush or blast injuries. The

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Figure 23. Carpal-metacarpal dislocation. (a) PA view shows normal parallel lines at metacarpal-carpal joints are missing at fifth metacarpal-carpal joint. Note large overlap between the base of fifth metacarpal (arrowhead) and hamate, in addition to fracture at base of fifth metacarpal. (b) Oblique and (c) lateral views show volar dislocation of fifth metacarpal (arrow). Fracture of distal third metacarpal is also seen. Figure 24. Carpal dislocation. (a) PA and (b) lateral views show that lunate (arrow) and proximal pole of scaphoid (arrowhead) have been ejected into volar compartment of distal forearm. Gas in soft tissues indicates open injury. Dislocation is classified as transscaphoid scapholunate dislocation.

fourth and fifth metacarpal-hamate joint is most often involved, and severe soft-tissue injuries are common.

the proximal pole of the scaphoid were ejected into the volar compartment of the distal forearm (Fig 24).

Other Carpal Dislocations A wide variety of carpal dislocations and fracturedislocations have been described, in addition to the typical patterns described in the previous paragraphs. Recently, we observed a case in which the lunate and

Suggested Reading
Rogers LF, ed. Radiology of skeletal trauma. 3rd ed. Philadelphia, Pa: Churchill Livingstone, 2002; 593–929 (chap 15–18). Dandy DJ, Edwards DJ, eds. Essential orthopedics and trauma, 4th ed. Philadelphia, Pa: Churchill Livingstone, 2003; 179– 230 (chap 12, 13).

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Viktor M. Metz, MD, and Marcel O. Philipp, MD

Imaging Low-Energy Upper Extremity Injuries1

Kinetic energy is defined as mass multiplied by velocity, and no absolute physiologic threshold exists demarcating high energy and low energy. Further, radiologic evaluations are not specifically guided by the magnitude of injury forces but will generally follow limitations imposed on available imaging techniques by patient- and injuryspecific factors. That said, for the purposes of our discussion, low-energy trauma is defined as a result of (a) a fall from standing or sitting height or (b) a motor vehicle accident at a speed of less than 15 mph (24 km/h). In this chapter, we describe injuries of the upper extremity that generally, but not exclusively, result from low-energy trauma.

INJURIES TO THE CLAVICLE
The clavicle functions as a bony support connecting the trunk and the arm (1,2). The clavicle is S-shaped and is tubular in the proximal and medial aspect and flattened distally. The clavicle has multiple muscle insertions and origins that may lead to typical dislocations in some cases of fracture. The coracoclavicular ligaments bind the clavicle to the coracoid process, and the acromioclavicular ligaments bind the clavicle to the acromion. Because of the specific anatomic position of the clavicle with respect to the trunk, radiographs will always show some overlap of the clavicle, such that one is not able to isolate the clavicle and get two perpendicular views. The basic protocol is an anteroposterior view and a 50° cephalic angulated view. Angling the beam to 50° cephalad, as suggested by Neer, produces more detailed information concerning the medial aspect of the clavicle. In the absence of obvious dislocation or subluxation at the acromioclavicular joint, stress views with 10–15 lb (4.5–6.8 kg) of weight are important for detection or exclusion of ligamentous injuries. In any case, the injured arm must hang down unsupported by the side of the body to avoid understaging ligamentous injury. Computed tomography (CT) may be helpful, especially for detection of subtle fractures of the sternoclavicular side of the clavicle. Injuries to the clavicle are frequent. They are most frequent in childhood, and the clavicle is the most common fracture location during birth. In adults, the mechanism of trauma is a fall directly on the shoulder in 90% of the cases. In rare cases, a direct blow may lead to injuries of the clavicle. Clavicular injuries are rare in cases of a fall on the outstretched hand.

RSNA Categorical Course in Diagnostic Radiology: Emergency Radiology 2004; pp 187–196.
1From the Department of Radiology, Medical University of Vienna, Waehringer-Guertel 18-20, A-1090 Vienna, Austria (e-mail: [email protected]).

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Eighty percent of the fractures are located within the middle third of the clavicle, with a typical step-off at the fracture site, caused by the pull of the sternocleidomastoid muscle on the medial side and the weight of the arm on the lateral side (Fig 1). In 15% of the cases, fractures of the clavicle are located in the outer third, and as mentioned previously, stress views should be considered for evaluation of otherwise occult coraco- and acromioclavicular ligamentous injuries (Fig 2). In 5% of the cases, the fractures are located within the inner third.

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DISLOCATIONS OF THE ACROMIOCLAVICULAR JOINT
Dislocations of the acromioclavicular joint account for 12% of all dislocations within the shoulder (2,3). The mechanism of injury may be (a) direct, by a fall on the shoulder, or (b) indirect, by a fall on the outstretched hand. The joint space width of the normal acromioclavicular articulation is between 5 and 8 mm (2 mm in the elderly). The coraco-clavicular interval distance normally is between 11 and 13 mm. Compared with the contralateral side, an asymmetry of 3–4 mm may be normal. Asymmetry of the distance between the coracoid process and the clavicle of more than 5 mm, however, strongly suggests ligamentous injury. Radiography should be performed with a view in the anteroposterior direction and a 15° cephalic view. To distinguish between type 1 and type 2 ligamentous injuries, as mentioned previously, views should be obtained without and with 10–15 lb (4.5–6.8 kg) of weight. In subtle or forensic cases, magnetic resonance (MR) imaging may be helpful. On radiographs, acromioclavicular joint dislocations appear in sequence according to the severity of the force. In the initial stages, there is just a stretch or partial tear of the acromioclavicular ligaments, and radiographs are (a) normal without and with weights (type 1) or (b) normal without weights and abnormal with weights (type 2). If there is a complete tear of the acromioclavicular ligaments, the tear will lead to a widening of the acromioclavicular joint space on radiographs obtained without weights (type 3), with or without superior displacement of the clavicle (Fig 3). In severe cases, there is an additional tear of the coracoclavicular ligaments and detachment of the deltoid muscle and the trapezoid muscle. In addition, there may be a fracture of the clavicle, the coracoid process, or the acromion.

Figure 1. Fracture of middle third of clavicle. Anteroposterior cephalic angulated view shows typical step-off at fracture site (arrows), caused by pull of sternocleidomastoid muscle on medial side and weight of arm on lateral side.

Figure 2. Radiograph showing fracture of clavicle (arrow) at outer third near acromioclavicular joint.

FRACTURES OF THE PROXIMAL HUMERUS
Fractures of the proximal humerus (2,4) are one of the most common fractures in the elderly. The incidence is three times higher in women than in men because of the differential presence of osteoporosis. There is

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often a combination of proximal humerus fractures with other fractures (eg, proximal femur, distal radius, or the cervical spine). The mechanism of injury is a fall on the outstretched hand or a direct blow. For radiographic examination, an anteroposterior view in internal and external rotation should be obtained. During internal rotation, the lesser tuberosity projects medially, and the globe-shaped humeral head profiles the posterosuperior humeral head (eg, usual site of the Hill-Sachs deformity). In external rotation, the greater tuberosity is projected more laterally, facilitating its evaluation. A Grashey view (45° posterior oblique projection), which is a 40°–45° anteroposterior oblique view, should be obtained to profile the glenohumeral joint. An axillary lateral projection and a scapula Y view (45° anterior oblique projection) may be obtained for better evaluation of displacement. CT is of importance in complex comminuted fracture-dislocations. As a classification scheme, the Neer classification is the most widely used and is based on the indirect assessment of the functional integrity of the soft-tissue structures supporting physiologic function (eg, periosteum, muscles of the rotator cuff). For developmental and anatomic reasons, Neer divided the proximal humerus into four parts: the articular head, the surgical neck, the greater tuberosity, and the

Imaging Low-Energy Upper Extremity Injuries

Figure 3. Acromioclavicular dislocation. (a) Radiograph shows that joint space on right is widened, and there is step-off compared with left side (arrows). (b) Coronal MR image shows that joint space (star) is obviously widened. Coracoclavicular ligaments are torn and retracted (arrow).

Figure 4. Two-part fracture of humeral head at site of greater tuberosity and site of surgical neck. (a) Radiograph shows typical eggshell appearance (arrow) because of coverage of muscles. (b) In external rotation, fracture of greater tuberosity (arrow) and fracture of surgical neck (star) are more evident on radiograph. Note presence of osteoporosis.

lesser tuberosity. A fracture of the humeral head is defined as displaced if there is a displacement of more than 1 cm and/or if there is an angulation of more than 45° of any of the four parts mentioned previously. Grading of fractures of the proximal humerus is based on the total number of fracture parts that are displaced: Grades range from a one-part fracture, representing any combination of nondisplaced fractures, to a four-part fracture caused by displacements of the fractures of the surgical and anatomic necks and both tuberosities. Isolated fractures are rare. There are often combinations of fractures, and the number of complications increases with the number of fractured parts. In about 80% of the cases, there is no displacement, and the fracture is classified as a one-part fracture, which is considered stable. Because of the muscles that cover the humeral head, fractures commonly have an eggshell appearance (Fig 4). Often there is an impaction of the surgical neck. Fractures at the anatomic neck of the humeral head may disrupt blood supply and lead to osteonecrosis of the humeral head.

Complications of proximal humerus fractures are injuries of the brachial plexus and/or the axillary artery. Those complications are most likely in anteriorly displaced fractures of the surgical neck. Therefore, you should direct careful clinical examination to the possibility of those complications. Duplex ultrasonography or CT angiography may be helpful in predicting and grading vascular injuries. Another complication is the so-called frozen shoulder, which is caused by fibrosis and adhesive capsulitis. This complication may be prevented by early active or passive mobilization.

GLENOHUMERAL JOINT INJURIES
The glenohumeral joint consists of the shallow glenoid augmented by the cartilaginous labrum and surrounded by numerous muscles, which provides the greatest prehensile motion (2,5). For conventional radiography, the anteroposterior view, the Grashey view, the axillary lateral view, and the scapula Y view may be obtained. After reduction of anterior dislocations, an apical oblique view (Grashey projection with

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Figure 5. Anterior glenohumeral dislocation (arrow), with displacement of the humeral head in area of coracoid process, on (a) anteroposterior and (b) axillary lateral views. (a) Note impaction fracture of humeral head (arrowhead), which is described as Hill-Sachs deformity.

Figure 6. (a) Anterior dislocation of glenohumeral joint on radiograph. (b) Axial CT image clearly shows HillSachs deformity (arrow).

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an additional 45° caudal angulation of the central ray of the x-ray beam) best shows both the Hill-Sachs and bony Bankart deformities. For detection or exclusion of associated injuries, CT and MR imaging are important adjunctive modalities. Glenohumeral dislocations are among the most common dislocations within the body. In as many as 95% of the cases, the dislocation is anterior because of external rotation and abduction or because of indirect trauma (Fig 5). In those circumstances, the posterolateral surface of the humeral head impacts against the anteroinferior surface of the glenoid fossa. A less common trauma mechanism is a blow to the posterolateral side of an abducted arm, leading to a displacement of the humeral head into the area of the subcoracoid fossa. Posterior dislocations are rare and typically are subsequent to seizures, electrocution, or a posterior force with the arm in internal rotation. Superior dislocations, a rare variant of posterior dislocations, are thought to be due to a blow on the flexed elbow with the arm abducted. Luxatio erecta, an uncommon anterior dislocation variant, occurs with severe hyperabduction of the arm where the neck of the humerus impinges against the acromion, driving the head of the humerus both distal and anterior. The anterior glenohumeral dislocation with displacement of the humeral head into the subcoracoid

recess may lead to an impaction fracture of the posterolateral aspect of the humeral head against the anterior aspect of the glenoid and is known as a Hill-Sachs deformity (Fig 6). Similarly, anterior glenohumeral dislocation may cause a cartilaginous or osseocartilaginous fracture at the anteroinferior aspect of the glenoid, which has been described as a Bankart lesion or a bony Bankart lesion, respectively (Fig 7). In subtle cases, CT and MR imaging may be helpful for depiction of Hill-Sachs or bony Bankart lesions. In addition, MR imaging may be performed for further evaluation of other associated injuries, such as ligamentous tears or injuries of the rotator cuff. MR arthrography is the method of choice for precise evaluation of injuries of the cartilaginous labrum (Fig 8). Although posterior glenohumeral dislocations are rare, it should be mentioned that these injuries are clinically and radiographically often occult. Posterior glenohumeral dislocations are missed in 60% of the cases at initial evaluation. Posterior glenohumeral dislocations clinically appear as the inability to rotate the arm externally. On conventional radiographs, a directed search for the rim sign and the trough sign (Fig 9) will help to avoid misinterpretation of posterior glenohumeral dislocations.

