Moyamoya disease is a chronic cerebrovascular condition in which internal carotid artery or its terminal branches occlude progressively. New vessels develop, which bypass the stenotic arteries of the circle of Willis, creating a rich network of small fragile arteries. The dense angiographic appearance of newly formed collaterals is the hallmark of moyamoya, a Japanese term meaning “hazy, like a puff of smoke.”
Moyamoya disease is rare, with an incidence of 0.35 to 0.54 per 100 000 people in Asia,1-3whereas its incidence is much lower in Western countries.3It has a female predominance of 1.8:1,1which is less evident at younger ages.4