Short answer · Medically reviewed summary · Last updated: 2026-04-06
Moyamoya is a rare, progressive cerebrovascular disorder characterized by the narrowing of arteries at the base of the brain, which leads to the formation of a fragile network of tiny, collateral blood vessels that resemble a "puff of smoke" on imaging studies. Understanding the Condition In patients with Moyamoya, the internal carotid arteries—the primary vessels supplying blood to the brain—slowly become blocked or narrowed. To compensate for this restricted blood flow, the brain attempts to grow new, weaker vessels.
What is Moyamoya
What is Moyamoya? Plain-language, medically reviewed definition plus the lived reality told by patients.
Moyamoya is a rare, progressive cerebrovascular disorder characterized by the narrowing of arteries at the base of the brain, which leads to the formation of a fragile network of tiny, collateral blood vessels that resemble a "puff of smoke" on imaging studies.
Understanding the Condition
In patients with Moyamoya, the internal carotid arteries—the primary vessels supplying blood to the brain—slowly become blocked or narrowed. To compensate for this restricted blood flow, the brain attempts to grow new, weaker vessels. Because these collateral vessels are thin and brittle, they are highly prone to rupture, which may cause a hemorrhagic stroke, or they may fail to provide adequate oxygen, leading to ischemic events.
Who is Affected?
Moyamoya is most commonly diagnosed in two distinct age groups: children (typically between 5 and 10 years old) and adults (between 30 and 50 years old). While the disease was first identified in Japan and remains most prevalent in East Asian populations, it is now known to affect individuals of all ethnic backgrounds worldwide. Women are affected slightly more frequently than men.
Classifications and Mechanism
Clinicians classify this condition as either "Moyamoya disease," which is often idiopathic or hereditary, or "Moyamoya syndrome," when the arterial narrowing is associated with another underlying condition, such as Down syndrome, neurofibromatosis type 1, or sickle cell anemia. The pathophysiology involves a complex interaction between genetic predisposition and chronic inflammation, causing the smooth muscle cells of the arteries to thicken and occlude the vessel lumen.
What Sets It Apart
Unlike standard atherosclerosis, which typically affects older adults and involves plaque buildup in large arteries, Moyamoya involves a specific, localized narrowing at the base of the brain. The hallmark "puff of smoke" appearance on an angiogram is unique to this condition, distinguishing it from other types of vasculitis or generalized arterial disease.
Medical Disclaimer: This information is for educational purposes only and does not constitute medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health provider with any questions regarding a medical condition.
References
- NIH Genetic and Rare Diseases Information Center (GARD)
- Orphanet: The portal for rare diseases and orphan drugs
- Moyamoya Foundation
- OMIM (Online Mendelian Inheritance in Man)
