Ovarian fibroma with Leydig cell hyperplasia of the adjacent stroma: a light and electron microscopic study.

A virilizing left ovarian tumor removed from a 58-year-old woman was studied by light and electron microscopy. Histologically, the tumor was an ovarian fibroma around which Leydig cells, but no Sertoli cells, proliferated at a distance from the hilus. Although the fibroma itself did not contain Leydig cells, several Leydig cells were observed intermingled with ovarian stromal cells in the cortical tissue compressed by the fibroma. Ultrastructurally, in addition to mature Leydig cells with typical steroid-producing--cell features, immature cells with less-developed smooth endoplasmic reticulum and elementary tubular inclusions were identified. These light and electron microscopic findings suggest that the Leydig cells may have differentiated from ovarian stromal cells surrounding the fibroma. If so, this case should be distinguished from neoplastic disorders such as hilar cell tumors or stromal-Leydig cell tumors and be classified in the category of ovarian tumors with functioning stroma containing Leydig cells.