Recurrence and bleeding in hibernomas

Hibernomas are rare, benign, soft tissue tumors of brown fat. Despite being benign, we have experienced recurrent hibernomas and cases of significant bleeding at our institution. The current literature contains case reports of recurrence, and one large series that describes pathologic variants but contains little clinical data. We could not find data on bleeding. We hypothesized that recurrence is related to the resection type and/or the pathologic variant. We also postulated that atypical histologic findings correlate with excessive bleeding during excision. We sought to confirm that the MRI features of hibernomas could distinguish them from lipomas yet place them among lipomatous tumors. We retrospectively reviewed all hibernomas at our institution over 10 years. There were six hibernomas. Two were removed with a marginal excision and four with an intralesional excision. Two recurred after intralesional surgery. Histologic findings were typical for all patients. An MRI was available on only one patient and showed a fatty tumor that was distinguishable from a lipoma. Recurrences occurred after intralesional but not after marginal excisions. Histology could not predict recurrence. Hibernomas have the potential for significant bleeding during surgical excision, as seen in two of our cases. Level of Evidence: Prognostic study, Level IV (case series).