Moyamoya disease in monovular twins: case report.

The first reported instance of identical twins with moyamoya disease is presented. The involved portions of the main intracranial arteries were similar, but the formation of the moyamoya vessels was somewhat different. The cause fo obstructive changes in large intracranial arteries remains obscure, but the frequent familial occurrence suggests that the initial stages of this disease and the formation of the moyamoya vessels occur in the prenatal period.