Occlusion of Middle and Anterior Cerebral Arteries

DIAGNOSIS

The diagnosis of anterior circulation ischemia is often made by noninvasive methods, including ultrasound techniques, computed tomography, and magnetic resonance imaging techniques (see Plates 9-14 and 9-15). Digital subtraction angiography remains the gold standard for the evaluation of the supra-aortic vasculature. However, due to its potential risks of neurologic complications, this technique is usually reserved for select patients when the diagnosis is still not clear after noninvasive testing.

Ultrasound of the carotid arteries at their bifurcation in the neck can determine the presence of critically stenotic extracranial artery disease as well characterization of carotid plaques as “soft,” consisting of cholesterol deposits and clot. “Soft” plaques are more prone to ulcerate and cause artery-to-artery emboli. “Hard” plaques are those that have fibrosed and calcified over time; they are a less common source of emboli. The role of ultrasound in detection of internal carotid artery dissection, fibromuscular dysplasia, or giant cell arteritis is more limited because lesions often occur on its pharyngeal portions or distal to it, and only indirect signs of a distal carotid occlusion are found. Transcranial Doppler can assess the patency of the intracranial arteries; patterns of collateral flow through the circle of Willis also can be used for emboli monitoring (see Plate 9-14).

Advances in both CTA and contrast-enhanced MRA have allowed assessment of the entire supra-aortic tree, from the aortic arch to the circle of Willis. Each of these techniques is extremely valuable in the evaluation of the degree of stenosis in patients with extra- and intracranial atherosclerotic disease as well as with plaque characterization (see Plates 9-14 and 9-15). Recent studies have shown that multidetector CTA has a sensitivity of 98% to 100% and specificity of 96% to 100% for detection of severe carotid stenosis compared with angiography, whereas contrast-enhanced MRA has a sensitivity of 93% to 98% and a specificity of 96% to 100%. Regarding plaque characterization, MRI is able to qualitatively and quantitatively define carotid plaque morphology as well as identify vulnerable plaque features, such as intraplaque hemorrhages, whereas CTA is able to identify with precision the presence of plaque calcification and ulcerations.

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