Brain cysts are relatively common but sometimes can resemble brain cancer. Often found incidentally, many are asymptomatic. However, they may grow slowly over time, putting pressure on vital brain structures and causing neurological symptoms. Rarely, bleeding may occur. 

Only 5% of arachnoid cysts are symptomatic and may include headaches, seizures, hearing loss, dizziness, nausea, and/or vomiting. Typical arachnoid cysts are between 3 and 6 cm in diameter. Most do not grow in size. 

The location of arachnoid cysts affects symptoms differently. Suprasellar cysts (generally those located above the pituitary gland) may cause obstruction, leading to hydrocephalus, an abnormal buildup of cerebrospinal fluid.