Coloured magnetic resonance imaging (MRI) scan of the breasts of a 46 year old female patient with fibrocystic breast disease. Cysts (white) are fluid-filled sacs that are usually benign. Treatment is either with drainage of the fluid or surgical removal of the cyst. Fibrocystic disease, also called benign mammary change, arises from hormonal changes. The breast swelling that accompanies menstruation can cause cysts to form in blocked or enlarged milk ducts. Fibrocystic changes usually disappear after the menopause.