Diagnosis of Intraosseous Hibernoma of an Appendicular Skeleton in an Adult - A Rare Case Report.

Introduction: Hibernoma is an uncommon benign tumor composed of multivacuolated brown adipocytes described in the literature a decade back. Intraosseous hibernomas are extremely rare with propensity to affect axial skeleton. Involvement of appendicular skeleton has been reported only twice in the literature till date. Case Report: We present a case of solitary, painless mass in the left proximal tibia mimicking neoplasm in a 35-year-old male. The plain radiographs revealed a lytic lesion with well-defined margin at the junction of metaphyseal-diaphyseal region of the left proximal tibia. The lesion was hyperintense on T2 and hypointense on T1 with heterogenous enhancement on contrast imaging. FDG-PET showed high uptake of fluorodeoxyglucose. Histopathological examination revealed the presence of multivacuolated cytoplasm with abundant mitochondria suggestive of hibernoma. On immunohistochemistry, the cells were positive for S-100. Conclusion: The findings of imaging modalities are non-specific and histopathological examination is required to confirm the diagnosis of hibernoma. Intraosseous hibernoma needs to be considered as a differential diagnosis of sclerotic bone lesion. Further, evaluation with regular follow-up with imaging will be required if the mass undergoes any clinical changes. Both radiologists and pathologists, need to be aware of this rare entity to avoid misdiagnosis of the uncommon lesion.