BENIGN BREAST DISORDERS:

Fat Necrosis

Etiology: Benign breast condition caused by trauma, breast surgery/biopsy or breast radiation therapy; Develops as an area of focal fat necrosis becomes “walled off” by fibrous tissue over many years

Epidemiology: More common in women with large/pendulous breasts; onset can be delayed up to 10 years after breast surgery/trauma (most common traumatic cause of fat necrosis is seat belt injury/MVA)

Diagnosis: History and comparison with prior imaging, are helpful with diagnosis; Oil cyst (mammogram) with wall nodularity (US) and milky emulsified fat appearance (cyst aspiration) are diagnostic features, but the presentation is widely variable

Imaging:

–     Mammogram: Initial appearance may be alarming (irregular, spiculated mass-like area +/- associated calcifications); Findings can often be correlated with position of surgical scarring on breast; Progressive calcification over time starting with peripheral stippled calcifications around low-density centers (lucent "bubbles"); Eventually an oil cyst develops (radiolucent, round mass with very fine curvilinear wall calcification creating a "crescent moon" appearance)

–     US: Hypoechoic mass with well defined margins +/- mural nodule(s)

(Ikeda 2010, Georgian-Smith 2014, Sabel 2015, Knipe 2016)