Incidental Hibernoma With an Atypical Presentation: Diagnostic Approach, Pathologic Correlation, and Lessons Learned

Hibernomas are rare fluorodeoxyglucose (FDG)-avid benign tumors originating from brown adipocytes that have characteristics mimicking liposarcomas and lipomas on imaging such as magnetic resonance imaging (MRI) and positron emission tomography/computed tomography (PET/CT). Here, we present a patient who was found to have both an FDG-avid hibernoma and an FDG-avid lung hamartoma, which was initially concerning for metastatic liposarcoma based on imaging. Notable imaging differences that may help differentiate lipomatous tumors include higher maximum standardized uptake values (SUV_max) on PET/CT for hibernomas compared to liposarcomas and hamartomas. Additionally, on MRI, hibernomas and liposarcomas demonstrate the presence of hypervascularity, heterogeneous composition, and septations as opposed to lipomas. Hamartomas have a heterogeneous composition that may be differentiated by the presence of a cleft-like structure with intranodular fat, low SUV_max, and calcifications. Understanding the similarities and differences among lipomatous tumors may help guide the physician in devising treatment strategies.