In Japanese moyamoya means a haze, like a puff of smoke, and the term describes a characteristic, but rare, radiologically defined consequence of severe stenosis or occlusion of one or, more often, both distal ICAs, frequently with additional involvement of parts of the circle of Willis and sometimes of the proximal cerebral and basilar arteries. Fine anastomotic collaterals develop from the perforating and pial arteries at the base of the brain, orbital and ethmoidal branches of the external carotid artery, and leptomeningeal and transdural vessels, giving the characteristic ‘puff of smoke’ appearance on angiography (Chen et al. 1988).
The disorder seems to be almost confined to the Japanese and other Asians, and in most cases the cause is unknown (Bruno et al. 1988; Chiu et al. 1998). Some cases are familial (Kitahara et al. 1979), others appear to be due to a generalized fibrous disorder of arteries (Aoyagi et al. 1996), and a few may be due to a congenital hypoplastic anomaly affecting arteries at the base of the brain, or associated with Down's syndrome (Cramer et al. 1996).
Sometimes the arterial narrowing and obstruction is a result of basal meningeal or nasopharyngeal infection, vasculitis, irradiation, trauma, fibromuscular dysplasia, sickle-cell disease, or neurofibromatosis (Tomsick et al. 1976). Atheromatous disease of the distal ICA very rarely causes the moyamoya syndrome, perhaps because profuse collateral development is impossible except in children, or perhaps because such distal distribution of atheroma is so uncommon.
The syndrome presents in infancy with recurrent episodes of cerebral ischaemia and infarction, mental retardation, headache, epileptic seizures, and occasionally involuntary movements. In adults the presentation is as, or more, often with subarachnoid or primary intracerebral haemorrhage, because of rupture of the fine collateral system. There have also been a few reports of associated intracranial aneurysms (Iwama et al. 1997).