Clinical Suspicion and Diagnostic Imaging in Traumatic Aortic Injury
abstract & commentary
Source: Dyer DS, et al. Thoracic aortic injury: How predictive is mechanism and is chest computed tomography a reliable screening tool? A prospective study of 1,561 patients. J Trauma 2000;48:673-682.
The authors prospectively evaluated blunt trauma patients to determine mechanism of injury (MOI) characteristics predictive of traumatic aortic injury (TAI) and to evaluate the accuracy of chest computed tomography (CCT) in making this diagnosis. From 1991 to 1996, trauma patients at two trauma centers (Denver Health Medical Center and the University of Colorado Hospital) were studied. The treating emergency physician and surgeon made an initial risk assessment based on a series of MOI criteria (1 = low risk, 5 = high risk) and subjective interpretation of the initial chest x-ray (CXR) (1 = not worrisome for TAI, 5 = very worrisome for TAI). The decision to perform CCT vs. aortography in the initial study was based on a combination of these scores. Patients for whom there was a high suspicion for TAI (e.g., MOI score = 5 and CXR score = 4 or 5) underwent immediate aortography. High-suspicion patients in need of other studies and those with moderate/low suspicion underwent CCT first. Between 1991 and 1993, conventional CCT was used; after that, helical technology was introduced.
Criteria for "positive" findings on CCT included mediastinal hemorrhage, periaortic hematoma, change in caliber or contour of the aorta, and the presence of an intimal flap. Before 1995, follow-up aortography was performed for patients with positive or equivocal CCT findings and all patients with a high MOI score. After 1995, the authors concluded that a normal CCT excluded TAI, and follow-up aortography was not performed if this was the case.
A total of 1561 patients were evaluated for TAI. Of those with MOI characteristics often associated with TAI, only high speed and injury severity scores were found to be significant. No significant association was found between TAI and frontal and side impacts, ejection, associated fatalities, sudden deceleration, or vehicle damage. Aortography was performed in 223 (14%) patients with a high suspicion for TAI. CCT was the initial study in 1338 patients, and 486 of these had follow-up aortography. A total of 30 (1.9%) aortic injuries were identified. CCT had a sensitivity of 100%, negative predictive value of 100%, and positive predictive value of 39%.
COMMENT BY MICHAEL A. GIBBS, MD, FACEP
TAI is the second most common cause of death in trauma, surpassed only by traumatic brain injury. The diagnosis cannot be made or excluded at the bedside, as less than 50% of patients have clinical evidence of chest injury. Reliance on chest radiography alone is equally hazardous; findings are often subtle, and up to 7% of patients will have a normal CXR. While this study has several important design flaws (e.g., enrollment criteria not defined, subjective clinical and radiographic assessment criteria), the results support this basic tenet: History and physical plus chest x-ray are not enough.
This study is important because it supports the two largest studies published to date demonstrating the accuracy of helical CCT in making the diagnosis of TAI.1,2 Some day soon, the trauma arch-aortogram will be a thing of the past. However, before this diagnostic approach can be introduced at your hospital, you must answer the following questions: Do you have helical CT technology? Are your radiologists experienced? Will your surgeons operate without an aortogram? Food for thought.
References
1. Fabian TC. Prospective study of blunt aortic injury: Helical CT is diagnostic and antihypertensive therapy reduces rupture. Ann Surg 1998;213:666.
2. Mirvis SE. Use of spiral CT for the assessment of blunt trauma patients with potential aortic injury. J Trauma 1998;45:922.
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