Fibrocystic disease. Ultrasound scan of the breast of a patient with fibrocystic disease, showing a cyst at upper centre. Cysts 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. Ultrasound is a diagnostic technique that sends high frequency sound waves into the body via a transducer. The returning echoes are recorded and used to build an image of an internal structure.