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Brief information about Circle of willi

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Circle of Willis anatomy diagram cerebral arteries

Educational medical infographic containing three panels illustrating cerebral neurovasculature and acute ischemic stroke pathophysiology. The first panel, 'Cerebral Circulation', features a detailed anatomical diagram of the Circle of Willis, labeling the vertebral arteries, basilar artery, and its bifurcation into the posterior cerebral arteries (PCA). It further illustrates the internal carotid arteries, middle cerebral arteries (MCA), and the anterior cerebral arteries (ACA) connected by the anterior communicating artery. The second panel, 'Graphical representation of Acute Ischaemic Stroke', depicts a sagittal view of the brain showing an arterial blockage. It differentiates between the 'ischemic core' (irreversible damage) and the surrounding 'penumbra' (reversible/salvageable tissue). The third panel, 'Cerebral Artery Supply Zones', is a coronal brain cross-section color-coded to show perfusion territories, specifically highlighting regions supplied by the ACA (orange), MCA (green), PCA (blue), and anterior choroidal artery (red). This resource is designed for students learning about stroke mechanisms, vascular anatomy, and clinical neuro-perfusion.

Educational medical infographic containing three panels illustrating cerebral neurovasculature and acute ischemic stroke pathophysiology. The first panel, 'Cerebral Circulation', features a detailed anatomical diagram of the Circle of Willis, labeling the vertebral arteries, basilar artery, and its bifurcation into the posterior cerebral arteries (PCA). It further illustrates the internal carotid arteries, middle cerebral arteries (MCA), and the anterior cerebral arteries (ACA) connected by the anterior communicating artery. The second panel, 'Graphical representation of Acute Ischaemic Stroke', depicts a sagittal view of the brain showing an arterial blockage. It differentiates between the 'ischemic core' (irreversible damage) and the surrounding 'penumbra' (reversible/salvageable tissue). The third panel, 'Cerebral Artery Supply Zones', is a coronal brain cross-section color-coded to show perfusion territories, specifically highlighting regions supplied by the ACA (orange), MCA (green), PCA (blue), and anterior choroidal artery (red). This resource is designed for students learning about stroke mechanisms, vascular anatomy, and clinical neuro-perfusion.

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Circle of Willis - Brief Overview

The circle of Willis is an anastomotic ring of arteries at the base of the brain where the anterior circulation (from the internal carotid arteries) and posterior circulation (from the vertebral/basilar arteries) meet, giving rise to all the major cerebral vessels (Neuroanatomy through Clinical Cases, p. 416-417).
Circle of Willis and its main branches

Components (anterior to posterior)

  • 2 Internal carotid arteries (ICA) - terminal branches, enter the ring anterolaterally
  • 2 Anterior cerebral arteries (ACA) - branches of the ICA, joined together by the...
  • Anterior communicating artery (AComm) - a single midline vessel linking the two ACAs
  • 2 Middle cerebral arteries (MCA) - the other terminal branch of each ICA (technically outside the ring itself, but arise from it)
  • 2 Posterior communicating arteries (PComm) - connect each ICA to the corresponding PCA, linking anterior and posterior circulations
  • 2 Posterior cerebral arteries (PCA) - arise from the top of the basilar artery
  • Basilar artery - formed by the union of the two vertebral arteries, sits at the posterior aspect of the ring

Function

It provides collateral circulation - if one contributing vessel (e.g., a carotid or vertebral artery) becomes narrowed or occluded, blood can be redistributed around the ring from the other vessels to maintain perfusion of the brain. This protects against stroke when a single feeding artery is compromised.

Clinical Notes

  • A complete, full-caliber ring is present in only about 34% of people - anatomical variants (hypoplastic or absent segments, most often the PComm or AComm) are common, which affects how well collateral flow can compensate for a blocked vessel.
  • The AComm and PComm are the most common sites of saccular (berry) aneurysms, which can rupture and cause subarachnoid hemorrhage.
  • Location: it encircles the optic chiasm and infundibulum of the pituitary stalk at the base of the brain (interpeduncular/suprasellar region).
Would you like more detail on clinical correlations (e.g., stroke syndromes by vessel, aneurysm sites) or a labeled image of the anterior/posterior circulation pathways?
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