Rapid multidetector imaging assesses multiple injuries in stable patients

Trauma CT offers one-stop diagnosis

By: Mark P. Bernstein, M.D., And Stuart E. Mirvis, M.D.

Over the last decade, CT has become the primary diagnostic tool in the evaluation of the hemodynamically stable trauma patient. The mid-1970s witnessed the emergence of CT for assessment of neurological injury in the setting of head trauma: For the first time, noninvasive intracranial imaging was possible to diagnose and exclude hemorrhage and herniation. By the 1980s, emergency CT had revolutionized the diagnosis of traumatic brain injury. As technology advanced, CT scanners acquired more data more quickly, enabling scanning of a greater spectrum of patients. By the mid-1980s, leading trauma centers began using CT in the stable blunt trauma patient to assess potential abdominal injury.

Early experience found CT to be highly sensitive, specific, and accurate. CT reduced dramatically the need for exploratory laparotomy and eliminated the use of radionuclide imaging and abdominal aortography for diagnosis.¹ CT's role in trauma looked promising, but further progress was still necessary before comprehensive imaging of the true polytrauma patient could be performed in a single visit to the CT suite.

The helical, or spiral, CT scanner became available in the late 1980s. Advances in both slip-ring gantry design and computer technology allowed much faster scanning, as the patient traveled through the CT gantry in one continuous motion. Respiratory artifact decreased as acquisition times dropped markedly. Computer processing was key to handling this new "volume" of acquired data. Faster microprocessors enabled rapid image reconstruction, so the acutely injured patient could be imaged without a major time burden. Spiral CT with rapid power-bolus injection of intravenous contrast material became the standard of care to evaluate thoracic and abdominal organs, as well as vascular structures-especially the aorta-in the hemodynamically stable blunt trauma victim.

The newest generation of multidetector-row scanners uses subsecond scanning times to collect up to 16 slices of data in a single revolution, making larger patient coverage possible in a single breath-hold with thinner slices and greater spatial resolution. Motion and arterial pulsation artifact are minimized. Collimation can be retrospectively changed thanks to near-isotropic imaging that allows for exquisite multiplanar reformations and 3D reconstructions. Three-D CT images from volume data sets provide additional information with improved diagnostic accuracy, allowing the surgeon to better visualize complex injuries such as facial and pelvic fractures. Moreover, faster scanning techniques can optimize and more precisely separate arterial and venous phase imaging. These developments have stimulated interest in CT angiography in trauma.

MULTITRAUMA PATIENTS

The widespread availability of spiral CT has altered the management of both blunt and penetrating injury. CT evaluation provides essential information for triage and management of the multitrauma patient. Precise localization and extent of organ injury and hemoperitoneum can be accurately determined with increasingly confident interpretation. Injuries such as high-grade hepatic or splenic lacerations that, until recently, would routinely have prompted surgical exploration are often managed by observation, with close monitoring and repeat CT evaluation or angiographic assessment with potential intervention. Contrast-enhanced spiral CT can indicate the presence of vascular injury such as active arterial extravasation or pseudoaneurysm formation. CT also plays a major role in follow-up of the trauma patient, determining injury resolution or progression and potential development of associated complications.

Stabilization at the scene, rapid transport to a trauma center, and thorough assessment by an experienced trauma team with accurate, timely diagnoses and appropriate management is critical to treatment. A small window of time, referred to as the "golden hour," is necessary for stabilization to occur so that morbidity and mortality can be minimized. The University of Maryland Medical System/Shock Trauma Center in Baltimore receives approximately 7000 trauma victims annually. The center serves as the hub of the statewide Maryland Institute for Emergency Medical Services Systems (MIEMSS), supported by a team of ambulances and a dozen helicopters. The trauma team assesses and resuscitates the patient according to standard advanced trauma life support (ATLS) protocols. The unstable patient requires urgent intervention and does not belong in a CT suite.

