Microsurgical anatomy of the cisternal course of the perforating branches of the posterior communicating artery.

Both the perforating branches--especially the extracerebral segments--and the arachnoidal anatomy at the level of the posterior communicating artery were studied in 60 human brains previously fixed in formalin. The close relationships between this artery and the oculomotor nerve are described, and it is noted that each of them is enclosed in its own arachnoidal compartment, which in the case of the posterior communicating artery is to be distinguished from the interpeduncular cistern. The latter cistern was found to contain only the terminal segments of the posterior communicating artery. The hypothalamic branches were within the inner wall of the arachnoidal cistern surrounding the posterior communicating artery. The variations in diameter of this artery are explained by its embryological development and are not related to the number and the diameter of the perforators. The posterior communicating artery was absent at times. The surgical implications of such a variable anatomical arrangement are discussed in the light of the literature.