Rosai-Dorfman disease of the genito-urinary tract: Analysis of six cases from the testis and kidney

Aims: Rosai-Dorfman disease (RDD) commonly occurs in lymph nodes, but it can also affect the genitourinary (GU) system. In a search of GU RDD, we identified three cases involving the testis and three the kidney. Methods and results: The mean age was 52.4 (35-76) years. Tumour sizes were 3.6 cm on average (1.5-4.3) for testicular cases and 15.5 cm for the renal case treated by nephrectomy. All renal cases showed typical morphology similar to nodal RDD with scattered foci of lymphocytic aggregation. In contrast, all three testicular cases had an evenly distributed lymphocyte and plasma cell infiltration with entrapment of Sertoli-only seminiferous tubules. In all six cases, immunohistochemistry (IHC) for S100 showed strong reactivity in the lesional histiocytes and highlighted the hallmark emperipolesis. One testicular case had pleural and pericardial effusions but resolved after removal of the RDD lesion. Another renal case subsequently involved bone and then lung over a 3-year period. Conclusions: RDD involving the GU system is rare with it most commonly involving the kidney followed by testis. Our three renal cases were similar in morphology to typical nodal RDD. The testicular cases had a somewhat different histological picture and needed IHC for S100 to verify the diagnosis.