Circle of Willis, Gross Anatomy

Description

Viewed from the inferior aspect of the brain, the arterial circle at the base of the cerebrum is formed by the paired internal carotid arteries giving rise to the anterior cerebral arteries, joined across the midline by the anterior communicating artery, then continuing posteriorly as the posterior communicating arteries to meet the posterior cerebral arteries. The basilar artery ascends on the ventral surface of the pons and bifurcates into the posterior cerebral arteries just superior to the pontomesencephalic junction. Anteriorly, the optic nerves (CN II) converge into the optic chiasm, positioned superior to the pituitary region and just anterior to the circle. Nearby landmarks include the cerebral peduncles, mammillary bodies, pons, and medulla, with the cerebellum lying posterior and inferior. An inferior brain view is the clearest way to teach why the Circle of Willis is an anastomosis rather than a single vessel, and where collateral flow can compensate when one inflow limb fails. Occlusion or stenosis of the internal carotid artery shifts perfusion across the anterior communicating artery, while posterior communicating patency can partially support anterior circulation in select patients. Berry aneurysms also cluster at these branch points, classically at the anterior communicating artery and posterior communicating artery origin, so the spatial relationship to the optic chiasm and midline basal cisterns matters when correlating symptoms such as painful third nerve palsy or subarachnoid hemorrhage patterns. Small vessels. Big consequences. Use this illustration in neuroanatomy and gross anatomy curricula, neurosurgery and neuroradiology teaching files, and publisher figures discussing collateral circulation, aneurysm locations, or the vascular territories of the anterior and posterior cerebral arteries. Anatomical accuracy verified by SciePro's Medical Advisory Board.