The accessory middle cerebral artery as a collateral blood supply.

We describe two cases of acute embolic occlusion of the internal carotid artery and the middle cerebral artery in association with a patent accessory middle cerebral artery. Because of the presence of the accessory middle cerebral artery, the frontal lobe was salvaged to some extent, but it did not provide sufficient collateral blood supply to the middle cerebral artery territory to spare the rest of the frontal lobe, the temporal lobe, and the basal ganglia.