Morphological characterization of ductular reactions in canine liver disease.

Intrahepatic bile duct proliferation (ductular reaction) was examined histologically, immunohistochemically and ultrastructurally in four cases of canine liver disease, diagnosed as chronic hepatitis, liver fibrosis, cirrhosis and cholangiocellular carcinoma. Ductular reaction was a common finding in all cases. Most of the proliferated bile ducts were similar to normal bile ducts. In addition, duct-like structures occurred, consisting of hepatocytes and of intermediate cells that had phenotypic characteristics of both cholangiocytes and hepatocytes. The proliferated bile ducts were immunohistochemically negative for proliferating cell nuclear antigen (PCNA) and stem cell factor (SCF). The proliferated bile ducts in these four cases of canine liver disease thus showed both typical ductular reactions, such as elongation and tortuosity of the existing bile ducts, and atypical ductular reactions resulting from metaplasia of hepatocytes.