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

Abstract

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 (SUV_max 2.4), while subsequent ⁶⁸Ga-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 ¹⁸F-FDG uptake and only minimal ⁶⁸Ga-FAPI avidity (SUV_max 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.