What Is Moyamoya Disease? A Plain-Language Guide to This Rare Brain Blood Vessel Condition

Medically reviewed by Dr. Baraa Alnahhal, MD · Last reviewed: October 2026

Quick Answer: Key Facts About Moyamoya Disease

Moyamoya disease is a rare condition in which the carotid artery supplying the brain becomes narrowed or blocked, and tiny new vessels grow at the brain's base to compensate. In children, the first sign is usually a stroke or ministroke. Children under 15 and people of Asian heritage are at higher risk. Treatment can help prevent strokes. [1] [2]

Feature	Details
What is moyamoya disease?	A rare condition where the brain's main supply artery (the carotid artery) becomes narrowed or blocked, and the brain grows tiny new vessels at its base to compensate. [1]
What does it feel like?	In children, the first sign is usually a stroke or a ministroke (TIA); adults may also have bleeding in the brain. Other signs include headache, seizures, one-sided weakness or numbness, vision problems, and trouble speaking or understanding (called aphasia). [1]
Who is at higher risk?	Children under 15, people of Asian heritage, women (slightly), people with a family history (30 to 40 times higher risk), and people with certain conditions like sickle cell disease, Down syndrome, or neurofibromatosis type 1. [1]
What causes it?	The exact cause is unknown, but it is most common in Japan, Korea, and China, which strongly suggests a genetic factor in some populations. [1]
How is it treated?	Medicines such as blood thinners, bypass-style surgery that restores blood flow to the brain, and therapy — treatment can't cure the disease, but it can help prevent strokes. [2]

What the research says

• Bypass surgery cut the risk of repeat bleeding. In the Japan Adult Moyamoya Trial, 80 adults who had recently had bleeding in the brain were randomized to bilateral direct bypass (42) or conservative care (38). Over 5 years, rebleeding occurred in 11.9% of the surgical group vs 31.6% of the nonsurgical group (2.7%/year vs 7.6%/year). The authors described the result as statistically marginal. (Miyamoto et al., Stroke, 2014) [5]

• Revascularization carries a low surgical risk in experienced hands. In a Stanford series of 450 procedures in 264 patients (mean follow-up 4.9 years), surgical morbidity was 3.5% and mortality 0.7% per treated hemisphere, the cumulative 5-year risk of stroke or death was 5.5%, and 91.8% of patients who presented with TIAs were TIA-free at one year or later. (Guzman et al., J Neurosurg, 2009) [6]

• A single gene change explains much of the genetic link in East Asia. A Japanese study identified RNF213 as the first moyamoya susceptibility gene; the p.R4859K variant was found in 95% of moyamoya families, 73% of non-familial cases, and 1.4% of controls (odds ratio 190.8). (Kamada et al., J Hum Genet, 2011) [7]

What is moyamoya disease?

Moyamoya disease is a rare blood vessel condition in which the carotid artery — the major artery that brings blood to the brain — becomes blocked or narrowed inside the skull. When it's blocked, blood flow to the brain is reduced. [1] [4]

The body has a backup response. Tiny blood vessels form at the base of the brain to supply it with blood. These tiny vessels are the condition's signature. [1] [4]

Figure 1: In moyamoya disease, the carotid artery narrows or closes, oxygen-rich blood delivery drops, and tiny vessels form at the base of the brain to compensate.

Because the brain is getting less oxygen-rich blood, the condition can cause a ministroke, a full stroke, or bleeding in the brain. It also can affect how well the brain functions and can cause cognitive and developmental delays or disability. [1]

Here is the hopeful part: spotting symptoms early is very important, because early detection and treatment can help prevent a stroke and serious complications. [1]

What are the symptoms of moyamoya disease?

