Atypical fibromuscular hyperplasia. Report of two cases.

Two cases of atypical fibromuscular hyperplasia of the internal carotid artery (ICA) are reported. These cases are unique because the changes involve the intima of the vessels without involvement of medial structures as seen in the more common form of fibromuscular hyperplasia. Case 1 is only the fourth report of a symptomatic fibromuscular stenosis at the origin of the ICA. Case 2 is the first report of fibromuscular hyperplasia involving the common carotid artery. Changes similar to those in Case 2 (an elongated area of tubular fibromuscular stenosis) have been reported in the ICA. These atypical or intimal forms of fibromuscular hyperplasia appear to be more common in males and blacks, and may be more often unilateral as well.