Lipoma-like hibernoma: a rare soft tissue tumor—a case series and review of the literature

Hibernomas are rare and benign lipomatous tumors which consist of lobules of cells derived from brown fat. Less than 200 overall cases are reported in the literature which necessitates the need to report more cases for better understanding of this neoplasm. Hibernomas are slowly progressing, painless tumors most frequently located in the subcutaneous thigh, upper trunk, and neck. Hibernomas generally occur in areas close to the axial skeleton where brown fat used to exist in the fetus and persisted during adulthood. They are rare to be discovered for the first time in older adults, most commonly presenting in adults 20–40 years of age. Core biopsies are simple to perform under local anesthetic and provide pathological differentiation prior to planned excision, hence are recommended, especially with larger lesions. Based on case presentation, watchful waiting for non-growing asymptomatic cases of hibernoma is possible, but more frequent follow-up and/or a core biopsy would be advised to rule out a more aggressive diagnosis. Compared with lipoma-like hibernomas, atypical lipomatous tumor/well-differentiated liposarcoma recurs and might dedifferentiate to a dedifferentiated liposarcoma with the ability to metastasize in up to 5% of the recurrences. Hibernomas, including the lipoma-like variant, are typically treated by surgical excision, rarely recur and do not metastasize. We report two rare presentations of hibernoma and lipoma-like hibernoma. Awareness of this clinicopathological entity is crucial to avoid misdiagnosis as malignant lipomatous neoplasm.