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What is moyamoya?

Moyamoya is a rare condition in which the blood vessels (internal carotid arteries) that supply blood to the brain become narrowed. This limits the flow of blood to the brain, and puts them at risk for stroke.

The brain tries to make up for reduced blood flow by growing new blood vessels, called collaterals. While these blood vessels can temporarily help increase blood supply, they eventually stop working. The name “moyamoya,” which means “puff of smoke” in Japanese, refers to the wispy, smoke-like appearance of these new blood vessels on an x-ray.

Moyamoya is a progressive condition, meaning that it gets worse over time, so children need treatment to reduce their risk of stroke.

Some children with moyamoya also have another medical condition, such as:

Watch: Learn more about moyamoya


What is moyamoya?


How serious is moyamoya?


How we diagnose moyamoya


What happens after a diagnosis? Part 1


What happens after a diagnosis? Part 2


What happens during surgery for moyamoya?


What happens after surgery for moyamoya?


Moyamoya Disease | Symptoms & Causes

What are the symptoms of moyamoya?

Children with moyamoya may have symptoms that are similar to a stroke, such as:

  • weakness on one side of the body
  • blurry or otherwise affected vision
  • slurred speech
  • headaches
  • seizures

These symptoms can either begin gradually and get better over time, or develop suddenly and persist.

Rarely, a child with moyamoya may have a brain hemorrhage (bleeding in the brain), though this occurs much more often in adults with moyamoya. Warning signs of a brain hemorrhage can include:

  • nausea
  • vomiting
  • fatigue and lethargy
  • changes in vision
  • severe headache
  • numbness in part of the body

You should seek medical treatment right away if your child has any of the warning signs above.

What causes moyamoya in children?

Because moyamoya is so rare, its causes are not fully understood. Experts believe that a variety of factors — ranging from genetic defects to traumatic injury — may trigger the condition. There may also be a genetic component. About seven percent of children with moyamoya are believed to have an inherited gene defect. However, in at least half of all known cases of moyamoya, the disease has no identifiable cause.

Moyamoya disease is slightly more common in girls than in boys, and somewhat more common in children of Asian descent than in other ethnic backgrounds.

Connor, wearing a Celtics jersey, gives a thumbs-up while attending a Celtics game.

Getting back in the game after brain surgery

Conner and his family came to Boston Children's Hospital to find answers after he was diagnosed moyamoya.

Moyamoya Disease | Diagnosis & Treatments

How is moyamoya diagnosed?

The standard test for both diagnosing moyamoya and planning for surgery is a cerebral angiogram. This is a minimally invasive procedure that produces a “map” of your child’s carotid arteries.

How is moyamoya treated?

Moymoya is treated with surgery to fix the narrowed arteries in the brain and decrease the risk of stroke. While surgery is the only viable treatment for moyamoya disease in the long term, your doctor may also recommend medication to manage some of your child’s symptoms. These may include aspirin (to help prevent blood from clotting) and calcium channel blockers, such as verapamil (to help lower blood pressure).

Several surgical treatments for moyamoya are effective at bypassing narrowed arteries and creating a new blood supply for the affected areas of the brain.

There are several types of surgical treatments for moyamoya:

  • Pial synangiosis. This is a type of surgery that reroutes the healthy scalp blood vessel to the brain, bypassing the narrowed vessels.
  • EDAS (encephaloduroarteriosynangiosis). In this procedure, the superficial temporal artery in the child’s brain is laid over an opening in the cortex. The artery is then sewed to the dura (the firm layer of tissue that covers the brain). Over time, small new arterial vessels begin to develop.
  • EMS (encephalomyosynangiosis). In this procedure, small portions of the temporalis muscle in the jaw are attached in a parallel direction to the surface of the child’s brain. The transplanted muscle gradually generates new blood vessels, forming a supplementary source of blood flow to the brain.
  • Omental transposition/transfer. In this procedure, the child’s omentum, the blood-rich lining that surrounds the organs in the abdomen, is laid over the surface of the brain. New vessels eventually develop and grow into the brain.
  • Dural inversion. In this procedure, neurosurgeons invert the flaps of fibrous dural tissue on the child’s meningeal vessel, a large artery within the skull. This places the outer dural surface, which has plentiful blood vessels, in direct contact with the parts of the brain that were previously deprived of essential blood flow.
  • Direct arterial bypass. This surgery is also known as superficial temporal to middle cerebral artery anastomosis, or STA-MCA bypass. During this procedure, neurosurgeons join a blood vessel from the child’s scalp directly to a vessel in the brain. Blood flow throughout the brain should improve over the next several months.

Moyamoya Disease | Innovation

Our areas of innovation for moyamoya

The experts in our Moyamoya Program are international leaders in understanding and treating this life-threatening condition. More than 25 years ago, our physicians developed an effective surgery for moyamoya, called pial synangiosis. This surgery works by allowing new blood vessels to grow from the new scalp artery, which brings more blood to the brain.

Over the past 25 years, our surgeons have performed more than 50 of these procedures each year. Boston Children’s neurosurgeon Edward Smith, MD, is the most experienced surgeon performing this surgery in the country today, with the best results worldwide.

Our Moyamoya Program treats adults as well as children. Contact us to request an appointment, second opinion or consultation.

Moyamoya Disease | Frequently Asked Questions

At what age do children typically develop moyamoya symptoms?
Are there different types of moyamoya?
Is it possible that my child’s moyamoya will go away without surgery?
Does my child need to cut back on physical activity?
Should my other children be screened for moyamoya?
Is there a genetic test for moyamoya?
What is the long-term outlook for kids with moyamoya?

Moyamoya Disease | Programs & Services