2013 Volume 32 Pages 49-54
Corneal dermoid and squamous epithelial tumors arising from the cornea, sclera and eyelids are known ocular tumors in rats. However, tumors arising from the intraocular tissues are rare, especially melanoma. In this paper, we report a spontaneous intraocular malignant melanoma in a SD rat. A mass was first recognized by clinical examination in the right iris at week 88 of age. As the mass grew, the affected eyeball protruded, a scab was formed on the whole cornea, and the mass was finally exposed by corneal perforation 1 week before the scheduled sacrifice (week 109 of age). In the histopathological examination of the H & E stained specimen, tumor cells occupied the whole ocular space, having a spindle- or oval-shaped nucleus and eosinophilic cytoplasm showing a whorl growth pattern. Highly atypical cells and mitotic figures were occasionally seen. Tumor cells contained occasionally brown granules in their cytoplasm, and the granules were demonstrated to be melanin pigments by Fontana-Masson staining. Therefore, the tumor was diagnosed as melanotic melanoma, which likely originated from the iris or ciliary body. Distant metastasis was not found.