Figure 7. Bony Bankart lesion (arrow) after anterior dislocation of glenohumeral joint on (a) axial CT image and (b) coronal CT reformation.

Imaging Low-Energy Upper Extremity Injuries

Figure 8. Fat-suppressed axial MR image of shoulder after anterior dislocation. There is clear evidence of cartilaginous Bankart lesion (arrow) at anterior aspect of glenoid. In addition, note area of high signal intensity (star) at humeral head, indicating Hill-Sachs impression fracture.

Figure 9. Posterior glenohumeral dislocation on radiograph. Joint space is more than 6 mm wide (white arrow), which is described as rim sign. Note impaction fracture (black arrows) seen as vertical line. This has been described as trough line.

INJURIES OF THE ELBOW
The elbow consists of three joints: the humeroulnar joint, the humeroradial joint, and the radioulnar joint (6,7). For conventional radiography, the standard views are (a) an anteroposterior view in the supine position with full extension of the elbow and (b) a lateral view with the elbow flexed 90° with the lower arm and with the hands in the neutral thumb-side-up position. Additional views include internal and external oblique views and the radio-capitellum view (positioned as for a neutral lateral view and additional angling of the central ray of the x-ray beam 45° cephalad). In complex or subtle cases, CT or MR imaging will lead to precise diagnosis. Radial head fractures are the most common elbow injuries in adults and account for approximately 60% of all elbow injuries. The mechanisms of trauma include a fall on the outstretched hand or a force transmitted to the long axis of the radius, leading to a compression of the radial head against the capitellum. The Mason classification is the most commonly used classification scheme for radial head fractures. The Mason type I fracture is a fracture with a displacement of the fracture fragment of less than 2 mm (50% of the cases) (Fig 10). Type II fractures are segmental frac-

tures consisting of one-quarter of the radial head with a displacement or compression of more than 2 mm, and type III fractures are defined as comminuted fractures of the entire radial head. Fractures of the olecranon account for 20% of elbow fractures. The mechanisms of trauma are a fall on the elbow with the elbow flexed or a direct blow to the elbow. In most cases, the fracture line runs transversely and may be overlooked on the anteroposterior view (Fig 11) but commonly is easily diagnosed on the lateral view. In rare cases, the fracture line runs obliquely because of valgus forces. Coronoid process fractures are rarely isolated fractures and are most commonly associated with posterior dislocation of the elbow (Fig 12). Isolated fractures of the coronoid process may be difficult to see on anteroposterior and lateral views. Therefore, oblique views should be obtained.

FRACTURES OF THE SHAFT OF THE RADIUS AND/OR ULNA
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Figure 10. Fracture of radial head. (a) On anteroposterior view, there is no clear evidence of fracture. (b) On lateral view with elbow flexed 90°, note fracture of radial head (arrow) with displacement of more than 2 mm (Mason type II).

Figure 11. Fracture of olecranon (arrow) on (a) anteroposterior and (b) lateral views.

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force (6,8). In most cases, both the radius and the ulnar shaft are fractured. Isolated single-bone fractures are less common. Not uncommonly, one of the bones is fractured while the other is dislocated, and usually the fracture shows obvious displacement or rotation. The Monteggia fracture is defined as a fracture of the ulna with a dislocation of the proximal radius. The trauma mechanism is a fall on the outstretched hand combined with a forced pronation of the forearm. The radiocapitellar line (created by bisecting the radial shaft proximal to the radial tubercle) should always be drawn to avoid overlooking subluxation or dislocation of the proximal radius. Under normal conditions, the line runs through the central third of the capitellum.

The Galeazzi fracture (Fig 13) is an isolated fracture of the distal radius in combination with subluxation at the distal radioulnar joint. In contrast to Monteggia fractures, the mechanism of trauma in Galeazzi fracture-dislocations is a fall on the outstretched hand with maximal pronation of the arm, although a direct blow may uncommonly lead to the injury. Subluxation or dislocation of the distal radioulnar joint may be overlooked. Therefore, a neutral lateral view of the distal forearm, which can be achieved by adducting the arm to the trunk and flexing the elbow 90° and the hand 90° to the cassette (in between maximal pronation and supination), should be searched for distal, dorsal, or ulnar

Imaging Low-Energy Upper Extremity Injuries

Figure 12. Fracture of coronoid process associated with posterior dislocation of elbow. (a) On lateral radiograph, there is evidence of fracture of radial head (arrowhead) and dislocation of elbow (arrow) but no evidence of fracture of coronoid process. (b) On anteroposterior view, fracture of coronoid process is not well shown (lower arrow), but there is clear evidence of dislocation of joint (upper arrow). (c) On CT reformation, fractures of radial head (short arrow) and coronoid process (arrowhead), with displacement of small fracture fragment (long arrow), are well depicted.

Figure 13. Galeazzi fracture. (a) On posteroanterior radiograph, fracture of distal radius shaft (long arrow) and some subluxation of distal radioulnar joint (short arrow) can be seen. (b) On lateral radiograph, dislocation of distal radioulnar joint (arrow) is much more evident.

displacement of the distal ulna relative to the distal radius metaphysis.

DISTAL RADIUS FRACTURES
Fractures of the distal radius are the most common fractures of the skeleton (8,9). The mechanism of trauma is most commonly a fall on the outstretched hand, although less commonly the fracture may occur because of high-energy trauma. Fractures of the distal radius are common in children, because of physeal injuries, and are also common in the elderly, because of osteoporo-

sis. In the elderly, concurrent fracture of the distal radius and fracture of the humeral head or the cervical spine may occur with falls from standing or seated height. Several classification schemes for distal forearm fractures have been introduced, but none is widely accepted. For example, Fryckman has introduced a classification scheme for distal radius fractures that recognizes the importance of associated ulna fractures, and he has classified distal radius fractures into eight types (Fig 14). The most common type of distal radial fracture is the Colles fracture, which occurs because of a fall on

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Figure 15. (a) Posteroanterior and (b) lateral views of patient with Colles fracture. Typically, distal fracture fragment is displaced and/or angulated dorsally (arrow).

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the dorsally flexed hand. In this Colles fracture, the distal fracture fragment is displaced dorsally (Fig 15). The classic Colles fracture is an extraarticular fracture. The second most common fracture of the distal radius is the Smith fracture, which, in contrast to the Colles fracture, occurs because of a fall on the palmar flexed hand. In this type of fracture, the distal fracture fragment is displaced or angulated palmar. The typical Smith fracture is also an extraarticular fracture. Barton has described a third type of distal radius fracture. Barton fractures and reverse Barton fractures are intraarticular fractures of the anterior or posterior rim of the distal radius. These types of fractures occur after a more axially applied force. The chauffeur fracture is an intraarticular fracture of the radial styloid process. This type of fracture arises after an axially applied force or is caused by a direct blow (Fig 16). In any type of distal radius fracture, a careful examination of the carpal bones should be performed because distal radial fractures are often associated with scaphoid fractures or intercarpal ligamentous injuries (eg, scapholunate ligament injuries). Although there are numerous classifications and classification schemes for distal radial fractures, the important question is what the surgeon or orthopedist wants to know. Therefore radial inclination and palmar inclination should be reported. In normal individuals, average radial inclination is 21°, and mean palmar inclination is 11°. In addition, the radiologist should report whether the fracture is comminuted and whether the fracture is intra- or extraarticular. In addition, bone quality (eg, osteoporosis) is important to know for further treatment and should be mentioned.

Figure 14. Schematic of Fryckman classification of distal radius fractures.

DISLOCATIONS OF THE DISTAL RADIOULNAR JOINT
Dislocation of the distal radioulnar joint may occur as an isolated injury (9). More commonly, dislocations of the distal radioulnar joint are found in association with distal radius fractures. For radiologic diagnosis of dislocation of the distal radioulnar joint, it is important to obtain a true neutral lateral radiograph. The true lateral radiograph is obtained by adducting the arm to the trunk and flexing the elbow 90°, and the distal forearm forms a straight line with the metacarpal bones and is perpendicular to the cassette. Even slight supination or pronation must be avoided. With this arrangement, the distal radius and the distal ulna are superimposed.

FRACTURES OF CARPAL BONES
The wrist consists of complex bony and ligamentous anatomic structures (9,10). Standard radiographs should include a posteroanterior view in the neutral position (the arm abducted 90°, the elbow flexed 90°,

Figure 16. Chauffeur fracture (arrow) without dislocation on (a) posteroanterior and (b) lateral radiographs.

Imaging Low-Energy Upper Extremity Injuries

Figure 17. Vulnerable zone for carpal bone fractures. Lunate bone is not included in vulnerable zone.

Figure 18. Arcs described by Gilula. On normal wrist radiographs, three smooth arcs can be drawn along proximal and distal carpal rows. Arc I joins convexity of proximal carpal row, arc II joins concavity of proximal carpal row, and arc III joins convexity of the distal carpal row. In some people, there may be small step-off at site of the lunotriquetral joint, which is normal.

and the hand flat on the cassette, with the radius and the third finger colinear), a 30° pronated oblique view, a true neutral lateral view, and a dedicated scaphoid view (eg, a posteroanterior view with ulnar deviation of the wrist and 20° proximal angulation of the central ray of the x-ray beam). CT is helpful in complex cases. MR imaging is important in patients with questionable occult fractures and for precise evaluation of carpal ligaments and the triangular fibrocartilage complex. The mechanism of trauma for carpal fractures most commonly is a fall on the outstretched hand with a slight dorsiflexion and ulnar deviation and some type of supination. A vulnerable zone (Fig 17) has been described for carpal bone fractures. This zone includes the scaphoid, the trapezium, the trapezoid, the capitate, and the triquetrum and excludes the lunate. Gilula has described three arcs (Fig 18), which are smooth parallel lines that should be evaluated carefully to assist in the recognition of intercarpal malalignments. A broken arc or a step-off to any side of one or more arcs always indicates fracture, dislocation, or subluxation.

SCAPHOID FRACTURES
Scaphoid fractures constitute 60%–70% of all carpal bone fractures (9,10). They are common in the 15- to 40-year-old age group and are rare in children and in the elderly. Seventy percent of the fractures of the scaphoid run through the scaphoid waist, 20% run through the proximal pole, and 10% run through the distal pole. Avascular necrosis of the proximal pole of the fractured scaphoid may complicate scaphoid fractures and may result in activity-limiting loss of wrist and hand function. Fractures at greatest risk of avascular necrosis include those displaced greater than 2

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Figure 19. (a) Posteroanterior radiograph with fracture (arrow) at proximal fifth of scaphoid. (b) Corresponding coronal T1weighted MR image demonstrates early stage of avascular necrosis of proximal fracture fragment (arrow), while distal part of scaphoid bone (star) is vital.

mm, and the likelihood of avascular necrosis directly increases by scaphoid waist fracture location from distally to proximally. In the distal fifth of the scaphoid, necrosis occurs in 15% of the cases, and in the proximal fifth of the scaphoid bone, necrosis occurs in nearly 100% of the cases (Fig 19). MR imaging is an important imaging modality for early detection of this complication because MR imaging allows immediate diagnosis and classification of avascular necrosis. Only early stages of avascular necrosis (grades 1 or 2) may respond to therapy. If avascular necrosis of the fractured scaphoid bone is depicted on conventional radiographs, primary treatment of the fracture may not be possible. Other complications of scaphoid fractures include nonunions or delayed unions. CT, as well as MR imaging, may be helpful in the diagnosis of these potential complications.

References
1. Craige EV. Fractures of the clavicle. In: Rockwood CA, Green DP, eds. Fractures in adults. 4th ed. Vol 1. Philadelphia, Pa: Lippincott-Raven, 1996; 1109–1161. 2. Rogers LF. The shoulder and humeral shaft. In: Rogers LF, ed. Radiology of skeletal trauma. 2nd ed. Vol 1. New York, NY: Churchill Livingstone, 1992; 653–748.

