An Ozark hellbender (Cryptobranchus alleganiensis bishopi) with multiple, large, warty skin lesions was collected in the Spring River, Fulton County, Arkansas, in 1994. The specimen was a female, 560 mm in total length, and had a mass of 1,947 g. Tissues were formalin-fixed, and three lesions were processed for histopathology. The normal skin at the tumor margins had a stratified squamous epidermis overlying a loose, well-vascularized, heavily pigmented dermis. Poison glands and mucous glands extended from the epidermis into the dermis. The lesions, in contrast, were masses of epidermal cells up to 100 times thicker than the normal epidermis. They consisted of long, thick, branching epidermal pegs separated by thin fibrovascular papillae. The base of the lesions and all pegs had sharp boundaries bordered by a basement membrane, ruling out invasion. Tumor cells were differentiated into scattered glandular structures suggestive of dermal glands. Cells within the pegs were poorly organized. Nuclei usually contained basophilic granules. Mitotic figures were numerous. By electron microscopy, the cells appeared to be pulling apart except where held together by desmosomes. The sum of the above observations is consistent with a pathological diagnosis of epidermal papilloma.

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