Equine Cholelithiasis and Choledocholithiasis

Introduction:  Gall stones occur more commonly in horses than in any of the other domestic large animals.  They can occur secondary to hepatic pathology or as the primary cause.  The terminology is very accurate in the description of the location of the stone.  Cholelithiasis indicates stones in either the duct or the gall bladder.  Choledocholithiasis refers to stones found in the common bile duct, and is the most common cause of biliary obstruction.  Hepatolithiasis is a condition in which stones are found in the intrahepatic bile ducts.  

Pathogenesis:  The exact pathogenesis of cholelith formation is unknown, though several possibilities exist.  Ascaridiasis, ascending infections, biliary stasis, change in the bile composition, or a foreign body may all be contributing factors to the formation of stones in the biliary tree.  Analysis of choleliths collected from horses indicates the composition varies in combination of bilirubin, bile pigments, cholesterol esters, esters of colic and carboxylic acids, calcium phosphate, and sodium taurodeoxycholate.

Gross Pathology:  Necropsy findings generally revel an enlarged liver, however, reports of shrunken livers have also been made.  In cases in which the liver is enlarged, the liver will be firmer than normal and will vary from red to green-brown.  The hepatic ducts and common bile ducts are generally dilated and may contain visible calculi. Click on the image (right) for a larger view.

Histopathology:  The most common reported finding is periportal fibrosis, accompanied by bile duct stasis and hyperplasia of the ducts.

Clinical Signs:  Presenting clinical signs will vary depending on the degree of obstruction due to cholelithiasis.  

• Intermittent colic, pyrexia, and icterus are common presenting clinical signs.  Pyrexia will be more pronounced if cholelithiasis is accompanied by hepatitis. 

• Less common clinical signs are hepatic encephalopathy, hepatic photosensitization, and weight loss with chronic disease.

Clinical Pathology:  

• Elevations in liver enzymes, especially alkaline phosphatase (AP), aspartate aminotransferase (AST), and gamma glutamyltransferase (GGT).

• Both total and direct bilirubin will be elevated.  In general, cholestasis should be expected if greater than 30% of the increase in bilirubin is due to direct bilirubin.  

• Serum bile acids will be elevated.  

• Less common clinical findings include hyperammonemia, bilirubinuria, prolonged OSPT and APTT, neutrophilic leukocytosis, hyperglobulinemia, and hyperfibrinogenemia.

For more information . . .

• Robinson, N. Edward, Current Therapy in Equine Medicine 4, 1997, pp 216-217.
• Smith, Brad P., Large Animal Internal Medicine, 1996.