Intraosseous Hibernoma in the Sacrum of an Adult.

Hibernoma is an uncommon lipomatous tumor composed of brown adipose cells that until recently has only ever been described in soft tissue locations. This report describes the histological features of a discrete lesion in the sacrum of an 84-year-old lady. Biopsy of this lesion demonstrated that it consisted predominantly of multivacuolated lipocytes with a morphological and immunohistochemical profile consistent with brown fat cells. The lesion was diagnosed as an intraosseous hibernoma. This is the 16th report in the English literature of a hibernoma occurring outside of a soft tissue location.