A Study of the Anatomical Variations of the Circle of Willis Using Magnetic Resonance Imaging. Haripriya

Variations in the circle of Willis was studied using Magnetic Resonance Imaging Angiography in fifty patients of South Indian population at random. Variations have been found in 16 cases. All arteries in the circle of Willis showed variations except the anterior communicating artery, 5 cases showed variations in the anterior cerebral artery, 6 cases in the internal carotid artery, 2 cases in the posterior cerebral artery, 1 case in the posterior communicating artery and 2 cases in the basilar artery. Magnetic Resonance Imaging is the best tool to show the collateral circulation and the anastomotic variants of the circle of Willis. Circle of Willis is a large arterial ring which unites the internal carotid and vertebro-basilar systems. It is formed of an anastomosis between the internal carotid artery, anterior cerebral artery, anterior communicating artery, posterior communicating artery and posterior cerebral artery (Williams et al., 1995). The anastomosis thus provided by this vascular ring is of great significance when one of the major arteries supplying the brain becomes occluded. The neurological deficit suffered as well as the ability of a patient to withstand occlusion of one or more of these major vessels depend on the presence of collateral circulation to the affected area. The haemodynamics of the circle is influenced by the variations in the caliber of communicating arteries and in the segments of the anterior and posterior cerebral arteries which lie between their origins and their junctions with the corresponding communicating arteries. A detailed knowledge of the normal anatomy of the circle of Willis, its anomalies, and the clinical significance of its variations is valuable to the clinicians and neuroradiologists. Therefore this study was carried out to find out the variations of the circle of Willis using Magnetic Resonance Imaging Angiography. Materials and Methods Fifty patients at random from the Out Patient Department of Radiology and Imaging Sciences, Sri Ramachandra Medical College and Research Institute, Sri Ramachandra University for undergoing MRI were chosen for the study. The technique used was three Dimensional Time of Flight Magnetic Resonance Angiography (3D-TOF-MRA). Only the arteries forming the circle of Willis were studied. For the purpose of identification,the circle of Willis is divided into anterior and posterior configurations.The anterior configuration consisting of the anterior cerebral artery, Correspondance to: Haripriya M, Department of Anatomy, SRMC & RI, Sri Ramachandra University Chennai600 116, India. Email: [email protected] Accepted: 02-August-2010