These are congenital disorders formed by the pathological development of one of the membranes of the brain, namely the arachnoid mater. Normally this meninge is a thin membrane that covers the brain, leaving only minimal space, where the cerebrospinal fluid is located and circulating. If, due anatomical damage, this membrane allows for the accumulation of this fluid, this causes cysts to form, trapping fluid and exercising pressure on the brain. The diagnosis is possible via computed tomography and magnetic resonance imaging. There may be no clinical symptom, or there may be seizures, severe headaches, increased intracranial pressure, and other symptoms. These are benign conditions that may require a simple surgery, in which the fluid is drained towards its normal circulatory pathway, so that the brain can be decompressed.