Breast hibernoma

Clinical History

Patient was accidentally found to have a non-palpable, painless right breast mass through PET-CT

Imaging Findings

The patient, who was previously well and fit, was accidentally found to have a non-palpable, painless right breast mass. Mediolateral and craniocaudad mammography showed an isodense and partially encapsulated mass in the right breast, not easily seen. Sonography showed hypo-echoic and hyper-vascular mass with indistinct borders, not easily seen. Magnetic resonance with gadolinium revealed large hyper-enhanced (early and marked contrast enhancement) mass. PET-CT showed a zone of hyper-metabolism in the lower outer quadrant of the right breast suspicious of neoplasm. Histologically, the lesion showed large multivacuolated cells with scanty granular eosinophilic cytoplasm and eccentric nuclei. The patient was diagnosed as having a breast hibernoma.

Discussion

Hibernomas are extremely rare benign soft tissues tumours, derived from brown fat. Most hibernomas occur in sites where brown fat persists beyond fetal life (usually in the inter-scapular region or thigh), but they also occur in sites where brown fat is usually absent. There are few cases reported, and in the breast is still more rare. They are asymptomatic unless they have rapid growth [1, 3]. Radiological findings [2]:
- Mammography: may be normal or isodense compared to breast fatty tissue.
- Ultrasound: hyperechogenic and highly vascularized lesion.
- Magnetic Resonance with gadolinium: On T1 and T2 weighted imaging, it is similar to subcutaneous fat. Gadolinium : early and marked contrast enhancement. The enhancement kinetics curves shows a rapid initial rise, followed by a drop-off whit time (washout) in delayed phase.
- FDG-PET scan: area of intense FDG hyperfixation with an SUVmax high (more than 10) [4, 5].
- Microscopically, the tumour is characterized by large multivacuolated cells with scanty granular eosinophilic cytoplasm and eccentric nuclei, univacuolated cells, with peripheral nuclei, and smaller round cells with granular cytoplasm.

The hibernoma is a benign tumour, which simulates characteristics of malignancy in some imaging tests for tissue and physiological characteristics, pathologic examination being definitive diagnosis. You have to make differential diagnosis with malignant fatty tumours like liposarcoma [3].

Differential Diagnosis List

Final Diagnosis

Breast hibernoma.

URL:	https://www.eurorad.org/case/12965
DOI:	10.1594/EURORAD/CASE.12965
ISSN:	1563-4086