Arachnoidea mater

The arachnoid mater or simply arachnoid is a part of the leptomeninges (soft meninges). It is the middle meninx between the dura mater and the pia mater[^1].

Anatomy

Like the dura mater, the arachnoid spans the sulci of the brain and derives its name from the strong whitish pattern of fine fibrous collagenous connective tissue that gives it a web-like appearance. Button-shaped protrusions of the arachnoid extend into the venous blood channels in the dura mater. These protrusions are referred to as arachnoid granulations or Pacchionian granulations and are sites of cerebrospinal fluid absorption. Intraoperative injuries to the Pacchionian granulations can lead to significant venous bleeding. Beneath the arachnoid is the subarachnoid space, which is filled with cerebrospinal fluid and thus forms the external cerebrospinal fluid space. In this space between the arachnoid and pia mater lie numerous superficial arteries and veins of the brain.

Figure