Internal carotid artery hypoplasia.

Hypoplasia of the carotid arteries is a rare congenital anomaly which when clinically symptomatic presents as cerebral ischemia or hemorrhage. Patients with this anomaly commonly have associated variations of the circle of Willis, an increased incidence of intracranial aneurysms and extensive networks of collateral vessels to accommodate the diminished carotid flow. Carotid artery hypoplasia should not be confused with other conditions which may have a similar appearance such as arterial dissection, vasculitis, and tubular fibromuscular hyperplasia.