MSH: Intracranial or spinal cavities containing a cerebrospinal-like fluid, the wall of which is composed of arachnoidal cells. They are most often developmental or related to trauma. Intracranial arachnoid cysts usually occur adjacent to arachnoidal cistern and may present with HYDROCEPHALUS; HEADACHE; SEIZURES; and focal neurologic signs. (From Joynt, Clinical Neurology, 1994, Ch44, pp105-115),NCI: An intracranial or spinal cyst which contains fluid and is composed of arachnoid cells. Intracranial arachnoid cysts may present with headaches, seizures and hydrocephalus. Spinal arachnoid cysts may present with symptoms of radiculopathy.