Choleliths are calculi that develop within the biliary tree. Their formation can be associated with signs of liver disease, and if they are large enough to obstruct the common bile duct then liver failure can occur. Biliary calculi formation commonly occur as a consequence to other hepatobiliary diseases, such as ascending bacterial cholangiohepatitis.
Bilirubin is excreted into the biliary system in a conjugated (direct) form, it is conjugated with glucuronate. It is thought that the enzyme β-glucuronidase increases in bile under certain disease states. This enzyme frees bilirubin from its conjugated form, allowing it to bind with calcium. This calcium bilirubin can precipitate to form choleliths, particularly when biliary flow is slow.
The diagnosis is based on signalment (middle aged horses 6-15 years of age most common; broodmares more susceptible), clinical signs, lab work and ultrasound. Clinical features could include colic, icterus, fever and weight loss. Signs will be persistent if the common bile duct is blocked. Lab features include large elevations in GGT, alkaline phosphatase, and GLDH. Total bilirubin will be elevated, and the percentage of conjugated of total bilirubin will typically exceed 25%. Bile acids will also be elevated. Ultrasound may pick up choleliths, understanding that a large proportion of liver is not seen due to its central position in the abdomen. Choleliths can be palpated within the liver at surgery.
Treatment is often focused on management of primary or concurrent liver diseases, such as infectious cholangiohepatitis. This usually involves a prolonged course of antibiotics and general hepatic supportive care. There are techniques to remove choleliths surgically.
Tags: Liver