Circle of Willis

Description

Arising at the base of the cerebrum, the circle of Willis is rendered as an arterial anastomosis surrounding the optic chiasm and infundibular region, where the internal carotid arteries give rise to the anterior cerebral arteries joined by the anterior communicating artery, and continue as the middle cerebral arteries laterally into the Sylvian fissures. Posteriorly, the basilar artery courses along the ventral pons and bifurcates into the posterior cerebral arteries, which connect to the carotid system through the paired posterior communicating arteries. Nearby midline landmarks, including the brainstem (midbrain, pons, medulla oblongata) and the cerebellum inferiorly and posteriorly, anchor the vascular ring in true cranial base orientation. Cranial nerves are shown emerging from the brainstem in close proximity to these vessels. Tight anatomy. For teaching and clinical reasoning, this view clarifies where collateral flow can compensate when a proximal segment narrows or occludes, and it also highlights why variant anatomy matters. Hypoplasia of a posterior communicating artery, for example, limits cross filling between the carotid and vertebrobasilar territories, while aneurysms at the anterior communicating artery complex or the posterior communicating artery origin often present with subarachnoid hemorrhage and can compress the oculomotor nerve, producing a painful, pupil-involving third nerve palsy. The relationship between the basilar apex and the posterior cerebral arteries is a key landmark when discussing basilar tip aneurysms and perforator risk. Neuroanatomy and neuroradiology courses can pair this illustration with MR angiography or CTA to reinforce arterial territories and common sites of saccular aneurysm formation. It also reads well in stroke education materials, neurosurgical atlases, and endovascular planning content where clear depiction of cerebral artery anastomosis supports discussion of collateral pathways and cross-circulation. Anatomical accuracy verified by SciePro's Medical Advisory Board.