Plexiform tumors of the uterus: ultrastructural study

Two cases of plexiform tumor of the uterus are presented. Both were incidental microscopic findings in leiomyomatous uteri and had the typical branching cords of small, polygonal cells with scanty cytoplasm and vesicular nuclei. Ultrastructurally the cells had features of smooth muscle differentiation such as actin-like filaments, dense bodies, peripheral dense plaques, pinocytotic vesicles, and incomplete basal lamina. Their close relationship to capillaries resembled the structure of glomus tumor and vascular leiomyoma and suggested histogenetic kinship among these neoplasms.