Circle of Willis Variants in Nepali Population Evaluated in TOF MR Angiography

The brain, though it constitutes only 2% of total body weight, receives 20% of the cardiac output. Blood supply to the brain comes from two major pairs of arteries: the anterior carotid arteries and the posterior vertebral arteries, which form an important collateral network. This network ensures that blood flow is maintained even if one of the arteries is obstructed. In 1664, Sir Thomas Willis first described this system, which was later named the "Circle of Willis" (COW) after him. Normally, there is little blood mixing between the branches of the circle, but during blockages in the main arteries, these collaterals can activate to maintain cerebral perfusion. The COW consists of an anterior and posterior portion. The anterior portion, supplied by the carotid arteries and their branches, and the posterior portion, formed by the vertebrobasilar system, provide critical blood flow to the brain. The key arteries involved in the COW include the internal carotid arteries (ICAs), anterior cerebral arteries (ACAs), anterior communicating artery (ACom), posterior cerebral arteries (PCAs), basilar artery (BA), and posterior communicating arteries (PComs). Anatomical variations in the COW are common, with a complete arterial circle being rare. Studies have documented a range of normal variants of the COW, which are likely to arise during vasculogenesis. Magnetic resonance imaging (MRI), using the non-invasive time of flight (TOF) technique, is a cost-effective and contrast-free method for visualizing the COW in three dimensions, making it preferable to conventional angiography. The variants of COW and diameters of arteries of COW are of clinical importance given its critical role in brain blood supply. Understanding CoW variants can reveal predispositions to conditions like stroke and aneurysms. This research will provide prevalence data on CoW configurations, aiding diagnostic and treatment strategies for cerebrovascular diseases, and may offer insights into vascular devel