An arachnoid cyst is a type of cyst that develops on the arachnoid membrane of the brain. This condition is also referred to as an arachnoid brain cyst or an intracranial arachnoid cyst. Other synonyms for arachnoid cyst include leptomeningeal cyst, meningeal cyst, and cystic meningioma. While this condition is generally benign and asymptomatic, in rare cases, it can lead to symptoms such as headaches, seizures, and vision problems if it grows large enough to put pressure on the brain. Treatment options for arachnoid cysts range from observation to surgical intervention, depending on the size and location of the cyst.