Moyamoya disease is a rare condition in which the walls of the carotid arteries thicken and the arteries narrow, restricting or blocking the blood flow to the brain. Moyamoya disease is progressive, which means that the vessels will continue to narrow over time, and affects mostly children and adolescents.
The cause of moyamoya disease is unknown, although genetics are a likely factor. In response to the narrowing of the blood vessels, the body will begin to grow many small blood vessels to bypass the blockage.
“Moyamoya” means “puff of smoke” in Japanese, and refers to the appearance of these networks of new blood vessels on a cerebral angiogram (a test that shows the blood flow in the brain). The condition first was identified in Japan, where its incidence is higher.
Moyamoya disease can cause episodes of weakness, paralysis in a limb or on one side of the body, sensory impairment, involuntary movements, headaches, speech problems, dizziness, or seizures. The disease also carries the risk of mental retardation and sustained neurological problems. Severe immediate problems include the risk of transient ischemic attack (TIA or “mini-stroke”), in which the blood flow to the brain is temporarily completely blocked; stroke, in which the blockage is sustained; or intracranial hemorrhage, bleeding in the brain. Hemorrhage and stroke are neurological emergencies that require immediate treatment.
Computed tomography (CT) and magnetic resonance imaging (MRI) scans may provide initial indications of the disease. If the disease is suspected, cerebral angiography, a test that creates images of the blood flow through the brain, is conducted to establish the diagnosis. For this test, an x-ray is taken after a special dye is injected into the arteries.
Magnetic resonance angiography (MRA), another imaging study that shows the blood vessels in the brain, also may be used. In a child with moyamoya disease, the angiogram will show blockage of the internal carotid artery, an abnormal network of blood vessels (the “puff of smoke”), and similar attributes on both sides of the brain. In addition, single photon emission computerized tomography (SPECT) scans may be used to identify the regions of the brain that are not receiving sufficient oxygen.
Moyamoya disease is progressive, and some children may experience significant neurological impairment before treatment can be administered. In these cases, treatment addresses only the symptoms of the disease. There is no evidence that medications slow the progession of moya moya disease. However, selected children suffering from recurrent or progressive loss of blood flow to certain parts of the brain may be candidates for surgery.
These surgical procedures, called revascularization procedures, involve diverting blood flow from other regions, such as the scalp or nearby muscles, to the oxygen-deprived region of the brain. The brain then grows new blood vessels to take advantage of the new blood source. These surgeries often provide a good long-term outlook for children with moyamoya disease, but carry risks of bleeding or stroke. Prompt treatment is essential; once a child has suffered a stroke or hemorrhage, there may be serious permanent neurological effects.
Other treatments for moyamoya disease address only its symptoms or effects. For example, children at risk of stroke may be treated with anticoagulants and those at risk of hemorrhage may be treated with high blood pressure drugs. Rehabilitation is used for patients with neurological deficits, such as speech problems or paralysis.