Secondary Biliary Hepatic Fibrosis Caused by Cholelithiasis in Two Horses

Cholelithiasis is a rare condition in horses that may cause biliary obstruction and consequent hepatic fibrosis. Two horses with a history of icterus were presented for clinical examination. Horse #1, an 18-year-old crossbred gelding, presented inappetence, head pressing, and abnormal gait in both pelvic limbs. Horse #2, a 14-year-old crossbred stallion presented severe cachexia. At necropsy, the liver was firm with prominence of the lobular pattern and a reticular whitish aspect. The common hepatic duct of horse #1 and horse #2 contained, respectively, a 6 cm diameter and numerous 2.5-5 cm diameter choledocholiths. Bile ducts proximal to these were distended with numerous choleliths. Microscopically, diffuse bridging portal fibrosis, feathery degeneration of hepatocytes and bile microgranulomas were observed, besides Alzheimer type II astrocytes in the telencephalic cortex. Secondary biliary hepatic fibrosis may cause hepatic encephalopathy and icterus in horses. Histologically, bridging portal fibrosis, feathery degeneration of hepatocytes and bile microgranulomas are characteristic of this condition.