BACKGROUND: Subcutaneous lipomatous lesions are commonly encountered in clinical practice. Hibernoma is a rare subtype of the benign lipomatous tumor, representing 1% of all types. It poses a challenge due to the difficulty of differentiating it from atypical lipomatous lesions and liposarcomas, which may lead to possible inappropriate diagnosis and management.

CASE REPORT: We report a case of a 33-year-old male who presented with a right upper thigh swelling noticed some time prior to presentation that had started increasing in size prior to his presentation. The magnetic resonance imaging (MRI) was unable to rule out atypical lipomatous tumor and liposarcoma. An ultrasound-guided biopsy gave a diagnosis of hibernoma. The patient underwent a wide local excision, which confirmed the diagnosis of hibernoma. At the 3-year follow-up, there was no evidence of local recurrence.

CONCLUSIONS: Hibernoma has been reported in the literature to be discovered incidentally by radiological imaging done for other causes. However, hibernomas raise a diagnostic challenge because in most imaging modalities they are indistinguishable from other malignant tumors. A wide local excision with negative margins is key to resolving the diagnostic dilemma that a hibernoma presents, as it will provide a definitive diagnosis differentiating it from other lipomatous lesions and prevent any future recurrence. Caution is advised when dealing with lipomatous lesions, as they often overlap with malignancy. Furthermore, an MRI should be done for any subcutaneous lesion that is larger than 5 cm or shows recent growth. A biopsy can resolve the diagnostic dilemma with caution to the hypervascularity of such tumors.

Keywords: Lipoma, Liposarcoma, Neoplasms, Adipose Tissue, Diagnosis, Differential, Image-Guided Biopsy, Subcutaneous Tissue