Right proatlantal artery type I, right internal carotid occlusion, and left internal carotid stenosis: case report and review of the literature.

A 66-year-old man presented with right cerebellar infarction and ischemic lesions in the left dorsal thalamus and right upper parietal lobe. Angiography showed occlusion of the right internal carotid artery proximal to an ipsilateral proatlantal artery type I, 70% stenosis of the left internal carotid artery, and aplasia of both posterior communicating arteries. The carotid occlusion was successfully treated by thrombendarterectomy. Persistence of a proatlantal artery is a rare condition. In relation to the 38 literature reports on proatlantal arteries, this case demonstrates the clinical significance of a persistent proatlantal artery in the evolution of atypical ischemic cerebrovascular disease.