Fusiform aneurysm of a persistent trigeminal artery associated with rare intracranial arterial variations and subarachnoid hemorrhage.

The trigeminal artery is one of four primitive anastomoses between the internal carotid artery and vertebrobasilar system that regresses in the sixth week of fetal development. A persistent trigeminal artery (PTA) is generally an incidental finding but may also be associated with intracranial vascular pathologies such as aneurysms, arteriovenous malformations, and cranial nerve compression syndromes. We present an extremely rare case of a right PTA with an associated bleeding fusiform aneurysm located in the carotidian (lateral) part of the PTA. In addition, this rare anatomic variation was associated with bilateral absence of the posterior communicating arteries, a left posterior cerebral artery originating from the left internal carotid artery, and agenesis of the A1 segment of the left anterior cerebral artery.