Moyamoya disease (MD) is a rare, heritable neurologic disorder characterized by narrowing and occlusion (blockage) of arteries in the neck and brain. Moyamoya is a Japanese term meaning “hazy, like a puff of smoke drifting in the wind.” This nomenclature originates from the appearance of cerebral angiograms (X rays of the brain done after injecting dye into arteries in the neck), which demonstrate an abnormal cloudiness in basal ganglia (structures on the underside of the brain). This finding is secondary to dilation of small arteries and capillaries (telangiectasia).