Moyamoya Disease

What Is It?

Moyamoya disease is a rare disorder of the blood vessels the supply the brain. The name Moyamoya means "puff of smoke" in Japanese, referring to the unique appearance of abnormal blood vessels on a cerebral angiogram of a patient with this disease.

The disease is characterized by a progressive thickening of the inner walls of the arteries at the base of the brain. As this thickening occurs the blood supply is slowly cut off, eventually completely occluding (blocking) the normal flow of blood into the brain. As this progressive change occurs slowly over time, new blood vessels grow and enlarge to attempt to get more blood flow to the brain. This leads to small, abnormal blood vessels which give the "puff of smoke" appearance on an angiogram. While it typically affects both sides of the brian, in a small subset of patients it may be one-sided.

Because of the blockage of blood flow, patients with Moya Moya are prone to ischemic strokes, meaning that parts of the brain can be injured by the blood supply being too low to support the normal functioning of the nerve cells. Additionally, because of the abnormal, fragile blood vessels that develop as the moyamoya obstruction becomes more severe, patients can also suffer hemorrhages into the brain from rupture of the abnormal Moya blood vessels.

The cause of Moyamoya disease is unknown. In some patients there appears to be a hereditary component, maybe autosomal dominant with low penetrance, as some cases occur in families with other members who have the disease. However, it is probably multifactorial, without any one definitive cause in all patients. As the name suggests, the highest risk appears to be in people of Japanese and other Asian ancestry. However, moyamoya can occur in people of all ethnicities. It is a rare disease, even in Japan, and while it can occur in both men and women there is a slightly higher rate in females.

What Types of Symptoms Are Typical?

The onset of this disease can vary, some presenting in childhood and others not presenting until adulthood. Generally there is a gradual decline in neurological functioning. However, this may be punctuated by sudden events of neurological worsening caused either by ischemic events (stroke), which is more common in children, or brain hemorrhage, which is more common in adults.

These events can lead to various nervous system symptoms depending on where the stroke or hemorrhage occurs. Infarction (stroke) can lead to weakness and numbness as well as progressive decline in general cognition and neurological functioning. Hemorrhage can be into the brain itself (intracerebral) but can also occur into the ventricles, the fluid-filled spaces in the brain, or into the subarachnoid space around the brain.

Over time, decline in neurological function can be due to these sudden, large events or may seem more slowly progressive and is presumably due to many small ischemic events that slowly injury many areas of the brain.

How Is The Diagnosis Typically Made?

After a full neurological assessment, most patients with signs and symptoms suggestive of Moyamoya disease will undergo some imaging studies to determine if there are abnormalities of the blood vessels consistent with the disease. Some patients may undergo an MRI scan with MR angiography to visualize the blood vessels and to rule out other potential causes of the symptoms. However, the gold-standard test to make the diagnosis of Moyamoya is cerebral angiography. This test, which is performed by injecting radio-dense dye into the blood vessels while taking x-rays of the head, allows the radiologist to visualize the blood vessels of the brain. The abnormal occlusion of the arteries at the base of the brain, along with the abnormal blood vessels, help to confirm the diagnosis.

Other causes of stroke and blood vessel occlusion are generally also ruled out by various tests. For example, carotid artery stenosis (blockage) in the neck, abnormal clotting of the blood (hypercoagulability), and vasculitis (inflammatory disease of blood vessels) should be ruled out as their treatment and prognosis can be quite different from Moya Moya.

What Are Some Common Treatments?

Every patient is slightly different and therefore their ideal treatments vary. Patients tend to present at different points in the natural evolution of this disease and their treatment may vary depending on the specifics of each case, the patient's age and the degree of occlusion of the arteries at the time of diagnosis.

For patients who have had a significant hemorrhage or stroke, they will often require hospitalization and may require medical or surgical treatments such as anticoagulation for ischemic stroke or prevention of high blood pressure (hypertension) in patients who have had a hemorrhage.

For patient who have the disease there are some surgical treatments which aim at improving blood flow to the brain so that ischemic stroke and hemorrhage will be less likely in the future. Most of these procedures use the blood vessels in the scalp to improve the circulation of the brain. In an encephaloduroarteriosynagniosis (EDAS) or encephaloduroarteriomyosynangiosis (EDAMS) the scalp blood vessel, called the superficial temporal artery (STA), with or without muscle, is isolated and laid onto the surface of the brain. The goal is that over time the brain will recruit new growth of blood vessels in from this large blood vessel, improving the circulation of the brain.

In some cases, if the disease is caught early when the blood vessels of the brain are not yet fully occluded, a bypass procedure, called an STA-MCA anastomosis (connecting the superficial temporal artery of the scalp to the middle cerebral artery of the brain) can be performed to directly improve the circulation getting to the brain.

Many patients who have significant neurological injury may require general rehabilitation with physical therapy, occupational therapy and/or speech therapy to help deal with their irreversible neurological deficits.

Each patient should discuss their appropriate medical and surgical treatment with their treating physician.

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