The Relationship between Carotid Artery Diameter and Percentage of Stenosis

In order to understand percentage of stenosis from the residual lumen of the carotid artery, we explored the relationship between the residual diameter at the carotid stenosis, its stenosis percentage and the size of the internal carotid artery. Diameters of 103 carotid arteries of Taiwan residents were retrospectively measured from digital subtraction angiograms. Severe cases of near occlusion with the angiographic string sign, and cases with tandem lesions or intracranial occlusion were excluded. Of the total 103 carotid arteries, 22 (21%) had one or both of the following signs of reduced distal arterial caliber: (1) obvious narrowing of the distal carotid artery; (2) the caliber of the cervical internal carotid artery was smaller than the caliber of the corresponding external carotid artery. That the diameter of the distal carotid artery was smaller when the stenosis was greater at the site of minimal lumen was true in the group of patients with signs of reduced distal caliber and in the group of patients without such signs. Therefore, reduced distal caliber may be present in patients without such signs. After excluding cases with at least one of the above signs of reduced distal arterial caliber, the relation between percentage of stenosis (y) and the absolute value of the diameter at the stenosis (x) can be represented by the formula: y = 96.83-18.27 x. From our data, a diameter of 2 mm is about 60% stenosis and 1.5 mm is 70% stenosis. According to this formula, we can estimate percentage of carotid stenosis using residual diameter at the site of minimal lumen obtained from other imaging modalities, such as carotid Doppler, CT angiogram or MR angiogram.