Moyamoya disease is a rare condition in which the flow of blood to the brain is blocked or restricted by narrowed arteries at the skull base. The body tries to develop more small blood vessels to compensate for the blockage, which results in a tangle of vessels that’s still not sufficient to get blood to the entire brain. The cloud of small vessels in that tangle look like a cloud on imaging tests, which is where the condition’s name comes from. "Moyamoya" means "puff of smoke" in Japanese, and while it occurs more often in Asian ethnicities, Moyamoya disease is increasingly recognized in Caucasians, African Americans, and Latinos. It occurs most commonly in children, although it can occur in adults.
In most patients with Moyamoya disease the blockage is bilateral, with arteries on both sides of the brain affected. This creates a crisis within the brain as critical areas are deprived of blood supply, which eventually leads to neurological symptoms and may cause a stroke, or “brain attack.” Even in patients who present with unilateral Moyamoya disease, the blood vessels on the “good” side can become compromised over time. In some patients, a stroke or transient ischemic attack (TIA, or mini-stroke) is the first symptom of Moyamoya, although many patients will exhibit earlier signs such as headache, dizziness, or seizures. Some patients may also present with intracerebral hemorrhage, which usually results from bursting of an overcompensated “moyamoya” vessel (see Symptoms of Moyamoya Disease).
Moyamoya disease is a relentlessly progressive disease, and without treatment patients will have persistent and worsening symptoms as the diseased blood vessels continue to narrow. The disease can be fatal if not treated. Fortunately, there are surgical solutions to bypass the vascular blockage and restore blood flow to the brain (see Surgery for Moyamoya).
Early diagnosis can help prevent permanent neurological damage. Brain damage can get worse the longer blood flow is blocked, making a prompt and accurate diagnosis critically important (see Diagnosing and Treating Moyamoya Disease).
What Causes Moyamoya Disease?
The exact cause of Moyamoya disease remains unknown. However, Moyamoya disease tends to run in families and is mostly commonly seen in Asian ethnicities such as Japanese, Korean, and Chinese populations. Children with Moyamoya disease may also have syndromic conditions including sickle cell disease, Down syndrome, and neurofibromatosis type I.
Reviewed by: Ning Lin, M.D.
Last reviewed/updated: March 2024
Illustration by Thom Graves, CMI