What is Moyamoya Disease?

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Cerebrovascular Center

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Moyamoya is a rare cerebrovascular disease that reduces the flow of blood to the brain.

Moyamoya can result in brain hemorrhaging, transient ischemic attack (TIA, or "mini-stroke:) or a major stroke. It is also associated with brain aneurysms.

It was first described in Japan, where moyamoya means "puff of smoke." It was so named because it results in a tangle of fragile blood vessels that resembles a puff of smoke when viewed on an angiogram.

Moyamoya: a Progressive Disease
Who does Moyamoya Affect?
Diagnosing Moyamoya
Treating Moyamoya
Why Swedish?

Moyamoya: a Progressive Disease

Moyamoya causes a narrowing or blockage of the carotid arteries where they enter the brain at the base of the skull. The carotid arteries are the main arteries that supply blood and oxygen to the brain. This narrowing restricts blood flow – and therefore oxygen – to the brain.

It is a progressive disease, causing other blood vessels in the brain to continue to narrow over time.

The body tries to compensate and restore blood flow by creating a network of tiny blood vessels that branch off from the arteries. Unfortunately, the newly formed blood vessels are fragile, and ineffective in restoring blood flow. These fragile vessels can rupture and bleed.

The underlying cause of moyamoya is unknown, but it is thought to be linked to genetics and environmental triggers.

Who does Moyamoya Affect?

The greatest incidences of moyamoya are found in Asian countries – particularly Japan and Korea – but it is also found in the U.S. and around the world.

There are two ages where the disease tends to peak — one at about age 5, and the other at about age 40. Children with moyamoya are more likely to have TIAs or strokes. In adults, moyamoya more often leads to brain hemorrhaging.

Diagnosing Moyamoya

Severe headaches, seizures or stroke-like symptoms can be the first clinical signs of the disease.
A diagnosis of moyamoya is confirmed with a cerebral angiogram – a medical imaging study used to visualize the inside of blood vessels in the brain.

A number of other imaging tools are used to lead to this diagnosis, including:

  •  CT, CTA or MRI scans that show details of inner structures of the brain
  •  Doppler ultrasound, including transcranial Doppler that measures blood flow velocity
  • Brain blood flow studies using various tools, including SPECT (single photon emission computerized tomography) that show how blood flows to tissues

Although other conditions – including atherosclerosis (hardening of the arteries), meningitis, and brain tumors – can also cause a narrowing of major arteries, they are not associated with moyamoya.

Treating Moyamoya

While a number of medications have been tried in patients with moyamoya, surgery remains the most effective treatment.

Without surgery, most patients would experience mental decline and multiple strokes because of the progressive narrowing of the arteries. When it results in brain hemorrhaging, moyamoya can be fatal.

Two surgical options that have proven successful are indirect revascularization and direct revascularization. The goal of both procedures is to restore blood flow to the brain.


Direct revascularization

Direct revascularization involves suturing blood vessels in the scalp to blood vessels in the brain. Using microsurgery, neurosurgeons often suture the superficial temporal artery to the middle cerebral artery.

(The superficial temporal artery is along the side of the head, and the middle cerebral artery is one of the main arteries supplying blood to the forward part of the brain.) 

This procedure is often very effective in rapidly increasing blood flow.

Indirect revascularization

Indirect revascularization encourages healthy new blood vessels to growth in the brain. The procedure involves taking a small section of scalp tissue containing blood vessels, and sewing it to the firm layer of tissue that covers the brain.


Over time, new blood vessels develop. This procedure is used primarily on children, because their blood vessels are most often too small to connect them directly.


Surgical Outcomes

Revascularization surgery is done to reduce the risk of TIAs, stroke and brain hemorrhage. In most moyamoya patients, blood flow to the brain improves almost immediately.

Any surgery carries some risk, and potential complications from revascularization can include infection, bleeding and stroke. Fortunately, these complications are uncommon.

Why Swedish?

The specialists at the Swedish Cerebrovascular Center are highly skilled and experienced in treating patients with moyamoya.

Our expert team includes our neurosurgeon, neuro-anestheologist, neuro-interventional radiologists, stroke neurologist, as well as our clinical nurses and scheduling staff.

Everyone on the team collaborates and communicates with each other to ensure our patients receive the highest level of care.