Sertoli cell tumor with benign peritoneal implants associated with gonadoblastoma.

We present a unique case of bilateral gonadoblastoma in a 23-year-old patient with Swyer syndrome. The gonadoblastoma on both sides underwent synchronous neoplastic transformation, into a stage I germinoma in the right streak gonad and a highly differentiated Sertoli cell tumor in the left one. The latter was associated with a myriad of microscopic, Sertoli cell implants on the peritoneal surface, which were considered benign as they had a high grade of differentiation, minimal proliferative activity, and an absence of invasion.