Right hepatic lobe atrophy in horses: 17 cases (1983-1993).

The case records of 17 horses with atrophy of the right hepatic lobe were reviewed. Fifteen horses had signs of colic. Two horses had clinical problems that were unassociated with gastrointestinal tract disease. Ages ranged from 5 to 30 years (mean, 12.6 years) and there was no breed or sex predisposition. In clinically normal horses, the right hepatic lobe constitutes half of the total liver weight. The right hepatic lobe in the 17 horses in this study ranged from 11.0 to 38.3% of the total liver weight (mean, 27.8%). Findings on histologic examination of hepatic tissue from horses in the study were variable. Most had loss of hepatocytes, with condensation of hepatic stroma and thick wrinkled hepatic capsules. Additional findings in the horses included torsion of the large colon (15), ileus without gastric rupture (3), typhlocolitis (2), colon infarction secondary to mesenteric strangulation (1), colon infarction secondary to sepsis (1), strangulation of the small intestine from pendulous lipoma (1), and nephrosplenic entrapment (1). No morphologic evidence of angiopathic disease involving the arterial or venous blood supply to the right hepatic lobe was found. Additionally, there was no evidence of biliary tract disease in this portion of the liver. Right hepatic lobe atrophy is believed to result from long-term, insidious, compression of this portion of the liver from abnormal distention of the right dorsal colon and base of the cecum. The practice of feeding horses high-concentrate, low-fiber diets may contribute to atony of the right dorsal colon, with resultant distention that compresses the right hepatic lobe against the rigid, visceral surface of the diaphragm.