A brain cyst or cystic brain lesion is a fluid-filled sac in the brain. They can be benign (not cancer) or malignant (cancer). Benign means that the growth does not spread to other parts of the body. A cyst may contain blood, pus, or other material. In the brain, cysts sometimes contain cerebrospinal fluid (CSF). CSF is a clear liquid that bathes and cushions the brain and spinal cord. Some brain cysts begin before birth.
Even if a brain cyst is not cancer, it can still cause problems. The cyst may press against brain tissue and cause symptoms, such as headache, vision problems, or nausea. If this happens, you may need surgery to remove the cyst. In some cases, if the cyst is small and not growing and is not likely to cause symptoms, your healthcare provider may advise watching it instead of surgery.