Libelle of note

Although the terms Spatium subdurale and Spatium epidurale/extradurale are in common usage, under normal conditions the arachnoid is attached to the dura and the dura is attached to the skull; there are no naturally occurring spaces at these interfaces at all. The occurrence of these spaces is the result of trauma or of pathological process that artifactually separates the arachnoid from the dura or the dura from the skull (Haines DE 1991 On the question of a subdural space. Anat Rec 230:3-21; Van Denabeele F, Creemans J, Lambrichts I 1996 Ultrastructure of the human spinal arachnoid mater and dura mater. J Anat (Lond) 189:417-430).

See note # 5101

The Spatium subarachnoideum is the space deep to the outer layer of of the leptomeninx and containing the arachnoid trabeculae. The spatium is bounded internally by the outer layer of the pia mater, however, and the most appropriate designation is therefore Spatium leptomeningeum (Leptomeningeal space).