Glossary term:


An infolding of the dura lining the skull forms a near-complete membrane that separates the lowermost part of the cranial cavity – the posterior fossa – from the remaining volume inside the skull. This tentorium does have an opening within it, through which the upper part of the brain stem passes, leaving only a relatively narrow channel through which cerebrospinal fluid can flow. An important consequence is that the posterior fossa is a relatively isolated part of the cranial cavity and problems can develop here without there being any associated abnormalities supra-tentorially – i.e. above the tentorium.