Atherosclerotic ICA stenosis coinciding with ICA asymmetry associated with Circle of Willis variations can mimic near-occlusion.

Differentiating carotid near-occlusion (tight atherosclerotic stenosis causing distal artery size reduction) from conventional stenosis is the first step when grading carotid stenoses with NASCET method. The internal carotid artery (ICA) can be asymmetrically associated with Circle of Willis variations. When such ICA asymmetry coincides with stenosis, it may mimic near-occlusion. We studied ICA anatomical variant prevalence in 4042 consecutive CTA exams from all indications, 53 excluded due to carotid occlusion, 814 with any ≥ 50% steno-occlusive disease intra- or extracranially, 3228 without. Of the 3989 included cases, 568 (14%) had ICA asymmetry, of which 335 (59%) were from associated with Circle of Willis variations. Of 3228 patients without ≥ 50% stenosis or other steno-occlusive disease intra- and extracranially; 257 (8.0%) demonstrated ICA asymmetry associated with Circle of Willis variations, equally common among sexes and age unrelated and most frequently attributed to an ipsilateral A1 hypoplasia/aplasia, less often attributed to large contralateral posterior communicating artery. As ICA asymmetry associated with Circle of Willis variations are common, caution should be exercised diagnosing near-occlusion on asymmetry alone.