Testicular stromal tumor with myofilaments: ultrastructural comparison with normal gonadal stroma.

The ultrastructural features of two testicular stromal tumors were compared with those of normal gonadal stroma. The two patients with tumor were 28 and 48 years old and had no endocrine abnormalities. No metastases or recurrences occurred after 32 and 12 months of follow-up, respectively. The tumors were composed of bundles of oval to spindle-shaped cells. Ultrastructurally, intracytoplasmic myofilaments were characteristic of the tumor cells, which resembled the contractile peritubular and interfollicular cells of normal testis and ovary. In normal testicular tissue, an intertubular mesenchymal cell may differentiate into a peritubular contractile cell or into an interstitial (Leydig) cell. Therefore, testicular stromal tumors with myofilaments may originate from an intertubular mesenchymal cell that is capable of differentiating into a cell with contractile elements.