The arachnoid membrane is an important structure in the human brain, which is located in the central nervous system of the human body and is a translucent membrane-like structure composed of very thin connective tissue. The surface of the human brain normally consists of three membranes, from inside to outside, the soft meninges, the arachnoid membrane, and the dura mater. The arachnoid membrane is located in the deep part of the dura mater in the brain, and it mainly plays a role in protecting the brain tissue and the spinal cord. Diseases related to the arachnoid membrane commonly include: arachnoiditis, arachnoid cysts, subarachnoid hemorrhage, etc. It is usually necessary to perform cerebrospinal fluid examination, CT or MRI of the brain to make a clear diagnosis under the guidance of a doctor to determine whether further treatment and therapy are needed.