Metastatic cholangiocarcinoma in a cow presenting as suspect bovine tuberculosis in Ireland

Cholangiocarcinoma is a malignant tumour of bile duct epithelial cells, an uncommon primary hepatic neoplasm in cattle. A 9‐year‐old Simmental cow presented with watery diarrhoea, crusty skin lesions, loss of appetite and hepatomegaly. Suspecting severe liver disease, the cow was euthanased due to poor prognosis. During gross postmortem examination, large numbers of multifocal to coalescing nodules often with soft necrotic centres ranging from miliary to 7 cm in size were present in the liver, lung, mesentery, peritoneum and lymph nodes. These features were suggestive of bovine tuberculosis. However, direct tissue smears stained by Ziehl Neelsen stain were negative for the presence of acid‐fast bacteria, and subsequent histopathological and immunohistochemical investigations confirmed the presence of metastasizing cholangiocarcinoma. This case reminds clinicians and pathologists to keep an open mind during the diagnostic process and serves to highlight the value of histopathology in diagnosing seemingly characteristic gross lesions.