[A Case of Bilateral Renal Tumors, Renal Cell Carcinoma and IgG4- Related Retroperitoneal Fibrosis].

A 69-year-old man was referred to our hospital for a right renal pelvic tumor noted on a computed tomography (CT) scan at another hospital. Urine cytology was negative. Dynamic CT revealed a right renal pelvic tumor and, accidentally, a small left renal tumor enhanced in the arterial phase and washed out in the venous phase. No defect in the urinary tract was found on retrograde urography, and upper urinary cytology was negative. The patient's level of IgG4 was high, but other tumor markers were negative. We judged the right renal pelvic tumor to be an extrapelvic lesion, probably IgG4-related disease. We temporarily followed up the right renal pelvic tumor but performed retroperitoneal left partial nephrectomy for the small left renal tumor. Histopathology led to a diagnosis of clear cell renal cell carcinoma. Follow-up CT showed no change in the right renal pelvic tumor. We diagnosed the right renal tumor as IgG4-related disease and began steroid administration. After one monthof administration, the IgG4 value and the size of the tumor were reduced.