Background and Purpose--Although the development of a noninvasive MR examination has increased the opportunity to identify asymptomatic patients with moyamoya disease who have experienced no stroke episodes, their clinical features are still unclear. This was the first multicenter, nation-wide survey focused on asymptomatic moyamoya disease in Japan and was designed to clarify their clinical features.

Methods--A clinical database of asymptomatic patients with moyamoya disease was collected from 12 participating hospitals in Japan between 2003 and 2006. In total, 40 patients were enrolled in this historical prospective cohort study. Of these, 6 underwent surgical revascularization, including superficial temporal artery to middle cerebral artery anastomosis and/or pial synangiosis. Their demographic and radiological findings as well as outcome were evaluated.

Results--On initial evaluation, cerebral infarction and disturbed cerebral hemodynamics were detected in 20% and 40% of the involved hemispheres, respectively. Angiographical stage was more advanced in more elderly patients. Of 34 nonsurgically treated patients, 7 experienced transient ischemic attack (n=3), ischemic stroke (n=1), or intracranial bleeding (n=3) during follow-up periods (mean, 43.7 months). The annual risk for any stroke was 3.2%. Disease progression was associated with ischemic events or silent infarction in 4 of 5 patients. No cerebrovascular event occurred in the 6 patients who underwent surgical revascularization.

Conclusions--The findings revealed that asymptomatic moyamoya disease is not a silent disorder and may potentially cause ischemic or hemorrhagic stroke. Asymptomatic patients with moyamoya disease should be carefully followed-up to further clarify their outcome and to establish the management guideline for them.