An arachnoid cyst is a type of brain cyst that forms due to the splitting of the arachnoid membrane, according to Johns Hopkins Medicine. It is a fluid-filled sac that appears in the tissues covering the central nervous system.
The symptoms of arachnoid cysts vary depending on its location, notes Johns Hopkins Medicine. This includes headache, nausea, lethargy, seizures, mass protrusion in the skull and visual impairment. Patients undergo CT or MRI scans to determine the necessary treatment option such as craniotomy, minimally invasive endoscopic fenestration, burr hole drainage of the cyst and shunting. Cysts that do not cause symptoms or affect surrounding areas do not require treatment.