Congenital Vascular Anomalies and Moyamoya Disease Congenital vascular anomaly here means the persistence of the primitive arteries in the early embryological stages. Arteriovenous malformation (AVM) is not this type of vascular anomaly. It is believed that this congenital vascular anomaly is not clinically important, but the associated AVMs or cerebral aneurysms are occasionally reported. The etiology of moyamoya disease is still unknown. For the investigation of the etiologies, or discussion on the congenital or acquired theories, the persistence of primitive arteries in the early embryological stages is regarded as one of the evidences to support the congenital theory. The persistent primitive arteries include persistent trigeminal artery, its variant, persistent hypoglossal artery, etc. The rare arterial variations include duplicated middle cerebral artery, accessory middle cerebral artery, etc. The accessory middle cerebral artery leaves the anterior cerebral artery near the anterior communicating artery, and courses near the terminal portion of the internal carotid artery, runs parallel to the middle cerebral artery, and then supplies some part of the anterior frontal lobe. Interestingly, in the case of steno-occlusive changes of the distal internal carotid arteries, this accessory middle cerebral artery does not always show steno-occlusive changes. In moyamoya disease, it indicates that there is topological difference in the steno-occlusive changes. Progression of such changes may be different between the internal carotid artery and accessory middle cerebral artery. References 1. Komiyama M, Kitano S, Sakamoto H, Shiomi M: An additional variant of the persistent primitive trigeminal artery: accessory meningeal artery - antero-superior cerebellar artery anastomosis associated with moyamoya disease. Acta Neurochir (Wien) 140: 1037-1042, 1998 [abstract] 2. Komiyama M, Nakajima H, Nishikawa M, Yasui T: Middle cerebral artery variations: duplicated and accessory arteries. AJNR 19: 45-49, 1998 [abstract] 3. Komiyama M, Nakajima H, Nishikawa M, Yasui T, Kitano S, Sakamoto H, Fu Y: High incidence of persistent primitive arteries in moyamoya and quasi-moyamoya diseases. Neurol Med Chir (Tokyo) 39: 416-422, 1999 [abstract] 4. Komiyama M, Yasui T: Accessory middle cerebral artery and moyamoya disease. J Neurol Neurosurg Psychiatr 71: 129-130, 2001 [abstract]