An Illustration of the Circle of Willis and it’s Variations

The Cerebral Arterial Circle (of Willis) is an important anastomosis. It is located between the four arteries that supply blood to the brain. They are the two vertebral and two internal carotid arteries. The circle is formed from the anterior cerebral, anterior communicating, internal carotid, posterior cerebral, and posterior communicating arteries. There are commonly four variations of the Cerebral Arterial Circle: classical, A1-asymmetry, incomplete psoterior communicationg artery, and fetal circulation. In one of three people the posterior cerebral artery is a major branch of the internal carotid artery. It is possible that these variations may lead to aneurysms and atherosclerosis in aging adults. This is due to high resistance to flow and an imbalanced bifurcation at the apex.