3. Rockwood CA Jr, Williams GR, Young DC. Injuries to the acromio-clavicular joint. In: Rockwood CA, Green DP, eds. Fractures in adults. 4th ed. Vol 2. Philadelphia, Pa: Lippincott-Raven, 1996; 1341–1413. 4. Bigliani LU, Flatow EL, Pollock RG. Fractures of the proximal humerus. In: Rockwood CA, Green DP, eds. Fractures in adults. 4th ed. Vol 1. Philadelphia, Pa: Lippincott-Raven, 1996; 1055–1107. 5. Rockwood CA Jr, Wirth MA. Subluxations and dislocations about the glenohumeral joint. In: Rockwood CA, Green DP, eds. Fractures in adults. 4th ed. Vol 2. Philadelphia, Pa: Lippincott-Raven, 1996; 1193–1339. 6. Rogers LF. The elbow and forearm. In: Rogers LF, ed. Radiology of skeletal trauma. 2nd ed. Vol 2. New York, NY: Churchill Livingstone, 1992; 749–836. 7. Hotchkiss RN. Fractures and dislocations of the elbow. In: Rockwood CA, Green DP, eds. Fractures in adults. 4th ed. Vol 1. Philadelphia, Pa: Lippincott-Raven, 1996; 929–1024. 8. Richards RR, Corley FG Jr. Fractures of the shaft of the radius and ulna. In: Rockwood CA, Green DP, eds. Fractures in adults. 4th ed. Vol 1. Philadelphia, Pa: Lippincott-Raven, 1996; 869–928. 9. Rogers LF. The wrist. In: Rogers LF, ed. Radiology of skeletal trauma. 2nd ed. Vol 2. New York, NY: Churchill Livingstone, 1992; 837–938. 10. Cooney WP III, Linscheid RL, Dobyns JH. Fractures and dislocations of the wrist. In: Rockwood CA, Green DP, eds. Fractures in adults. 4th ed. Vol 1. Philadelphia, Pa: Lippincott-Raven, 1996; 745–867.

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Philip M. Hughes, MBBS, MRCP, FRCP

Low-Energy Injuries of the Lower Limb1

The distinction between low- and high-energy injuries is arbitrary, but for the purposes of this chapter, the low-energy section will consider injuries sustained as a result of forces applied in a repetitive or sporting setting and will also include falls and contusions sustained through direct impact. The injuries will be considered according to body part, in the following order: (a) pelvis and hips, (b) thigh, (c) knee, (d) lower part of the leg, and (e) ankle and foot; but muscle injury will be considered initially to establish specific principles and patterns that will subsequently be qualified by examples of injuries commonly encountered in each of the specified areas.

MUSCLE INJURY
Muscle injury is common and is mainly encountered in the setting of sports-related activity. There are two main types of injury, each of which has a typical clinical history and imaging appearance. The more common type is the muscle strain or tear, usually sustained as a result of isometric muscle contraction, while the muscle contusion occurs through direct impact during combative sports or consequent to a fall.

Muscle Sprains and Tears Tears and sprains are some of the most common injuries and are particularly prevalent in the lower limb. Muscles particularly prone to injury during isometric contraction include the so-called two-joint muscles that bridge two articulations, including the hamstring muscles, rectus femoris, and gastrocnemius. Although the exact muscletendon configuration may vary, the basic principle dictates that the tendon extends into the muscle and that the site of maximum weakness that is most prone to injury is the muscle-tendon junction, where elasticity is limited. There are three basic grades of injury. Although an element of muscle or muscletendon injury will be microscopically evident in all grades, ultrasonography (US) and magnetic resonance (MR) imaging show no macroscopic fiber disruption. Grade 1 injuries usually show a localized increase in echogenicity at US (Fig 1), although diffuse hypoechoic areas may also be observed. Increased edema associated with grade 1 injuries is manifest as diffuse high signal intensity on short inversion time inversionrecovery (STIR) or equivalent T2-weighted fast spin-echo (SE) MR images obtained with fat saturation (Fig 2) (1).

RSNA Categorical Course in Diagnostic Radiology: Emergency Radiology 2004; pp 197–215.
1From

X-ray West, Derriford Hospital, Derriford Rd, Plymouth, Devon, England PL6 8DH (e-mail: philip.hughes@phnt .swest.nhs.uk).

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Figure 2. Grade 1 hamstring injury in a 44-year-old elite distance walker. Transverse STIR MR image demonstrates subtle increased signal intensity in injured semimembranosus muscle (arrows) with prominent vessels (arrowhead) indicative of hyperemia. Figure 1. Grade 1 hamstring injury in a 24-year-old soccer player. US images of right (R) and (L) hamstring compartments in transverse section show increased echogenicity in region of injured right semimembranosus muscle but no fiber disruption.

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Grade 2 injuries represent overt muscle tears, and clinically the muscle has a restricted range of movement and is tender to palpation. US reveals focal fiber disruption that appears hypoechoic and is usually identified at the muscle-tendon junction. The disruption at these sites may vary from a minor tear to near total rupture (Figs 3, 4). MR imaging is equally efficacious, with the proviso that muscle edema can sometimes make the distinction between grade 1 and minor grade 2 injuries difficult (Fig 5). Grade 1 and grade 2 injuries are usually more easily distinguished at US. The clinical effect can be important because grade 1 injuries usually allow a return to full activity in 10–14 days, while grade 2 injuries may take as long as 4 weeks. Grade 3 injuries represent complete muscle rupture, a condition that may be accompanied by considerable discomfort. Not uncommonly, however, symptoms may be relatively mild in individuals who have completely disconnected the muscle unit, but function will be absent. These patients may require surgical repair, but most are managed conservatively. Recovery depends on whether healing is feasible. If it is, 3 months of reduced activity is the norm. If the tear is distal, the tendon end may be retracted and not likely to heal. However, if other muscle groups are compensating, some patients return to sporting activity within 2–3 weeks (Fig 6). The grades of these injuries are rough guides to the recommended recuperative period, which is further influenced by recurrent injury and uncorrected biomechanical imbalances, which may require a longer recovery phase. Grade 2 injuries vary greatly from minor tears, requiring 4 weeks of rehabilitation, to severe near-total tears, requiring 12 weeks. The rehabilitation period is also inversely related to the amount of expert physiotherapy and supervised retraining.

Figure 3. Grade 2 tear of gastrocnemius in a 34year-old runner. Sagittal US image demonstrates focal hypoechoic zone with loss of fiber continuity at medial side of gastrocnemius muscle-tendon junction (arrow), indicative of localized tear.

Figure 4. Mass in anterior midportion of thigh of a 15-year-old soccer player. Sagittal US image with quadriceps contracted shows proximal retraction and mass effect of torn rectus femoris muscle (arrows), which other images demonstrated to be a partial tear.

Muscle Contusion Muscle contusion occurs following direct impact, results in muscle fiber disruption, rather than muscle tendon injury, and is often accompanied by intramuscular hemorrhage and hematoma formation. The muscle is swollen and acutely tender, with severe limitation in the range of movement. Compartment syndrome can ensue, and in the presence of severe pain or neurovascular compromise, US-guided or surgical hematoma evacuation may be required. Hematomas associated with contusion may have ill-defined irregular margins when associated with fiber disruption, but most are well defined and oval in

Figure 5. Partial grade 2 tear of rectus femoris in a 21-yearold female high-hurdler. (a) Sagittal STIR MR image demonstrates focal high signal intensity with fluid characteristics indicative of rectus femoris tear. (b) Transverse STIR MR image shows residual intact muscle component medially (arrow).

Low-Energy Injuries of the Lower Limb

Figure 6. Mild tenderness and bruising along posterolateral portion of knee, with biceps femoris tear, in a 28-year-old soccer player. Patient returned to professional soccer within 4 weeks. (a) Sagittal far lateral STIR MR image shows rupture and retraction of biceps femoris tendon (arrow). (b) Equivalent sagittal US image demonstrates "bellclapper" configuration of retracted tendon end (arrow) and surrounding hematoma.

Figure 7. Persistent mass in anterior part of thigh following contusion in a 44-year-old man, despite a delayed surgical drainage. US image shows chronic hypoechoic hematoma with retained drain (arrow), which was unsuspected at time of referral. No sepsis was identified when this hematoma was subsequently drained surgically.

globin. With increasing age, hematomas acquire a more homogeneous fluid density and appear hypoechoic on US images (Fig 7), low in signal intensity on T1-weighted SE MR images, and high in signal intensity on T2-weighted SE or STIR MR images. Calcification is commonly associated with muscle contusion (Fig 8). Hematomas are usually avascular, but rarely, organizing hematomas or areas of myositis ossificans may manifest as hyperemic masses. Contused muscle in the reparative hyperemic phase is prone to acute hemorrhage if the muscle unit is inadvertently loaded and the neovascularization disrupted.

configuration. Within days of injury, acute hematomas show high-signal-intensity areas on T1-weighted SE MR images because of the presence of methemo-

Sequelae of Muscle Injury There are several late sequelae of muscle injury. Masses may manifest in the lower limb, representing either (a) retracting muscle fibers caused by a substantial tear with no healing or (b) muscle herniation. Muscle hernias.—Muscle hernias and retractile muscle masses frequently involve the rectus femoris and are more obvious with the muscle functioning. The examination should always be performed with the patient standing or while isometrically contracting the muscle unit. Hernias are due to trauma-related defects in the epimysium investing the muscle (Fig 9),

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Figure 9. Intermittent lump (muscle hernia) on anterolateral side of lower portion of right leg of a 15-year-old soccer player. (a) Sagittal US image of normal (left) tibialis anterior muscle shows epimysium (arrows). (b) Sagittal US image of symptomatic right side obtained with patient standing shows loss of definition of investing epimysium, with bulging of tibialis anterior muscle at site of defect (arrows).

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and retractile muscle masses are indicative of substantial partial or complete rupture of the muscle unit with retraction of the ends of the disrupted muscle (Fig 10). Neither of these abnormalities can be positively diagnosed with MR imaging but benefit from dynamic US evaluation. Fibrous scarring.—Fibrous scarring results from severe or recurrent injuries, but most muscle injuries heal without cicatrization. Fibrosis is demonstrable at MR imaging as an area of low signal intensity with all pulse sequences (Fig 11) and is seen at US as a linear or stellate hyperechoic area (Fig 12). The fibrosis affects the muscle-tendon junction and predisposes to recurrent tears. Hematomas.—Hematomas are more commonly associated with contusion, rather than tears. Hematomas may manifest as a mass lesion that can be difficult to distinguish from a tumor without the appropriate medical history, which may on occasion require focused questioning of the patient following imaging. This is particularly true of sportsmen or children because the history may not be immediately associated with the mass in the patient’s mind if there is a temporal delay in manifestation. Conventional radiographs and computed tomography (CT) show curvilinear peripheral calcification in a long-established mass, a feature characteristic of hematoma and atypical for mineralizing sarcomas (Fig 13). Myositis ossificans.—Myositis ossificans follows severe contusions and reportedly occurs in 9%–20% of such injuries, particularly in the anterior thigh and adductor compartments (2–4). When superficial muscle groups are affected, patients present with (a) severe pain, often disproportionate to the initial injury, (b) reduced function, and (c) a mass. The mass has ill-defined margins at US and MR imaging, enhances in the early stages after administration of gadolinium-based contrast material, and shows neovascularization at US. Differentiation from a soft-tissue tumor can be difficult without the characteristic history of severe localized trauma. Myositis ossificans is distinct from osseous avulsion. The calcification is most often sheetlike, is ori-

Figure 8. Calcification in a 24-year-old rugby player with recurrent quadriceps pain after a contusional injury that had occurred months earlier. Transverse US images of both thighs were obtained. Hyperechoic foci with posterior shadowing in right rectus femoris muscle represents dystrophic calcification (arrows).

entated in the long axis of the injured muscle, and emanates from pluripotential mesenchymal muscle cells. Less frequently, a more discrete mass emanating from and attached to bone may be encountered. The latter may represent rupture of subperiosteal hemorrhage into the surrounding tissues. The associated calcification is first identified on conventional radiographs approximately 6 weeks following injury. US is a highly sensitive method of identifying myositis ossificans (Fig 14) as early as the 3rd week and is generally more sensitive at identifying calcification than is MR imaging (Fig 15) (5). Calcific myonecrosis.—Whereas myositis ossificans is associated with a relatively recent history of trauma, calcific myonecrosis is a late sequel, occurring between 10 and 64 years after the initial episode of trauma (6). Trauma is a common antecedent of calcific myonecrosis, like myositis ossificans. However, calcific myonecrosis may also follow thermal, electrical, or neurologic injury, where a compartment

Figure 10. Intermittent mass in anterior portion of thigh of a 25year-old marine. Sagittal US images of rectus femoris muscle in relaxed and contracted states confirm substantial muscle tear, with mass representing the retracting proximal muscle fibers (arrows).

