History: 50 year old woman presenting for screening mammogram.
This is a case of a breast lipoma. This is a benign tumor of the breast composed of mature adipose (fat) cells. They can be present in the breast, axilla, chest wall, or subcutaneous tissues, and typically appear circumscribed, oval or round. If they necrose, they can show dystrophic calcification. On ultrasound they appear hyperechoic or isoechoic to subcutaneous fat. The classic differential diagnosis of fat containing breast masses includes:
1. Hamartoma (fibroadenolipoma, or breast within breast)
2. Oil cyst (fat necrosis)
3. Galactocele in lactating or post-lactation patients
4. Lymph node
5. Steatocystoma multiplex
6. Liposarcoma – very rare, large fatty mass with thick septations and soft tissue nodules