ABSTRACT
Moyamoya disease is characterized by a bilateral progressive narrowing of the distal internal carotid and proximal portions of the anterior and middle cerebral arteries. The cerebral vessels of the 11 to 14 mm embryonic period are extremely similar to these moyamoya vessels. The vertebral arteries unite with a contralateral homologue to form the basilar artery during embryonic development and rarely, the failure of complete fusion results in duplication of these arteries. It is well known that moyamoya disease sometimes is accompanied by persistent primitive arteries, cerebral aneurysm, or rarely arteriovenous malformation. However, no case of the moyamoya disease with complete duplication of basilar artery has been previously reported. These two types of vascular abnormality are probably associated in certain developmental period, and moyamoya disease causes hemodynamic load in the basilar artery system as a collateral pathway and these effects are also involved in duplication of basilar artery. The relationship between these two varieties of vascular abnormality and possible pathogenesis of the moyamoya disease are discussed.