Anatomic basis for surgical approach to the distal segment of the posterior cerebral artery.

The distal segment of the posterior cerebral artery (PCA), which extends from the junction with the posterior communicating artery to its terminal division into the parieto-occipital and calcarine arteries, was examined in 37 brains. Three types of distal segment were distinguished. In the first type (42.9%), the terminal division was located either in the calcarine sulcus or in the quadrigeminal cistern. In the second type (41.4%), the terminal division had the same position, but the distal segment, in addition to its terminal stems, also gave off the common temporal artery. In the third type (15.7%), the terminal division was seen in the ambient cistern. The distal segment of the PCA gave rise to several collateral branches: the collicular artery (2.8%), the anterior (28.6%), middle (30.0%), and posterior (28.6%) hippocampal arteries, the proximal (82.9%) and distal (20.0%) lateral posterior choroidal arteries, the proximal (40.0%) and distal (41.4%) medial posterior choroidal arteries, the peduncular, thalamogeniculate and splenial branches, the lingual gyri artery and the temporal arteries. Several anatomic variants of the distal segment were observed in this study: fenestration of the distal segment (1.4%), location of the distal segment dorsal to the uncus (2.8%), origin of the collicular (2.8%) and anterior choroidal arteries (1.4%) from the distal segment, and protrusion of the parieto-occipital arterial loop into the lateral ventricle (2.8%). The authors discuss the clinical significance of these anatomic data.