Inflammatory Pseudotumour in Common Seal (Phoca vitulina): A Case Report

Pinnipeds, including seals, sea lions and walruses, are marine mammals susceptible to a variety of pathological conditions. Although neoplastic lesions in these species are receiving increased attention, relatively little information is available compared to neoplastic studies in domestic animals. In this report, a 19-year-old intact male common seal (Phoca vitulina) presented with a chronic ulcer on the fifth phalanx. Radiological examination revealed cortical reaction with significant osseous alterations in this animal and in another companion common seal, although the flipper appeared macroscopically normal. Histopathological analysis identified nests of fusiform to oval cells accompanied by mixed lymphohistiocytic inflammation. Immunohistochemical evaluation demonstrated that neoplastic cells were positive for vimentin, α-smooth muscle actin and calponin. Negative results were for pancytokeratin, desmin, CD31 and IRF4, supporting a myofibroblastic phenotype. The Ki-67 proliferation index was low (5%). All histopathological and immunohistochemical features were consistent with an inflammatory pseudotumour. Microbiological culture isolated Vibrio alginolyticus from the lesion, a marine and fish pathogen previously linked to chronic cutaneous infections in humans. No herpesviral DNA was detected by polymerase chain reaction (PCR). Chronic bacterial infection and repeated microtrauma may have contributed to lesion development, consistent with reports of inflammatory pseudotumours arising in the context of persistent inflammatory stimuli.