Some brain cysts arise in uterus like arachnoids cyst, dermoid, epidermoid cyst also due to abnormality in
brain development, pineal cysts grow on pineal gland in
fetal stage or puberty, cysts caused due to tumors, secondary arachnoid cysts etc. It is difficult to comment on the type of a cyst on an MRI though the location can provide some idea. This would be diagnosed only on excision and pathological evaluation.