IgG4-associated inflammatory pseudotumor of ureter: clinicopathologic and immunohistochemical study of 3 cases.

Inflammatory pseudotumors are lesions characterized by proliferation of fibroblasts/myofibroblasts with variable chronic inflammatory cell infiltration. Recent studies have suggested that inflammatory pseudotumor with abundant IgG4-positive plasma cells may be a unique entity associated with systemic IgG4-related sclerosing disease and should be distinguished from other similar lesions such as inflammatory myofibroblastic tumor and fibrohistiocytic-type inflammatory pseudotumor. Localized inflammatory pseudotumor has been rarely reported in the ureter, and IgG4-associated inflammatory pseudotumor of ureter has not been described. We describe herein 3 cases of ureteral inflammatory pseudotumor of IgG4-associated lymphoplasmacytic type, focusing on density of IgG4-positive plasma cells; infiltration pattern of eosinophils and histiocytes; presence of obliterative phlebitis; and immunohistochemical profiles of smooth muscle actin, anaplastic lymphoma kinase, and CD68. Three patients, 45- and 47-year-old men and 84-year-old woman, all presented with flank pain and ureteral narrowing by a mass effect. Microscopic examination of the resected ureters showed suburothelial masslike lesions with fibroblasts/myofibroblasts without atypia, abundant plasma cells, and scattered eosinophils and histiocytes. The lesion of the 47-year-old man showed obliterative phlebitis in addition to the above findings. The lesion of the 84-year-old woman was accompanied by urothelial carcinoma in situ in the overlying urothelium. Spindle cells were diffusely or focally positive for smooth muscle actin but negative for anaplastic lymphoma kinase in all 3 cases. For each case, respectively, an average of 154, 112, and 50 plasma cells per high-power fields were immunoreactive for IgG4, a diagnostic feature of IgG4 inflammatory pseudotumor. We described 3 cases of IgG4-associated inflammatory pseudotumor of ureter with pathologic and immunohistochemical features that are compatible for lymphoplasmacytic type of inflammatory pseudotumor. Further study is needed to characterize any relationship between this entity and systemic sclerosing disease and/or urothelial carcinogenesis.