What is the major blood supply circle that ensures collateral circulation to the brain?

• A. Circle of Corti
• B. Circle of Broca
• C. Circle of Haller
• D. Circle of Willis

Answer: (D)

The major arterial ring at the base of the brain provides collateral flow to keep brain tissue perfused when a single vessel is compromised. This Circle of Willis connects the internal carotid arteries with the basilar artery through the anterior and posterior communicating arteries, forming a loop that includes the anterior and posterior cerebral arteries. Because of this arrangement, blood can be shared between the front and back territories and between the two sides of the brain, allowing one pathway to compensate if another is narrowed or blocked. This redundancy helps maintain cerebral perfusion during vascular challenges. Variations in anatomy are common, and sometimes the circle isn’t complete, but when intact it serves as a crucial mechanism for collateral circulation in the brain.