Intraosseous Hibernoma

Study Design. A case report and a literature review are presented. Objective. To describe and review the clinical presentation and characteristic imaging and pathology findings of intraosseous hibernoma. Summary of Background Data. Hibernomas are lesions of brown fat. Brown fat is typically found in newborn mammals and is rich in mitochondria, thus enabling its role in thermoregulation. It represents a small proportion of adult fat and is distinct from the more common "white fat." Rarely does a hibernoma occur within bone. To the authors' knowledge, 5 cases in all have been reported in the literature. Methods. We report the first case to our knowledge of an intraosseous hibernoma occurring within the lumbar spine as well as a review of the literature. Results. Characteristic findings from magnetic resonance studies include variable T1W signal relative to skeletal muscle and hyperintense signal on fluid-sensitive imaging. Computed tomography has consistently demonstrated a sclerotic lesion with variable definition. Pathologic findings include sheets of multivacuolated cells with centrally placed nuclei and numerous tiny surrounding cytoplasmic vacuoles overlying bony trabeculae. Conclusion. Our review of the literature demonstrates that intraosseous hibernoma is most likely an incidental finding with a predilection for the lower extremities in middle-aged females. Key words: chordoma, hibernoma, lumbar spine, middle-aged females, benign intraosseous lesion, brown fat, lipoma, hemangioma, lower extremity.