Hydronephrosis caused by a relapse of granulomatosis with polyangiitis (Wegener's).

We describe a case of relapsed granulomatosis with polyangiitis (Wegener's) (GPA) that presented with abdominal pain. (18)F-fluoro-2-deoxy-D: -glucose positron emission tomography (FDG-PET)/computed tomography (CT) clearly depicted an inflammation of the left peri-iliac arterial soft tissue, which was thought to be the cause of the ureteral obstruction and hydronephrosis. Our case shows that peri-iliac arterial inflammation occurs in GPA and causes hydronephrosis. In addition, FDG-PET/CT is a useful tool for management of this systemic inflammatory disease.