Evaluation for Carotid Artery Stenosis

From: www.uptodate.com

CHOICE OF IMAGING TEST —
Conventional cerebral angiography has been considered the gold standard for the evaluation of internal carotid artery stenosis [67]. However, angiography is associated with a small but real risk of stroke, which makes it ill suited to be used as a screening test. In addition, most patients with ischemic symptoms referable to the carotid vascular territory do not have severe carotid stenosis [68,69]. In one series of 261 patients with carotid ischemic strokes and 813 patients with carotid TIA, carotid disease was absent in 55 and 64 percent, respectively (and in 69 and 77 percent of those without a carotid bruit) [69].

As a result, patients are generally selected for angiography using one of the noninvasive tests (CDUS, TOF MRA, CEMRA, and CTA). These noninvasive tests have essentially replaced conventional cerebral angiography in the presurgical evaluation of carotid stenosis.
In a meta-analysis of 41 studies and 2541 patients published in 2006 that assessed different noninvasive imaging methods, the following observations were made [23]:
CDUS, MRA, CEMRA and CTA all have high sensitivities and specificities for diagnosing 70 to 99 percent carotid stenosis in patients with ipsilateral carotid territory ischemic symptoms.
CEMRA may be marginally more accurate than the other noninvasive methods, but this technique is relatively new and the published studies included in the meta-analysis came from research environments as opposed to routine clinical practice environments.

The accuracy of the noninvasive tests for 50 to 69 percent carotid stenosis appears to be substantially reduced compared with 79 to 99 percent stenosis. However, the data are sparse.

The combination of carotid ultrasound and MRA may obviate the need for conventional angiography in the presurgical assessment of patients with carotid artery disease, particularly when the tests agree [33,70,71]. Some have reported that the combination of ultrasound and MRA is cost-effective [72,73] and results in an overall error rate that is comparable to the interobserver reliability when two radiologists are presented with the same conventional angiogram revealing carotid artery disease [74]. (See "Carotid endarterectomy: Preoperative evaluation; surgical technique; and complications").

Bypassing angiography before surgery requires that noninvasive tests be highly specific as well as sensitive. TCD may be beneficial in this setting, increasing the specificity of carotid duplex ultrasound in detecting a <1.5 onclick="javascript:return viewAbstract('topicKey=cva_dise/4600&refNum=42');" href="http://www.uptodate.com/online/content/abstract.do?topicKey=cva_dise/4600&refNum=42">42].

Conclusions — Our general approach to patients with suspected carotid stenosis is to first perform carotid duplex ultrasound. Those with stenosis <50 percent are followed with serial examinations, usually on an annual basis to determine if there is progression. Those with stenosis ≥50 percent are evaluated with transcranial Doppler examination and MRA. CTA is performed in lieu of MRA if there is a contraindication to magnetic resonance imaging and in cases where the duplex ultrasound and MRA do not agree.
Conventional angiography is rarely performed; indications include patients who cannot tolerate an MRA and in whom the risk of dye is sufficient to warrant bypassing CTA in favor of the gold standard examination. Angiography is also done if nonatherosclerotic disease is suspected (eg, dissection, vasculitis).