Microvascular Anatomy of the Middle and Posterior Segments of the Medial Temporal Region. A, Mediobasal surface of the left cerebral hemisphere. The PCA is the main feeding vessel of the MTR. The P2 is divided into 2 portions: the P2a courses in the crural cistern and the P2p courses in the ambient cistern. B, Enlarged view of the same specimen. Branches of the PCA supply the middle segment of the MTR. The PCA typically has a proximal and a distal bifurcation. The proximal bifurcation is most commonly adjacent to the middle segment of the MTR, and the distal bifurcation is adjacent to the posterior segment. The most common pattern of proximal bifurcation is formed by the posterior inferior temporal artery and the parieto-occipital arterial trunk (P2p), as seen in this case. Just before its proximal bifurcation, the PCA gives off the anterior-inferior temporal artery, from which the anterior parahippocampal artery arises. The middle inferior temporal artery and the posterior parahippocampal artery arise from the posterior inferior temporal artery. The medial posterior choroidal artery and the quadrigeminal artery arise from the proximal part of P2a. C, Further enlarged view of the same specimen. The distal bifurcation of the P2p into the parieto-occipital and calcarine arteries is exposed. Branches of the PCA supply the posterior segment of the MTR. The splenial artery arises from the parieto-occipital artery and anastomoses with the posterior pericallosal artery. D, PCA in a different specimen that trifurcates into the middle and posterior inferior temporal arteries and the parieto-occipital trunk (P2p) adjacent the middle segment of the MTR. The AITA arises from the P2a, the posterior parahippocampal artery from the middle inferior temporal artery, the splenial artery from the posterior inferior temporal artery, and the medial posterior choroidal artery from the parieto-occipital trunk (P3). (Images courtesy of AL Rhoton, Jr.)