Moyamoya Disease

Moyamoya disease is a chronic, progressive steno-occlusive arteriopathy centred on the terminal portion of the intracranial internal carotid artery (ICA), often extending into the proximal anterior and middle cerebral arteries (ACA, MCA). The arterial wall shows intimal thickening, waviness of the internal elastic lamina and thinning of the media, and the outer diameter of the affected artery shrinks. This is different from atherosclerotic stenosis, in which the lumen narrows but the outer diameter of the vessel does not shrink. As flow through the main arteries falls, small perforating and anastomotic vessels around the base of the brain enlarge to compensate. On angiography this network looks like a hazy "puff of smoke", the meaning of the Japanese word moyamoya. These collaterals preserve perfusion for a time, but they are fragile. The same disease therefore produces two opposite events: low flow causes transient ischemic attack (TIA) or infarction, and rupture of a fragile collateral causes intracranial hemorrhage. Perfusion reserve is small. Brain tissue supplied through collaterals depends on adequate systemic blood pressure, circulating volume and normal breathing. Hyperventilation lowers arterial carbon dioxide...