Hibernoma : Microscopic Features

Hibernoma is a rare benign lipomatous tumor composed of cells resembling brown fat. It accounts for < 2% of benign and 1% of all lipomatous tumors. It usually occurs in the subcutaneous tissues of back (interscapular region) and thigh in adults. It is slow growing with no risk of recurrence following resection. Most cases show complex genomic rearrangements involving 11q13-21 region that result in codeletion of tumor suppressor genes MEN1 and AIP. The classic hibernoma consists of >70% areas resembling brown fat. It shows an admixture of large polygonal cells with abundant granular eosinophilic cytoplasm, multivacuolated large adipocytes with central nuclei, and mature univacuolated adipocytes (white fat). Lipoma-like hibernomas contain a larger proportion of mature fat. Some cases show prominent myxoid change or spindle cell morphology.