moyamoya

Moyamoya is a rare, chronic, progressive cerebrovascular disorder characterized by stenosis or occlusion of the intracranial portions of the internal carotid arteries and their proximal branches, with the development of abnormal collateral vessels at the base of the brain. The term moyamoya, meaning “hazy” or “a puff of smoke” in Japanese, describes the appearance of these collateral networks on cerebral angiography.

The disease often presents in childhood or adulthood. Its cause is not fully understood, and cases are categorized as moyamoya disease when idiopathic, or moyamoya syndrome when associated with other conditions such as neurofibromatosis type 1, Down syndrome, sickle cell disease, or thyroid disorders. Genetic factors have been identified, including variants in RNF213 (notably p.R4810K), which are more common in East Asian populations and contribute to disease susceptibility.

Clinically, children commonly experience ischemic symptoms such as transient ischemic attacks or strokes, with possible cognitive or motor deficits. Adults may present with hemorrhagic strokes due to rupture of fragile collateral vessels, headaches, or seizures. The disease can lead to progressive neurologic decline if not treated.

Diagnosis relies on imaging. MRI and MR angiography assess brain perfusion and the extent of arterial stenosis. Digital subtraction angiography classically shows bilateral distal internal carotid artery stenosis with a network of abnormal collateral vessels, producing the characteristic “puff of smoke” appearance.

Management aims to prevent stroke and improve cerebral perfusion. Many patients undergo cerebral revascularization surgery, either direct bypass (such as STA-MCA) or indirect methods (encephaloduroarteriosynangiosis, encephalomyosynangiosis), or a combination. Antiplatelet therapy and risk factor modification may be used, particularly in asymptomatic or mild cases. Prognosis improves after revascularization, though long-term risk persists.