LAUSR

Abstract Objective The extradural neural axis compartment (EDNAC) is an adipovenous zone located between the meningeal and endosteal layers of dura and has been minimally investigated. It runs along the neuraxis from the orbits down to the coccyx and contains fat, valveless veins, arteries and nerves. This review aims to outline the current knowledge regarding the structural and functional significance of the EDNAC. Methods A narrative review of EDNAC literature was conducted. Results The EDNAC can be organised into four regional enlargements along its length. These are the orbital, lateral sellar, clival and spinal segments with a lateral sellar orbital junction linking the orbital and lateral sellar segments. The orbital EDNAC facilitates movement of the eyeball, while elsewhere it allows limited motility for the meningeal dura. Major nerves and vessels are cushioned and supported by the EDNAC. Raised intraabdominal pressure (IAP) is also conveyed along the spinal EDNAC causing increased venous pressure in the spine and cranium. From a pathological perspective, the EDNAC functions as a low-resistance, extradural passageway that might facilitate tumour encroachment and expansion. Conclusions Clinicians should be aware of the extent and significance of the EDNAC which may impact on skull base/spine surgery and present understanding of tumour spread pathways and growth patterns. Comparatively little research has focussed on the EDNAC since its initial description therefore future investigations will provide more information on this underappreciated component of neuraxial anatomy.