Fenestration of the supraclinoid internal carotid artery.

A twenty-eight year old woman presenting with subarachnoid hemorrhage was found at angiography to have a left anterior cerebral-anterior communicating artery aneurysm. Also identified was a fenestration of the right supraclinoid internal carotid artery with an associated accessory middle cerebral artery. This appears to be the second reported case of fenestration of the intracranial internal carotid artery. Fenestrations of cerebral vessels and their possible embryologic origins are briefly reviewed.