Imaging description

One of the popular measures for calculating the degree of stenosis uses ratio calculations to determine the percentage stenosis of the carotid bulb, as in the North American Symptomatic Carotid Endarterectomy Trial (NASCET) [1]. The formula for this calculation is: 1 – diameter of the stenotic segment of carotid/diameter of normal distal carotid × 100. The NASCET trial has shown that carotid endarterectomy is highly beneficial in symptomatic patients with ≥70% stenosis.

A particular subset of patients with high-grade stenosis have “near-occlusive” stenosis. When such a high degree of stenosis occurs, there is invariably a collapse of the lumen of the internal carotid artery (ICA) distal to the lesion. A collapsed ICA lumen may appear threadlike, and is referred to as the “string sign” on angiography [1]. These patients may later progress to complete carotid occlusion. Traditionally, patients with near-occlusive stenoses were treated with emergency revascularization, but it is now apparent that these patients actually have a lower risk of stroke under medical therapy than patients with marked (but not near-occlusive) stenosis, which is likely related to the presence of a better developed collateral vascular network.