Craniocervical Vascular Anatomy

Abstract Cerebral blood flow is provided by the paired internal carotid arteries (ICAs) and vertebral arteries. The intradural branches of the ICA supply the anterior cerebral circulation (i.e., cerebral hemispheres, including basal ganglia) and the orbit; these branches include the ophthalmic artery, posterior communicating artery, anterior choroidal artery, and anterior and middle cerebral arteries. The vertebrobasilar system, formed by fusion of the vertebral arteries into the basilar artery, supplies the posterior cerebral circulation, including the brainstem, cerebellum, and posterior aspect of the cerebral hemispheres via the posterior cerebral arteries. Connections between the anterior and posterior circulations occur through the circle of Willis and its branches or through occasionally persistent embryologic carotid-vertebral and carotid-basilar connections (i.e., persistent trigeminal, hypoglossal, and proatlantal arteries). Cortical (or leptomeningeal) anastomoses also exist over the surface of the cerebral convexity and connect the anterior, middle, and posterior cerebral arteries. These anastomoses may provide important collateral pathways in patients with stenoocclusive disorders such as atheromatous disease or moyamoya syndrome. Finally, so-called watershed areas exist between the terminal vascular territories of the principal cerebral arteries. Watershed areas represent zones at risk for ischemic injury in patients with hemodynamically significant stenosis of the ICA, low cardiac output, or severe prolonged hypotension.