Interesting ImagesIdiopathic Retroperitoneal Fibrosis With Intense Uptake of 68Ga-Fibroblast Activation Protein Inhibitor and 18F-FDGPan, Qingqing MD∗,†; Luo, Yaping MD∗,†; Zhang, Wen MD‡Author Information From the ∗Department of Nuclear Medicine, Chinese Academy of Medical Sciences and Peking Union Medical College Hospital †Beijing Key Laboratory of Molecular Targeted Diagnosis and Therapy in Nuclear Medicine ‡Department of Rheumatology, Chinese Academy of Medical Sciences and Peking Union Medical College Hospital, Beijing, People’s Republic of China. Received for publication October 1, 2020; revision accepted October 1, 2020. Conflicts of interest and sources of funding: This work is supported by the CAMS Initiative for Innovative Medicine (CAMS-I2M, 2017-I2M-3-001). None declared to all authors. Correspondence to: Yaping Luo, MD, Peking Union Medical College Hospital, Wangfujing, Dongcheng District, Beijing 100730, People’s Republic of China. E-mail: [email protected]. Clinical Nuclear Medicine: February 2021 - Volume 46 - Issue 2 - p 175-176 doi: 10.1097/RLU.0000000000003402 Buy Metrics Abstract 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. Copyright © 2020 Wolters Kluwer Health, Inc. All rights reserved.