Iridociliary adenoma with ballooning change in a dog

An ocular mass was noted in the right iridociliary region of a 13-year-old male beagle dog. The right eyeball was surgically removed. Histopathologically, the mass was located mainly in the ciliary body and appeared to be continuous with non-pigmented epithelial cells. The polygonal neoplastic cells proliferated in sheets with periodic acid-Schiff-positive basement membrane material. Neoplastic cells had small round nuclei with no atypia or mitosis, and abundant, pale eosinophilic, granular, and rarified cytoplasm displayed ballooning change. No invasive growth or metastasis was observed. Immunohistochemically, the cells were positive for vimentin, neuron-specific enolase, and S100, and negative for cytokeratin AE1/AE3, Iba-1, CD204, MelanA, Sox10, and PNL2. Based on these findings, the lesion was diagnosed as an iridociliary adenoma with ballooning change.