Lymphoproliferative disease of the kidney developing in fibro-inflammatory lesion

An 80-year-old man presented with continuous spike fever and night sweats. Computed tomographic scans revealed a poorly demarcated mass in the upper part of the right kidney, which was resected. At surgery, tumorous lesions were not found in the abdominal cavity. Serum IgG4 level measured after surgery was 40.1 mg/dl. Macroscopically, renal parenchyma of the upper part was replaced by an irregularly shaped grayish-white lesion of elastic, firm consistency. Histologically, the lesion consisted mostly of fibrous tissue in which small lymphoid cells, often with formation of aggregates, were evident. IgG4-positive plasma cells were few in number. Careful macroscopic examination revealed several minute nodules, which histologically consisted of large lymphoid cells, small lymphoid cells, and macrophages. These large lymphoid cells were positive for CD20 and contained Epstein-Barr virus (EBV) genome. Taken together, a diagnosis of EBV-positive B-cell lymphoproliferative disease (LPD) developing in inflammatory pseudotumor (IPT) of the kidney was made. This is the first report of B-LPD in IPT of the kidney. In addition, a presence of EBV in renal lymphoma cells has not yet been reported.