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