The term “gallbladder mucocele” (MC) commonly refers to an over-distended gallbladder filled with an immobile mixture of mucus and inspissated bile that can cause obstruction of the biliary tract.
Gallbladder mucoceles are commonly diagnosed and a reason for biliary tract surgery in dogs. Its etiology is unclear, however it is believed to be related to many other disorders of the biliary tract. Most dogs with MC are asymptomatic and they are diagnosed while performing an abdominal ultrasound for other reasons; however, these patients are at risk of further complications such as gallbladder rupture, peritonitis, sepsis and related coagulopathies, and should be considered for surgical intervention. Some MC produce severe clinical signs and they need to be treated promptly.
Predisposing factors
It has been found that MC usually occur in geriatric patients with a median age of 10 years. No sex predisposition has been noted. Smaller dogs (<20 kg) seem to be more commonly diagnosed, but could occur in any size breed. Breeds like Miniature Schnauzer, Cocker spaniel, Broder collie and Shetland sheepdog are among the high-risk breeds, but other breeds like terriers, maltese, shih Tzu, Bichon frise may be affected. Felines can also be affected although is less common.
Coinciding pathologies
Gallbladder mucoceles have been found to occur with cholelithiasis, cholangitis, cholecystitis, extra- hepatic bile duct obstruction, neoplasia obstructing the biliary tract, pancreatitis, hyperadrenocorticism, diabetes mellitus, hyperlipidemia and hypothyroidism. These last three conditions can affect bile acid production.
Dogs with MC should be tested for hyperadrenocorticism, hypothyroidism, and diabetes mellitus, as these conditions are commonly diagnosed together with MC.
Clinical pathology
Although not specific for MC, the most common abnormalities are:
· Stress leukogram (neutrophilic leukocytosis)
· Hyperbilirubinaemia
· Increase in; ALP (11-15x), ALT (4-6x), GGT (2-8x), Cholesterol.
· Bacteria have been reported in up to 30% of cases with E. coli, Streptococcus and Enterococcus often isolated.
Imaging
Ultrasound is the gold standard diagnostic method for a definitive MC diagnosis. This is because ultrasound can clearly evaluate the gallbladder wall and its lumen, including evaluation of the cystic and common bile duct, and the hepatic parenchyma.
Ultrasound can also differentiate MC from other pathologies associated with the same clinical signs, such as pancreatitis with extrahepatic biliary obstruction, cholecystitis, cholelithiasis and acute hepatitis.
Ultrasound is also sensitive to detect abdominal free fluid when gallbladder rupture is suspected, and ultrasound-guided abdominocentesis can be used to evaluate the fluid IMPORTANT: Cholecystocentesis is not recommended in cases of gallbladder mucoceles.
Classification
In 2013, Choi, J, Et al, published a classification for gallbladder mucocele in dogs based on a retrospective study. This classification based on its content and shape includes 6 types of mucoceles, and being type 2 the most common in this study.
Type 1, immobile echogenic bile
Type 2, incomplete stellate pattern;
Type 3, typical stellate pattern;
Type 4, kiwi like pattern and stellate combination;
Type 5, kiwi like pattern with residual central echogenic bile;
Type 6, kiwi like pattern
A lot of sonographers also categorize the gallbladder mucoceles based on appearance and on how the sediment is presented and if any changes are associated to it:
Emerging or "immature" mucocele, (type 1) when there is evidence of stationary sediment, and organized bile sludge that only encompasses a small portion of the gallbladder and some bile is still observed surrounding it.
Mucocele: when the gallbladder is almost completely or completely filled with a stellate appearing sludge that is non-gravity dependent with attachments to the wall. A dilated cystic duct might be present. (Type 3).
Inflamed mucocele: Usually pain is present while scanning, the gallbladder wall is thickened and the peritoneal fat surrounding it is echogenic. A double-layer appearance of the wall can be observed especially when free fluid is present and this could be a concern as rupture is possible.
Treatment: Cholecystectomy is usually the preferred treatment for gallbladder mucocele, because of the high risk of rupture and secondary peritonitis. Medical therapy is often ineffective once the mucocele has formed.
Duodenostomy and catheterization of the bile duct is sometimes performed at the same time to flush the bile duct retrograde. Culture of the gallbladder content should be performed to determine if an infection is present. Liver biopsy should be recommended for histopathological evaluation. And if the gallbladder has ruptured, abdominal lavage is warranted.
Post-operative care should include:
• Antibiotics if culture is positive (4-6 weeks)
• Ursodeoxycholic acid (Ursodiol) (10-15mg/kg SID) for long term treatment to ensure choleresis
• Low fat diet
• Monitor liver enzymes.
The most common post-operative complications include pancreatitis, necrosis of the common bile duct and bile peritonitis.
Medical therapy can be attempted, especially if the patient is asymptomatic, if surgery presents a risk to the patient, or if the owner has declined to follow surgical intervention. If medical therapy is attempted consider close monitoring of the gallbladder with ultrasound and follow up blood work.
Medical therapy usually consists of:
• Antibiotics like Amoxicillin and Clavulanic acid or Fluoroquinolone with Metronidazole.
• Ursodeoxycholic acid (not recommended if there is suspected perforation or inflammation)
• S-adenosyl methionine (SAMe) at 20-40 mg/kg per day
• Fat restricted diet
• Identify and treat endocrinopathies
Bibliography
Besso JG, Wrigley RH, Gliatto JM, Webster CR: Ultrasonographic appearance and clinical findings in 14 dogs with gallbladder mucocele. Veterinary Radiology & Ultrasound 2000 Vol 41 (3) pp. 261-271.
Bowlus RA, Armbrust LJ, Biller DS, Moore LE. Clinical management of 20 dogs with Gallbladder Mucocele. American College of Veterinary Radiology Conference 2005.
Center S. Gallbladder Disorders. Proceedings of the NYSVMS Conference 2007.
Cook, Audrey. Gallbladder Mucoceles: The endocrine Connection ACVIM 2012.
Cornejo L and Webster CRL. Canine Gallbladder Mucoceles. Compendium of Continuing Education December 2005, 912-927.
Crews LJ, Feeney DA, Jessen CR et al. Clinical, ultrasonographic, and laboratory findings associated with gallbladder disease and rupture in dogs: 45 cases (1997-2007). Journal of American Veterinary Medical Association 2009 Vol 234 (3) 359-366.
Frank J, Lindquist E, Gallbladder mucoceles. NJMVD article, 2011.
Hook, P.H. et al., Microbiologic Evaluation of Gallbladder Bile in Healthy Dogs and Dogs with
Iatrogenic Hypercortisolism, 17th ECVIM-CA Congress, 2007
Mehler SJ and Bennett RA. Canine Extrahepatic Biliary Tract Disease and
Surgery. Compendium of Continuing Education April 2006, 302-314.
Pike FS, Berg J, King NW, et al: Gallbladder mucocele in dogs: 30 cases (2000-2002). J Am Vet Med Assoc 2004 Vol 224 (10) pp. 1615-1622.
Worley DR, Hottinger HA, Lawrence HJ: Surgical management of gallbladder mucoceles in dogs: 22 cases (1999-2003). J Am Vet Med Assoc 2004 Vol 225 (8) pp.1418-22.
Waldron, Donald R. Gall Bladder Mucoceles. Atlantic Coast Veterinary Conference 2012
Dr. Veronica Damian MVZ, MVS, MANZCVSc (Radiology)
Soundiagnosis Mobile Veterinary Ultrasound
www.soundiagnosis.com.au