MSH: A noninflammatory, progressive occlusion of the intracranial CAROTID ARTERIES and the formation of netlike collateral arteries arising from the CIRCLE OF WILLIS. Cerebral angiogram shows the puff-of-smoke (moyamoya) collaterals at the base of the brain. It is characterized by endothelial HYPERPLASIA and FIBROSIS with thickening of arterial walls. This disease primarily affects children but can also occur in adults.,NCI: A rare inherited vascular disorder characterized by constriction of arteries at the base of the brain, resulting in the formation of collateral circulation in order to compensate for the constriction. The name "moyamoya" in Japanese means "puff of smoke" and derives from the characteristic radiographic appearance of the collateral vessels.