Accessory middle cerebral artery and duplication of middle cerebral artery--terminology, incidence, vascular etiology, and developmental significance.

A series of 455 bilateral carotid angiographies included 14 accessory middle cerebral arteries (Acc-MCAs) and seven duplication of middle cerebral arteries (Dup-MCAs). The branching patterns of Dup-MCA could be classified as "direct bifurcation" from the internal carotid artery, since most lacked the essential bifurcation or trifurcation at the distal end of the M1 portion. On the other hand, Acc-MCAs are probably residual congenital arteries. These anomalous MCAs were apparently associated with epilepsy. Five Acc-MCAs were associated with anterior communicating artery aneurysm at the origin. In addition, a rare case of Dup-MCA with arteriovenous malformation at its origin was found.