Fat necrosis of the breast may be associated with a history of trauma (35-40%) and is an important clinical entity because it can mimic breast carcinoma. Surgical trauma secondary to biopsy or plastic surgical procedures on the breast, or injection of silicone or narcotics into the breast can cause fat necrosis.

Clinical Features
Patients may present with an irregular, painless mass that may be associated with overlying skin thickening or tethering. Therefore it can sometimes be difficult to distinguish fat necrosis from carcinoma on clinical examination.

Radiology
Mammography
Frequently the mammogram is normal. When present, mammographic changes are often variable. In the early phase, there is usually a soft-tissue density, which may change over a period of weeks to a low-attenuation area with a thin, surrounding capsule. These capsules may undergo subsequent rim calcification.

Ultrasound
Ultrasound is extremely successful at detecting fat necrosis. The appearances vary from superficial hyperechoic, mixed echogenecity or cystic-like structures. Aspiration of such cysts produces oily fluid.

Pathology
Macroscopic Appearance
Most isolated lesions are small (average <2 cm in diameter). The lesion is usually firm, indurated and may have an irregular or rounded outline. The cut surface in early lesions shows mottled yellow and red areas and in older lesions cystic spaces may be apparent. Eventually, in long-standing lesions, there will be dense fibrosis and sclerosis with possible foci of calcification.

Microscopic Appearance
Foamy macrophages, occasional lymphocytes and foreign-body giant cells are seen infiltrating adipose tissue in the earliest stages. The adipocytes may be uneven in size and lack nuclei. In older lesions, free-lying fat globules surrounded by a rim of foamy macrophages and giant cells are seen.

Fibrosis, hemosiderin-laden macrophages and calcification are features of long-standing cases.

Management
In our experience, an unequivocal diagnosis of fat necrosis can be made on core biopsy. Simple observation will result in resolution of the palpable mass. In the absence of a firm diagnosis, open excision biopsy is recommended.

A.D. Purushotham, P. Britton and L. Bobrow
A prospective study of benign breast disease and the risk of breast cancer. JAMA 2002

References