While clinical examination is crucial to evaluate hemodynamic status, determine life- and limb-threatening trauma, and assess mechanisms and patterns of injury, many internal injuries can escape detection. A decreased level of consciousness or distracting injuries may severely limit clinical assessment of the multitrauma patient. Many thoracic injuries such as pneumothorax, hemothorax, and pulmonary contusion or laceration cannot be readily evaluated clinically. It is not possible to exclude abdominal or pelvic organ injury on a clinical basis, according to ATLS standards. Only proper management with the combined efforts of the trauma team and emergency radiologist will permit timely triage of patients into "expectant management"-observation, angiographic intervention, or surgery. Contrast-enhanced spiral CT is thus vital for the assessment and evaluation of injury in the hemodynamically stable multitrauma patient.

sigma Head injury. Traumatic brain injury accounts for 52,000 deaths in the U.S. annually.² Trauma is the leading cause of death in patients under 40, and approximately 50% of these fatalities are related to severe head injury. The greatest number of traumatic brain injuries come from motor vehicle collisions, followed by falls, and the populations most affected are young adult males and the elderly. Alcohol use further increases these risks. Fortunately, however, the use of seatbelts, airbags, and helmets has brought about a decline in incidence of traumatic brain injury.³

The primary goal in managing severe head injury patients is to preserve life and neurologic function. The secondary goal is to identify intracranial lesions that will negatively affect outcome. CT is the method of choice for rapid, accurate evaluation of intracranial and craniofacial injury.

Neurological examination in the acute trauma victim is often unreliable and may underestimate the severity of injury. The Glasgow Coma Scale (GCS), a measure of best motor, verbal, and eye-opening response, has been used as a guide to manage trauma patients. A GCS of 8 to 14 indicates moderate injury and mandates CT evaluation, and a score of 7 or less represents severe injury with emergent CT scanning and neurosurgical assessment. Only patients with a GCS of 15 are managed conservatively. The GCS score is unable to accurately predict which patients will demonstrate intracranial injury, and CT remains the standard of care in the evaluation of traumatic brain injury.

At the Shock Trauma Center, we perform unenhanced multislice CT at 5-mm collimation in all stable trauma patients with head injury. The spectrum of intracranial disease identifiable with CT includes subdural hematoma, epidural hematoma, subarachnoid hemorrhage, contusion and diffuse axonal injury, cerebral edema and herniation, and infarction.

sigma Facial bone fractures. Facial injuries are clinically undetected in more than half of intubated multitrauma patients.⁴ Conventional CT first overcame the limitations of plain film interpretation by removal of overlapping bony structures. Spiral CT further simplified diagnosis of facial trauma by allowing for multiplanar reformations and 3D reconstruction, while reducing patient motion and registration artifact. Not surprisingly, spiral CT of the facial bones has proven to be more accurate than plain film for fracture detection and displacement and for diagnosis of soft-tissue injury.^5-7 Our protocol involves 1-mm beam collimation with unenhanced scanning from the hard palate to the top of the frontal sinuses. Fused 3-mm images are used for workstation viewing and interpretation while the unfused data are used to generate near-isotropic coronal reconstructions.

sigma Cervical spine injury. Cervical spine fractures can lead to devastating neurologic injury, and clinical evaluation of the cervical spine in the patient with multiple injuries is fraught with difficulty. Patients may be comatose, unreliable, intoxicated, or combative. More than two thirds of patients with cervical spine fractures initially present neurologically intact. Imaging of the cervical spine is therefore critical to prevent delayed diagnosis and potential neurologic deficit.

Spinal injury is a major source of disability, predominately affecting young adult males and elderly females. Traumatic lesions are most commonly identified at the C1/C2 and C4-C7 levels. CT provides accurate bony detail without the superimposition that plagues plain film interpretations. Plain film sensitivity for fracture is only 65%,^8,9 and specificity in high-risk patients is less than 75%.¹⁰ Several studies advocate the use of CT as a screening tool for evaluation of the entire cervical spine in the emergency setting.

Nunez et al first compared screening the entire cervical spine with spiral CT to plain radiography and found 98% sensitivity for CT.⁹ Hanson et al evaluated more than 600 adult blunt trauma patients with spiral CT and reported a 95% sensitivity, 93% specificity, and overall accuracy of 93%. Ptak et al screened 676 multitrauma patients with 98% sensitivity, 100% specificity, and accuracy of 99.9%. Positive and negative predictive values were 100% and 99.8%, respectively.

