Endoscopic anatomical study of the arachnoid architecture on the base of the skull. Part II: Level of the tentorium, posterior fossa and the craniovertebral junction

Abstract

Interest in surgical anatomy of arachnoid mem- branes is relatively new and became more important with the development of endoscopic techniques in neurosur- gery. In the first part we introduced the term arachnoid membrane system and arachnoid membrane groups and described them in the anterior and middle cranial fossa. The objective of this second part is to discuss the arachnoid membranes of the tentorial level, posterior fossa and the craniovertebral junction. Rigid endoscopes were introduced through defined keyhole craniotomies to explore the arachnoid in 127 fresh human cadavers. We defined 12 inner membranes that are arranged in three membrane groups. The tentorial membrane group consists of five paired membranes forming an almost complete barrier between the supra- and infratentorial spaces. The clival membrane group consists of three membranes and completes the separation created by the tentorial group. The superior part of the perimedullary group located around the medulla oblongata and con- sists of three inner membranes. The inferior part located in the craniovertebral junction consisting of four mem- branes. Intracranial arachnoid membranes are constant and defined structures that are well arranged in distinct groups. These new findings are essential in understand- ing the three-dimensional architecture of the arachnoid and its importance in endoscopic neurosurgery.