Gross, cytological and histological features of a cholangiocarcinoma, with immunolabelling of cytokeratin 19, in a bronze-winged parrot (Pionus chalcopterus)

An adult bronze-winged parrot (Pionus chalcopterus) was presented for post-mortem examination following death without antecedent clinical signs. Macroscopically, the liver was expanded by a 14 × 12 × 10 mm, off-white to grey, infiltrative mass with 3-8 mm diameter nodular masses on the serosa of the duodenum. Cytology of impression smears of the hepatic mass revealed a monomorphic population of epithelial cells, arranged in cohesive clusters, occasionally with an acinar-like arrangement. Histologically, the neoplasm was unencapsulated, infiltrative, well-demarcated and moderately densely cellular. Neoplastic cells were arranged in well-defined, variably sized acini and tubules that were supported by a fine collagenous stroma. Acini and tubules frequently contained intraluminal eosinophilic proteinaceous material. Neoplastic cells were small to moderately sized and were generally columnar or cuboidal with well-delineated cell boundaries and a small amount of eosinophilic to basophilic cytoplasm. The nuclei were round, frequently basally located and had densely stippled chromatin and usually a single, prominent, magenta nucleolus. There were two mitoses in 10 high-power fields (2.37 mm²). Vascular invasion was observed and metastatic nodules of similar neoplastic cells were present on the duodenal serosa. Immunohistochemical labelling for cytokeratin 19 revealed weak to moderate, punctate cytoplasmic expression in <10% of neoplastic cells. Macroscopically, cytologically and histologically the neoplasm was consistent with a cholangiocarcinoma.