A Rare Soft Tissue Tumor in Adults: Hibernoma a Case Report

Hibernoma is a rare lipomatous tumor of brown fat origin that emerges from remnants of fetal brown adipose tissue. They are encapsulated, yellow- tan colored, painless and benign soft tissue tumors, usually seen in adults and occur with large cells that have acidophilic, granular and vacuolar cytoplasm and central nuclei. Our case is a 31-year-old male who had swelling in the neck. Imaging studies depicted a lesion compatible with lipoma. Macroscopic evaluation of the excision specimen revealed brown, tan-yellow colored and haemorrhagic cut surface compatible with fat tissue. In microscopic examination, a tumor composed of cells with vacuolar, granular and eosinophilic cytoplasm, centrally or peripherally localized small, round nuclei, were observed. These cells were stained with histochemical Oil-Red-O and were evaluated to be comparable with lipocytes. With these findings, the patient was diagnosed as having hibernoma. Histopathologically, hibernoma must be distinguished from granular cell myoblastoma, round cell liposarcoma, lipoblastomatosis, sebaceous adenoma, pleomorphic lipoma and normal brown fat accumulation. Total excision of the tumor is sufficient. We present this case for its rarity, and for the fact that it can be treated with simple excision, and should be kept in mind especially in the differential diagnosis of lesions with high vascularity