Application of 99mTc-FAPI-46 SPECT/CT in Evaluation of Idiopathic Retroperitoneal Fibrosis: Case Report of a Novel Promising Experience

This case report describes a 59-year-old man with fatigue and bilateral lower limb edema, diagnosed with retroperitoneal fibrosis (RPF). Laboratory tests showed elevated serum creatinine, ESR, and CRP levels, while imaging revealed left hydroureteronephrosis and a pelvic mass encasing the iliac vessels. A biopsy indicated fibrotic changes without malignancy, confirming RPF. This experience of using 99m Tc-FAPI-46 as a novel agent for conventional imaging demonstrated a high target-to-background ratio in the RPF, suggesting its utility in diagnosis and assessing disease activity, also aiding in ruling out the distant malignant neoplasms, especially where PET/CT is not available.