A common cause of bile duct obstruction in dogs
Gallbladder mucocele, recognized only in the past 20 years, is slowly progressive
[From Tufts May 2010 Issue]
Unlike people, dogs rarely develop painful gallstones. Instead, they’re more likely to fall victim to a blockage known as gallbladder mucocele, seen most often in dogs at the average age of 9.
Cocker spaniels and Shetland sheepdogs in particular seem to be predisposed, but any dog can develop the disease. Neither sex appears to be disproportionately affected.
Gallbladder mucocele is a relatively new condition recognized only in the past 20 years. “We see maybe 10 to 20 cases a year,” says John Berg, DVM, a surgical specialist at Cummings School of Veterinary Medicine at Tufts University. “Interestingly, it is a disease that seems to cluster in certain areas.” Two of the largest series of published cases came from Cummings School in North Grafton, Mass., and Cornell University in Ithaca, N.Y., but Dr. Berg says he knows veterinarians from other areas who have never seen a case. “Now it’s probably the most common cause of biliary (bile duct) obstruction that we see.”
If an obstructed gallbladder ruptures, it can be fatal, According to the results of a retrospective study published in the February 2009 issue of the Journal of the American Veterinary Medical Association, the overall survival rate among 43 dogs undergoing surgery for gallbladder disease was 86 percent. Of those dogs, 47 percent had a gallbladder mucocele and 43 percent of these suffered gallbladder rupture.
“The dogs that have the worst prognosis are the ones with gallbladders that are either ruptured or nearly ruptured, but even dogs with a ruptured gallbladder can often be saved,” Dr. Berg says.
Gallbladder mucocele occurs when the epithelial cells in the gallbladder wall begin secreting a thick mucus into the normally liquid bile. (Epithelial cells are specialized cells that line the inner surfaces of many internal organs.) The bile then becomes less motile and can no longer easily flow out through the bile duct and into the intestine. The backup of bile may cause dogs to become jaundiced, or icteric, with a yellow tinge to their mucous membranes and the whites of their eyes. They may be lethargic, with little appetite, and they may vomit or have a low-grade fever. Most dogs with mucoceles exhibit abdominal pain.
Veterinarians are unsure of the problem’s cause. It’s unclear whether the excess mucus production is caused by a genetic disorder of the gallbladder epithelium or dietary or environmental factors.
The condition is easily diagnosed with ultrasound, which will show the affected gallbladder’s unmistakable appearance. The gallbladder, distended with sludge that has striations, or lines, running through it, looks rather like a cross-section of kiwi fruit. In fact, veterinarians sometimes refer to the condition as “kiwi gallbladder.”
In the worst-case scenario, if it appears a mucocele will cause imminent rupture of the gallbladder, surgeons will remove the gallbladder, a procedure known as a cholecystectomy. If the common bile duct, a tube that carries bile from the gallbladder to the duodenum, or small intestine, is obstructed by the mucoid bile, the surgeon may flush it with saline during the surgery to improve the flow of bile.
A gallbladder mucocele is a slowly progressive disease, and sometimes dogs don’t show signs of it. The mucocele may be discovered during an abdominal ultrasound being performed for another purpose. In these cases, there may be no need to rush to surgery.
The best candidates
The dog’s age is a factor in the decision to perform surgery. In older dogs who have no signs and aren’t obstructed, veterinarians may recommend monitoring with ultrasound, bloodwork and physical exams. They’re more inclined to remove the gallbladder in young or middle-aged dogs because of the greater likelihood that the disease will progress and cause a rupture.
“Older dogs might die with it but not of it, whereas younger dogs are a little more likely to eventually become ill because of the condition,” Dr. Berg says. “We’re a little more aggressive in the younger dogs.”
The gallbladder isn’t essential for life, so removing it has no detrimental effects. Bile continues to be made in the liver, passing directly from the liver through the common bile duct and into the intestines, simply bypassing the storage phase in the gallbladder.