What is An Arachnoid Cyst?
An arachnoid (pronounced ah-RACK-noid) cyst is a fluid-filled sac located inside the head or spine. Arachnoid cysts develop between the brain or spinal cord and the arachnoid membrane. This is one of three membranes that cover the brain and spinal cord. The fluid in the cyst often is cerebrospinal fluid (CSF), a clear liquid that protects and nourishes the brain and spinal cord. Arachnoid cysts that are located around the spinal cord are less common than those that appear inside the head. In a child’s head, an arachnoid cyst can be located between the brain and the skull. A cyst can also be located inside the brain. Arachnoid cysts in the brain form in open spaces called ventricles that normally contain and circulate cerebrospinal fluid. About two-thirds of the arachnoid cysts we find in the head are located in the upper part of the brain. The other third are in the cerebellum, located in the lower part of the brain.
