Extrahepatic Biliary Obstruction

Extrahepatic biliary tract obstruction (EHBO) refers to blockage of the normal flow of bile from the liver into the intestinal tract. The most common causes of EHBO include:

• pancreatic disease
• formation of stones within the biliary system (gallstones)
• cancer involving the pancreas, bile duct, or intestine

In dogs and cats, bile (a secretion produced by the liver) moves from the bile canaliculi (very small ducts inside the liver) into progressively larger ducts that exit the liver and ultimately feed into the bile duct, and bile is then stored in the gallbladder. The gallbladder empties through the cystic duct into the common bile duct, which drains into the first segment of the small intestine, the duodenum. Bile supports digestion and contains bilirubin, a breakdown product of red blood cells.

It follows that if bile cannot reach the intestine, the animal can become severely ill. Accumulation in the bloodstream of products from red blood cell breakdown can adversely affect multiple organs, including the heart, kidneys, lungs, and brain. If bile salts are prevented from entering the intestine, digestion and absorption of fats and fat-soluble vitamins are impaired, and toxic bacteria can proliferate.

Pets with biliary obstruction are often among the most critically ill animals seen by primary care veterinarians. In dogs and cats, clinical signs associated with surgical diseases of the biliary tract and gallbladder are nonspecific and can resemble other abdominal disorders. Signs may intermittently appear and disappear over several weeks before veterinary evaluation. The most commonly reported signs include:

• reduced appetite
• vomiting
• diarrhea
• lethargy
• icterus (jaundice; yellow discoloration of mucous membranes, the whites of the eyes, and the skin)

Many animals with bile duct obstruction are not brought for examination until icterus is noted. By that point, these patients often have complete biliary obstruction and may be significantly sicker than they seem externally.

Figure 1: Lateral radiograph of a cat showing multiple radiopaque gallbladder stones and a large stone likely located in the terminal bile duct.
Figure 2: Focused ultrasound of the extrahepatic biliary tract showing a cholelith (stone) in the cystic duct with minimal acoustic shadowing and dilation of the cystic duct.

Bile duct obstruction typically causes elevated total serum bilirubin (the body’s mechanism for clearing red blood cell breakdown products) and often leads to abnormal increases in liver enzyme values. In very severe cases, pets may also show elevated kidney values, impaired clotting function, low blood pressure, high fever, and increased circulating white blood cell counts.

Radiographs (x-rays) are obtained in animals with clinical and laboratory findings suggestive of biliary disease. X-rays can help detect biliary stones and identify other abdominal conditions that may be associated with the obstruction (Figure 1). Abdominal ultrasound is highly sensitive for determining the cause of obstruction and should be performed in any patient suspected of bile duct obstruction or gallbladder disease (Figure 2).

Bile peritonitis is inflammation of the abdominal lining caused by free bile within the abdominal cavity. It results from rupture of the extrahepatic bile ducts, rupture of the gallbladder, or tears in liver lobes that allow bile to leak into the abdomen. Rupture may occur due to blunt trauma, neoplasia, gallbladder mucocele, inflammation of the gallbladder wall, or obstruction caused by gallstones, cancer, or parasites. Veterinarians may compare bilirubin levels in abdominal fluid to bilirubin levels in blood to support diagnosis. Bile peritonitis is a surgical emergency.

The primary objectives of surgery are to confirm the underlying cause, re-establish an open and functioning biliary pathway, and reduce perioperative complications. Because biliary surgery is complex, referral to an ACVS board-certified veterinary surgeon may be recommended. Potential surgical options include:

• cholecystectomy – removal of the gallbladder
• cholecystotomy – incision into the gallbladder
• cholecystostomy tube – tube placement in the gallbladder to provide drainage
• choledochotomy – incision into the bile duct, typically to remove a stone
• choledochoduodenostomy – reattaching the bile duct to a new site in the duodenum
• biliary-enteric anastomoses (cholecystoenterostomy) – connecting the gallbladder to the small intestine for permanent drainage
• choledochal stenting – placing a temporary or permanent stent in the bile duct
• laparoscopic cholecystectomy – gallbladder removal using laparoscopic surgery

After biliary surgery, many patients require intensive postoperative support in a hospital with 24-hour nursing care and may remain hospitalized for several days. Temporary feeding tubes are often needed for nutritional support. Pain control, antibiotics, and medications targeted to liver function are commonly administered.

Biliary surgery is associated with a high mortality rate (28–60%), although the rate varies substantially depending on the underlying cause.

Dogs with biliary obstruction have an increased risk of acute kidney failure related to bacterial endotoxemia. Across studies in dogs and cats undergoing extrahepatic biliary tract surgery, outcome has been associated with multiple risk factors in addition to kidney failure, including:

• septic bile peritonitis
• increased white blood cell count
• prolonged clotting times
• low blood pressure
• sepsis
• disseminated intravascular coagulation

Prognosis for dogs and cats with bile peritonitis varies widely. If bacteria are present in the abdominal fluid (septic bile peritonitis), prognosis is poor. If abdominal fluid is sterile, surgical outcomes are favorable provided the underlying cause can be corrected.

In cats, surgical biliary intervention for EHBO carries an overall mortality of about 50%, and mortality is close to 100% when cancer is the cause. Reported causes of death include clinical deterioration, bile leakage, and cardiopulmonary arrest. Cats that survive the initial surgery may develop long-term complications such as cholangiohepatitis (inflammation/infection of the liver), chronic weight loss, and recurrent obstruction.