<unk>  syndrome is a<unk>  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<unk> " in Japanese). The<unk>  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.<unk>  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.
Moyamoya disease
Cerebral arteriovenous malformation
Temporal arteritis
Meningism
Arnold–Chiari malformation
Intracranial berry aneurysm
Gliomatosis cerebri
Cerebral vasculitis