Each of your breasts contains lobes of glandular tissue, arranged like petals of a daisy. The lobes are further divided into smaller lobules that produce milk during pregnancy and breast-feeding. Small ducts move the milk to your nipple. The supporting tissue that gives the breast its shape is made up of fatty tissue and fibrous connective tissue. Breast cysts develop when an overgrowth of glands and connective tissue (fibrocystic changes) block milk ducts, causing them to widen (dilate) and fill with fluid.

  • Microcysts are too small to feel, but may be seen during imaging tests, such as mammography or ultrasound.
  • Macrocysts are large enough to be felt and can grow to about 1 to 2 inches (2.5 to 5 centimeters) in diameter. Large breast cysts can put pressure on nearby breast tissue, causing breast pain or discomfort.

The cause of breast cysts remains unknown. Some evidence suggests that excess estrogen in your body, which can stimulate the breast tissue, may play a role in breast cyst development.

Nov. 09, 2012