Anatomical aberration of posterior part of circle of Willis with special reference to third nerve palsy

Due to the close anatomical proximity, aneurysm of posterior communicating artery may cause oculomotor nerve palsy, which is a common manifestation and it may present with pupil involving extra ocular muscle paresis. The onset may be acute due to sudden aneurysm dissection along with subarachnoid hemorrhage. This may warrant urgent lifesaving surgical intervention along with the options of interventional radiological procedures.Normally, the occipital lobe is supplied by the posterior cerebral artery (PCA). When the pre-communicating portion of the PCA is larger than the posterior communicating artery (PCA), the occipital lobe is primarily supplied by the vertebrobasilar artery. Sometimes the pre-communicating portion of the PCA may be smaller than the PCoA in which the occipital lobe is primarily supplied by the internal carotid artery.Understanding the posterior circulation anomalies of Circle of Willis. This study involved 50 fetal brains belonging to perinatal age group and 30 adult brains of human cadavers by dissection. The PCoA was missing in 14% of the samples. The difference between the outer diameters of the P1 portion of the PCA and the PCoA was very significant.So, a detailed anatomical understanding of Circle of Willis and manifestation of the third nerve palsy is sometimes equivocal for a clinician for better management and patient outcome.