Moyamoya disease may happen at any age, but symptoms are most common in children between ages 5 and 10 and in adults between ages 30 and 50. [1] [4]

The condition causes different symptoms in adults and children. In children, the first symptom is usually a stroke or a recurrent transient ischemic attack — a series of ministrokes (TIAs). Adults may have these symptoms too, and they may also experience bleeding in the brain, known as a hemorrhagic stroke. The bleeding happens because of the way the blood vessels in the brain formed. [1]

Symptoms caused by reduced blood flow to the brain include: [1]

Symptom	What it looks like
Headache	Head pain [1]
Seizures	Sudden electrical disturbances in the brain
Weakness, numbness, or paralysis	Usually in the face, arm, or leg — typically on one side of the body [1]
Vision problems	Changes or loss of vision
Trouble speaking or understanding	Called aphasia — difficulty talking or making sense of what others say [1]
Cognitive or developmental delays	Trouble with thinking, learning, or development
Involuntary movements	Movements that happen without the person's control

An important detail: these symptoms can be triggered by exercise, crying, coughing, straining, or a fever. [1] If you have any of these symptoms, see your healthcare professional.

How is moyamoya disease different from moyamoya syndrome?

Sometimes changes to the blood vessels mimic moyamoya disease. These changes may have different causes and symptoms, and they are known as moyamoya syndrome. [1]

The key difference is the cause. Moyamoya syndrome can be linked to certain conditions, such as Down syndrome, sickle cell anemia, neurofibromatosis type 1, and hyperthyroidism. [1]

Figure 2: Moyamoya disease has an unknown cause with a likely genetic link; moyamoya syndrome looks similar but is tied to other conditions such as Down syndrome, sickle cell anemia, and neurofibromatosis type 1.

What causes moyamoya disease?

The exact cause of moyamoya disease isn't known. It is most commonly seen in Japan, Korea, and China, but it also happens in other parts of the world. [1]

Because the condition is most common in these Asian countries, researchers believe this strongly suggests a genetic factor in some populations. [1]

Who is at higher risk?

Though the cause is not known, certain factors may increase the risk of having the condition. [1]

Risk factor	What it means
Asian heritage	Found worldwide but more common in East Asian countries, especially Korea, Japan, and China, likely due to genetic factors in those populations; people with Asian heritage living in Western countries also have a higher risk [1]
Family history	If a family member has moyamoya disease, the risk is 30 to 40 times higher than that of the general population — strongly suggesting a genetic link [1]
Medical conditions	Sometimes happens with other disorders, including neurofibromatosis type 1, sickle cell disease, and Down syndrome, among many others [1]
Being female	Slightly more common in females [1] [3]
Being young	Most commonly affects children younger than 15 years old, though adults can have it [1]

What are the complications?

Most complications from moyamoya disease are linked to the effects of strokes. They include seizures, paralysis, and vision problems. Other complications include speech problems, movement disorders, and developmental delays. [1]

Moyamoya disease can cause serious and permanent damage to the brain. [1] This is why early detection and treatment matter so much.

The good news on prevention: there is no way to prevent moyamoya disease itself, but treatments can prevent strokes and other complications. [1]

When should you seek emergency help?

Seek immediate medical attention if you notice any symptoms of a stroke or ministroke, even if the symptoms seem to come and go or disappear. [1]

To check for signs of stroke, think "FAST":

Letter	Check	What to look for
F — Face	Ask the person to smile	Does one side of the face droop? [1]
A — Arms	Ask the person to raise both arms	Does one arm drift downward, or is it unable to rise? [1]
S — Speech	Ask the person to repeat a simple phrase	Is the speech slurred or strange? [1]
T — Time	If you observe any of these signs	Call 911 or emergency medical help right away [1]

Don't wait to see if symptoms go away. Every minute counts. The longer a stroke goes untreated, the greater the potential for brain damage and disability. If you're with someone you suspect is having a stroke, watch the person carefully while waiting for emergency assistance. [1]

How is moyamoya disease diagnosed?

