Intraosseous hibernoma of the appendicular skeleton

Hibernomas are rare lipomatous tumors composed of brown adipocytes. The relative paucity of reported cases involving the bones accounts for the poor understanding of this entity, which is known to affect almost exclusively the axial skeleton. We present a case of intraosseous hibernoma of the humerus, which was found incidentally in a 52-year-old woman and initially misinterpreted as a cartilaginous tumor on magnetic resonance imaging (MRI). The lesion was unchanged in size and morphology at short interval follow-up but increased in size during follow-up over 6 years with an 11 mm increase in the largest diameter. Given the patient's concerns and lesion growth, curettage was performed. Pathology analysis revealed brown fat in keeping with the diagnosis of intraosseous hibernoma. Radiological and pathological findings and pitfalls are herein highlighted to enforce knowledge on this lesion rarely affecting the long bones. Radiologists should think of intraosseous hibernoma if they come across a sclerotic lesion on X-ray or computed tomography, which contains macroscopic fat and shows enhancement on contrast-enhanced MRI. In addition, an intraosseous hibernoma may be picked up incidentally on positron emission tomography-computed tomography due to high fluorodeoxyglucose avidity.