Posterior cerebral artery anatomy. The posterior cerebral artery (PCA) is the major artery within this dissection and is divided into segments: P1 (precommunicating), P2 (postcommunicating), P3 (quadrigeminal) and P4 (cortical branches). The PCA runs along with the basal vein of Rosenthal through the crural and ambient cisterns. Lateral to the dorsal midbrain, the P3 segment divides into cortical branches which irrigate the cortex. The basal vein of Rosenthal lies proceed to join the precentral cerebellar vein and internal cerebral veins to form the great cerebral vein of Galen within the quadrigeminal cistern. Anteriorly, the posterior communicating artery is visible in its entirety along with its perforating arteries just medial to the uncus. (Image courtesy of AL Rhoton, Jr.)