Mesectodermal leiomyoma of the ciliary body. An ultrastructural study
T. Takagi, Y. Ueno and N. Matsuya
Electron microscopic observation of a mesectodermal leiomyoma of the
ciliary body, in which clear perinuclear halos were present, revealed the
ultrastructural characteristics of smooth muscle cells, which include
myofilaments with fusiform densities, dense attachments, external lamina,
and pinocytotic vesicles. In addition, fibrillary cytoplasmic processes
containing large numbers of myofilaments with fusiform densities were
notably arranged in a neurogenic pattern when observed under a light
microscope. These are characteristic of and specific to mesectodermal
leiomyomas. Masses or cords of large, polygonal cells with clear halos
surrounding the large, round-to-oval nuclei were found to contain only a
few myofilaments. Such features are atypical of mesectodermal leiomyomas.
Melanocytes were scattered throughout the tumor, providing additional
evidence for the neural crest theory of origination of mesectodermal
leiomyomas, since melanocytes are well-recognized descendants of the neural
crest. A small number of lipid droplets, abundant lysosomes, and,
occasionally, phagosomes were also observed in the cells of this
mesectodermal leiomyoma.
