Moyamoya is a progressive syndrome characterized by narrowing of the blood vessels in the brain. Moyamoya is the Japanese term for 'cloud of smoke drifting in the air.'
The term moyamoya is used to describe how the arteries in the brain look in this syndrome, which was first described in the 1950s. There is no clear cause for this disease. It can be caused genetically, but can also occur as a result of having other diseases. Moyamoya is seen in patients with a variety of diseases, including: neurofibromatosis , trisomy 21 (Down syndrome ), sickle cell disease, chronic meningitis, and as a side effect of irradiation.
Moyamoya is a disease of the blood vessels in the brain. The carotid arteries are two of the large arteries that allow blood to flow into the brain. The external carotid artery allows blood to reach areas within the neck, while the internal carotid artery travels to the brain and branches off into smaller vessels to reach all areas of the brain. In patients with moyamoya, there is a symmetric thinning of the width of the internal carotid arteries. The brain responds to this thinning by making the smaller blood vessels bigger, trying to get blood to the areas of the brain that are not getting enough. When dye is injected into the arteries of the brain (a cerebral angiogram), a characteristic pattern is seen. On the angiogram, this looks like a cloud of smoke.
The primary form of moyamoya is seen most often in Japan. Studies have found the familial form to account for 7–10% of the cases. A recent study focused on 16 families in order to find the genetic marker for the disease. The gene locus was found to be present on the short arm of chromosome 3, specifically 3p26–p24.2. Other studies have found possible involvement of genes on chromosomes 6 and 17 as well.
Although the disease seems to occur most often in Japanese people, patients have been found throughout the world. It is thought that one in a million people are affected each year. The age of onset of the disease has two peaks, the first being in children under 10 years old, and the second in adults in their 20s–40s. Fifty percent of moyamoya cases are found in patients younger than ten years of age. Females seem to have moyamoya more often than males. The female-to-male ratio is 3:2.
Signs and symptoms
The first signs and symptoms of moyamoya tend to be different in children and adults. Children most often present with a sudden seizure or a stroke. Strokes can cause weakness on one side of the body. These are often brought on with exercise or fast breathing. Less severe strokes, called transient ischemic attacks (TIAs), can occur very often. During these TIAs, the weakness in the body is temporary and will not last more than a few hours. But, over a period of years, strokes and TIAs will leave patients with permanent weakness on both sides of the body, seizure disorders, and mental retardation. While children will present with seizures or strokes, adults tend to present with intracerebral hemorrhage (bleeding within the brain). Depending on where the bleeding or strokes occur, there can be a variety of chronic symptoms including: speech disturbance, visual disturbance, headaches, difficulties with sensation and involuntary movements (moving parts of the body when you do not intend to).
Cerebral angiography is the main method of diagnosis. Today, this is the best way to see the arteries in the brain and to assess their level of occlusion (blockage). Other methods of imaging have been used in an attempt to diagnose moyamoya. High resolution imaging such as computed tomography scans (CT scans) do not show findings specific to this syndrome. However, areas of old strokes or bleeding can be seen. Magnetic resonance imaging (MRI) is also very sensitive at looking for old areas of stroke but cannot show which blood vessels may be blocked as compared with angiography. These non-invasive imaging techniques may however, provide clues for the diagnosis. The doctor would then recommend angiography to confirm the diagnosis.
Treatment and management
There is no one best treatment for moyamoya. Medical therapy consists of drugs that prevent blood clot formation such as aspirin. Drugs that help dilate the narrowed blood vessels, such as calcium channel blockers, are also used. Calcium channel blockers that have been successful include nicardipine and verapamil. These calcium channel blockers may also help with the headaches that some patients may get during the course of their illness.
Many different surgical approaches have been used to help improve blood flow in these patients. It is not known what the long term outcome of these procedures are. As of 2001, the most popular operations are: encephaloduroanteriosynangiosis (EDAS), encephalomyosynangiosis (EMS), and superficial temporal artery-middle cerebral artery (STA-MCA) anastamosis.
In EDAS, an artery that sits under the scalp called the superficial temporal artery, is separated from the skin. A small opening in the skull is then made. The artery from the scalp is then sewn into the surface of the brain. The piece of skull that was removed is then put back in place to protect the new connection. This procedure has also been termed pial syngiosis.
In the EMS procedure, a muscle overlying the temple region of the forehead, called the temporalis muscle, is detached. Once again, an opening in the skull is made and the muscle is placed on the surface of the brain.
In the STA-MCA operation, the scalp artery is directly connected to an artery in the brain. All of the these surgical procedures attempt to provide blood to areas of the brain that are not getting enough. Although symptoms may be improved soon after surgery, it usually takes months for the new blood vessels to form.
It is unclear what the long-term risk for complications is in people with moyamoya disease. A study published in 2000 looked at 334 patients with moyamoya disease diagnosed between 1976 and 1994. Approximately 60% of the adults who had moyamoya had a cerebral hemorrhage at some point. Approximately 60% of the children who had moyamoya had a stroke or TIA at some point. Cerebral hemorrhage was found to be the most important factor that predicted a poor outcome. The overall effect of medical and surgical treatment on long term outcomes is not well known at this time.
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Families with Moyamoya Support Network. 4900 McGowen St. SE, Cedar Rapids, IA 54203.
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David E. Greenberg, MD