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EDUCATION EXHIBIT |
Department of Radiology, Memorial Sloan-Kettering Cancer Center New York, New York
I appreciate the opportunity to comment on the article by Fishman et al (1) in this issue of RadioGraphics. Documented with spectacular images, the article demonstrates how vascular trauma of the extremities can be diagnosed with noninvasive imaging techniques made possible by multidetector CT.
The introduction of single-section spiral CT in the early 1990s made CT angiography possible. Early studies were limited by relatively long scanning times and thick sections that required large volumes of contrast material and yielded limited resolution of fine structures. The quantum leap to multidetector CT with four, 16, and 64 detectors provided a means of performing arterial phase imaging from head to toe with submillimeter resolution.
Very soon after its introduction into clinical practice, CT angiography replaced pulmonary angiography and thoracic aortography for the diagnosis of pulmonary emboli and traumatic aortic injury, respectively (2,3). Catheter angiography has all but been replaced by MR angiography for the diagnosis of peripheral vascular disease, proving that a noninvasive imaging modality could provide the same diagnostic information as catheter angiography in most cases.
In a perfect world, diagnosis of vascular trauma would be made with a widely available, inexpensive, noninvasive volumetric acquisition that provides high contrast between vessel and soft tissue without ionizing radiation. Of course, ours is not a perfect world, but using these criteria to compare the current standard of reference—namely, catheter angiography—with CT angiography suggests significant advantages for CT angiography.
CT is readily available in every trauma center, and it is almost unheard of for a trauma patient to leave the emergency department without undergoing CT. CT angiography is more expedient than catheter angiography for making a diagnosis and does not require removing the patient from the emergency department, where evaluation and management of other injuries is most efficient. In practical terms, at night or on weekends (when most trauma occurs), catheter angiography can result in a delay in diagnosis because the angiography team often has to be called in from home.
Volumetric data acquisition with multidetector CT allows MPR that is not currently available in most angiography suites. A typical catheter angiogram for trauma includes two oblique projections of the involved extremity without the possibility of significant postacquisition image manipulation. Importantly, in addition to imaging of the vasculature, CT angiography provides information about surrounding structures, including soft tissue, bone, and even the venous system. This information is particularly valuable in cases involving blunt trauma, in which associated nonvascular injuries are more common.
Recently, the potential risks of ionizing radiation have been highlighted by reports in the lay press (4). One study comparing 16-detector CT angiography with catheter angiography found the effective radiation doses to be 1.6–3.9 mSv and 6.4–16 mSv, respectively (5). In other words, the highest effective dose calculated for CT angiography was a little more than one-half of the lowest dose calculated for catheter angiography.
Fishman et al (1) scan "those whose clinical history and findings warrant CT angiography" and note that "definitive clinical evidence of arterial injury may require emergent surgical intervention without imaging." As a vascular interventional radiologist, I would be remiss not to at least mention the fact that catheter angiography cannot only help definitively diagnose specific traumatic arterial lesions, but in some cases can help treat the injury as well.
For example, if physical examination reveals the presence of a bruit, a finding that is highly suggestive of an arteriovenous fistula, catheter angiography may be more useful than CT angiography because diagnosis and immediate treatment (embolization) can be combined. In the appropriate clinical setting, covered stents or stent-grafts can be used to exclude pseudoaneurysms from the circulation, leaving the native vessel patent, and to tack down intimal tears to prevent progression to dissection. In considering stent placement for trauma, however, one should proceed with caution, since open surgical repair is likely to be more durable in a young patient with a long life expectancy. Advances in microcatheters and coil technology provide the tools that allow treatment of previously inaccessible bleeding vessels. Many significant traumatic arterial injuries that once required surgical intervention are now amenable to minimally invasive treatment in the interventional suite.
As yet, we do not have the experience with CT angiography that would allow us to determine whether it will be useful in all patient populations—for example, elderly or diabetic patients with significant vessel wall calcification (6,7)—or whether the resolution of CT angiography will help detect the more subtle sequelae of vascular trauma, including spasm and intimal injury. In one of the few articles written about CT angiography following extremity trauma, Rieger et al (8) highlight the challenge of differentiating vascular spasm from normal or occluded vessels. Hoffer et al (9) reported that such "minimal vascular injuries" accounted for almost two-thirds of traumatic arterial injuries detected with catheter angiography. More important, they found that these lesions had a variable and unpredictable course: In their study, 40% progressed with observation (9).
In addition to streamlining diagnosis, judicious use of CT angiography has the potential to be less costly to the healthcare system than catheter angiography. The caveat is that there is a great temptation to overutilize a new technology or application. For example, it was thought that laparoscopic cholecystectomy would make removal of the gallbladder less costly to the healthcare system than open surgery. As it turns out, the low morbidity rate and short hospital stay lowered the threshold for cholecystectomy to such a degree that, despite a lower cost per patient, more healthcare dollars are spent on the procedure now because it is performed more often. We must be careful not to overutilize CT angiography in the trauma setting simply because it is available.
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