Moyamoya Disease

Moyamoya disease is a chronic, progressive steno-occlusive arteriopathy centred on the terminal intracranial internal carotid artery and the proximal anterior and middle cerebral arteries. Intimal hyperplasia and medial thinning narrow the arterial lumen; this is not the same process as an atherosclerotic plaque gradually accumulating inside the vessel. As flow through the major arteries falls, the brain recruits small collateral vessels around the basal ganglia and nearby structures. These vessels may preserve perfusion for a time, but they are fragile and vulnerable to rupture. Catheter angiography shows the resulting fine vascular network as a “puff of smoke.” The same disease can therefore produce two apparently opposite stroke patterns: inadequate flow causes transient ischaemic attacks or infarction, while rupture of fragile collaterals causes intracranial haemorrhage. Cerebral autoregulation is impaired. Cerebral blood flow becomes unusually dependent on systemic pressure and carbon dioxide levels. A fall in blood pressure or circulating volume can reduce cerebral perfusion; hypocapnia from hyperventilation can constrict vessels that are already working at maximal dilation. Conversely, uncontrolled hypertension increases stress on abnormal collateral vessels and raises haemorrhage risk. Moyamoya...