what is an arachnoid cyst
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.