Definition of Moyamoya disease
Moyamoya disease is a rare blood vessel (vascular) disorder in which a ring of blood vessels at the base of your brain (the circle of Willis) and the uppermost (distal) segments of the arteries supplying the brain progressively narrow, causing blood flow to your brain to become reduced.
The condition may cause a ministroke (transient ischemic attack), stroke or other symptoms.
Moyamoya disease mainly affects children, but adults may have the condition. Moyamoya disease usually occurs in people from Japan and other Asian countries, but people in North America, Europe and other areas also have moyamoya disease.