SKEINOID FIBERS IN MESECTODERMAL LEIOMYOMA OF THE CILIARY BODY

Unlike smooth muscle elsewhere in the body, the smooth muscle of the i ris and ciliary body is derived from neuroectoderm (mesectoderm). Leio myomas that arise from the ciliary body, and therefore are of mesectod ermal origin, may resemble spindle cell neurogenic tumors by light mic roscopy. They show positive immunostaining for smooth muscle actin but negative staining for neural markers. Ultrastructurally, the cells ha ve the features of smooth muscle cells. The authors report a typical c ase of mesectodermal leiomyoma in a 47-year-old woman in which skeinoi d fibers, considered to be an ultrastructural marker of neurogenic spi ndle cell tumors, were frequent together with other ultrastructural fe atures often seen in neuroglial cell tumors. The findings indicate tha t mesectodermal leiomyoma is unique in its histogenesis as well as in its morphology.