Fat necrosis is a rare lesion of the breast but is of clinical importance because it produces a mass, often accompanied by skin or nipple retraction, which is indistinguishable from carcinoma. Trauma is presumed to be the cause, though only about 50% of patients give a history of injury. Ecchymosis is occasionally present. If untreated, the mass effect gradually disappears. The safest course is to obtain a biopsy. Needle biopsy is often adequate, but frequently the entire mass must be excised, primarily to exclude carcinoma. Fat necrosis is common after segmental resection, radiation therapy, or flap reconstruction after mastectomy.

_{Pui MH et al: Fatty tissue breast lesions. Clin Imaging 2003;27:150.}