Low-Energy Injuries of the Lower Limb

Figure 11. Recurrent quadriceps injury in a 35-year-old athlete. Transverse STIR MR image demonstrates tear of rectus femoris (short arrow), with low-signal-intensity fibrosis (arrowhead) surrounding normal central tendon (long arrow).

Figure 12. Recurrent tears along posteromedial side of lower portion of leg of a 44-year-old jogger. Sagittal US image shows linear hyperechoic zone (arrows) within distal gastrocnemius adjacent to muscletendon junction, indicative of scarring.

Figure 13. Mass in left groin of a 12-year-old boy. History of trauma was eventually elicited. (a) Pelvic radiograph and (b) transverse CT image show peripheral well-defined curvilinear calcification indicative of ossifying hematoma. Findings from other imaging examinations were less diagnostic: (c) Radioisotope bone scan after administration of technetium-labeled methylene diphosphonate (MDP) demonstrates nonspecific area of increased uptake ("hot spot"). (d) Transverse T2-weighted fast SE MR image demonstrates central mass lesion with surrounding edema.

syndrome and subsequent myonecrosis of the muscle unit represent the single common pathway shared by these varied causes. Patients present with an expanding mass, commonly in the lower portion of the leg, and show platelike calcification extending throughout at least one muscle compartment (Fig 16).

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Figure 14. Myositis ossificans in a 27-year-old professional soccer goalkeeper with injury to left thigh. Injury was sustained 8 weeks prior to imaging. (a) Coronal US image of asymptomatic thigh demonstrates linear interface between femur (arrows) and adductor magnus muscle. (b) US image of injured thigh shows undulating irregular echogenic mass at muscletendon junction of adductor magnus, which represents myositis ossificans (arrows).

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Figure 15. Myositis ossificans in right thigh of a 10-year-old boy with injury sustained in bicycling accident. (a) Conventional radiograph and (b) transverse CT image show sheetlike ossification indicative of myositis ossificans. (c) Nonenhanced and (d) gadolinium-enhanced sagittal T1-weighted SE MR images show rim enhancement in periosseous region along most of length of femur, representing resolving hematoma, but myositis ossificans cannot be appreciated.

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The calcification is amorphous, unlike that of myositis ossificans, which exhibits a trabecular structure when mature. Because calcific myonecrosis occurs in an older age group and occasionally involves the periosteum, the condition must be distinguished from neoplastic masses. The extent and the compartmentalization of calcification are indicative of the diagnosis. MR imaging shows a partially cystic mass and no evidence of soft-tissue enhancement (7).

Low-Energy Injuries of the Lower Limb

Figure 16. Calcific myonecrosis in a 29-year-old drug abuser who had pain and swelling in lower portion of leg with no acute inflammatory changes. History of trauma to lower part of leg in a motor vehicle accident 8 years earlier was elicited. (a) Conventional radiograph and (b) transverse CT image show extensive sheetlike calcification throughout tibialis anterior compartment, indicative of calcific myonecrosis.

Figure 17. Stress reaction in a 24-year-old marine with painful right hip. Transverse STIR MR image shows marrow edema in posterior column of right hip, which, in the absence of joint effusion or inflammatory markers, was considered to represent training-related stress reaction because no discrete fracture line was identified. Training recommenced at 6 weeks.

PELVIS AND HIPS
Low-energy injuries to the pelvic ring are encountered (a) in the form of stress fractures, when excessive force is applied to the normal bones of the pelvis, or (b) as an insufficiency fracture, when normal forces applied across the pelvis result in fractures because of intrinsic deficiency in bone structure (most frequently the result of osteoporosis). A third distinctive pattern of relatively low-energy pelvic fractures includes avulsion injuries, which are encountered predominantly in individuals following sporting activity and are more frequent in the immature skeleton.

occur anywhere in the pelvic ring. The posterior column of the acetabulum and the sacrum (Fig 17) are favored sites because of their relatively high loading (8). Sacral fractures or stress reactions often parallel the sacroiliac joint. The fracture line may be identifiable but is often obscured on STIR or fat-saturated MR images and is best shown on T1-weighted SE (Fig 18), T2-weighted fast SE (Fig 19), or gadolinium-enhanced MR images. The absence of a fracture line is not uncommon and is suggestive of trabecular microfracture or a stress reaction; such cases usually resolve more quickly and allow recommencement of graded physical activity within 2–3 weeks and running at 6 weeks. Atypical, eccentric, nonlinear stress reactions can be encountered where excessive loading is tractional at tendon insertions (Fig 20). CT, although good for depicting overt fractures (Fig 21), is less capable of depicting stress reactions without a fracture line and does not provide adequate information to assess other potential differential diagnoses relating to soft-tissue injury. Bone scintigraphy has good sensitivity for identifying stress injuries, but unless the findings are bilateral and symmetric, scintigraphic findings are often nonspecific and cannot be used to distinguish an early stress reaction from overt fracture, a point that can influence substantially the planning of a rehabilitation program versus surgical intervention.

Stress Fractures Stress fractures are sustained when the pelvis is subjected to excessive loading. This most frequently occurs during athletic training, in either elite or recreational athletes. The vogue for distance running in the general population has caused an increase in stress injuries of the lower limbs, including the pelvis. Conventional radiographs usually show normal findings, and in these circumstances, MR imaging is the preferred method of investigation. The injury is usually associated with marrow edema, which may have a linear orientation and

Insufficiency Fractures Insufficiency fractures occur when normal loads are applied to a structurally deficient pelvic ring. These fractures are frequently multiple and characteristically are bilateral and relatively symmetric (Fig 22). MR imaging is the investigation of choice in elderly patients with pelvic pain who are suspected of having insufficiency fractures because the specificity is high when symmetric abnormality is identified, even in the absence of a discrete fracture line. CT is an alternative to MR imaging and can also be used when the findings at

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Figure 18. Sacral stress fracture in a 41-year-old distance jogger. (a) Coronal STIR MR image shows right-sided sacral edema and normal joint. (b) Axial T1-weighted SE MR image shows incomplete fracture line. Training was successfully recommenced gradually at 4 weeks. Figure 19. Clinical presumption of pubic symphysitis in a 22year-old soccer player. Coronal T2-weighted fast SE MR image shows parasymphyseal stress fracture (black arrow) and edema at adductor insertions (white arrow).

Figure 20. Atypical stress reaction in a 40-year-old power walker with groin and left hip pain. Coronal STIR MR image shows focal edema around left lesser trochanter (arrow), which was considered to represent less typical pattern of stress reaction. Symptoms resolved rapidly with rest.

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MR imaging are equivocal, particularly in the presence of known malignancy, because CT excludes destructive change that is usually seen in pathologic fractures, but CT is generally less sensitive than MR imaging. Bone scintigraphy is also a useful screening test, but cases demonstrating asymmetry often require investigation with either CT or MR imaging. Insufficiency fractures commonly occur because of osteoporosis, but other metabolic disorders predisposing to fracture include osteomalacia and parathyroidrelated bone disease. In patients receiving radiation therapy for gynecologic malignancy, Blomlie et al (9) identified insufficiency fractures occurring in as many as 79% of the patients within 2 years of treatment. The MR imaging features either resolved or improved within the 30-month duration of the study. Abe et al (10) also found insufficiency fractures, but these oc-

Figure 21. Insufficiency fractures in a 71-year-old woman with low back, sacral, and hip pain. CT image shows typical insufficiency fractures (arrows) in both iliac bones.

Low-Energy Injuries of the Lower Limb
Figure 23. Radiograph of the three common sites of pelvic avulsion injuries: the anterior superior iliac spine (origin of sartorius) (arrowhead), the anterior inferior iliac spine (origin of rectus femoris) (long arrow), and the ischial tuberosity (origin of hamstrings) (short arrow).

Figure 22. Insufficiency fractures in a 65-year-old woman with unexplained low back and pelvic pain. Coronal STIR MR image shows bilateral symmetric areas of marrow edema in sacral alae and ischial regions (arrows), typical of insufficiency fractures.

Figure 24. Avulsion injury in a 25-year-old athlete with acute hip pain. Conventional radiograph shows avulsion by sartorius of anterior superior iliac spine (arrow).

curred in only 34% of the patients following pelvic irradiation and in 84% of the patients with pelvic pain. Multiple fractures were found in 85%, and fractures were symmetric in 67%. Unlike the insufficiency fractures, metastases, which were found in 3% of the patients, were all outside the radiation field.

Avulsion Injuries Avulsion injuries of the pelvic ring usually occur in young or skeletally immature individuals, commonly athletes. The injuries follow isometric muscle contraction and affect three main sites (Fig 23): the anterior superior iliac spine (origin of sartorius) (Fig 24), the anterior inferior iliac spine (origin of rectus femoris), and the ischial tuberosity (origin of the hamstrings).

Conventional radiographic evaluation is usually adequate to establish the diagnosis, but diagnostic difficulty can be encountered in the skeletally immature individual in whom ossification at the origins of these muscles is limited. Both MR imaging and US can be used to establish a positive diagnosis in these cases, but the US option is dependent on there being local musculoskeletal US expertise. US is usually immediately available and well tolerated by young children (Fig 25), but MR imaging is often preferred because it provides a more comprehensive evaluation in relation to more subtle muscle injuries or occult fractures in and around the pelvis, which are part of the working differential diagnosis in such cases. US is generally less accurate around the pelvis because limited access and increased depth of injury result in reduced image quality and sensitivity. Greater trochanteric avulsions are more commonly encountered in elderly patients and require further investigation. Associated intertrochanteric fractures are reported in as many as 66% of the patients, and most of these fractures are occult and are best demonstrated by MR imaging (11,12). Intertrochanteric injuries that extend across the femoral neck at MR imaging may warrant fixation of the femoral neck with nailing to avoid subsequent overt fracture (Fig 25). Long-standing and maturing avulsions may manifest as either (a) hypertrophic ossification simulating a mass lesion or (b) localized erosion caused by hyperemic osteolysis, which may be interpreted in error as erosion by an adjacent mass lesion. In both cases, the site of the lesion should suggest the diagnosis, and MR imaging can be used to exclude a mass lesion (Fig 26). MR imaging can also be used to identify coexistent pathologic findings that can contribute to

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Figure 25. Hamstring apophyseal avulsion in a 12-year-old boy. Sagittal US images of hamstring origin show normal left side (L), with cortical line (white arrow) capped with cartilaginous growth zone, and right side (R) with cortical avulsion (black arrow) with surrounding hypoechoic hematoma.

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Figure 26. Greater trochanteric avulsion in a 68-year-old man following a minor fall. (a) Pelvic radiograph shows greater trochanteric avulsion (arrow). On strength of conventional radiograph, MR imaging was suggested. (b) Coronal STIR MR image shows intertrochanteric edema (arrows), but (c) coronal T1-weighted SE MR image demonstrates incomplete fracture line (arrows). This patient was managed nonoperatively and was allowed to partially weight-bear at 4 weeks.

symptoms in avulsion injuries, such as the association of sciatic neuritis with injury of the ischial tuberosity (Fig 27).

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Occult Fractures and Soft-Tissue Injury As indicated in the previous paragraphs, MR imaging provides the most efficient and accurate method of diagnosing insufficiency fractures, but MR imaging should also be considered early in the work-up of patients with acute hip and pelvic pain following relatively low-energy falls in whom conventional radiographs are normal. Bone density need not necessarily be abnormal, and injuries to structures other than the pelvic ring are often encountered, including the femoral neck and surrounding soft tissues, in these patients. Bogost et al (13) showed pelvic ring fractures in 23%, femoral neck fractures in 37%, and soft-tissue injury in 74% of the patients with normal pelvic radiographs who were suspected of having occult injury. Screening with coronal STIR MR imaging is usually

sufficient to exclude injury, but additional coronal and axial T1-weighted SE and STIR MR images are required to fully evaluate abnormalities identified with the screening pulse sequence (Fig 28).