Moyamoya disease is usually diagnosed by a neurologist — a doctor who specializes in conditions of the brain. The neurologist reviews symptoms and family and medical history, and may perform a physical exam. Several tests are generally needed. [2]

Test	How it works
MRI (magnetic resonance imaging)	Uses powerful magnets and radio waves to create detailed brain images; a magnetic resonance angiogram uses injected dye to view arteries and veins; a perfusion MRI measures blood passing through vessels and shows decreased blood supply [2]
CT scan (computerized tomography)	Uses a series of X-rays to create detailed brain images; a CT angiogram uses injected dye to highlight blood flow; can't diagnose early stages but may find blood vessel problems [2]
Cerebral angiogram	A long, thin tube (catheter) is inserted into a blood vessel in the groin and guided to the brain with X-rays; dye makes the brain's blood vessels visible [2]
PET scan or SPECT	A small amount of safe radioactive material is injected; PET provides visual images of brain activity; SPECT measures blood flow to the brain [2]
EEG (electroencephalogram)	Electrodes on the scalp monitor the brain's electrical activity; children with moyamoya disease often have results outside the typical range [2]
Transcranial Doppler ultrasound	Sound waves image the head and neck to evaluate blood flow in the neck's blood vessels [2]

If necessary, the neurologist may order other tests to rule out other conditions. [2]

How is moyamoya disease treated?

Treatment doesn't cure moyamoya disease, but it can help prevent strokes. The goal is to reduce symptoms, improve blood flow to the brain, and lower the risk of complications, which include ischemic stroke caused by a lack of blood flow, bleeding in the brain, and death. [2]

The outlook (also called the prognosis) depends on how early the disease was diagnosed, how much damage has happened when treatment is sought, whether treatment is undergone, and age. [2]

Treatment may include medicine, surgery, and therapy. [2]

Figure 3: The three treatment paths for moyamoya disease — medicines to prevent strokes and manage symptoms, revascularization surgery to restore blood flow, and therapy to address the effects of stroke.

Which medicines are used?

Medicines may be prescribed to manage symptoms, reduce the risk of a stroke, or aid in seizure control. [2]

Medicine	What it does
Blood thinners	Typically recommended if symptoms are mild or absent; aspirin or another blood thinner helps prevent strokes [2]
Calcium channel blockers	May help manage headaches and reduce TIA symptoms; managing blood pressure also helps prevent blood vessel damage [2]
Anti-seizure medicines	Helpful for people who have had seizures [2]

When is surgery needed?

Early surgical treatment can help slow the progression of moyamoya disease. A neurologist may recommend revascularization surgery if symptoms or strokes develop, or if tests show evidence of low blood flow to the brain. [2]

In revascularization surgery, surgeons bypass the blocked arteries by connecting blood vessels on the outside of the skull to the inside of the skull to help restore blood flow. This may be done with direct procedures, indirect procedures, or a combination of both. [2]

Direct revascularization stitches a scalp artery directly to a brain artery (called superficial temporal artery to middle cerebral artery bypass surgery). It increases blood flow to the brain immediately. It may be difficult to perform in children due to the size of the blood vessels, but it is the preferred option in adults — and it can be performed safely and effectively by an experienced surgical team that treats people with moyamoya disease daily. [2]

Indirect revascularization aims to increase blood flow gradually. In adults treated at high-volume surgical centers, indirect revascularization is almost always combined with direct revascularization. It includes: [2]

Procedure	What the surgeon does
EDAS (encephaloduroarteriosynangiosis)	Makes a small temporary opening on the scalp to expose the artery, then opens the skull directly beneath it and lays the intact scalp artery onto the brain's surface, letting new blood vessels grow into the brain over time [2]
EMS (encephalomyosynangiosis)	Separates a muscle in the temple region of the forehead and places it onto the brain's surface through an opening in the skull to help restore blood flow [2]
EMS combined with EDAS	The muscle holds the attached scalp artery in place as blood vessels grow into the brain over time [2]

There are possible surgery risks, including changes in pressure in the brain's blood vessels that can cause headaches, bleeding, and seizures. However, the benefits of surgery largely outweigh the risks. [2]

One more thing to know: some people with moyamoya disease develop a brain aneurysm — a bulge or ballooning of a blood vessel in the brain. If this happens, surgery may be necessary to prevent or treat a ruptured brain aneurysm. [2]

What role does therapy play?

