Study of Variant Posterior Cerebral Circulation and its Clinical Relevance

The cerebral blood flow is divided into an anterior circulation and a posterior circulation connected to each other in the form of a circle called Circle of Willis (CW). It is formed by the unification of the internal carotid (ICA) and vertebrobasilar systems Posteriorly, the basilar artery, formed by the left and right vertebral arteries, branches into a left and right posterior cerebral artery (PCA), forming the posterior circulation. The internal carotid system lies anteriorly and is joined to the posterior circulation by posterior communicating (PCoA) arteries. The internal carotid artery divides into anterior and middle cerebral artery. The two anterior cerebral arteries are joined to each other by an anterior communicating artery. The posterior cerebral artery before it joins the posterior communicating artery that means its proximal part is named as the pre communicating part (P1) and the distal part as the post communicating part (P2). In the adult P1 has a diameter larger than the PCoA so that the occipital lobe gets its blood supply mainly via the vertebrobasilar system whereas in the fetus the diameter of the ipsilateral precommunicating (P1) segment of PCA is less than the diameter of PCoA, so that the blood supply to [1] the occipital lobe is mainly via the internal carotid arteries. In some persons, there is a transitional configuration in which the PCoA is equal in diameter to the P1 segment of the PCA. These variations can cause complications if thrombotic material present in atherosclerotic plaques of ICA gets dislodged into PCA through a PCoA which has a larger diameter. In the present study, the configuration of posterior cerebral circulation and its clinical relevance was studied in 40 human brains in the department of anatomy at KJSMC. Adult Type PCA was found in 60% of the specimens studied, Fetal Type PCA was found in 12.5% of the specimens, Transitional Type PCA was found in 25% of the specimens and a combination of Adult and Transitional Type was found in 2.5% of the specimens.