Groin Pain Pain in the anterior portion of the pelvis and groin is a common manifestation of pelvic injury. In the United Kingdom, most injuries are encountered in sportsmen and particularly soccer players, because many of these injuries occur as a result of twisting, turning, and kicking movements across the line of the body. Symptoms and signs may guide clinical decision

Low-Energy Injuries of the Lower Limb

Figure 27. Repetitive tractional injury of left ischial tuberosity in a 12-year-old boy. (a) Anteroposterior radiograph shows bone resorption (arrows). (b) Coronal STIR MR image shows granulating hyperemic interface (arrowheads).

Figure 28. Hamstring avulsion injury in a 27-yearold man. (a) Transverse CT image shows ischial avulsion (arrows). (b) Axial T1weighted SE and (c) axial STIR MR images show associated sciatic neuritis (arrow), which caused severe radiating leg pain.

making, but the differential diagnosis is broad and includes adductor injuries, hernias, pubic symphysitis, and stress fractures of the pubic rami. The investigative pathway is influenced by the most likely clinical diagnosis. If a hernia is most likely, US is preferred. MR imaging is substantially less capable of providing information to establish the diagnosis of hernia, given that nearly all hernias are reducible, and the posterior wall defects are not identifiable with nonstraining MR imaging. MR imaging is preferred if the other diagnoses outlined previously are more probable than a hernia. These patients should be encouraged to exercise or stress the injury in the 48 hours preceding MR imaging because subtle tears or sprains will be identified only by the presence of edema (Fig 29). Overt inguinal hernias are well recognized in middleaged nonathletic adults but are now increasingly diagnosed as a cause of performance-limiting injury in sports and athletics. The spectrum of disorder ranges from small tears in the transversalis fascia (sportsman hernia) and posterior wall weakness without herniation to direct or indirect herniation. Although a small number of hernias are indirect, most are direct and are acquired through injury to the posterior wall of the medial end of the canal in the region of the external inguinal ring. US of the inguinal canal is best achieved in transverse section, revealing an oval structure including the testicular artery and vein that can be identified with color flow imaging. The posterior wall is seen as a linear reflective line that moves away from the probe with straining. Weakness of the posterior wall without a defect or hernia is manifest by the posterior wall bulging toward the probe. A hernia is more focal and has more angular interface with the posterior wall and can be massaged back through the defect with gentle pressure applied through the probe head. Most hernias contain fat, but bowel is occasionally identified.

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Figure 30. Adductor brevis injury in a 26-year-old squash player with groin pain. Previous MR images had shown pubic symphysitis, but when the patient was imaged within 24 hours of exercise, (a) transverse and (b) coronal MR images demonstrate left-sided grade 1 adductor brevis injury (arrow), in addition to pubic symphysitis (arrowheads).

In patients in whom a hernia is not the most likely diagnosis, MR imaging is the preferred investigation. Coronal and axial T1-weighted SE and STIR (or T2weighted fast SE with fat saturation) MR images provide a good screening series but must include the proximal thighs and adductors. Both sides should be included to allow for comparison. T2-weighted fast SE MR images without fat saturation should not be used in preference to a fat-saturated pulse sequence because they have reduced sensitivity for muscle sprains and marrow edema. Pubic symphysitis is a stress-related reaction comprising degeneration and herniation of the symphyseal disk and reactive edema in the parasymphyseal bone. Determining clinical significance is difficult because this abnormality occurs commonly in otherwise asymptomatic sportsmen, particularly soccer players. Gross asymmetry in parasymphyseal marrow edema, although not uncommon, can indicate stress fracture of the pubic rami, rather than primary symphysitis (Fig 19). Injection of long-acting local anesthetic drugs and steroids into the symphysis can clarify the clinical significance of symphyseal abnormality.

Figure 29. Incomplete stress fracture or reaction in a 26-yearold marine with left hip pain exacerbated by exercise. Coronal STIR MR image shows incomplete stress fracture or reaction across femoral neck.

THIGH
Adductor Injuries Tears and strains of the adductor musculature are common (Fig 30), and this location is one of the more frequent sites to encounter myositis ossificans. Chronic or subacute adductor insertion avulsion injuries are also encountered and manifest clinically as “thigh splints.” These injuries have been recorded in adults (14) and, more recently, in the pediatric population (15). The manifestation comprises exerciserelated pain in the medial side of the thigh associated with periosteal reaction, periosteal edema at MR imaging, or increased radiotracer uptake at bone scintigraphy in children. There are no associated mass lesions.

Knowledge of this entity is important because it can avoid the need for biopsy. Similar tractional periostitis can also be encountered at the insertion of the vastus medialis and vastus intermedius (15).

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Hamstrings The hamstring unit is the most frequently injured muscle group in sportsmen. The semimembranosus and biceps femoris are most commonly affected. The prognosis in these patients relates to the magnitude of cross-sectional involvement of the muscle affected and is unrelated to the presence of fluid collections, areas of hemorrhage, or distal injury (16). As with all tears, identification of the muscle injured is primarily achieved by examination of the axial T1-weighted SE and STIR MR images, but unlike adductor tears, in which coronal images are supportive of axial data sets,

Figure 31. Recurrent hamstring tears in a 24-year-old soccer player who had recent severe pain radiating into lower portion of leg. Axial STIR MR image shows semimembranosus tear, with edema surrounding sciatic nerve (arrow).

pair. Because a large number of the referrals with suspected quadriceps rupture are erroneous, we usually screen with US and reserve MR imaging for cases in which US cannot distinguish a high-grade partial tear from complete rupture, or if internal derangement of the knee is suspected. Without the option or expertise to offer a US examination, it would be appropriate to default to MR imaging as the primary investigation. Secondary features of quadriceps rupture include waviness of the infrapatellar tendon, but this is a nonspecific sign and may also be found following knee injuries due to inhibition of quadriceps muscles.

Low-Energy Injuries of the Lower Limb

KNEE
Avulsion and Osteochondral Injuries Formal review of MR imaging of the knee is beyond the scope of this chapter, but several signs of ligamentous and osteochondral injury can be inferred from conventional radiographic evaluation of the injured knee, which should alert the reporting radiologist and clinician to associated injury. Arcuate Sign or Fracture Avulsion of the fibular collateral ligament insertion can be identified on anteroposterior and lateral views, providing the head of the fibula is not superimposed on the tibia. This injury is often associated with arcuate ligament, popliteus tendon, and anterior cruciate ligament disruption, and commonly requires surgical intervention (18). Bone bruising is often an accompaniment (Fig 32). Segond Fracture Lateral capsular avulsions extract a small fragment of bone from the tibia posterior to the attachment of the iliotibial tract at Gerdy’s tubercle. Segond fractures are associated with anterior cruciate ligament tears in more than 90% of the patients (Fig 33). Gerdy’s Avulsion Injury to Gerdy’s tubercle results from a varus injury; the tubercle is avulsed by the iliotibial tract. The detached fragment is usually much larger than the Segond fracture fragment and is associated with lateral capsular, fibular collateral, and anterior cruciate ligament injury (Fig 34). Osteochondral Fracture Shearing injuries at the osteochondral junction not infrequently follow minor trauma. The cartilage defects may be substantial; nonetheless, many are not identifiable on conventional radiographs. A thin layer of bone may be avulsed across the base of the hyaline cartilage, and the identification of a linear intraarticular flake can usually be interpreted to represent a substantial osteochondral injury. MR imaging is advisable to determine

Figure 32. Avulsion injuries in a 15-year-old soccer player injured in a tackle. Anteroposterior radiograph shows avulsion of fibular head (arcuate sign) (long arrow). In addition, second large lateral fragment (short arrow) and smaller intercondylar fragment (arrowhead) are suggestive of avulsions of iliotibial tract and anterior cruciate ligament, respectively.

sagittal T1-weighted SE and STIR MR images are preferred in a patient who is suspected of having hamstring injury. Tears occur in either the distal tendon or at the muscle-tendon junction anywhere along its length (17). Patients with chronic and sometimes acute hamstring injury can present with sciatica caused by irritation and inflammation of the sciatic nerve, which should be scrutinized on the axial images (Fig 31).

Quadriceps and Infrapatellar Tendons Injuries to the quadriceps and infrapatellar tendons, as opposed to the muscle units, are uncommon and are as frequently seen in athletic as nonathletic individuals. The diagnosis of infrapatellar tendon rupture is easily made at US, but the complexity of the multilayered quadriceps mechanism proximal to the patella is often challenging with either MR imaging or US. The main clinical question is to distinguish a partial from a complete tear, the latter requiring surgical re-

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Figure 33. Segond fracture in a 16-year-old male adolescent with twisting injury of knee. (a) Radiograph shows Segond fracture fragment (arrow) along lateral joint line. (b) Coronal T1-weighted SE MR image shows loss of definition of anterior cruciate ligament (black arrow) indicative of tear. The Segond fragment (white arrow) and donor site (arrowhead) are not easily appreciated.

its true size and origin. The patella is most frequently affected, with the medial facet of the patella being swept of its cartilage during lateral dislocation (Fig 35). Personal review of attempts to reattach such osteochondral fragments would suggest that these are generally unsuccessful.

LOWER PART OF LEG
Stress Fractures and “Shin Splints” Stress fractures in the lower limb are most common in the tibia and foot. Although the injury may merely reflect repetitive overloading in a biomechanically normal limb, gait disorders and footwear can predispose to injury. Most stress fractures occur in runners at the junction of the mid and proximal thirds of the tibia. The earliest conventional radiographic sign is loss of definition of the posterior cortex, followed by periostitis (Fig 36) and finally a linear zone of sclerosis. Schweitzer and White (19) found that hyperpronation of the foot could elicit stress-related MR imaging changes in the bone marrow of the foot and, to a lesser extent, the tibia and femur. In our practice, armed forces personnel not infrequently show changes consistent with stress-related injuries related to alterations in standard-issue footwear. Sagittal and axial images are useful in distinguishing stress fractures from nutrient foramen. The axial image also can be used to distinguish longitudinal stress fractures, with cortical clefts on axial images, from the more common transverse fracture pattern (20). STIR images are the most sensitive MR images in the identification of stress fractures (21). Stress-related injury in the tibia may also manifest with a distinct clinical entity commonly called shin

Figure 34. Gerdy’s avulsion in a 20-year-old man injured in a rugby tackle. Coronal proton-density–weighted (PD) MR image with fat saturation demonstrates iliotibial tract avulsion (black arrow). Bone fragment is larger than Segond fragment and arises from Gerdy’s tubercle in line with anterior meniscus, which is unstable in this case (black arrowhead). Medial collateral injury (white arrow) and bone bruising (white arrowheads) are evident.

splints. These patients have normal findings on conventional radiographs but can have MR imaging findings ranging from normalcy to stress fractures. Other patients will have periosteal fluid and diffuse marrow change, usually along the anteromedial border of the midportion of the tibia. Chronic shin pain is invariably associated with normal findings at imaging, indicating that MR imaging has less utility in this group (22).

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Achilles Injury The Achilles tendon, in reality, is best considered as a muscle-tendon unit that comprises the tendon it-

Low-Energy Injuries of the Lower Limb

Figure 35. Osteochondral fracture in a 22-year-old woman with twisted knee and laterally dislocated patella. (a) Anteroposterior radiograph shows ossific fragments (arrow) in lateral joint recess. (b) Coronal PD fat-saturated MR image confirms intraarticular loose body (arrows). (c) Axial PD fat-saturated MR image shows normal hyaline cartilage on lateral facet (long black arrow), but absent cartilage medially (short black arrow) and associated bone defect (arrowhead). Impaction bruising (white arrow) confirms lateral patellar dislocation.