All of these studies encountered difficulties diagnosing undisplaced fractures, particularly transaxial scan plane fractures such as type II odontoid, and purely ligamentous injuries. These limitations emphasize the need for review of the sagittal and coronal reformations before injury is excluded (Figure 1). With the use of high-resolution reformations, the radiographic features indicating instability or ligamentous injury also apply to CT and include widened interspinous distance, widened facet joints, widened interpedicle distance, subluxation, and dislocation.

Screening cervical spine studies at the Shock Trauma Center are acquired on a four-slice scanner with a 1-mm collimation and a 4-mm per rotation table speed using optimal kVp and mAs. Scans are made from the skull base to the T2 level and viewed as fused 3.2-mm images in bone algorithm. The acquired 1-mm spaced images are then reformatted to generate near-isotropic coronal and sagittal images for evaluation on a PACS workstation.

Improved fracture pattern classification with differentiation between stable or unstable is now possible with spiral CT. Diagnostic accuracy has risen as a result of high-resolution scanning and multiplanar reformations, particularly in the sagittal and coronal planes, that improve upon the conventional lateral, open-mouth odontoid, and anterior-posterior radiographs.

sigma Chest trauma. Associated thoracic trauma occurs in 10% of all accident victims and 60% of multitrauma patients. The spectrum includes traumatic aortic injury, pneumothorax and pneumomediastinum, tracheobronchial rupture, esophageal disruption, pulmonary contusion and laceration, diaphragmatic tear, pericardial tamponade, cardiac contusion, and pneumopericardium.

Chest radiography, which remains the primary screening modality in the assessment of patients with thoracic trauma, is obtained during patient resuscitation efforts. An abnormal mediastinal contour on chest radiography mandates further investigation to exclude aortic injury. An upright chest radiograph, if possible, may be able to clear a questionable mediastinum. Any persisting abnormality in a stable trauma patient requires contrast-enhanced CT evaluation.

Traumatic aortic injury occurs with high-speed deceleration and has a very high mortality rate. Patients at risk require prompt diagnosis and surgical treatment. Rapid assessment leading to surgical stabilization during the golden hour makes possible a 70% survival rate in patients still alive upon arrival at the hospital. Other factors contributing to survival include age and coexisting cardiac, pulmonary, or renal disease. Most surviving patients have injuries at or near the ligament arteriosum. Contrast-enhanced spiral CT demonstrates traumatic aortic injury as mediastinal hematoma, pseudoaneurysm, aortic contour deformity, intraluminal thrombus, and pseudocoarctation. Mirvis et al have reported 100% sensitivity, 99.7% specificity, 89% positive predictive value, 100% negative predictive value, and an accuracy of 99.7%.^11,12

Spiral CT diagnosis has become increasingly accurate and confident, leading to a decline in the use of aortography (Figure 2). Trauma surgeons have become more comfortable operating for aortic injury based on CT criteria alone, thus reducing patient time to definitive therapy and increasing the chance for survival.

CT is superior to chest radiographs for most other thoracic injuries as well. It can demonstrate pulmonary contusions, lacerations, pneumothoraces, and hemothoraces that may be occult on plain radiographs. Disruption of the tracheobronchial tree should also be considered in any patient with penetrating injury to the neck or chest. Radiographic findings are subcutaneous emphysema, persistent pneumothorax, "fallen lung" sign, and a malpositioned endotracheal tube. The majority (80%) of blunt tracheobronchial injuries occur within 2.5 cm of the carina and most commonly involve the right mainstem bronchus. Esophageal injury usually presents as left-sided pneumothorax, pneumomediastinum, subcutaneous emphysema, left-sided pleural effusion, and atelectasis. It typically involves the upper esophagus and may be associated with adjacent spinal injury.

Diaphragmatic injuries occur in 3% to 8% of blunt trauma patients and may first be suspected on screening admission chest radiography.13 Left-sided injuries predominate. Thin-section spiral CT with multiplanar reformation is the next study of choice.

