Fig. 1

Radiology and histopathology of ureter mass in the ureteropelvic junction; a Contrast-enhanced CT showed ureter mass in the right ureteropelvic junction (arrow); b Right kidney presented mild hydronephrosis, while renal parenchyma showed no abnormalities; c Preoperative chemotherapy decreased the size of the ureter mass from 21 mm to 12 mm (arrow). The mass encased the ureter and had a smooth intraluminal surface of the ureter wall; d Histologically, mononuclear cells infiltrated outside the muscularis of the ureter [Hematoxylin-Eosin (HE) staining, × 40]; e, f Storiform fibrosis was observed [HE staining, (e) × 100, (f) × 400]; g Mononuclear cells also infiltrated the venules, indicating obliterative phlebitis (Elastica van Gieson staining, × 100); h, i Many IgG4-positive plasma cells infiltrated and surrounded germinal center-like structures [IgG4 immunostaining, (h) × 400, (i) × 40]