title: IgG4-related inflammatory pseudotumor of the renal pelvis involving renal parenchyma, mimicking malignancy.
abstract: BACKGROUND
  IgG4-related disease is a recently recognized systemic disease characterized by storiform fibrosis with infiltration of IgG4-positive plasma cells. In rare incidences, IgG4-related renal disease can present as a solitary mass lesion at renal pelvis and can pose a diagnostic challenge since these lesions mimic malignancy. Herein, we present a rare case of IgG4-related disease presenting as inflammatory pseudotumor lesion, involving the renal pelvis and also neighboring renal parenchyma.
  
  
  METHODS
  A 75-year-old man with no history of IgG4-related disease underwent computed tomography (CT) scan for evaluation of prostatic cancer. The CT scan incidentally revealed a mass lesion located at the right renal pelvis. Radiologic findings were highly suggestive of malignancy. Therefore, the patient underwent right nephroureterectomy. Microscopically, the mass lesion showed storiform fibrosis with diffuse and intense inflammatory cell infiltration. Infiltrating cells were mainly histiocytes and plasma cells. Tubulointerstitium adjacent to the lesion also showed fibrosis with abundant plasmacytic infiltration. Immunohistochemical staining revealed the presence of IgG4-positive plasma cells in both the mass lesion and tubulointerstitium (mean of 94/HPF per field).
  
  
  CONCLUSIONS
  Considering these findings, we diagnosed the mass lesion as IgG4-related inflammatory pseudotumor of the renal pelvis. In patients with renal pelvic masses, IgG4-related inflammatory pesudotumor should be considered in the differential diagnosis to avoid unnecessary surgical intervention.
authors.affiliation: Department of Urology, Chonbuk National University Medical School, Jeonju, Republic of Korea. zemizemi00@gmail.com.
authors.forename: Ho Gyun
authors.initials: HG
authors.lastname: Park
authors.affiliation: Department of Pathology, Chonbuk National University Medical School, Research Institute of Clinical Medicine and Research Institute for Endocrine Sciences, Jeonju, Republic of Korea. kmkim84@jbnu.ac.kr.
authors.forename: Kyoung Min
authors.initials: KM
authors.lastname: Kim
mesh_terms: D000368:Aged; D001706:Biopsy; D003937:Diagnosis, Differential; D006104:Granuloma, Plasma Cell / Q000175:diagnosis* / Q000276:immunology / Q000473:pathology / Q000601:surgery; D006801:Humans; D007074:Immunoglobulin G / Q000032:analysis*; D007150:Immunohistochemistry; D033162:Incidental Findings; D007674:Kidney Diseases / Q000175:diagnosis* / Q000276:immunology / Q000473:pathology / Q000601:surgery; D007680:Kidney Neoplasms / Q000175:diagnosis*; D007682:Kidney Pelvis / Q000276:immunology* / Q000473:pathology / Q000601:surgery; D008297:Male; D009392:Nephrectomy; D011237:Predictive Value of Tests; D014057:Tomography, X-Ray Computed
chemical_list: D007074:Immunoglobulin G