To address the physical and mental effects of a stroke, the healthcare professional may recommend an evaluation by a psychiatrist or therapist. Without surgery, moyamoya disease can cause cognitive decline due to narrowing blood vessels. A psychiatrist may look for problems with thinking and reasoning skills and monitor for signs that those problems are worsening. [2]

Cognitive behavioral therapy can help address emotional issues related to having moyamoya disease, such as how to cope with fears and uncertainties about future strokes. [2]

Physical and occupational therapy can help regain any lost physical function caused by a stroke. [2]

What can you do before seeing a doctor?

If you or your child has been diagnosed with moyamoya disease, you'll most likely be referred to a neurologist. [2]

Here's how to get ready for the appointment. Be aware of anything you need to do ahead of time — at the time you make the appointment, ask if there's anything you or your child needs to do in advance, such as restricting your diet. Write down symptoms you or your child has, including any that may not seem related. Write down important personal information, including major stresses or recent life changes. Make a list of all medicines, vitamins, or supplements you or your child is taking, with doses. Take a family member or friend along — someone else may remember information you missed or forgot. And write down questions to ask, ordered from most to least important. [2]

Here are some basic questions to bring along:

• What is likely causing my or my child's symptoms or condition?

• What tests are necessary? Do they require any special preparation?

• What treatments are available, and which do you recommend?

• What side effects can be expected from treatment?

• Is surgery a possibility?

• Are you prescribing medicine? If so, is there a generic alternative?

• I have other medical problems — how can they be managed together?

• Will I or my child have any restrictions on physical activity?

• Are there brochures or other printed materials I can take with me? What websites do you recommend?

The healthcare professional is also likely to ask questions, such as when symptoms first began, how often they occur, whether certain activities trigger them, and whether anyone in your immediate family has ever had moyamoya disease. [2]

Conclusion and next steps

Moyamoya disease is a rare condition in which the brain's main supply artery becomes narrowed or blocked, and the brain grows tiny new blood vessels at its base to compensate. It can cause ministrokes, strokes, and bleeding in the brain, and it most commonly affects children — though adults between 30 and 50 are the other common group. [1]

The cause isn't known, but the condition's concentration in Japan, Korea, and China, along with a striking family-history link (a 30 to 40 times higher risk when a family member has it), points strongly to genetics in some populations. [1]

The encouraging part: treatment doesn't cure the disease, but it can prevent strokes and other complications. Medicines, bypass-style surgery that restores blood flow, and therapy all play a role — and early detection and treatment can help prevent a stroke and serious complications. If you or your child has unexplained strokes, ministrokes, one-sided weakness, or seizures (especially triggered by crying, exercise, or fever), a conversation with your healthcare professional is the right first step. [1] [2]

Talk with a healthcare professional. If you've noticed any signs of a stroke or ministroke — one-sided weakness, slurred speech, facial drooping, seizures, or vision changes — don't wait. If stroke-like symptoms are happening, call 911 or emergency medical help right away — every minute counts. If moyamoya disease has been diagnosed, a neurologist can help you build a treatment plan to protect your brain. For plain-language guides to what tests and treatments involve, explore the related articles on Rinnit.com.

Frequently Asked Questions

What is moyamoya disease?

Moyamoya disease is a rare blood vessel condition in which the carotid artery in the skull becomes blocked or narrowed, reducing blood flow to the brain. The brain responds by growing tiny blood vessels at its base. [1]

Who gets moyamoya disease?

