Anomalous carotid-basilar anastomoses in cerebrovascular surgery.

Primitive embryonic anastomotic vessels between the internal carotid and basilar arterial systems occasionally persist into adult life. We encountered six such patients in a series of 765 carotid endarterectomies (0.8%). These arteries are named for the cranial nerves with which they run. The most commonly found vessel is the trigeminal artery, followed by the hypoglossal and proatlantal intersegmental arteries. The primitive otic artery is the rarest of the four anomalous vessels. These vessels are usually large and are associated with hypoplasia or aplasia of the normal intracranial anastomotic channels. Cerebral ischemia is common during temporary intraoperative carotid occlusion and was encountered in two of three patients who had intraoperative electroencephalographic monitoring. Thus cerebral ischemia should be anticipated during carotid cross-clamping and cerebral protective measures should be instituted when persistent primitive cranial vessels are encountered.