Biliary mucoceles have become a common cause of extrahepatic biliary obstruction in dogs over the last two decades. The accumulation of mucinous bile in the gall bladder, cystic duct and common bile duct causes distension, and eventually rupture of the gallbladder. Many of these dogs present with jaundice and abdominal pain, though my impression is that we are detecting biliary mucoceles in asymptomatic dogs as well.
Biliary mucoceles are caused by mucinous hyperplasia of the epithelium of the gall bladder. The hyperplastic wall and resulting gelatinous mucocele are stellate or striated on ultrasonograhy. It is unclear how much of the peripheral material and wall thickening we see is the hyperplastic epithelium, and how much is the mucocele. The material in the gallbladder is fixed in position regardless of the position of the animal (1). The gall bladder does not contain gas, and appears distended in about 50-100% of the animals (1,3). The common bile duct may appear distended (16-61%),(1,3), with a mean diameter of 0.68 cm in those which were visible (3) . Intrahepatic bile duct distension is less common (2,3) but occurs in up to 23% of cases (3). Ultrasound is a very good technique for detecting mucoceles. All dogs were diagnosed with or suspected of having biliary mucocele prior to surgery (1,2,3).
There are many complications and associated findings in dogs with biliary mucoceles. Rupture of the gallbladder is a common sequela, and these dogs may have an interrupted gallbladder wall, hyperechoic mesentery in the cranial abdomen, and peritoneal effusion. Reports of the sensitivity, specificity and positive predictive value (85.7%, 100%, 100%) of gallbladder rupture were high in one report (3) and detection of rupture on ultrasound (1/5) was lower in another (2).
Pancreatitis can occur in these dogs pre- and post-operatively (2). Additionally, there may be hepatic abnormalities in up to 60% of dogs, such as hepatomegaly and mottled hepatic parenchyma (3). Post-operatively, the bile duct remained visible in 1/3 of dogs examined, with a range of 0.3-2.1 cm (3), but no intrahepatic bile ducts were visible.
With larger studies emerging, we are getting a better picture of our ability to diagnose biliary mucocele and its complications on abdominal ultrasound. We still have little information on the progression of mucoceles in asymptomatic dogs, both clinically and ultrasonographically.
1. Besso JG, Wrigley RH, Gliatto JM, et al. Ultrasonographic appearance and clinical findings in 14 dogs with gallbladder mucocele. Vet Radiol Ultrasound 2000;41:261-271.
2. Worley DR, Hottinger HA, Lawrence HJ. Surgical management of gallbladder mucoceles in dogs: 22 cases (1999-2003). J Am Vet Med Assoc 2004;225:1418-1422.
3. Pike FS, Berg J, King NW, et al. Gallbladder mucocele in dogs: 30 cases (2000-2002). J Am Vet Med Assoc 2004;224:1615-1622.