Morphological Variation of Circle of Willis in Nepali Population: A 3D Time-of-Flight Magnetic Resonance Angiography Based Study

Introduction: The Circle of Willis (COW) is an anatomic ring of vessels located at the base of the brain connecting the anterior and posterior circulation by uniting the internal carotid and vertebrobasilar systems to maintain adequate cerebral perfusion. The importance of detailed information of the COW morphology and integrity in any patient cannot be overemphasized, especially for neurophysicians, neurosurgeons, and interventional neuroradiologists who are considering intervention to the intracranial arteries. This study was conducted to study the variation of COW among the Nepalese population and compare the results with those of other nationalities. Methods: It was a prospective cross-sectional study performed using a 1.5 Tesla MRI machine. Complete anatomical assessment of the COW was done. The anterior and posterior components of COW were defined as per the standard literature and evaluated in detail. Results: A total of 118 patients were studied during the period out of which 75 (63.6%) were males and 43 (36.4%) were females. A morphologically normal COW configuration was found only in 55 (46.6%) cases whereas a variant configuration was present in 63 (53.4%) cases. The most common variation was noted in the posterior communicating artery (PCOM) which was present in 42 (67%) cases. The most common single variation in abnormal COW configuration was absent right PCOM. Conclusion: The morphologic variation of the COW is more common than the normal textbook configuration in the Nepalese population, PCOM being the most commonly involved vessel.