Pre-optic origin of the anterior cerebral artery.

Division of the internal carotid artery immediately after the siphon at the level of the ophthalmic artery is described in a 55-year-old woman. Because of the early division, the anterior cerebral artery lay between the optic nerves. This anomaly was combined with agenesis of the horizontal part of the opposite anterior cerebral artery. The problems concerning ligation of a ruptured anterior communicating artery aneurysm are discussed.