Rhabdomyosarcomatous differentiation in malignant intraocular medulloepitheliomas

Four intraocular medulloepitheliomas have been found to contain rhabdomyosarcomatous elements. In three tumors, typical rhabdomyoblasts containing myofibrils with cross striations could be easily identified by light microscopy, but, in one case, electron microscopy was necessary to establish the rhabdomyosarcomatous nature of large ganglioform cells contained among the medulloepitheliomatous elements. In two of the tumors, there were islands of hyaline cartilage within the tumor and in one of the others, in which only a portion of the original specimen was available for study, and in which no cartilage was found in the primary tumor, the neoplasm recurred in the orbit as a chondrosarcoma. In all cases, there was a remarkable blending of all components of the tumors—the medulloepitheliomatous, the mesenchymal, and the undifferentiated. Some suggestions as to the embryogenesis of these teratoid medulloepitheliomas are discussed.