Ultrastructure of feminizing testicular Leydig cell tumors.

The ultrastructure of a feminizing testicular Leydig cell tumor was analytically compared with that of the five reported feminizing neoplasms and with that of the eight published masculinizing or hormonally inactive tumors. Certain observations were noteworthy but of uncertain significance. In the current case, nuclear outlines tended to be irregular, nuclear pores were relatively few, chromatin was often uniformly dispersed, and nucleoli were frequently multiple. Membranous whorls and "myelin figures" were common. Collectively, the nuclear aberrations were noted only in the two feminizing neoplasms studied by us. Other findings in the present case included abundant endoplasmic reticulum, swollen pleomorphic mitochondria, numerous lysosomes, "dark" and "light" Leydig cell nuclei, and specialized modifications of the plasma membrane. These observations were inconstantly present in the group as a whole, irrespective of hormonal activity. Employing present methods it is not feasible to correlate the fine anatomy of testicular Leydig cell tumors with their capability of hormonal function.