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

Abstract

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.

A case of a rare hibernoma tumour and a brief literature review

“…8 Hibernomas are classified into four different sub types of morphology, most common is typical found in 82% of cases, myxoid found in 8%, lipoma like in 7% and rest are spindle cell. 2 This reported case formed part of the typical subtype as the histology had reported the findings of multi-vacuolated cytoplasm.…”

“…With age, brown fat is replaced by white fat, whilst brown fat persists in specific areas in which hibernomas may form (Gabra et al). 2 Hibernomas usually present as incidental findings, as painless, mobile, firm, slow growing lumps in the subcutaneous tissue. A differential diagnosis may include fat necrosis, angiolipoma, giant cell tumour, rhabdomyosarcoma in children and an atypical lipoma or liposarcoma (Nasner et al).…”

A Rare Case of Large Lateral Chest Wall Hibernoma

“…Hibernoma cells typically have a polygonal shape and exhibit cytological features considered benign, including small central nuclei, noticeable nucleoli, and few instances of abnormal cell morphology or mitotic figures [11]. Unlike hibernomas, conventional lipomas consist mainly of white fat cells [13]. Histologically, hibernomas are categorized into four subtypes based on varying degrees of cytoplasmic eosinophilia, the presence of myxoid stroma, and spindle cell configuration, with their prevalence influenced by demographic factors [11].…”