A milk filled cyst caused by a blocked mammary duct.
It can be caused by an infection or postpartum.
Taking into account the patient's postpartum history, this lesion may be related to breastfeeding. However, no definite areas of fat are seen on the mammogram to confirm a galactocele. There is a small hyperechoic region which could represent fat on ultrasound, but this is not definitive. These images suggest abscess, breast cancer, fibroadenoma or galactocele. For a lucent mass, the differential diagnosis includes oil cyst (which may occur following hematoma or biopsy), lipoma, or galactocele (associated with lactation). For a mass of mixed density, fibroadenolipoma, galactocele, intramammary lymph node, and hamartoma should be considered. Breast cancers typically do not contain fat, but may trap fat; therefore, breast cancer should not be discounted if a lesion has areas of radiolucency.