Moyamoya disease is a rare, progressive blood vessel (vascular) disorder in which the carotid artery in the skull becomes blocked or narrowed, reducing blood flow to your brain. Tiny blood vessels then open up at the base of the brain in an attempt to supply the brain with blood. The word "moyamoya" means "puff of smoke" in Japanese, a term describing the appearance of this cluster of tiny blood vessels.
These tiny clusters of blood vessels cannot supply the necessary blood and oxygen to the brain, resulting in temporary or permanent brain injury.
The condition may cause a ministroke (transient ischemic attack, or TIA), stroke, bulge or ballooning in a blood vessel (aneurysm) or bleeding in the brain. It can also affect how well your brain functions and cause cognitive and developmental delays or disability.
Moyamoya disease most commonly affects children, but adults may have the condition. Moyamoya disease is found all over the world, but it's more common in East Asian countries, especially Korea, Japan and China and in people of East Asian descent.
Moyamoya disease care at Mayo Clinic