Moyamoya Disease

Abstract

Moyamoya disease (MMD) is a rare disease, with typical characteristics including progressive stenosis or occlusion of the bilateral internal carotid artery and accompanying basal collateral formation. Although MMD only accounts for a small portion of stroke in the elderly, it is the most common cause of pediatric stroke in East Asia. East Asian regional predilection and female predominance are well-known epidemiologic features, and the age of onset follows a bimodal distribution. The affected blood vessel shows intimal hyperplasia with shrinkage of the outer diameter. Owing to stenosis or occlusion, cerebral perfusion decreases, resulting in ischemic symptoms that include transient ischemic attack or cerebral infarction. In these cases, cerebral revascularization surgery is effective to prevent stroke reoccurrence and neurological deterioration. The fragility of fine collateral vascular networks is another problem. These are prone to rupture leading to intraventricular or intracerebral hemorrhage. Cerebral revascularization surgery can reduce the extent of fragile collaterals by augmenting cerebral blood flow. One study reported that extensive bilateral direct bypass surgery could prevent further hemorrhage by decreasing blood flow through fragile collaterals. Another reported option to prevent further hemorrhage is endovascular obliteration of the aneurysm (or pseudoaneurysm) at the site of hemorrhage.