Intraocular Tumor in an Aged Kyo: Wistar Rat

Abstract

An aged male rat of the Kyo: Wistar strain showed an intraocular tumor in the left globe. The neoplastic lesion consisted mostly of spindle to polygonal-shaped cells packed closely. The neoplastic cells had oval nuclei and acidophilic cytoplasm, and little atypia. The choroid was increased in thickness by neoplastic proliferation, and the neoplastic tissue extended partly beyond the sclera. The neoplastic cells were strongly positive to the S-100 protein test. Electromicroscopically, the neoplastic cells were almost unconnected to each other and stretched long processes into the intercellular space. The cytoplasm contained many organellae and dense spherical structures which were similar to melanosomes. From these findings, this tumor was diagnosed as malignant melanoma of the choroid.