Anatomical Variations of Circle of Willis in 57 Human Brains

Purpose: The circle of willis is responsible for blood supply of brain, which may suffer from anatomical variations. These disturbances can lead to aneurysm or even arterial rupture. The purpose of this study was to evaluate the anatomical structure of the cerebral arteries forming the circle of willis in adult cadavers. Also, cerebral versus non- cerebral versus non-cerebral arterial walls were studied using light microscopy. Materials and Methods: A total of 57 brains from normal adult cadavers were studied and arterial variations of hyperplasia, multiplications, aplasia and common trunk between two arteries were put into consideration. Seven vessels of anterior, middle, posterior, anterior communicating, posterior communicating, vertebral, and basilar arteries were studied. Also, cross section of cerebral (MCA) and non-cerebral arterial walls were made using microtome and stained with hemotoxyline-eosin. Results: The results showed that 19 cases (33.3%) of arteries forming willis were abnormal and the most common variation was noticed in posterior cerebral artery which was a branch of internal carotid rather than basilar artery. In addition, 22 cases had only one anomaly and the rest showed more than one anomaly. The microscopic results showed that cerebral vessels were lacking external elastic membrane and vasa vasorum. Conclusion: With the presence of variations in circle of Willis of adult brains, especially in posterior circulation, evaluation of cerebrovascular variations in regards to clinical status of the patients is recommended.