Background: Pitfalls in 18F Fluorodeoxy-glucose Positron Emission Tomography Computed Tomography (18F FDG PET-CT) can mislead PET readers to interpret images incorrectly, particularly in oncologic staging and restaging. Although FDG uptake reflects increased glucose metabolism, it is not specific for malignancy. Hibernoma, a rare benign tumor arising from brown adipose tissue, may show intense FDG avidity and closely mimic metastatic disease, representing an important diagnostic pitfall.

Case Presentation: A 45-year-old man with stage IIIB non-small cell lung carcinoma (NSCLC) underwent PETCT for post-treatment re-staging. An incidental, false-positive FDG-avid fatty lesion was found in the right gluteal region. Follow-up 18F FDG PET-CT showed partial remission of the right upper lobe lung mass and mediastinal lymphadenopathy, but metastatic lesions progressed in the left upper lobe and T12 vertebra. The prior right gluteal fatty lesion showed altered glucose metabolism with FDG avidity, suspicious for metastasis.

A biopsy of the right gluteal lesion confirmed a hibernoma. The patient was started on the standard doses of the cyclophosphamide, doxorubicin, and etoposide (CAE) regimen (1,000 mg/m2 cyclophosphamide, 60 mg/m2 doxorubicin, and 50 mg/m2 vincristine) for six cycles, at 4-week intervals. The patient opted for conservative treatment with maintenance dose chemotherapy tablets (erlotinib 150 mg once/day).

Conclusions: An appropriate 18F FDG PET-CT characterization of a hibernoma in a patient with NSCLC may avert futile treatment, as it potentially resembles a false-positive malignant lesion.