Moyamoya disease is a rare neurological disorder involving the progressive narrowing of two of the major arteries (internal carotid arteries) supplying blood to the brain. As a result of this progressive narrowing, a new network of small blood vessels form around the base of the brain in an attempt to compensate for the reduced blood flow. The appearance of this new network of blood vessels resembles a “puff of smoke” on cerebral angiogram giving rise to the name “moyamoya” - from the Japanese expression for something “hazy just like a puff of smoke drifting in the air.” In many instances, this new vessel formation is insufficient to compensate for the progressive occlusion and blockage of the internal carotid arteries resulting in transient or permanent brain damage (see symptoms below). Although a high incidence of Moyamoya disease is found in people of Asian descent, especially Japanese, it has now been recognized world-wide, and in all ethnic groups. It appears to be more common in females and is more common in children accounting for about 6% of childhood strokes in Western counties. Adult onset may also occur. The etiology or cause of Moyamoya disease is unknown, although rare familial cases have suggested a genetic influence (and three genes have tentatively been identified in primary Moyamoya disease).
Moyamoya syndrome (or “secondary” Moyamoya) is different from primary or idiopathic Moyamoya disease as it develops secondary to an underlying disorder such as Down syndrome, sickle cell disease, William syndrome, or neurofibromatosis, or may occur after brain radiation therapy.
Symptoms in Moyamoya disease result from progressive blockage of the major intracranial blood vessels and results in loss of neurological function which may be either transient or permanent.
This is an angiogram taken in the anterior-posterior direction (front to back) that shows the obliteration of the carotid artery that now is trying to grow new arteries to supply the brain.
This is one of the images obtained from a Diamox SPECT scan. The various colors reflect differing levels of blood flow to the brain.
Diagnosis of Moyamoya disease involves four components:
- Detailed neurological and genetic evaluation to differentiate primary from secondary forms of Moyamoya.
- Brain imaging: in the acute setting, special stroke protocol imaging studies are necessary to look for evidence of stroke or ischemic brain injury.
- Vascular or Vessel Imaging: a range of modalities for vessel-specific imaging are used, including CT and MR angiography, and the “gold standard”, cerebral angiography.
- Perfusion Studies: special neuroimaging modalities are often necessary to assess and quantify the degree of hypoperfusion (lack of blood supply) of the brain. This includes state of the art equipment such as CT or MR perfusion scans, Diamox SPECT scans, and PET scans.
The diagnosis, treatment and management of Moyamoya disease requires a collaborative team approach between numerous specialists including neurosurgery, neuroradiology, genetics, neuropsychologists, physical, occupational and speech therapists.
Treatment strategies are aimed at preventing recurrent symptoms, including stroke, and non-stroke symptoms such as progressive cognitive or learning impairment.
General treatment strategies aim at preventing the clotting of blood in the narrowed blood vessels includes the use of anti-platelet therapies (such as aspirin or clopidogrel), or specific revascularization procedures.
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