Inverted papilloma in Russian Hamster

Introduction: Cutaneous papilloma is a benign epithelial neoplasm arising in epidermal keratinocytes. Papillomaviruses belong to papovavirus family, causing single or multiple verrucous projections, variable in size, well circumscribed and keratinized. This type of tumour is common in horses, cattle and humans; less frequent in dogs and goats and rare in sheep, pigs, cats, guinea pigs and hamsters. Medical History: A 1-and a half year old entire Russian hamster was presented with a right lateral axilar subcutaneous ulcerated nodule. No other abnormalities were detected on clinical examination. The approach taken was total surgical excision. Material and Methods: The samples were fixed in 10 % buffered formalin solution for histological evaluation and were sent to the Anatomic Pathology Laboratory of the Agrarian Superior School of Viseu, in Portugal. Results: Macroscopically, the cut section revealed whitish tissues with radiated aspect, converging on the ulcerated area. Microscopic examination revealed a cystic cavity, lined by hiperplasic squamous epithelium, apparently inverted, with ortho and parakeratotic hyperkeratosis, presenting peniforme pattern. The epithelium showed acanthosis, hypergranulosis, with very large keratohyalin granules. Koilocytosis was also observed, as well as sparse eosinophilic intracytoplasmic bodies, in the cells with ballooning degeneration. Discussion and Conclusion: The histopathological features observed were compatible with the diagnosis of papilloma. However, the uncharacteristic inverted image of the epithelium, producing keratin convergent to the cystic cavity, which acquired a peniforme appearance, would fit the descriptions of inverted papilloma, although, apparently, this type of tumor, especially of such large dimensions, never been described in the hamster.

This work was supported by Portuguese Foundation for Science and Technology, Center for Studies in Education, Technologies and by Health and by strategic project PEst-OE/CED/UI4016/2011