Figure 36. Periostitis and stress fracture in a 20-year-old marine recruit with pain in lower portion of leg. (a) Lateral radiograph obtained at 5 days shows normalcy of initial conventional radiograph. (b) Lateral radiograph at 15 days shows subsequent evolution of periosteal reaction (arrows) consistent with stress fracture.

self, the gastrocnemius and soleus muscles, and their common muscle-tendon junction, which extends high into the calf (Fig 37). Injuries can be encountered at many sites, including the origins of the gastrocnemius and the Achilles tendon itself, but most injuries affect the muscle-tendon junction along its medial side (Figs 38, 39).

Achilles Tendinopathy Tendinopathy is the most common manifestation of chronic Achilles tendon overload, most frequently

manifests in middle age, and is more prevalent in flatfooted and obese individuals. Histopathologic analysis of these tendons reveals mucoid degeneration, with varying degrees of neovascularization. MR imaging is unnecessary in these patients because US better shows the distribution of tendon degeneration (Fig 40) and neovascularization (Fig 41). As a practical matter, US of the Achilles tendon can be mastered with limited experience. Neovascularization is linked to the symptoms but does not reflect a poor ultimate outcome (23).

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Figure 38. Grade 1 injury of medial side of muscle-tendon junction of right gastrocnemius in a 41-year-old man. Sagittal US images show normal left side (LT) and on right side (RT) demonstrate edema or hemorrhage separating muscle fibers (arrows) but little fiber disruption.

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Figure 37. Normal muscletendon junction on medial side of calf in a 24-year-old man. US image shows gastrocnemius and soleus feeding into common tendon, which on high-resolution US images often has a bilayered appearance (arrows).

Figure 39. Grade 2 injury of medial side of muscletendon junction of soleus in a 44-yearold man. Sagittal US image demonstrates muscle fiber disruption at tendon junction (arrows).

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Achilles Tendon Tears The main clinical dilemma in relation to Achilles tendon tears is to distinguish the following: (a) ruptured tendon from ruptured muscle-tendon junction, (b) the position and size of the tendon deficit, (c) the ability to oppose ruptured tendon ends with the foot plantar flexed, (d) partial from complete tear, and (e) tendinopathy from interstitial tear. Although MR imaging can perform well in relation to many of these questions, US is more accurate in relation to identifying tendon ends and the size of defects and can also be used to evaluate whether tendon ends can be brought within 1 cm of each other during plantar flexion, which allows an equinus plaster to be applied as an alternative to surgical intervention. US also takes a fraction of the time that MR imaging takes and can be performed while the patient is in the emergency department. Both MR imaging and US should be extended proximally to include the muscle bellies and muscle-tendon junction in the midportion of the calf.

Figure 40. Mucoid degeneration of right Achilles tendon in a 35-year-old man. Sagittal US images of both Achilles tendons show superficial (long arrows) and deep (short arrows) aspects of tendons. The right tendon is expanded with a hypoechoic ventral aspect (∗) indicative of mucoid degeneration.

ANKLE
Ankle injuries are one of the most common causes for patients to come to the hospital emergency department. While most injuries result from inversion (supination) of the foot, eversion (pronation) and associated rotation can result in specific patterns of ligamentous disruption and fracture. Although such injuries are not associated with high-energy impaction or

Figure 42. Pronation–lateral rotation type 3 injury. Radiograph shows high spiral fracture (arrow) typical of this pattern of fracture. Deltoid and distal tibiofibular ligaments should be suspected in this situation, as they would usually precede high fibular fracture.

Low-Energy Injuries of the Lower Limb

Figure 41. Hyperemic degenerative Achilles tendon in a 35year-old male distance runner. Sagittal US image obtained with color Doppler flow imaging demonstrates superficial hypoechoic tendon degeneration (arrow) and associated hyperemia (arrowheads).

Figure 43. Pronation–lateral rotation injury type 4. Radiograph shows posterior malleolar fracture (arrow). High fibular fracture is not included on this image (additional images were required). Deltoid and distal tibiofibular injuries are likely to coexist.

rapid deceleration, it could be argued that the forces applied through focused redirection of the body weight across the mortise does in fact represent a high-energy injury. The spectrum of abnormality includes ligament strains and tears, tibia and fibula fractures, talar dome injuries, tendon injury, and sinus tarsi syndrome.

Fractures Appropriate use of conventional radiographs remains the primary investigation of an ankle injury. Application of the Ottawa ankle rules (24) can allow safe triage and onward referral for imaging without unnecessary x-ray exposures by either medical or nursing staff. The optimal imaging protocol varies, but an anteroposterior ankle view is standard, while institutions vary in their use of a true lateral view and/or a mortise view. Marginal benefits have been

shown in the identification of medial and lateral malleolar fractures by combining all three views (25). The important point in interpretation is to appreciate the mechanism and true extent of the injury from the radiographic appearances, rather than merely reporting the presence of fractures. This will allow a far greater appreciation of associated ligamentous injury and is facilitated by an understanding of the Lauge-Hansen classification of ankle fractures. This classification identifies specific patterns of lateral malleolar fracture that help to categorize fractures into one of four main patterns (Fig 42). Within each pattern, there is a constant order of structural failure that includes the associated ligamentous structures. This system allows ligamentous injuries to be inferred in certain circumstances and also forms a framework for systematic analysis of the radiographs (Fig 43). Regardless of the views employed or the technical expertise of the radiologist, approximately 5% of the fractures cannot be identified. In many of these patients, the injury is managed clinically as a fracture, but cross-sectional imaging can be a great advantage to the diagnosis of occult bone and soft-tissue injury in these patients. MR imaging can be used to identify occult medial and lateral malleolar fractures, osteochondral injury, and bone bruising of the talar dome (Fig 44). Ligamentous and tendon injuries and sinus tarsi inflammation can also be identified. Because most of these patients are non–weight bearing and because all would have plaster (backslab) cast applied, MR imaging is not usually considered until the patient is reviewed at a fracture clinic at 7–10 days, assuming the diagnosis remains unclear from the repeat radiographs.

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Figure 45. Chondral injury of talar dome in a 25-yearold marine. Coronal T1-weighted SE MR arthrogram image demonstrates a chondral flap (arrow) projecting into superolateral joint space.

Hughes

Figure 44. Bone bruising of talar dome following a fall in a 20year-old man. Coronal STIR MR image demonstrates extensive high signal intensity (arrow) in superomedial aspect of left talus, consistent with posttraumatic bone bruising.

Ligament Injury Given the commonly associated effusions, acute ligamentous injury can often be assessed adequately with conventional MR imaging. Cases of long-standing instability without an effusion, however, are better assessed with MR arthrography, which also has superior sensitivity for subtle chondral defects (Fig 45) or impingement lesions (Fig 46), which are often included as part of the differential diagnosis at referral. US, although capable of depicting the anterior talofibular ligament, does not allow a complete evaluation of all ligaments and is not capable of addressing the alternative or coexistent pathologic findings outlined previously and is not, therefore, of primary use in this circumstance. Sinus Tarsi Abnormality The sinus tarsi syndrome refers to the presence of an inflammatory process in the sinus tarsi following an inversion (supination) injury. Patients are initially considered to have sustained lateral ligament injury or occult fracture but are referred for investigation when their condition fails to respond to standard immobilization. Clinical examination may identify pain during movement at the subtalar articulation. MR imaging in the acute setting identifies an inflammatory mass in the sinus tarsi that usually results from injury to the interosseous ligaments and consequently leads to subtalar instability. In later imaging of this disorder, associated degenerative change will also be identified in the posterior facets of the subtalar joint (Fig 47).

Figure 46. Softtissue impingement in lateral ankle gutter in a 29-year-old soldier. Transverse T1-weighted SE MR arthrogram image with fat saturation demonstrates soft tissues interposed in lateral gutter (arrow).

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Tendon Injury Evaluation of a specific tendon should be performed with US because it is quick and comprehensive, allows comparison with the contralateral side, and is unaffected by changing tendon orientation and associated MR artifacts around the malleoli. MR imaging is an alternative if US expertise is unavailable or if the differential diagnosis is broader and includes structures such as the spring ligament or osseous abnormality that are beyond the scope of US. In summary, this chapter covers some of the lowenergy or repetitive-strain injuries encountered in the lower limb. Although conventional radiographs have an important role in these injuries, early diagnosis of preradiographic bone abnormality and soft-tissue in-

Low-Energy Injuries of the Lower Limb

Figure 47. Sinus tarsi syndrome and associated subtalar joint degeneration in a 45-year-old man. (a) Coronal STIR MR image demonstrates an edematous inflammatory mass in sinus tarsi (arrows). (b) Sagittal STIR MR image shows focal areas of edema and early cyst formation in the posterior facet of the talus (arrows), indicative of advanced degenerative change.

jury can often be accelerated and a definitive diagnosis established by the appropriate use of MR and US imaging and occasionally CT and nuclear radiography.

References
1. Takebayashi S, Takasawa H, Banzai Y, et al. Sonographic findings in muscle strain injury: clinical and MR imaging correlation. J Ultrasound Med 1995; 14:899–905. 2. Jackson DW, Feagin JA. Quadriceps contusion in young athletes. J Bone Joint Surg Am 1973; 55:95–105. 3. Rothwell AG. Quadriceps hematoma: a prospective clinical study. Clin Orthop 1982; 171:97–103. 4. Ryan JB, Wheeler JH, Hopkinson WJ, et al. Quadriceps contusions. Am J Sports Med 1991; 19:299–304. 5. Peck RJ, Metreweli C. Early myositis ossificans: a new echographic sign. Clin Radiol 1988; 39:586–588. 6. Holobinko JN, Damron TA, Scerpella PR, Hojnowski L. Calcific myonecrosis: keys to early recognition. Skeletal Radiol 2003; 32:35–40. 7. O’Keefe RJ, O’Connell JX, Temple HT, et al. Calcific myonecrosis: a late sequela to compartment syndrome of the leg. Clin Orthop 1995; 318:205–213. 8. Major NM, Helms CA. Sacral stress fractures in long-distance runners. AJR Am J Roentgenol 2000; 174:727–729. 9. Blomlie V, Rofstad EK, Talle K, Sundfor K, Winderen M, Lien HH. Incidence of radiation-induced insufficiency fractures of the female pelvis: evaluation with MR imaging. AJR Am J Roentgenol 1996; 167:1205–1210. 10. Abe H, Nakamura M, Takahashi S, Maruoka S, Ogawa Y, Sakamoto K. Radiation-induced insufficiency fractures of the pelvis: evaluation with 99mTc-methylene diphosphonate scintigraphy. AJR Am J Roentgenol 1992; 158:599–602. 11. Craig JG, Moed BR, Eyler WR, van Holsbeeck M. Fractures of the greater trochanter: intertrochanteric extension shown by MR imaging. Skeletal Radiol 2000; 29:572–576. 12. Learch TJ, Pathria MN. Greater trochanteric fractures: MR assessment and its influence on patient management. Emerg Radiol 2000; 7:89–92. 13. Bogost GA, Lizerbram EK, Crues JV III. MR imaging in evaluation of suspected hip fracture: frequency of unsuspected bone and soft-tissue injury. Radiology 1995; 197:263–267.

14. Charkes ND, Siddhivarn N, Schneck CD. Bone scanning in the adductor insertion avulsion syndrome ("thigh splints"). J Nucl Med 1987; 28:1835–1838. 15. Anderson SE, Johnston JO, O’Donnell R, Steinbach LS. MR imaging of sports-related pseudotumor in children: mid femoral diaphyseal periostitis at insertion site of adductor musculature. AJR Am J Roentgenol 2001; 176:1227–1231. 16. Slavotinek JP, Verrall GM, Fon GT. Hamstring injury in athletes: using MR imaging measurements to compare extent of muscle injury with amount of time lost from competition. AJR Am J Roentgenol 2002; 179:1621–1628. 17. De Smet AA, Best TM. MR imaging of the distribution and location of acute hamstring injuries in athletes. AJR Am J Roentgenol 2000; 174:393–399. 18. Juhng SK, Lee JK, Choi SS, Yoon KH, Roh BS, Won JJ. MR evaluation of the "arcuate" sign of posterolateral knee instability. AJR Am J Roentgenol 2002; 178:583–588. 19. Schweitzer ME, White LM. Does altered biomechanics cause marrow edema? Radiology 1996; 198:851–853. 20. Craig JG, Widman D, van Holsbeeck M. Longitudinal stress fracture: patterns of edema and the importance of the nutrient foramen. Skeletal Radiol 2003; 32:22–27. 21. Schmid MR, Hodler J, Vienne P, Binkert CA, Zanetti M. Bone marrow abnormalities of foot and ankle: STIR versus T1-weighted contrast-enhanced fat-suppressed spin-echo MR imaging. Radiology 2002; 224:463–469. 22. Anderson MW, Ugalde V, Batt M, Gacayan J. Shin splints: MR appearance in a preliminary study. Radiology 1997; 204: 177–180. 23. Zanetti M, Metzdorf A, Kundert HP, et al. Achilles tendons: clinical relevance of neovascularization diagnosed with power Doppler US. Radiology 2003; 227:556–560. 24. Verma S, Hamilton K, Hawkins HH, et al. Clinical application of the Ottawa ankle rules for the use of radiography in acute ankle injuries: an independent site assessment. AJR Am J Roentgenol 1997; 169:825–827. 25. Brandser EA, Berbaum KS, Dorfman DD, et al. Contribution of individual projections alone and in combination for radiographic detection of ankle fractures. AJR Am J Roentgenol 2000; 174:1691–1697.

