Moyamoya syndrome is a disease in which certain arteries in the brain are constricted. Blood flow is blocked by the constriction, and also by blood clots (thrombosis).
The blood vessels develop collateral circulation around the blocked vessels to compensate for the blockage, but the collateral vessels are small, weak, and prone to hemorrhage, aneurysm and thrombosis. On X-rays, these collateral vessels have the appearance of a "puff of smoke" ("もやもや (moyamoya)" in Japanese).
The disease causes constrictions primarily in the internal carotid artery, which travels from the neck up inside the skull just under the brain in the cavernous sinus. At the Circle of Willis, the internal carotid artery flows into the middle cerebral artery, which continues into the brain, and the anterior cerebral artery, which is part of the Circle of Willis. Moyamoya disease often extends to the middle and anterior cerebral arteries.
When the internal carotid artery becomes completely blocked, the fine collateral circulation that it supplies is obliterated. Patients often survive on the collateral circulation from the back (posterior) of the Circle of Willis, from the basilar artery.
Drugs such as antiplatelet agents (e.g., aspirin) are usually given to prevent clots, but surgery is usually recommended. Since moyamoya tends to affect only the internal carotid artery and nearby sections of the adjacent anterior and middle cerebral arteries, surgeons can direct other arteries, such as the external carotid artery or the superficial temporal artery to replace its circulation. The arteries are either sewn directly into the brain circulation, or placed on the surface of the brain to reestablish new circulation after a few weeks. Although there is a 4% risk of stroke soon (30 days) after surgery, there is a 96% probability of remaining stroke-free over the next 5 years.
The constrictions of the arteries in moyamoya disease are unlike the constrictions in atherosclerosis. In atherosclerosis, the inner layer (lumen) of the arteries suffers an immune reaction, fills with inflammatory cells, and accumulates fatty cells and debris. In moyamoya, the inner layer of the carotid artery overgrows inward to constrict the artery, and the artery also fills with blood clots, which cause strokes.
It is a disease that tends to affect children and adults in the third to fourth decades of life. In children it tends to cause strokes or seizures. In adults it tends to cause strokes or bleeding. The clinical features are cerebral ischemia (strokes), recurrent transient ischemic attacks (TIAs), sensorimotor paralysis (numbness and paralysis of the extremities), convulsions and/or migraine-like headaches. After an ischemic stroke, a hemorrhagic reperfusion stroke may occur. A hemorrhagic stroke may also stem from rupture of the weak neovascular vessel walls.
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