Angiokeratomatous papilloma associated with papillomavirus in a calf

A female 8-month-old Simmental calf was presented with a history of a gradually enlarging mass in the ventral abdominal skin since 4 months of age. The mass was well circumscribed, lightly pigmented, and rough surfaced with many fine fissures and was attached to the skin by a relatively broad pedicle. On cut section, there was a border between the reddish-black stroma and overlying epithelium, including hemorrhagic foci of variable sizes. Histologically, the tumor was papillomatous with angiokeratomatous features and irregular hyperplasia with epidermal rete ridges and dilated vascular channels filled with blood in the superficial dermis. In the epidermis, orthokeratotic hyperkeratosis, variably sized keratohyalin granules, and many koilocytes, some of which had papillomavirus (PV) genus-specific structural antigen-positive nuclei, were also observed. Cells lining the dilated vascular spaces were positive for vimentin and alpha-smooth muscle actin but negative for factor VIII-related antigen, desmin, and PV. The lesion was regarded as an angiokeratomatous papilloma and was similar to other angiomatous lesions.