Surgery for the biliary tract is considered amongst the most technically challenging of the intra-abdominal procedures and hence is not routinely performed by practitioners. However, there are some basic principles of biliary tract surgery that all experienced veterinarians should be familiar with. In addition, it is necessary for vets in practice to be comfortable with the decision-making process for patients with biliary tract disease in order to provide their clients with the best possible advice about management.

Anatomy of the Biliary Tree

Bile ductules coalesce in each liver lobe to produce a lobar duct. The lobar ducts converge at the hilus of the liver to join the cystic duct and proceed towards the duodenum as the common bile duct. Flow through the common bile duct is controlled by the duodenal sphincter (sphincter of Oddi). When the sphincter is contracted, dilute bile flowing from each liver lobe is diverted retrograde into the gall bladder, and concentrated. After eating, the sphincter relaxes and the gall bladder contracts, enabling flow of concentrated bile into the duodenum to aid digestion. In the cat, the pancreatic duct and bile duct enter the duodenum together, which is an important factor when considering the most appropriate form of biliary diversion to pursue. In the dog, the pancreatic and bile duct are separate, and there is an accessory pancreatic duct also. The gall bladder is supplied by the cystic artery, a branch of the hepatic artery, that follows the cystic duct from the porta hepatis.

Gall Bladder Mucocele

Previous reports suggest that gallbladder mucoceles are the result of dysfunction of mucus-secreting cells within the gallbladder mucosa. According to Pike et al. (2004)⁴, "these cells undergo cystic hyperplasia, and the cysts and individual glands become dilated by mucus with a similar histologic appearance to that within the gallbladder lumen. The inciting cause of mucus hypersecretion is unknown and may be multifactorial."

The diagnosis may be made incidentally during evaluation for other problems, or may be based on presence of abdominal pain, elevated liver enzymes and abnormalities on abdominal ultrasound. The sonographic features of gall bladder mucocele have been well-described and include evidence of organizing mucus accumulation within the gall bladder, showing a stellate or finely striated appearance and lacking the gravity-dependent movement of bile sludge.² Thickening and edema of the gall bladder wall and peritoneal fluid accumulation suggest a more advanced stage of the disease. Overt bile peritonitis, hyperbilirubinemia and systemic signs of disease indicate a surgical emergency. Cocker spaniels and Shetland sheep dogs are over-represented amongst reported breeds.^1,4,5 Results from Pike's retrospective study of 30 dogs⁴ suggest that surgical cholecystectomy is an effective treatment for gall bladder mucocele. Anecdotal observations show that the mortality rate for emergency cholecystectomy in patients with gall bladder rupture is higher than that for elective surgery (68% versus 32%)¹ leading many specialists to recommend cholecystectomy in all dogs diagnosed with gall bladder mucocele. An alternative in the asymptomatic dog with minimal or no signs is cautious observation with serial biochemistry and sonography. If the gall bladder wall thickens, or the liver enzymes become elevated, elective surgery should be scheduled prior to gall bladder rupture or biliary obstruction.

Biliary Trauma

The most common presenting sign for biliary trauma is bile peritonitis that may not be diagnosed for some days following injury. The bile duct most commonly ruptures at the junction between the cystic ducts and hepatic lobar ducts, although damage can be seen at any level. While preoperative diagnosis of biliary rupture is relatively straightforward, determination of the level of leakage can be extremely difficult and surgeons exploring patients with bile peritonitis should be prepared to carefully evaluate all segments of the biliary tree and be equipped to perform a repair at potentially any site. Facilities must be available for supportive treatment of these patients before and after surgery, as this is a significant prognostic factor for survival.³

Necrotizing cholangitis may be seen as a peracute phenomenon or as a chronic result of bacterial cholangiohepatitis. The gall bladder may appear edematous and inflamed, overtly necrotic or fragmented. Bile staining of peritoneal tissues around the gall bladder or bile ducts suggests impaired integrity of the wall and impending biliary rupture. In some instances, the gall bladder has already suffered an explosive rupture. Removal of the gall bladder and ligation of the cystic duct is indicated in these cases.

Laparoscopic cholecystectomy was one of the first minimally invasive procedures performed in humans, and is becoming more widespread for treatment of gall bladder disease in dogs. A recent report showed laparoscopic cholecystectomy to be successful in a series of dogs with gall bladder mucoceles.³

Bile Duct Obstruction and Biliary Diversion

Obstruction of the bile ducts may occur at any level from the liver lobe to the duodenal papilla. Bile duct obstruction amenable to surgical correction usually occurs at the level of the pancreas or duodenum, and results from extraluminal pressure (acute or chronic pancreatitis) or intraluminal choleliths or bile sludge.

A range of biliary diversion techniques are available, depending on the nature and level of obstruction. The most common traditional method is cholecystoduodenostomy, where an end to side anastomosis is created with the descending duodenum. This technique can be life saving, but is associated with a high complication rate, including ascending cholangiohepatitis. For obstructions occurring at the level of the duodenum, sphincterotomy or stent placement are options that preserve normal biliary anatomy and function, while facilitating bile flow into the duodenum. Repositioning of the bile duct into the duodenum by means of biliary neostomy is possible for very distal obstructions, but requires surgical magnification and advanced skills to avoid stricture formation. Placement of stents for biliary obstruction has been reported, using either self-securing expandable stents or red rubber catheters sutured to the duodenal mucosa.

Keys to Surgical Success

The most important factors that dictate success when performing biliary tract surgery in dogs and cats are:

1.  Good surgical decision-making. Is this the appropriate procedure for this patient?

2.  Careful perioperative monitoring and support, including blood products

3.  Excellent lighting

4.  Surgical assistant and retraction

5.  Sound knowledge of surgical anatomy

6.  Correct surgical instruments (atraumatic grasping and dissecting forceps, long-handled instruments for deep-chested patients, probes and catheters to test bile duct patency and act as stents during biliary repair)

References

1.  Aguirre AL, Center SA, Randolph JF, et al. Gallbladder disease in Shetland Sheepdogs: 38 cases (1995–2005). J Am Vet Med Assoc 2007;231:79–88.

2.  Besso JG, Wrigley RH, Gliattov JM, et al. Ultrasonographic appearance and clinical findings in 14 dogs with gallbladder mucocele. Vet Radiol Ultrasound 2000;41:261–271.

3.  Mehler SJ, Mayhew PD, Drobatz KJ, et al. Variables associated with outcome in dogs undergoing extrahepatic biliary surgery: 60 cases (1988–2002). Vet Surg 2004;33:644–649.

4.  Pike FS, Berg J, King NW, et al. Gall bladder mucocele in dogs: 30 cases (2000 –2002). J Am Vet Med Assoc 2004;224:1615–1622.

5.  Worley DR, Hottinger HA, Larence HJ. Surgical management of gallbladder mucoceles in dogs: 22 cases (1999–2003). J Am Vet Med Assoc 2004;225;1418–1422.