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 (SUVmax) 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 SUVmax, and calcifications. Understanding the similarities and differences among lipomatous tumors may help guide the physician in devising treatment strategies.