Fig. 13

Retroperitoneal fibrosis. Axial contrast CT (a) of the abdomen demonstrates retroperitoneal mass-like soft thickening enveloping the aorta without lifting it anteriorly (arrows), and a dilated left ureter (arrowhead). This mimics retroperitoneal lymphomatous disease, although lymphoma tends to lift/displace the aorta/IVC. F18-FGD PET/CT MIP (b) demonstrates a medialized left ureter (arrow). Note the lack of FDG avidity in the expected region of the retroperitoneal mass. Findings are consistent with retroperitoneal fibrosis