Moyamoya disease overview
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# Overview
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" (" (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.

# Causes
The condition is believed to be hereditary and linked to q25.3, on chromosome 17. Moyamoya can be either congenital or acquired.  Patients with Down syndrome, neurofibromatosis, or sickle cell disease can develop moyamoya malformations.  It is more common in women than in men, although about a third of those affected are male.  Brain radiation therapy in children with neurofibromatosis increases the risk of its development.

# Risk Factors
Women have a higher risk of recurrent stroke and may be experiencing a distinct underlying pathophysiology compared to patients from Japan.

# CT
The diagnosis is initially suggested by CT, MRI, or angiogram. In fact, the name derives from its angiographic image; the "puff of smoke," which is how moyamoya loosely translates from Japanese, refers to the appearance of multiple compensatorily dilated striate vessels seen on angiography. Contrast-enhanced T1-weighted images are better than FLAIR images for depicting the leptomeningeal ivy sign in moyamoya disease.

# MRI
MRI and MRA should be performed for the diagnosis and follow-up of moyamoya disease. Diffusion-weighted imaging can also be used for following the clinical course of children with moyamoya disease, in whom new focal deficits are highly suspicious of new infarcts.

# Other Imaging Findings
Often nuclear medicine studies such as SPECT (single photon emission computerized tomography) are used to demonstrate the decreased blood and oxygen supply to areas of the brain involved with moyamoya disease. Conventional angiography provided the conclusive diagnosis of moyamoya disease in most cases and should be performed before any surgical considerations.

# Treatment

## Medical Therapy
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.