Malignant intraocular teratoid medulloepithelioma in three dogs.

Tumors derived from the fully differentiated ciliary epithelium include adenomas and adenocarcinomas. Many such tumors in animal eyes have been reported. Medulloepitheliomas derived from the primitive medullary epithelium of the optic cup have rarely been seen in animal eyes. A teratoid variant of medulloepithelioma, recently described in human eyes, has also been seen in canine and bovine eyes. These tumors contain tissues resembling brain, cartilage, rhabdomyoblasts, and primitive mesenchyme, in addition to the poorly differentiated neuroepithelial and neuroblastic elements characteristic of malignant medulloepitheliomas.