the arachnoidal cistern. Spinal arachnoid cysts may be extradural, intradural, or perineural and tend to present with signs and symptoms indicative of a radiculopathy. Arachnoid cysts may also be classified as primary (congenital) or secondary (acquired) and have been reported in humans, cats, and dogs. Arachnoid cysts can be relatively asymptomatic or present with insidious symptoms; for this reason, diagnosis is often delayed. Treatment Most arachnoid cysts are asymptomatic and do not require treatment. Treatment may be necessary when symptomatic. A variety of procedures may be used to decompress (remove pressure from) the cyst. Surgical placement of a cerebral shunt: An internal shunt drains into the subdural compartment. A cystoperitoneal shunt drains to the peritoneal cavity. Fenestration: Craniotomy with excision Various endoscopic techniques are proving effective, including laser-assisted techniques. Drainage by needle aspiration or burr hole. Capsular resection Pharmacological treatments may address specific symptoms such as seizures or pain. Prognosis Most arachnoid cysts are asymptomatic, and do not require treatment. Where complications are present, leaving arachnoid cysts untreated may cause permanent severe neurological damage due to the progressive expansion of the cyst(s) or hemorrhage (bleeding). However, with treatment most individuals with symptomatic arachnoid cysts do well. More specific prognoses are listed below: Patients with impaired preoperative cognition had postoperative improvement after surgical decompression of the cyst. Surgery can resolve psychiatric manifestations in selected cases. Epidemiology Arachnoid cysts are seen in up to 1.1% of the population with a gender distribution of 2:1 male:female. Only 20% of these have symptoms, usually from secondary hydrocephalus. A study that looked at 2,536 healthy young males found a prevalence of 1.7% (95% CI 1.2 to 2.3%). Only a small percentage of the detected abnormalities require urgent medical attention. See also Acoustic neuroma Arachnoiditis Brain Tumors, General Dandy–Walker syndrome Empty sella syndrome Porencephaly Syringomyelia Hyperprolactinemia Panhypopituitarism Arnold–Chiari malformation Hydrocephalus References External links Congenital disorders Central nervous system disorders