Moyamoya disease is a specific chronic cerebrovascular occlusive disease first 
reported by Japanese surgeons in 1957. The disease is characterized by stenosis 
or occlusion of the terminal portions of the bilateral internal carotid arteries 
and abnormal vascular network in the vicinity of the arterial occlusion. It may 
cause ischemic attacks or cerebral infarction, which is more frequent in 
children than in adults. In adults, cerebral hemorrhage may occur. The disease 
is distributed in all age groups, but the highest peak is in childhood at less 
than 10 years of age. The characteristic histopathologic features of the 
steno-occlusive arteries are fibrocellular thickening of the intima containing 
proliferated smooth muscle cells and prominently tortuous and often duplicated 
internal elastic lamina. There is usually no atheromatous plaque in the arterial 
wall. Etiology of the disease is still unknown; however, multifactorial 
inheritance is considered possible because of a higher incidence of the disease 
in Japanese and Koreans and approximately 10% of familial occurrence among the 
Japanese. Recent genetic studies suggest some responsible genetic foci in 
chromosomes 3, 6 and 17.