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EDUCATION EXHIBIT |
Department of Radiology, University of Pennsylvania Medical Center, Philadelphia, Pennsylvania
What is the role of noninvasive imaging in evaluation of blunt and penetrating traumatic vascular injuries of the neck? Penetrating injuries are more common than blunt injuries, but both are potentially devastating. Decisions regarding the best diagnostic approach are difficult in these cases for the surgeon and the radiologist, and there is as yet no consensus. If the patient is in stable enough condition to undergo vascular imaging and the decision to screen for vascular injury is made by the clinician, imaging options include invasive techniques like digital subtraction angiography (DSA) and cross-sectional noninvasive techniques like CT angiography, MR angiography, and US. DSA is still considered the standard of reference, and there is certainly more experience with DSA in this setting.
However, one obvious disadvantage to use of DSA is its invasive and resource-intensive nature. The time from identification of a patient as a candidate for DSA to arrangement and completion of a study is unfortunately often much longer than we would like. Moreover, the risk of an adverse event, although low, remains higher than with any noninvasive technique. This is of particular concern given the number of screening studies with negative results. Another important point is that DSA is a study of the lumen only, whereas cross-sectional techniques image the vessel wall as well as the lumen. It is possible to find obvious wall disease on images from noninvasive studies that is nearly (or completely) invisible at DSA. CT angiography and MR angiography also have the added benefit of the ability to demonstrate surrounding structures such as the airway or the spine and spinal cord.
The optimal noninvasive technique in this setting would be fast, have low or no risk, be widely available at all hours, have a reasonable cost, provide easy access for physicians to sick patients, and be operator independent. Of the noninvasive techniques listed earlier, CT angiography most closely fits these criteria, especially with the increasing use of multi–detector row scanners. Since CT angiography is a three-dimensional technique, infinite projections or views can be created retrospectively, as opposed to standard DSA, where limited projections must be acquired prospectively (although rotational DSA is becoming increasingly available).
There are of course some drawbacks. CT angiography involves the use of ionizing radiation, and some experience is necessary in performing three-dimensional or multiplanar reformatting of the data and interpreting the results. Fortunately, the source images alone are often all that is required to make the diagnosis. A higher dose of iodinated contrast material is used compared with DSA, although the dose can be decreased substantially with increasing numbers of detectors in multi–detector row CT. Bullet fragments and dental hardware can limit detail. The shoulders create streak artifact, and vessels traveling through bony structures (eg, the vertebral and petrous carotid arteries) present problems for postprocessing. Mistakes in timing can create difficulties; for example, evaluation of the vertebral arteries can be limited by filling of the venous plexus around the arteries. Dynamic information is not available and so arteriovenous fistulas are not optimally evaluated. Motion in an uncooperative patient or even a cough in a cooperative patient can obscure detail or create false-positive findings. Despite these issues, nondiagnostic study results are the exception (around 1% [1]) and useful information can almost always be obtained.
In the preceding article, Núñez et al present several cases of traumatic vascular injuries in the neck evaluated by using CT angiography correlated with DSA. Common positive findings include partial or complete occlusion, vessel wall disruption and/or extravasation, pseudoaneurysm, and less commonly dissection or arteriovenous fistula. Penetrating injuries have a high prevalence of vascular injury (
25%), and the use of CT angiography makes sense in this setting, with reports of high sensitivity and specificity in detecting injury (1–3). Blunt injuries are relatively uncommon, although more aggressive screening has yielded a higher prevalence than originally thought. Arterial dissections are more common with blunt injury and significant morbidity can occur, symptoms often appearing hours after the initial injury (4). The appearance of the initial injury can help in assessment of prognosis and can guide selection of treatment options, but the role of CT angiography is not as compelling for blunt injury.
Hollingworth et al (5) performed a systematic review of CT angiography for traumatic or atherosclerotic arterial lesions in the neck and concluded that there was insufficient evidence to accurately assess its sensitivity and specificity for blunt or penetrating trauma, although they did conclude that CT angiography was a sensitive and specific technique for evaluating carotid atherosclerotic disease and occlusion. This review did not include the recent study by Múnera et al (1), which showed good accuracy of CT angiography in 175 patients with penetrating neck injuries, with no complications during follow-up in those with negative examination results (and demonstration of additional injuries like fractures and airway injuries in 35%). Indeed, occlusions and perhaps most clinically relevant injuries should be visible at CT angiography, but a subtle intimal injury may be undetectable given the limitations of CT angiography (6). MR imaging is probably more sensitive and specific for dissections, but it is uncertain whether missed diagnosis of very subtle injuries will be clinically relevant. With carotid dissection, for example, more severe injuries (grades II–IV) tend not to heal or progress, whereas most dissections with less than 25% narrowing (grade I) should heal (7).
In summary, there is growing evidence that CT angiography is a reasonable alternative for penetrating injuries and perhaps most clinically relevant blunt injuries. Nevertheless, we still have to think of DSA as the standard of reference in this setting and accept that there are injuries more appropriately addressed with DSA. It is important to keep in mind that techniques that directly demonstrate the vessel wall and surrounding structures as well as the vessel lumen may be better in detection and evaluation of some pathologic conditions, providing complementary diagnostic information that is unavailable with DSA.
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