Teaching Case

A 52-year-old female patient presented with a complaint of a painful lump in the left breast. The patient had a past operative history of bilateral reduction mammoplasty, a year before (in 2012). On clinical examination, there was a hard lump in the upper outer quadrant of the left breast.

Mammogram was performed (2013) revealing a few well circumscribed lucent lesions in both breasts, suggesting areas of fat necrosis. Correlated ultrasonography revealed few complex cystic lesion with internal echoes, septations and mural nodules without significant vascularisation, in both breasts, representing fat necrosis.
MR mammography revealed multiple clusters of prominent fat globules with T1, T2 hypointense rim which showed clustered ring enhancement at the site of mammographic abnormality.
Ultrasound-guided core biopsy of the left breast lump was performed, which was compatible with fat necrosis.
Follow-up mammogram (2015) revealed multiple areas of fat containing cysts with interval development of rim calcification in both breasts.
On further follow up after 3 years (2016), the mammogram revealed multiple clustered areas of rim calcifications with a central lucent centre. This appearance of clustered rim calcification is called Liponecrosis microcystica calcificans.

Fat necrosis of the breast is a challenging diagnosis due to the various appearances on mammography, ultrasound and MRI. The appearance of fat necrosis is the result of the amount of the inflammatory reaction, liquefied fat, and the degree of fibrosis. Fat necrosis results from injury to breast fat either from previous trauma or previous surgery like wide local excision including lumpectomy and reduction mammoplasty. Causes other than trauma and surgery are ischemia and chemical irritation. Ischemia occurs due to radiation induced arteritis. Chemical irritation occurs due to rupture of cyst/ectatic duct, plasma cell mastitis or bleeding into fatty tissue [1].
Fat necrosis may be asymptomatic or may present as a tender/nontender palpable lump. The clinical features of fat necrosis vary from single or multiple smooth round nodules to clinically worrisome fixed, irregular masses with overlying skin retraction. Other clinical features associated with fat necrosis include ecchymosis, erythema, inflammation, pain, skin retraction or thickening, nipple retraction, and occasionally reactive lymphadenopathy [2].
Initially mammography may appear normal. Later a mixed fat and water density lesion develops. Later on a well circumscribed lipid cyst with a thin water density capsule develops and with time, calcified salt of fat precipitates along the capsule of the oil cyst, known as liponecrosis macro/micro cystica calcificans [1]. In the fibrotic phase of fat necrosis, frank spiculation or architectural distortion with or without mass predominates.
Ultrasound also shows different appearance of fat necrosis according to its stages. In the early phase only edema of fat is visible, appearsing as hyper-reflective compared to surrounding fat [1]. Later it presents as a complex solid-cystic lesion with internal septations, mural nodules and debris. Early lipid cyst appears as an anechoic lesion with a thin echogenic well defined capsule without posterior acoustic enhancement.
MRI also has a wide spectrum of findings for fat necrosis. The most common appearance of fat necrosis on MRI is a lipid cyst, round or oval mass with hypo intense T1-weighted signal on fat saturation images & hyperintense on T2WI. It may also appear as low signal intensity on T1-weighted MRI, which may be due to its hemorrhagic and inflammatory content. Fat necrosis may show focal or diffuse and homogeneous or heterogeneous enhancement after the administration of IV contrast material. Thin clustered rim of enhancement is also common although it may also be thick, irregular, or spiculated mimicking malignancy [2].