Bile duct hamartoma in a dog.

An 11-year-old female Collie presented with a significantly increased abdominal circumference. Computed tomography of the abdomen revealed that the left lateral lobe of the liver contained a large mass, which was excised via laparotomy. Histologically, many small, dilated, cystic luminal structures were anastomosed and connected to a net-like structure. Immunohistochemistry revealed cytokeratin 19-immunopositive areas, representing bile duct structures in the cystic lumen. Based on these results, the tumour was diagnosed as a bile duct hamartoma. To our knowledge, this is the first report of a bile duct hamartoma in a dog.