68Ga-FAPI Avidity in Fat Necrosis and Adrenal Adenoma: Expanding the Spectrum of Benign Pitfalls in Oncologic Imaging

Fat necrosis, a benign postoperative process related to tissue injury and repair, may demonstrate variable findings on functional imaging.We report a case of postoperative fat necrosis following pancreaticoduodenectomy showing intense 68 Ga-FAPI uptake in the absence of significant 18 F-fluorodeoxyglucose ( 18 F-FDG) avidity.Surveillance 18 F-FDG positron emission tomography/computed tomography ( 18 F-FDG PET/CT) demonstrated only mild activity within the surgical bed maximum standard uptake value (SUV max 2.4), while subsequent 68 Ga-FAPI PET/CT revealed marked uptake corresponding to fat necrosis SUV max 9.9, consistent with pronounced fibroblast activation during postoperative healing.Additionally, a benign left adrenal adenoma showed low 18 F-FDG uptake and only minimal 68 Ga-FAPI avidity (SUV max 2.3), reflecting minimal stromal activation.This case highlights the tracer discordance between 18 F-FDG and 68 Ga-FAPI in fat necrosis and underscores the importance of correlating 68 Ga-FAPI findings with surgical history and anatomic imaging to ensure accurate interpretation.