Unusual gonadal stromal tumor of the testis. Case report with ultrastructural observations.

Ultrastructual observations on an unusual gonadal stromal tumor of the testis in a 4-year-old boy with gynecomastia revealed that the tumor cells lacked the abundant smooth endoplasmic reticulum usually found in neoplastic and nonneoplastic Sertoli and Leydig cells. The cells were rich in cytoplasmic microfilaments, with localized dense areas of the type seen in smooth muscle cells as well as intracytoplasmic lipid droplets. It is concluded that the tumor cells show important similarities to the immature fusiform interstitial cells and the peritubular contractile cells present in the normal testis.