Light microscopic and electron microscopic changes in the livers of cats with extrahepatic bile duct obstruction.

Light microscopic and transmission electron microscopic changes were studied in the livers of 6 cats at 25 to 54 days after their extrahepatic bile ducts were experimentally obstructed. Histologic findings included various degrees of bile duct dilatation, ductular proliferation, and peribiliary fibrosis. Concentric layers of dense, birefringent connective tissue surrounded midsized bile ducts. The degrees of bile duct proliferation, hepatocellular degeneration, and bile retention were similar in each cat, but the amount of periductular connective tissue increased with chronicity of bile duct obstruction. Ultrastructural changes included marked swelling of endoplasmic reticulum and mitochondrial inner compartments, marked dilatation and distention of the canaliculi by bile casts, and numerical reduction of canalicular microvilli. Microvilli were often swollen and blunt. Mitochondria were swollen and long, and the cristae lacked normal distribution and density. Cytoplasmic accumulations of granular, electron-dense material and concentrically laminated arrays of material indicative of bile substances were also observed.