The circle of Willis (also called Willis' Circle, Loop of Willis, cerebral arterial circle, and Willis Polygon) is a circle of arteries at the base of brain that supply blood to the brain and surrounding structures. Shubhangi Y. Willis describes a number of cases that demonstrate the function of the arterial circle in providing compensatory collateral blood flow (Vrselja, Brkic, Mrdenovic, Radic, & Curic, 2014). The circle of Willis thereby serves a safety valve function for the brain, allowing collateral circulation (or flow of blood through an alternate route) to take place if the flow is reduced to one area. the circle of Willis becomes important in ascertaining the effectiveness of the circulation of brain in surgeries like aneurysm coiling AVM embolisation, and also internal carotid artery ligation38. In the process, they may become compressed, which restricts blood flow. -cerebral arterial circle-critically important anastomosis among the 4 major arteries feeding the brain. This surgery involves ligating the left common carotid artery and a complete Circle of Willis is critical to enable the right carotid artery to provide the blood supply to the entire brain. The circle of Willis score of the patients with complete arterial occlusion was 1.33±1.52 in the fatal stroke group (n=3) and 3.20±1.64 in the asymptomatic group (n=6, p=0.099). ABSTRACT Aims and Objective: The blood supply of brain is of great importance because of the metabolic demands of the nervous tissue. The circle of Willis also allows blood to flow across the midline of the brain if an artery on one side is occluded. The anastomosis between the right and left ICAs and the vertebrobasilar circulation by means of communicating arteries form this ringlike structure. Circle of Willis is a very important anastomotic structure in the brain that provides blood supply to the fore-brain and hind-brain. The Circle of Willis is a network of blood vessels that connects the two hemispheres. A significant anastomosis, the Circle of Willis exists between the carotid and vertebral arterial systems. The circle of Willis (CW) was first described 400 years ago by Thomas Willis as an important vascular ring at the base of the brain (Vrselja, Brkic, Mrdenovic, Radic, & Curic, 2014). The absence of some CoW elements may be fatal for patients with internal carotid artery stenosis39. When you turn your head from side-to-side or up and down, the arteries in your neck stretch and flex. The circle of Willis encircles the stalk of the pituitary gland and provides important communications between the blood supply of the forebrain and hindbrain (ie, between the internal carotid and vertebro-basilar systems following obliteration of primitive embryonic connections). Variations of circle of Willis in human cadavers. This network of arteries provides blood to be distributed to both hemispheres from the internal carotid arteries or vertebral arteries. 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