CT findings of these injuries include discontinuity (73% to 82%), herniation of bowel or viscera into the chest (55%), and the "collar sign" (27%) (Figure 3).^14,15 The collar sign represents the waistlike constriction of the herniated organ at the site of herniation and is 100% specific and 63% sensitive for the diagnosis.16 CT-missed diagnosis usually is related to lack of herniation through the diaphragm tear.

sigma Abdominal and pelvic trauma. CT noninvasively evaluates the retroperitoneum and osseous structures and gives a specific diagnosis, unlike other imaging or diagnostic modalities such as diagnostic peritoneal lavage. Spiral CT is unsurpassed for the detection of blunt abdominal visceral injuries. Not only does CT evaluation of the trauma patient boast high sensitivity, specificity, and accuracy; it carries a 99.6% true-negative predictive value.17 The implication of a negative CT abdominal scan is thus very powerful, and clinical attention can be safely directed to other injuries or discharge if no other traumatic lesions exist.

Contrast-enhanced CT provides identification and precise delineation of organ and vascular injury, such as hematoma and active arterial extravasation, and indicates the presence of urinary extravasation or devitalized parenchyma. It can also differentiate trivial injuries from those requiring intervention.

Multislice CT of the abdomen and pelvis is performed at our institution from the dome of the diaphragm to the ischial tuberosities. Scanning is initiated 70 seconds following 150 cc intravenous administration of 60% nonionic contrast material power-injected at a rate of 3 cc/sec. Scan parameters are 2.5-mm collimation, pitch of 1.25, and reconstruction intervals of 7.5 mm. This timing allows for organ perfusion assessment with optimal vascular enhancement that helps identify injury to liver, spleen, and kidney, while revealing foci of active bleeding or vascular injury. The kidneys are scanned in the late cortical or early nephrographic phase. Delayed images are acquired through the abdomen to characterize potential vascular lesions and assess renal excretion and collecting system integrity (Figure 4).

The spleen is the organ most commonly injured in the setting of blunt abdominal trauma, followed by the liver. Contrast-enhanced CT can detect hepatic and splenic injuries with high accuracy. Most hepatic injuries can be managed conservatively, even when CT demonstrates parenchymal damage of multiple segments with significant hemoperitoneum. Repeat CT studies can readily assess delayed complications.

In contrast, the outcome of conservative splenic management is unpredictable, as delayed splenic rupture may occur in about 15% of cases despite an initial CT demonstrating minimal injury with little or no hemoperitoneum.¹⁸ Patients demonstrating intrasplenic "contrast blush," for example, are more likely to fail conservative management and benefit from angiographic embolization. Thus, CT evaluation for active extravasation or pseudoaneurysm formation in conjunction with application of a splenic injury grading scale may help predict candidates for observation, embolization, or surgical intervention (Figure 5).

The presence of free intraperitoneal fluid without direct evidence of solid organ injury should alert the radiologist to the possibility of underlying bowel trauma. Recent reports have shown spiral CT to be very accurate in detecting bowel and mesenteric injury. With proper technique and careful interpretation, overall sensitivities of approximately 95% can be achieved.¹⁹

CT findings of bowel injury include pneumoperitoneum, intraperitoneal free fluid, mesenteric hematoma or infiltration, bowel wall thickening, active bleeding from the mesentery, and oral contrast spillage.

sigma Thoracic and lumbar spine injury. CT is better than plain radiography for depicting fractures of the thoracic or lumbar vertebrae. Delay in diagnosis can lead to grave neurologic sequelae. Unfortunately, delayed diagnosis has been shown in 24% of thoracolumbar fractures, with 77% of these occurring in unstable patients.²⁰

The thoracic spine requires high energy to fracture because of the inherent stability provided by its connection to the protective rib cage and sternum. Consequently, the thoracic spine is injured less than the cervical and lumbar spines but has the highest rate of associated neurologic injury (50%) due to the force necessary to produce the fracture and dislocation or subluxation.²¹ Lumbar spine fractures are more common and classified as compression, burst, Chance (flexion-distraction), and fracture-dislocation. These fractures are graded using the three-column model as stable or unstable.

Sprial CT allows for high-resolution image acquisition and reformations for accurate diagnosis. The scans accurately demonstrate vertebral column damage and help identify patients at risk of acute neurologic compromise. Multidetector CT will probably replace screening plain radiographs of the thoracic and lumbar spine in trauma patients already coming to CT since adequate evaluation can be obtained from thin-slice profile chest and abdominal CT studies.

