[A case of stromal tumor of the testis with peculiar crystalloid structures].

A case of poorly differentiated stromal tumor occurring in the left testis of a 37-year-old man is reported. Microscopically, the tumor was composed of polygonal cells arranged in a sheet-like pattern. The ill-defined cytoplasm contained disease-resistant PAS positive granules. Ultrastructurally, peculiar crystalloid structures were found in the cytoplasm of the tumor cells appearing in tubular, beaded or lamellar form and connected with the nuclear membrane as well as with the rough endoplasmic reticulum. These are somewhat similar to annulate lamellae. Interdigitation of the plasma membranes and zonula adherens was observed. Basal laminae were recognized in parts. These findings suggest that this tumor is a case of poorly differentiated gonadal stromal tumor showing a tendency to differentiate into Sertoli's cells.