Ask FunTrivia strives to be the most accurate and complete source for answers to trivia questions on the web. Please cite all facts with citation links or references from trustable sources. Editors continuously recheck submissions and claims.
Definition of arachnoid. 1  1 : of or relating to a thin membrane of the brain and spinal cord that lies between the dura mater and the pia mater. 2  2 : covered with or composed of soft loose hairs or fibers.
An arachnoid cyst is a fluid-filled cyst that that occurs in the arachnoid membrane around the brain. While completely benign, and not a tumor per se, they can cause symptoms by compression of adjacent nervous system structures.he cyst wall is basically just arachnoid membrane and the cyst is filled with fluid which is essentially the same as cerebrospinal fluid. Some cysts do not appear to change in size while others can grow over time, compression adjacent neurological structures.