Extrahepatic Bile Duct Obstruction

Pathogenesis:  The etiology of this syndrome depends greatly upon the contributing cause.

Extraluminal obstructive lesions:
Neoplastic lesions	These are commonly seen from a variety of different origins.  The tumor may arise from the pancreas, bile ducts, intestine or lymph nodes.  The growth and location of the tumor may lead to obstruction of the bile ducts. See histopathology slide
Pancreatic disease	This is probably the common cause of extrahepatic biliary obstruction in dogs and may also be seen in cats.  Fibrotic, inflamed or neoplastic pancreatic tissue may compress the bile duct, or scar tissue created during the healing process may cause a stricture around the bile ducts and impede bile flow.  Pancreatic disease may also cause obstruction of bile flow in the horse, though less commonly.  Read more about pancreatitis.
Trauma	Trauma to the abdomen from automobile accidents or penetrating wounds can lead to biliary duct narrowing, facture of the liver lobes, avulsion, or cause entrapment of the whole hepatobiliary system in a diaphragmatic hernia (seen in the radiograph).
Blood Clots	Traumatic clots may induce intraluminal biliary obstruction.  This close-up gross photograph shows the biliary tract necrosis and subsequent bile leakage into the surrounding connective tissue associated with hepatic artery thrombosis.
Colonic Displacement	This is a common cause of biliary obstruction in horses.  The most common presentation is 180 degree torsion of the large colon for more than 3 days duration.  Horses will exhibit mild colic signs for 3 to 5 days accompanied by severe icterus.
Multiple biliary cysts	Biliary cysts are ductular in origin and arise from primitive ducts without functional connections to the rest of the biliary tree.  Often, these cysts are associated with cysts seen elsewhere in the body.  The cysts are generally clear, but may contain bile or blood.  Ruptured cysts may lead to fluid accumulation in the peritoneum.  This is of particular concern with a cyst containing  bile.  Acquired cysts are generally solitary, while congenital cysts tend to be multiple.  This is a contributing factor of obstruction seen only in cats.        See histopathology slide.  Click on image for a larger view.

Intraluminal obstruction
Inspissated bile	This is a particular obstruction seen in cats.   The flow of bile is impeded and forms pigmented stone.  This is either due to severe intrahepatic cholestasis from cholangiohepatitis or hepatic lipidosis. Note white arrow in the center of the image points to inspissated bile.
Choleliths	Stones can be a contributing factor or be an incidental finding.  Choleliths may form with hepatobiliary disease due to alterations of the normal hepatobiliary environment such as dehydration, bacterial infections, or anorectic derived gallbladder evacuations.  Choleliths are more commonly found in horses than any other domestic large animal.  Find out more about  Equine Cholelithiasis by clicking here.    See gross lesion
Parasitic Infections	Liver flukes are parasites that reside in the liver parenchyma and bile ducts.  They can cause obstructive biliary disease through inflammation and tissue damage.  In small animals, flukes are most common in the southern states especially Florida and Louisiana.  In ruminants, the parasites are more widely distributed.  In cats, fluke infestations may be accompanied by eosinophilic pericholangitis. Click on the image for a larger view and more information.

Species affected:  

• Large animals:   ruminants, camelids, and horses

• Small animals:  cats and dogs of varying ages

Clinical signs:  Depending upon the severity of the obstruction, signs can be acute onset or chronic.  Classic signs in small animals are similar to  other cholestatic hepatopathies. They include ascites (if there is leakage from the bile duct or gallbladder), anorexia, depression, hepatomegaly, icterus, and vomiting.  In large animals (particularly horses) signs include colic, icterus, weight loss, and poor hair coat.

Clinical Pathology:

• Increased Alanine Amino Trasferase (ALT) particularly if inflammation is involved.

• Increased Alkaline Phosphatase (AP) and/or Gamma Glutamyl Transferase (GGT).

• Hyperbilirubinemia is not always seen.

• Hypercholesterolemia, especially in cats.

• Urinalysis:  Bilirubinuria is seen quite frequently prior to hyperbilirubinemia.

• Horses often show evidence of protein-losing enteropathy with pancreatic-disease- associated biliary obstruction.  Decreased plasma protein and hypoglycemia commonly are seen.

For more information . . .

• Strombeck, D.  Strombeck's Small Animal Gastroenterology, 3rd Ed.  1996.