ABSTRACTcans posterior (AComP) which links a. carotis interna (ACI) to ACP and a basilaris in anterior middle part. ACIs, ACAs, AComA and their branches are defined as "anterior circulation/carotis system", ACPs, AComPs, a.vertebralis and a. basilaris are defined as "posterior circulation/vertebrobasilar system" (22).The circle of Willis, whose function is to protect the brain from ischemia, is the main structure that provides constant and regular blood flow to the brain. Despite the presence of detailed studies concerning each of the vessels that constitute █ INTRODUCTION Circulus arteriosus cerebri was defined by Thomas Willis in 1664 and is referred to by his name (12,25). The circle of Willis is an artery polygon, a vascular ring composed of branches of arteria (a) carotis interna and a. basilaris around infundibulum and chiasma opticum in cisterna interpedunculus in the brainstem and anastomoses between them. Vessels forming the circle of Willis are as follows: bilateral a. cerebri anterior (ACA) and a. communicans anterior (AComA) which links these two arteries, bilateral artery cerebri posterior (ACP), a. communiAIm: The function of the circle of Willis, an arterial polygon, is to protect the brain from ischemia. The aim of this study is to define the structural characteristics of the circle of Willis within the Turkish adult population, along with variations and arteries involved in the measurement of diameters and lengths on cadavers.
mATERIAl and mEThODS:The circle of Willis was evaluated in 100 fresh adult cadavers. structures of the circle of Willis were evaluated as being typical or atypical images and according to the diameter of AComP. All arteries forming the circle's length and diameters were measured.
RESUlTS:All arteries forming the circle of Willis as 91% were anatomically observed. The typical structure in which hypoplasia arteries is not involved was obtained as 8%. The atypical circle of Willis with aplasia was seen as 9%. 87% of adult, 9% fetal, and 4% transitional configuration in the samples were detected. The variations of the circle of Willis were more common in the posterior portion. Hypoplasia was found to be the most common variation and noted as a maximum in AComP (85%). Aplasia was noted as the second most common variation after hypoplasia and again the most common in AComP (5%).CONClUSION: Advances in radiological methods which provide images of cerebral vessels and the development of cerebrovascular surgery have increased the importance of the circle of Willis in neurosurgery and neurology. The structure of the circle of Willis is of great importance in occlusive cerebrovascular diseases and cerebrovascular surgery.