A brain cyst is a fluid-filled sac or cavity that can develop within the brain. It is a type of abnormal growth that can vary in size and location. Brain cysts can be congenital (present at birth) or acquired later in life. They may or may not cause symptoms, depending on their size and location. Treatment options for brain cysts depend on various factors, including the type, size, and symptoms they cause. Surgical removal or drainage of the cyst may be necessary in some cases.