CONCLUSION

Contrast-enhanced spiral CT has revolutionized the workup and diagnosis of the trauma patient. State-of-the-art CT technology with multislice capabilities allows for rapid breath-hold scanning, permitting greater coverage with greater spatial detail. CT may be performed in hemodynamically stable patients in whom injury is suspected in much less time than in the recent past with greater accuracy and diagnostic confidence.

These capabilities have led to a dramatic decrease in surgical exploration for often minor injuries, improved triage by presenting the total spectrum of injuries, permitted recognition of clinically unanticipated injuries, and fostered earlier discharge of patients without significant injury with a high level of confidence. These influences have, in turn, led to decreases in costs of patient management and, most likely, improved overall clinical outcomes.

DR. BERNSTEIN is a trauma radiology fellow, and DR. MIRVIS is a professor of radiology at the University of Maryland in Baltimore.

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References

1. Wing VW, Federle MP, Morris JA Jr, et al. The clinical impact of CT for blunt abdominal trauma. AJR 1985;145:1191-1194.
2. Waxweiler RJ, Thurman D, Sniezek J, et al. Monitoring the impact of traumatic brain injury: a review and update. J Neurotrauma 1995;12:509-516.
3. Sosin DM, Sniezek JE, Waxweiler RJ. Trends in death associated with traumatic brain injury, 1979 through 1992: success and failure. JAMA 1995;273:1778-1780.
4. Rehm CG, Ross SE. Diagnosis of unsuspected facial fractures on routine head computed tomographic scans in the unconscious multiply injured patient. J Oral Maxillofac Surg 1995;53:522-524.
5. Johnson DH Jr, Colman M, Larsson S, et al. Computed tomography in medial maxilla-orbital fractures. JCAT 1984;8:416-419.
6. Laine FJ, Conway WF, Laskin DM. Radiology of maxillofacial trauma. Curr Prob Diagn Radiol 1993;22:145-188.
7. Rhea JT, Rao PM, Novelline RA. Helical CT and three-dimensional CT of facial and orbital injury. Radiol Clin North Amer 1999;37:489-513.
8. Link TM, Schuierer G, Hufendiek A, et al. Substantial head trauma: value of routine CT examination of the cervicocranium. Radiology 1995;196:741-745.
9. Nunez DB Jr, 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.
10. Hanson JA, Blackmore CC, Mann FA, Wilson AJ. Cervical spine injury: accuracy of CT used as a screening technique. Emerg Radiol 2000;7:31-35.
11. Mirvis SE, Shanmuganathan K, Miller BH, et al. Traumatic aortic injury: diagnosis with contrast-enhanced thoracic CT-five-year experience at a major trauma center. Radiology 1996;200:413-422.
12. 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.
13. Mueller CF, Pendarvis RW. Traumatic injury of the diaphragm: report of seven cases and extensive literature review. Emerg Radiol 1994;1:118-132.
14. Murray JG, Caoili E, Gruden JF, et al. Acute rupture of the diaphragm due to blunt trauma: diagnostic sensitivity and specificity. AJR 1996;166:1035-1039.
15. Worthy SA, Kang EY, Hartman TE, et al. Diaphragmatic rupture: CT findings in 11 patients. Radiology 1995;194:885-888.
16. Killeen KL, Mirvis SE, Shanmuganathan K. Helical CT of diaphragmatic rupture caused by blunt trauma. AJR 1999;173:1611-1616.
17. Livingston DH, Lavery RF, Passannante MR, et al. Admission or observation is not necessary after a negative abdominal computed tomographic scan in patients with suspected abdominal trauma: results of a prospective, multi-institutional trial. J Trauma 1998;44:273-282.
18. Federle MP, Courcoulas AP, Powell M, et al. Blunt splenic injury in adults: clinical and CT criteria for management, with emphasis on active extravasation. Radiology 1998;206:137-142.
19. Killeen KL, Shanmuganathan K, Poletti PA, et al. Helical computed tomography of bowel and mesenteric injuries. J Trauma 2001;51:26-36.
20. Anderson S, Biros MH, Reardon RF. Delayed diagnosis of thoracolumbar fractures in multiple-trauma patients. Acad Emerg Med 1996;3:832-839.
21. Meyer S. Thoracic spine trauma. Semin Roentgenol 1992;27:254-261.