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NOTES

Susan D. John, MD

Pediatric Lower Extremity Trauma1

The patterns of musculoskeletal injury in infants, children, and adolescents differ considerably from those that occur in adults. The immature skeleton is structurally and mechanically different and responds differently to stress. The types of injury in the lower extremity are similar to those that occur in other portions of the immature skeleton, but unique types of injury exist in certain locations. A thorough understanding of the pathophysiology and imaging characteristics of the common and sometimes subtle injuries that occur in pediatric patients is crucial for prompt diagnosis and appropriate management. Despite well-established trauma protocols and improved imaging techniques, delays in diagnosis of such injuries still occur (1). Most fractures are adequately evaluated with radiographs, but cartilaginous and ligamentous injuries may require advanced imaging, such as magnetic resonance (MR) imaging. Computed tomography (CT) is useful for surgical planning with complex injuries at the joints. Ultrasonography (US) has limited usefulness in the detection of fractures and ligamentous injuries. This chapter illustrates the unique features of injuries in pediatric patients and includes discussion of optimal imaging strategies.

GENERAL CONSIDERATIONS IN EVALUATING THE IMMATURE SKELETON
The skeletal structures of young patients remain structurally and biomechanically immature. Bone is more porous, and the ratio of bone mineral to osteoid is lower in the pediatric skeleton throughout childhood. This difference in mineral content results in greater elasticity in immature bone, allowing the bone to recoil after traumatic forces up to the elastic limit. Forces that exceed the elastic limit result in fractures, which range from simple plastic deformation to complete displaced fractures. The cartilaginous physis and primary substantia spongiosa of the long bones are relatively weak in comparison with ossified bone. The physis is most susceptible to shearing forces, which commonly occur with twisting injuries or oblique trauma. The Salter-Harris classification of fractures is typically used to categorize epiphyseal-metaphyseal injuries. Physes are also present adjacent to various apophyses that exist in the pediatric pelvis, femur, and foot. Excessive force applied to the muscles attached to these ossification centers can result in avulsion fractures and chronic stress injuries. Ligaments are relatively strong when compared to the physes; thus, isolated ligamentous injuries are less common in children. However, ligament injuries associated with physeal fractures may require more aggressive treatment and should be recognized.

RSNA Categorical Course in Diagnostic Radiology: Emergency Radiology 2004; pp 217–226.
1From the Department of Radiology, MSB2.100, University of Texas Houston Medical School, 6431 Fannin, Houston, TX 77030 (e-mail: [email protected]).

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John
Figure 1. Salter-Harris type I fracture of distal tibia. (a–d) AP and lateral radiographs show (a, c) mild widening of distal physis (arrow) of right tibia, as compared with (b, d) normal contralateral tibial physis (arrow). (e) AP radiograph obtained 2 weeks later shows sclerosis along the metaphysis at the physis, with mild adjacent periosteal reaction, indicating healing.

FRACTURE TYPES
Epiphyseal-Metaphyseal Fractures Fractures involving the growing ends of the long and short tubular bones constitute 15%–30% of all fractures in childhood (2,3). The common feature of this category of fracture is injury to the cartilaginous physis, with separation of the epiphysis from the metaphysis. Associated fractures of the epiphysis or metaphysis and displacement of the epiphysis determine the prognosis and management of these injuries. Several classification systems have been proposed, but the most widely used classification is that described by Salter and Harris (4) in 1963. The number of categories has been expanded by other investigators, such as Ogden (5), who included new categories of fractures that do not directly involve the physis but

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can result in growth disturbance, and Shapiro (6), whose classification is based on epiphyseal and metaphyseal blood supply in an attempt to better predict which fractures will result in premature closure of the physis. A more recent classification by Peterson (7) adds categories for (a) transverse compression metaphyseal fractures with extension to the physis and (b) fractures with a portion of the physis missing (usually open fractures or gunshot wounds), because of the high incidence of unfavorable outcomes with such fractures. None of these classification systems include the Salter-Harris type V fracture, an isolated crush injury of the physis that is rare, if it occurs at all. Nevertheless, the Salter-Harris system continues to be favored by most physicians, probably because of its simplicity and familiarity.

Pediatric Lower Extremity Trauma
Figure 2. Salter-Harris type III fracture of distal tibia (Tillaux fracture). (a) AP radiograph shows that the displaced fragment (arrow) of the lateral epiphysis of the distal tibia is partially obscured by the overlying fibula. (b) AP radiograph from another patient shows subtle epiphyseal fracture (arrow). (c) Coronal reconstruction CT image of same patient as in b demonstrates more clearly the extent of the fracture and degree of displacement.

Detection of Salter-Harris injuries of the lower extremities on radiographs can be challenging when displacement of the fragments is minimal. In addition to well-positioned anteroposterior (AP) and lateral views, oblique views are often helpful for identifying subtle fracture lines and physeal widening. Salter-Harris type I fractures, which are manifest only as widening of the physeal line (Fig 1), can be difficult to diagnose with confidence without a comparison view of the contralateral normal extremity. The most common sites of physeal injuries of the lower extremities are the distal portions of the tibia and fibula (25% of epiphyseal injuries) (8) and the phalanges of the toes. Physeal injuries of the distal tibia and fibula can be serious because of the potential for asymmetric growth arrest, which leads to leg shortening and angular joint deformity. Inversion (supination) injuries of the ankle are the most common, and fractures caused by this mechanism have the highest incidence of complications. Distraction of the joint laterally results in Salter-Harris type I and II fractures of the distal fibula or cortical avulsion injuries of the fibular epiphysis. Small avulsion fragments must be differentiated from normal accessory ossicles that are common in the foot and ankle. US can be used to identify subperiosteal hematoma or swelling of the peroneus longus tendon that may signify an occult Salter-Harris type I fracture of the fibula (9). However, these injuries are often treated conservatively, with good results, on the basis of clinical evidence alone without elaborate imaging. Ankle inversion (supination) may also impact the medial malleolus on the hindfoot, usually causing a Salter-Harris type III or IV fracture of the tibia.

Eversion (pronation) injuries of the ankle often cause severe disruption of the ankle mortise. A wide variety of fractures can occur, including medial malleolar avulsions, distal fibular shaft fractures, and SalterHarris type III fractures through the lateral tibial epiphysis. The distal tibia is the most common site for Salter-Harris type III fractures, most often occurring when the physis is partially fused between the ages of 12 and 15 years. Fusion of the medial aspect of the physis precedes lateral fusion, and thus fractures tend to involve the lateral portion of the tibial epiphysis, the pediatric equivalent of a Tillaux fracture (Fig 2). Another type of fracture that occurs when the tibial physis is partially fused is the triplane fracture, a complex injury resulting from a combination of axial loading and external rotation of the foot on the tibia with the foot in plantar flexion. Fractures occur axially through the unfused portion of the distal tibial physis, sagittally through the epiphysis, and coronally through the metaphysis (Fig 3). The fracture may consist of two, three, or four components, depending on the locations of the fracture lines with respect to the partially fused physis. Optimal treatment requires internal fixation if greater than 2 mm of displacement of the fragments remains after attempted closed reduction. The complex anatomic structure of this fracture can be difficult to ascertain on radiographs, and CT is generally used to provide a higher degree of accuracy and detail (10). MR imaging can also be used and may be more sensitive for minimally displaced fractures. Epiphyseal-metaphyseal fractures are less common at the knee than at the ankle in children. Epiphyseal separations involve the distal femur more commonly

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Figure 3. Triplane fracture of distal tibia. (a) AP view shows fractures transversely through the physis (arrows) and sagittally through the epiphysis (arrowhead). (b) Coronal metaphyseal fracture (arrow) is clearly visible only on the lateral view.

John

Figure 4. Salter-Harris injury of the distal femur. (a, b) AP and lateral radiographs faintly show fracture (arrows) extending through distal femoral epiphysis. Only minimal irregularity is seen along the medial aspect of the distal femoral metaphysis. (c) Coronal proton-density–weighted fat-saturated MR image more accurately defines the fractures through the epiphysis and metaphysis.

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than the proximal tibia and are most often seen in adolescents with major trauma. When the fragments are displaced, the patient should be carefully examined for injuries to the popliteal artery or peroneal nerve. Salter-Harris injuries are common in the distal femur of older children and adolescents (Fig 4). Physeal injuries at the knee in infants usually are caused by birth trauma or child abuse. Nondisplaced fractures of the primary spongiosa paralleling the physis are common in child abuse and are virtually pathognomonic in an infant with healthy bones. Although these injuries resemble Salter-Harris type II fractures, Kleinman

et al (11) revealed that the injuries are generally confined to the metaphysis and differ from epiphyseal separations that tend to occur with accidental trauma. The classic metaphyseal fractures of child abuse occur with violent twisting of the lower extremities, either directly or indirectly during episodes of forceful shaking. Small corner fragments or entire rims of the metaphysis may be visible as separate fragments on radiographs (Fig 5). These fractures can be subtle and require high-resolution well-collimated images. Similar fractures can occur accidentally in infants with fragile bones caused by congenital infection or metabolic bone disease.

Pediatric Lower Extremity Trauma

Figure 6. Buckle fracture of distal femur. (a, b) Radiographs show mild buckling of the distal femoral metaphysis (arrow) that is more prominent anteriorly on (a) lateral view than medially on (b) AP view. (c) With healing, AP radiograph shows linear sclerosis that reveals the complete transverse extent of buckle fracture (arrows).

Figure 5. Metaphyseal fractures of child abuse in a young infant. AP radiograph shows healing corner-type fractures (arrows), caused by nonaccidental trauma.

The proximal femoral physis is a relatively weak point at the hip and is a fairly common site of physeal injuries, especially in young children. Salter-Harris type I and II fractures are most frequent and are manifest as widening of the physeal line. In some patients, the metaphysis becomes displaced from the epiphysis, either acutely with trauma or on a subacute or chronic basis with slipped capital femoral epiphysis. Whatever the cause of the displacement, prompt immobilization and open reduction with internal fixation usually are warranted. Complications such as avascular necrosis, varus deformity, early physeal closure, and nonunion are common and can result in serious longterm disability (12).

Buckle (Torus) Fractures Longitudinal (axial) force applied to long and short tubular bones in children often results in failure in the thin cortex, which buckles along with the underlying trabecular bone (13). Buckle fractures are much more common in young children but can be seen throughout childhood and adolescence. Such fractures are exceedingly rare in the mature skeleton. With buckle fractures, no radiolucent fracture line is visible, and cortical disruption is typically absent. This type of fracture is most common in the metaphysis near the growth plate, where the cortex is thinnest, but buckling can also occur some distance away in the diaphysis. The milder forms of this type of fracture may show cortical buckling that involves the cortex along only one side of the bone (Fig 6). In some cases, the fracture causes only slight angulation in the normally straight cortex. Care must be taken to identify subtle fracture extensions from the buckled cortex to the nearby physis, which may alter the treatment and prognosis of the injury. Young children frequently sustain buckle-type fractures in the proximal and distal metaphyses of the tibia and fibula. Buckling of the anterior cortex of the proximal tibia may be mistaken for the yet undeveloped tibial tuberosity if a comparison view of the normal contralateral tibia is not available (Fig 7). Buckle fractures of the metatarsals are also common and should be sought in young children who present with a limp and no history of known trauma. Such fractures often result from a fall accompanied by impaction of the forefoot against the ground. Buckle fractures of the first metatarsal are especially common

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Figure 7. Buckle fracture of the proximal tibia. (a, b) Radiographs show slight cortical buckling (arrow) of the proximal tibia, which is slightly more prominent on (b) lateral view than on (a) AP view.

