Moyamoya disease and moyamoya syndrome.

Copyright © 2009 Massachusetts Medical Society. The moyamoya syndrome is a cerebrovascular condition that predisposes affected patients to stroke in association with progressive stenosis of the intracranial internal carotid arteries and their proximal branches. Reduced blood flow in the major vessels of the anterior circulation of the brain leads to compensatory development of collateral vasculature by small vessels near the apex of the carotid, on the cortical surface, leptomeninges, and branches of the external carotid artery supplying the dura and the base of the skull. In rare cases, this process also involves the posterior circulation, including the basilar and posterior cerebral arteries. First described in 1957 as “hypoplasia of the bilateral internal carotid arteries,”1 the characteristic appearance of the associated network of abnormally dilated collateral vessels on angiography was later likened to “something hazy, like a puff of cigarette smoke,”2 which, in Japanese, is moyamoya (Fig. 1). Although “spontaneous occlusion of the circle of Willis” has recently been suggested as an alternative to the more evocative name “moyamoya,” the International Classification of Diseases recognizes “moyamoya” as the specific name for this condition.3 Patients with the characteristic moyamoya vasculopathy who also have wellrecognized associated conditions (described below) are categorized as having the moyamoya syndrome, whereas patients with no known associated risk factors are said to have moyamoya disease. By definition, the pathognomonic arteriographic findings are bilateral in moyamoya disease, although the severity can differ between sides.2 Patients with unilateral findings have the moyamoya syndrome, even if they have no other associated risk factors.3 However, contralateral disease eventually develops in up to 40% of patients initially presenting with unilateral findings.4,5 When used alone, without the distinguishing modifier of “disease” or “syndrome,” “moyamoya” refers solely to the distinctive findings on cerebral arteriography, independently of the cause.