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.