It all starts with a sick, usually middle-aged or older dog. He is listless, not eating, and maybe has vomiting and/or diarrhea and fever. These are symptoms that could mean any number of things, but usually, when he reaches the veterinarian’s examination table, he has jaundice (yellow pigmentation visible in the whites of his eyes and possibly on his skin and gums). Hospitalization is recommended to rehydrate him and provide supportive care. Blood tests point to a liver problem. Medications are given to minimize the liver’s workload, but soon, an ultrasound is being discussed to image the liver, and costs may rise quickly.

In a survey of dogs with hepatobiliary mucoceles, the following symptoms were observed:

BMucocele_chart.jpg - Caption. [Optional]

The alphabet soup of blood tests can be confusing, and it can be tempting to wait a few days and see how medical support works out before imaging. While this may be a fair choice depending on the patient, there is an important reason to image the liver quickly: the possibility that surgery is needed urgently.

 If Liver Disease is the Problem, Why is an Ultrasound Needed?

A veterinarian performs an ultrasound on a dog. Image courtesy MarVistaVet

While blood testing can point to the liver, the fact is that numerous diseases can affect the liver. The liver can have an infection, cancer, scarring (cirrhosis), or any number of conditions. The more specific our diagnosis gets, the more specific treatment can be.

Ultrasound is a non-invasive way to evaluate the internal texture of the liver and gallbladder. By looking at the liver’s texture, it is possible to see a tumor and determine if removing it is possible or if it has invaded too far. Ultrasound can evaluate scarring and abscesses. Through ultrasound, it is possible to guide a biopsy needle to an exact area to sample tissue should this be deemed necessary. Ultrasound evaluates the gallbladder and bile ducts. One of the more important diseases to rule out promptly is the biliary mucocele because it is commonly a surgical emergency. A biliary mucocele is a wad of sludged mucus inside the gallbladder. If you wait a few days to see how the patient responds to general liver support, it may be too late for surgery. Furthermore, ultrasound can evaluate the gallbladder’s integrity; if the mucocele ruptures and spills bile into the belly, the surgeon will need to know that as additional treatment is needed. Ultrasound also evaluates concurrent abdominal conditions that might impact recovery, including pancreatitis, which can occur alone with similar symptoms or in addition to a biliary mucocele.

What Is the Gallbladder, and What Is the Biliary System?

Illustration by Wendy Brooks, DVM

The liver serves as a toxic waste processing center for the body. It filters bacterial products (as well as nutrients) entering the body from the gastrointestinal tract and it removes toxic waste products from the bloodstream. This material is bound to special biochemicals called bile acids and the body would like to get rid of it, bile acids and all.  The solution of bile acids, water, mucus, pigments, and cholesterol forms the greenish-yellow fluid called bile.

Bile is made in the liver and then collected into small ducts called bile ductules and bile ducts. The bile is then moved for storage into the greenish round organ called the gallbladder. During food digestion, hormones cause the gallbladder to contract and squirt bile through the large common bile duct and into the intestine. The bile assists with digestion and carries toxins out of the body so they may be eliminated in feces. The gallbladder and its ducts represent the biliary system.

What Is a Biliary Mucocele?

The diseased gall bladder appears similar in texture pattern to the cut surface of a kiwi fruit. Photo courtesy of DVMSound.

One of the components of bile is mucus. Normal bile is probably less than 3% mucus, but when a mucocele develops, the bile becomes mostly mucus. Normal bile is liquid, but mucocele bile is thick and goopy and will not flow easily through the common bile duct. The gallbladder distends trying to pass the mucocele bile, and if it actually ruptures, the risk of serious complications and death is much higher. The gallbladder with a mucocele develops an appearance on ultrasound described as resembling the cut surface of kiwi fruit. The biliary mucocele is sometimes called a "kiwi gallbladder."

When this is seen on ultrasound in a sick, jaundiced patient, surgery to remove the diseased gallbladder should be performed as soon as possible.

Kiwi fruit. Photo by Marvistavet

The biliary mucocele is sometimes called a "kiwi gallbladder." Image courtesy MarVistaVet

Why Does This Happen?

Mucocele development starts with delayed gallbladder contraction, which allows bile acids to accumulate. Altered fat metabolism is also associated with reduced gallbladder contraction, resulting in an accumulation of bile acid. With that accumulation, the lining of the gallbladder feels inflamed and responds by making more mucus and more mucus-producing glands. Pretty soon, the bile is just a big wad of congealed mucus, and it will not flow. 

Several hormone imbalances have been associated with altered fat metabolism and reduced gallbladder contraction: diabetes mellitus, hypothyroidism, and Cushing's disease. Cushing's disease patients have an incidence of biliary mucocele development that is 29 times the incidence of patients without Cushing's disease. Mucocele development has been linked to pancreatitis (inflammation of the pancreas) as well.

No one knows why this might be so, but it does correspond to the mainstreaming of diagnostic ultrasound into general practice.

The Shetland sheepdog, cocker spaniel, miniature schnauzer, and dachshund seem predisposed to developing biliary mucoceles.

Removing the Gallbladder (Cholecystectomy)

Removing a dog’s gallbladder is a serious surgery that not all veterinarians are comfortable performing. Discuss with your veterinarian whether a referral to a specialist would be best for you and your pet.

The goal is to remove the gallbladder before it ruptures. If it has already ruptured, tissue damaged by the rupture must be cleansed or removed. Whether or not the gallbladder that has a mucocele is removed before or after rupture does not affect the rate of survival.

The gall bladder’s function is mainly one of bile storage. Without the gallbladder, bile simply dribbles into the intestine constantly rather than in controlled squirts. You might think this would be a problem, but it turns out not to be. Some patients require long-term medication for liver support but generally speaking, if the dog recovers from surgery, the prognosis is excellent, and the patient can return to normal life.

What if Surgery is Not an Option, or What if the Dog Isn't that Sick?

There is no question that surgery is the best treatment choice, but there is more to the story. Biliary mucoceles can be an incidental finding in dogs who are not sick or who are sick from something else and are having an ultrasound of the belly for some other reason. In a patient who is not experiencing problems with a mucocele, medication may be able to stave off illness in some cases.

As for skipping surgery on a dog that is sick from its mucocele, this is a very risky move.

It is possible to attempt treatment with general liver support medications, a low-fat diet, and choleretics (medications to help liquefy bile, such as ursodiol), but the problem is that the gallbladder is obstructed with a big wad of goop. This goop is unlikely to liquefy in a timely fashion, if at all, no matter what treatment is given. If medical management is attempted, it is important to regularly recheck the gallbladder by ultrasound to watch for any sign of progression that would indicate that surgery should no longer be postponed.