Malignant sex-cord stromal tumor of the testis: report of a case with special reference to its unusual intracytoplasmic substructures.

A case of malignant sex-cord stromal tumor (gonadal stromal tumor) in the left testis of a 42-year-old man with no sign of hormonal abnormality is reported. Histologically, a large portion of the tumor was composed of solid nests of round cells with a moderate amount of eosinophilic cytoplasm, but some areas contained small spaces somewhat resembling Call-Exner bodies and/or the follicular structures of granulosa cell tumors. In general, however, the tumor cells did not show a clear-cut differentiation into either Sertoli cells or granulosa cells. The tumor, because of its high mitotic rate, lymphatic, venous and capsular invasion, and metastasis to the para-aortic lymph nodes, was considered to be malignant. We simply designated this tumor, therefore, as a malignant sex-cord stromal tumor. An ultrastructural study revealed unique intracytoplasmic bodies composed of multiple stacks of tubular structures which superficially mimicked annulate lamellae. No lipid droplets, Reinke's crystalloids or Charcot-Böttcher filaments were seen. The rarity of the tumor and the presence of unusual substructures prompted us to report the case.