Fig. 5
Histopathological findings. a Hematoxylin and eosin staining showed abundant infiltration of lymphocytes with lymphoid follicles around the left ureter and peripheral proliferation of collagenous fibers (× 200). b Immunohistochemical staining showed that the mean IgG4-positive plasma cell count was 50 per high-power field, and the ratio of IgG4-positive/IgG-positive cells was 54% (IgG4, immunoperoxidase, × 100; arrow)