Medial type persistent trigeminal artery associated with a saccular aneurysm at its trunk

There are four types of fetal anastomosis between the carotid and vertebrobasilar arteries at 5 weeks gestation; from caudal to cranial position, these involve the proatlantal intersegmental, hypoglossal, otic, and trigeminal arteries. Excluding otic artery, these arteries may persist rarely. Persistent trigeminal artery (PTA) is the most common carotid-vertebrobasilar anastomosis, and the medial type (intrasellar) PTA is quite rare, accounting for approximately 10% of all PTA cases. An aneurysm is occasionally found at the origin of the PTA. Rarely, an aneurysm arises at the trunk of the PTA. Using magnetic resonance angiography, we identified a case of medial type PTA with an unruptured saccular aneurysm at its trunk.