Moyamoya disease most commonly affects children under 15, with symptoms most common between ages 5 and 10, and adults between 30 and 50. It's found worldwide but is more common in Japan, Korea, and China, slightly more common in females, and 30 to 40 times more likely if a family member has it. [1]

What are the first symptoms in children?

In children, the first symptom is usually a stroke or recurrent ministrokes (TIAs). Symptoms can be triggered by exercise, crying, coughing, straining, or fever. [1]

What is the difference between moyamoya disease and moyamoya syndrome?

Moyamoya disease and moyamoya syndrome look similar, but moyamoya syndrome is linked to other conditions — such as Down syndrome, sickle cell anemia, neurofibromatosis type 1, and hyperthyroidism — while moyamoya disease's cause is unknown but strongly suggests a genetic factor. [1]

Can moyamoya disease be cured?

Treatment doesn't cure moyamoya disease, but it can help prevent strokes and other complications through medicines, revascularization surgery, and therapy. [2]

What is revascularization surgery?

Surgery that bypasses the blocked arteries by connecting blood vessels outside the skull to blood vessels inside the skull, restoring blood flow to the brain. It can be direct (stitching a scalp artery directly to a brain artery), indirect (laying tissue on the brain's surface so new vessels grow over time), or a combination. [2]

Can moyamoya disease cause bleeding in the brain?

Yes. Adults, in particular, may experience bleeding in the brain (a hemorrhagic stroke), because of the way the blood vessels in the brain formed. [1]

What should I do if I suspect a stroke?

Use "FAST": check the Face (does one side droop?), Arms (does one drift downward?), Speech (is it slurred or strange?), and Time (call 911 right away). Don't wait to see if symptoms go away — every minute counts. [1]

Related Reading

Read next on Rinnit.com:

• Transient Ischemic Attack (TIA): The Mini-Stroke That Is Actually a Warning

• Brain Aneurysm: Symptoms, Causes, and Treatment

Cerebral Angiogram: What It Shows, How to Prepare, What to Expect, Risks and Recovery explains how a catheter and contrast dye show the brain's blood vessels, how to prepare and the risks.

References

1. Mayo Clinic Staff. Moyamoya disease - Symptoms and causes. Mayo Clinic. March 1, 2025. https://www.mayoclinic.org/diseases-conditions/moyamoya-disease/symptoms-causes/syc-20355586

2. Mayo Clinic Staff. Moyamoya disease - Diagnosis and treatment. Mayo Clinic. March 1, 2025. https://www.mayoclinic.org/diseases-conditions/moyamoya-disease/diagnosis-treatment/drc-20355591

3. National Institute of Neurological Disorders and Stroke. Moyamoya Disease. National Institute of Neurological Disorders and Stroke (NINDS). Last reviewed February 2, 2026. https://www.ninds.nih.gov/health-information/disorders/moyamoya-disease

4. National Organization for Rare Disorders. Moyamoya Disease. National Organization for Rare Disorders (NORD). Last updated February 9, 2023. https://rarediseases.org/rare-diseases/moyamoya-disease/

5. Miyamoto S, et al. Effects of extracranial-intracranial bypass for patients with hemorrhagic moyamoya disease: results of the Japan Adult Moyamoya Trial. Stroke. 2014;45(5):1415-1421. PMID 24668203. https://doi.org/10.1161/STROKEAHA.113.004386

6. Guzman R, et al. Clinical outcome after 450 revascularization procedures for moyamoya disease. J Neurosurg. 2009;111(5):927-935. PMID 19463046. https://doi.org/10.3171/2009.4.JNS081649

7. Kamada F, et al. A genome-wide association study identifies RNF213 as the first moyamoya disease gene. J Hum Genet. 2011;56(1):34-40. PMID 21048783. https://doi.org/10.1038/jhg.2010.132

Medical disclaimer

This article is for informational purposes only and is not medical advice. Always consult a qualified healthcare professional for diagnosis and treatment decisions.