Moyamoya disease is a rare progressive cerebrovascular disease characterized by bilateral stenosis of vasculature of the Circle of Willis, specifically the distal internal carotid arteries, that leads to extensive collateral circulation. These dilated collateral vessels are described as having a hazy “puff of smoke” appearance on angiography. “Moyamoya” is the Japanese word for this characteristic appearance. The disease was originally described in Japan in 1957 1 and introduced to the English literature in 1969.2 The disease is most known for its distribution in Asian populations, but recently there has been more research and attention given to moyamoya in Europe and North American Moyamoya disease presents clinically due to the ischemic and hemorrhagic complications of abnormal cerebral vascularity.3,4


Moyamoya disease was originally described in Japanese populations but is present in a variety of ethnicities.3,5,6 In Japan, the incidence per 100,000 patient years is between 0.35 to 0.943 with a male: female ratio of 1:1.87. In the US, incidence ranged from 0.05 to 0.17 per 100,000 patient years with a similar gender distribution.3,6 Other population studies have not been as robust but European studies show moyamoya statistics that are more similar to American findings than those of Asian moyamoya findings.4 There is a bimodal distribution of incidence: in early childhood and adulthood, but the doublepeaked incidence is less dramatic in the US and Europe.4,8 Children typically present with the ischemic symptoms and adults can present with either ischemic or hemorrhagic type, with the ischemic type predominating.5,9 Overall, the hemorrhagic type is more common in Asia than the U.S.9 The incidence has been increasing with time, which may be due to increased awareness.5