Mesectodermal leiomyoma of the ciliary body associated with a nevus.

A ciliary body tumor that was believed clinically to be a malignant melanoma developed in a 28-year-old woman and led to enucleation of her eye. The light microscopic appearance of the tumor was interpreted by light microscopy as a neurogenic neoplasm, possibly a choristomatous astrocytoma. Electron microscopic studies disclosed the smooth muscle origin of the tumor. Results of experimental embryologic studies performed on lower animals have proved that the neural crest contributes most of the connective tissues, "mesectoderm," of the globe and orbit in these species. The occurrence of hybrid neurogenic-myogenic tumors in the human eye supports the applicability of these embryologic discoveries to man. The association of a pigmented nevus with the present tumor is additional evidence of the neural crest origin of mesectodermal leiomyomas, since melanocytes are well-recognized descendants from the neural crest.