Peribiliary cysts associated with severe liver disease: A previously unrecognized tumor in a lion (Panthera leo)

A 13-year-old male lion (Panthera leo) from Dae Jeon Zoo, Republic of Korea, presented with clinical signs of lethargy and anorexia. Despite treatment with antibiotics and fluid therapy, the lion died 6 days after initial presentation. Postmortem examination revealed multiple masses measuring 5-10 cm in diameter and cysts throughout the liver. A diagnosis of spontaneous peribiliary cysts was made on the basis of microscopic lesions as well as special staining and immunohistochemical characteristics. Histologically, the neoplasm was surrounded and composed of compact collagenous tissue. The inner cystic single layer resembled biliary mucosa and was composed of cuboidal or flattened epithelial lining that was strongly immunopositive for cytokeratin AE1/AE3. This layer was surrounded by fibrous tissue that stained blue by Masson's trichrome staining. Given the presence of multiple organized cysts in the liver, the lesion was consistent with peribiliary cysts. To the authors' knowledge, this is the first report of peribiliary cysts in an animal.