Extranodal Rosai-Dorfman disease of the kidney: A case report

Extranodal Rosai-Dorfman disease (RDD) of the kidney is rare, with unknown etiology. We present a case of extranodal RDD of the kidney. Imaging revealed a nodular lesion in the right renal pelvis, with accompanying pelvic dilation and parenchymal atrophy, reminiscent of immunoglobulin G4 (IgG4)-related disease. With the clinical diagnosis of suspected renal pelvic cancer, laparoscopic right nephrectomy was performed. Macroscopic findings showed a mass with a white-tan cut surface. Histological examination revealed histiocytes with emperipolesis and patchy infiltration of plasma cells, lymphocytes and foamy macrophages in a fibrocollagenous stroma. Immunohistochemically, the histiocytes were positive for S100, CD68 and CD163, but negative for CD1a, p80/ALK and phospho-p44/42 MARK (Thr202/Tyr204). IgG4-positive plasma cells were not evident.

These findings indicated that the lesion represented extranodal RDD of the kidney. No mutations of the K- and N-RAS genes could be identified in this case. Although rare, extranodal RDD should be included in the differential diagnosis of a renal pelvic mass.