Idiopathic Retroperitoneal Fibrosis With Intense Uptake of 68Ga-Fibroblast Activation Protein Inhibitor and 18F-FDG.

A 26-year-old man presented with a retroperitoneal mass with left urinary tract obstruction and hydronephrosis recently. 18F-FDG PET/CT showed the retroperitoneal mass had intense and homogeneous FDG avidity. In 68Ga-FAPI PET/CT, the retroperitoneal mass showed intense radioactivity without other organ involvements. The patient was finally diagnosed with idiopathic retroperitoneal fibrosis. After treatment, the follow-up CT showed significant decrease in size of the retroperitoneal mass. The current case indicated that idiopathic retroperitoneal fibrosis had active uptake of 68Ga-FAPI.