John

after a child jumps from a height, thus acquiring the nickname of “bunk-bed fractures” (Fig 8). The same mechanism can lead to impaction fractures of the cuboid when stress is greater along the lateral aspect of the foot. Cuboid fractures may be occult acutely, only appearing as linear sclerosis during healing (Fig 9). Buckle and transverse fractures of the calcaneus are also seen. Calcaneal fractures tend to be more benign in children than in adults, despite a fairly high incidence of involvement of the posterior subtalar joint (14). Like tarsal fractures, calcaneal fractures can be difficult to detect when acute, but linear or archlike sclerosis develops as the fracture begins to heal (15).

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Plastic Deformation Injuries and Greenstick Fractures Immature bone is more resilient under bending forces because of greater elastic recoil, but when the elastic limit is reached, bowing deformity (plastic deformation) remains after the force is released. Such injuries are accompanied by microscopic infractions along the convex edge of the deformity; however, no fracture line is visible radiographically. The only evidence of plastic deformation on radiographs is the altered contour of the bone. Because the long bones of the extremities tend to have a normally curved contour, bowing fractures are difficult to detect unless they are severe. Comparison with the uninjured extremity is an invaluable aid in detecting these subtle injuries (16,17). The fibula is the most common bone in the lower extremity to sustain a plastic deformation injury. Greenstick fractures result from the same type of bending force that causes plastic deformation, but with greater intensity of force. Failure occurs through

Figure 8. "Bunk-bed" fracture of the first metatarsal. AP radiograph shows mild buckling (arrows) of the cortices of the proximal metaphysis of the first metatarsal, which indicates an impaction injury.

the cortex along the convex surface of the deformity only. In the leg, plastic deformation of one bone will often accompany a greenstick fracture of the adjacent bone. Although the bowing injury appears relatively

fracture. Therefore, plastic deformation injury must be identified promptly and reduced if necessary. Angulation deformity of less than 20° will usually remodel in young children, but in children older than 4 years or with a greater degree of angulation, correction of the deformity should be considered.

Pediatric Lower Extremity Trauma

Figure 9. Cuboid fracture. Radiograph shows linear sclerosis (arrow) without cortical buckling.

Figure 10. Hairline transverse fracture of proximal tibia. (a, b) AP and lateral radiographs show subtle transverse radiolucency (arrow). (b) Lateral view shows mild anterior buckling at fracture site.

innocuous, the deformity often remodels slowly and may interfere with adequate reduction of the adjacent

Transverse, Oblique, and Spiral Fractures Transverse, oblique, and spiral fractures are common in the lower extremities in children and adolescents, and imaging evaluation does not differ substantially from that used in adults. However, the incidence of fractures in certain locations is different in the immature skeleton. Femoral neck fractures are rare in otherwise healthy children and almost always are caused by high-velocity trauma, fall from a height, or other severe types of trauma (18). Transcervical fractures account for from 20% to 50% of femoral neck fractures in children (19–21). The higher incidence of fractures in this region is partially caused by the frequency of bone lesions, such as bone cysts and metastases, in the femoral neck. Careful assessment for such lesions should occur when a femoral neck fracture is found with no history of major trauma. Fractures of the femoral shaft can result from a variety of traumatic insults, including direct blows, rotational forces, and high-velocity axial loading. Femoral fractures in older children require forces of greater magnitude, but young ambulating children can sustain spiral or oblique fractures with relatively minor twisting injuries. In infants, femoral shaft fractures are uncommon and should raise at least moderate suspicion of nonaccidental trauma (22,23). The majority of femoral shaft fractures occur in the midportion of the shaft. The degree of overriding of the fracture fragments on a radiograph obtained without traction helps to determine whether the fracture should be managed with early cast immobilization or traction. A mild degree of overriding (1–2 cm) is desirable in children between the ages of 2 and 10 years to prevent overgrowth of the femur during healing. Supracondylar femur fractures tend to become anteriorly displaced because of contraction of the gastrocnemius, and thus they are usually managed with pin traction or external fixation. Most femoral shaft fractures are isolated injuries, but care should be taken to exclude an associated femoral neck or physeal fracture. Transverse fractures are more common in the proximal tibia than in the femur; and in younger children, these fractures can be hairline and subtle (Fig 10). Proximal tibial fractures in children often result from impaction and hyperextension of the leg at the knee and may be accompanied by buckling of the anterior cortex of the proximal tibia. A similar fracture can occur in older children who are injured while jumping on a trampoline. Valgus angulation at the fracture site during healing of these fractures is not uncommon. Relatively

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Figure 11. Toddler fracture of the tibia. Hairline spiral fracture (arrows) of the distal tibial diaphysis was faintly visible only on AP view.

Figure 12. Stress fracture of the proximal tibia. Lateral radiograph shows cortical thickening (arrow) along the dorsal aspect of the proximal tibial diaphysis.

John

Figure 13. Avulsion fractures around the hips. (a) AP radiograph of pelvis shows the subtle asymmetry (arrow) of the margins of the iliac bone just above the right acetabulum. (b) Oblique view of the right hip more clearly demonstrates avulsion of ossification center (arrow) from anterior inferior iliac spine. (c) AP radiograph obtained from another child shows avulsion (arrow) of the lesser trochanter.

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minor twisting injuries of the ankle and leg can cause nondisplaced spiral fractures of the tibial shaft (Fig 11). This fracture is so common in children between 1 and 2 years of age that it has been called the “toddler fracture.” Hairline spiral tibial fractures can present a diagnostic challenge because of their subtlety, the frequent lack of a history of trauma, and the tendency for manifestation in healing states when the fracture line may not be easily

Figure 14. Avulsion fracture of the tibial tuberosity. Lateral radiograph shows complete separation of the ossification center of the tibial tuberosity (arrow).

diographic confirmation of the fracture is made. Most pelvic avulsion injuries heal with conservative management. Avulsion fractures in the lower extremities, however, tend to be more unstable and require pin fixation. Acute avulsion of the tibial tubercle is a common example of such an injury (Fig 14). Tibial tuberosity avulsion fractures typically occur during sports, especially basketball (25). Acute tubercle avulsions should not be confused with the stable chronic form of injury at this site, Osgood-Schlatter disease. In conclusion, the unique properties of the immature skeleton are responsible for a relatively high incidence of extremity fractures that are subtle and difficult to detect. The best imaging tools available for evaluating extremity fractures in infants and children are well-positioned and optimally exposed radiographs. Such images will reveal the fractures in almost all cases, particularly when the interpreter has a thorough understanding of the peculiarities of fractures in the younger patient. CT and MR imaging can help to detect occult bone injuries and nonosseous structures.

Pediatric Lower Extremity Trauma

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visible. Symptoms may mimic an ankle injury, and tibial radiographs should be considered whenever the clinical findings are suggestive of an ankle fracture in a young patient but none is found.
1. Furnival RA, Woodward GA, Schunk JE. Delayed diagnosis of injury in pediatric trauma. Pediatrics 1996; 98:56–62. 2. Mann DC, Rajmaisa S. Distribution of physeal and nonphyseal fractures in 2,650 long-bone fractures in children aged 0-16. J Pediatr Orthop 1990; 10:713–716. 3. Mizuta T, Benson WM, Foster BK, et al. Statistical analysis of the incidence of physeal injuries. J Pediatr Orthop 1987; 7:518–523. 4. Salter RB, Harris WR. Injuries involving the epiphyseal plate. J Bone Joint Surg Am 1963; 45:587–622. 5. Ogden JA. Injury to the growth mechanism of the immature skeleton. Skeletal Radiol 1981; 6:237–253. 6. Shapiro F. Epiphyseal growth plate fracture-separation: a pathophysiologic approach. Orthopedics 1982; 5:720–736. 7. Peterson HA. Physeal fractures. III. Classification. J Pediatr Orthop 1994; 14:439–448. 8. Devalentine SJ. Epiphyseal injuries of the foot and ankle. Clin Podiatr Med Surg 1987; 4:279–310. 9. Gleeson AP, Stuart MJ, Wilson B, Phillips B. Ultrasound assessment and conservative management of inversion injuries of the ankle in children: plaster of Paris versus Tubigrip. J Bone Joint Surg Br 1996; 78:484–487. 10. Felman AH. Tillaux fractures of the tibia (in adolescents). Pediatr Radiol 1989; 20:87–89. 11. Kleinman PK, Marks SC, Blackbourne B. The metaphyseal lesion in abused infants: a radiologic-histopathologic study. AJR Am J Roentgenol 1986; 146:895–905. 12. Rattey T, Piehl F, Wright JG. Acute slipped capital femoral epiphysis. J Bone Joint Surg Am 1996; 78:398–402. 13. Light TR, Ogden DA, Ogden JA. The anatomy of metaphyseal torus fractures. Clin Orthop 1984; 188:103–111. 14. Wiley JJ, Profitt A. Fractures of the os calcis in children. Clin Orthop 1984; 188:131–138. 15. Schindler A, Mason DF, Allington NJ. Occult fracture of the calcaneus in toddlers. J Pediatr Orthop 1996; 16:201–205. 16. Borden S IV. Roentgen recognition of acute plastic bowing of the forearm in children. Am J Roentgenol Radium Ther Nucl Med 1975; 125:524–530. 17. Neumann L. Acute plastic bowing fractures of both the tibia and the fibula in a child. Injury 1990; 21:122–123.

Avulsion and Stress Fractures Stress fractures in children have the same imaging characteristics as those that occur in adults, but the distribution of stress fracture sites differs slightly in younger patients. Stress fractures are common in the proximal tibia (24), in the same location that hairline transverse and buckle-type fractures often occur. As they heal, cortical thickening becomes apparent along the dorsal aspect of the proximal tibia (Fig 12). Other common sites include the cuboid, fibula, and pelvis. As with adult stress fractures, the lesions are occult radiographically in the acute stage. MR imaging is sensitive for localizing acute stress injuries. Avulsion fractures in the immature skeleton usually result from excessive forces applied to ligaments that attach to unfused apophyseal centers. These injuries may occur acutely, but they more commonly occur subacutely from chronic repetitive traction. The multiple apophyses in the hips and pelvis fuse relatively late, allowing ample time for avulsion injuries to occur during adolescence. The separation of the apophyseal ossification centers from the femur (lesser or greater trochanter) or the pelvis (anterior superior iliac spine, anterior inferior iliac spine, ischium, iliac crest) may be subtle and sometimes requires oblique views (Fig 13) or comparison views for verification. MR imaging can be used to depict these injuries, but the findings can be less specific and may be suggestive of other conditions, such as osteomyelitis, unless ra-

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18. Azouz EM, Karamitsos C, Reed MH, Baker L, Lozlowski K, Hoeffel JC. Types and complications of femoral neck fractures in children. Pediatr Radiol 1993; 23:415–420. 19. Morrissy R. Hip fractures in children. Clin Orthop 1980; 152:202–210. 20. Swiontkowski MR, Winquist RA. Displaced hip fractures in children and adolescents. J Trauma 1986; 26:384–388. 21. Davison BL, Weinstein SL. Hip fractures in children: a longterm follow-up study. J Pediatr Orthop 1992; 12:355–358.

22. Gross RH, Stranger M. Causative factors responsible for femoral fractures in infants and young children. J Pediatr Orthop 1983; 3:341–343. 23. Dalton HJ, Slovis TM, Helfer RF, Comstock J, Schuerer S, Riolo S. Undiagnosed abuse in children younger than 3 years with femoral fractures. Am J Dis Child 1990; 144:875–878. 24. Ohta-Fukushima M, Mutoh Y, Takasugi S, Iwata H, Ishii S. Characteristics of stress fractures in young athletes under 20 years. J Sports Med Phys Fitness 2002; 42:198–206. 25. McKoy BE, Stanitski CL. Acute tibial tubercle avulsion fractures. Orthop Clin North Am 2003; 34:397–403.

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