Circle of Willis

**Definition:** A polygonal anastomosis at the base of the brain formed by the internal carotid (CAROTID ARTERY, INTERNAL), proximal parts of the anterior, middle, and posterior cerebral arteries (ANTERIOR CEREBRAL ARTERY; MIDDLE CEREBRAL ARTERY; POSTERIOR CEREBRAL ARTERY), the anterior communicating artery and the posterior communicating arteries.

**Tree numbers:** - A07.015.114.228.351

**Synonyms:** - Willis' Circle - Cerebral Arterial Circle