17 Potential Causes of Gallbladder Mucocele in Dogs

I go on “high alert” any time my dogs have gastrointestinal issues. They’re both well into their senior years, and that makes them more vulnerable to a variety of conditions, including gallbladder mucocele, one of the most common gallbladder diseases in dogs.

As your dog ages, it’s more important than ever to pay attention to signs that could point to developing disease. Gallbladder mucocele is no joke. Inflammation is painful and can lead to serious consequences if not treated.

Keep reading to learn what a gallbladder mucocele is, how they form, how they’re diagnosed, treatment options, and the long-term prognosis.

How Gallbladder Mucocele Affects Dogs

If your dog has been diagnosed with a gallbladder mucocele, it means that his or her gallbladder is swollen and full of backed-up mucus.

It’s easier to understand what causes a mucocele if you understand the purpose of bile and how it travels through hepatic ducts.

The Biliary Tree

The biliary system is made up of the gallbladder, liver, ducts, and supporting structures. Its function is to produce, store, secrete, and transport bile. Bile is a sticky, yellow-green fluid that aids in digestion. Bile salt is the component responsible for breaking down fats into fatty acids.

In order to do that, it first has to travel from the liver, where it’s produced, to the gallbladder, which acts as a reservoir. Think of it like a river flowing through small channels to increasing bigger channels known as ducts.

The common hepatic duct joins with another duct called the cystic duct, which is connected to the gallbladder.

Unfortunately, this process doesn’t always go as it should. Any obstruction in the ducts along the way can result in the backup of mucus and bile.

The Formation of a Gallbladder Mucocele in Dogs

The gallbladder, which sits between liver lobes in the abdomen, serves as a reservoir for bile and has a lining (gallbladder epithelium) that plays an important role in maintaining water and electrolyte balance.

In addition, the gallbladder lining manages cholesterol, lipid, amino acid, and bile acid levels.

Biliary Sludge

A gallbladder mucocele is formed when the lining over-secretes abnormally thick mucus. It can occur if something is blocking the duct, like a gallstone. As bile enters the gallbladder, it mixes with the mucus and becomes very thick. This is known as biliary sludge.

Biliary sludge blocks the duct and prevents bile from entering the common bile duct, a thin tube that passes through the pancreas before it empties into the first part of the small intestine.

Gallbladder Rupture

The bile has no place to go and gradually builds pressure within the gallbladder walls. Think of it like a balloon with too much air. Eventually, that balloon is going to burst. When that happens to the gallbladder, it’s called a rupture and is considered a surgical emergency.

The image below is a good visual of the biliary system.

Serious Risks Associated with Canine Gallbladder Mucocele

Unfortunately, the gallbladder doesn’t stop producing mucus whether it’s plugged or not. It just keeps adding to the biliary sludge until it becomes so big that it presses against the walls of the gallbladder.

Cholecystitis

Cholecystitis is the term used to define inflammation of the gallbladder. Inflammation happens when bile gets trapped in the gallbladder. Gallstones are a common reason for blockage.

Inflammation of the gallbladder is considered to be either non-necrotizing or necrotizing. It can also be sterile or infected.

Non-necrotizing cholecystitis

The term “non-necrotizing” means that the gallbladder lining hasn’t died. Non-necrotizing inflammation of the gallbladder can be associated with:

• Infectious agents
• Systemic disease
• Tumor (neoplasia)
• Blunt abdominal trauma or injury
• Gallstones

Necrotizing cholecystitis

Untreated gallbladder inflammation lead to pressure necrosis, a serious condition caused by the pressure of the built-up biliary sludge against the epithelium wall. The constant pressure prevents healthy blood supply from reaching the tissue, causing it to die.

The condition is associated with middle-aged or senior dogs. Clinical signs develop acutely and include abdominal pain and fever. Unfortunately, signs can also be vague and may come and go.

Necrotizing cholecystitis can cause a gallbladder rupture which is a surgical emergency.

Bile Peritonitis

If the gallbladder ruptures, it can lead to bile peritonitis. Bile peritonitis occurs when bile leaks into the abdominal cavity, resulting in inflammation of the abdominal lining.

Signs of peritonitis can develop suddenly. You may notice:

• Weakness
• Rapid respirations
• Vomiting
• Loss of appetite
• Diarrhea
• Black stools
• Unwillingness to lie down (may assume a “praying position” with the hind end elevated and the front end and head lying on the ground).

If your dog shows any of the signs noted above, particularly abdominal pain, get your dog to a veterinarian for a checkup as soon as possible.

Sadly, up to 50% of dogs with gallbladder mucocele will experience a ruptured gallbladder. This is a serious condition that needs to be treated right away.

Signs of Gallbladder Mucocele in Dogs

The most frequent signs of gallbladder mucocele in dogs include:

• vomiting
• abdominal discomfort
• lack of appetite
• weight loss
• jaundice
• fever
• diarrhea
• abdominal distension

Dogs with gallbladder mucocele may also have tachycardia (faster than normal heart rate), or tachypnea, which is defined as rapid and shallow breathing.

17 Potential Causes of Gallbladder Mucocele in Dogs

Several things, like endocrine disease, can make a dog more likely to get a gallbladder mucocele.

Mucocele forms when there is an excessive accumulation of mucus in the gallbladder. However, it’s not entirely known what causes that to happen. There are several theories including the following:

1. Gallstones

Gallstones, also called choleliths or cholelithiasis, are made up of parts of pile including cholesterol, bilirubin, and calcium. These stones form when the gallbladder isn’t functioning properly, or something is wrong with the bile.

2. Hypothyroidism

Hypothyroidism is a common autoimmune disorder that leaves the thyroid gland underactive.

A 2019 study (Investigation of adrenal and thyroid gland dysfunction in dogs with ultrasonographic diagnosis of gallbladder mucocele formation) recognize gallbladder mucocele as an emerging disease in dogs with hypothyroidism.

According to the study, “Affected dogs have a significantly increased likelihood of concurrent diagnosis of hyperadrenocorticism, hypothyroidism, and hyperlipidemia.”

Aicher KM, Cullen JM, Seiler GS, Lunn KF, Mathews KG, Gookin JL. Investigation of adrenal and thyroid gland dysfunction in dogs with ultrasonographic diagnosis of gallbladder mucocele formation. PLoS One. 2019 Feb 27;14(2):e0212638. doi: 10.1371/journal.pone.0212638. PMID: 30811473; PMCID: PMC6392329.

3. Diabetes Mellitus

Diabetes can be linked to several health conditions, including gallbladder problems. Any disruption to the healthy functioning of the gallbladder can lead to problems.

4. Hyperlipemia

Hyperlipidemia, or high cholesterol, means there are too many lipids (fats) in the bloodstream. High triglycerides and low HDL have been associated with gallstones.

5. Gallbladder Dysmotility

This condition results in decreased gallbladder contraction. The slowed functioning of the gallbladder can prevent bile from moving through the intestinal tract.

6. Glucocorticoid Therapy

Steroids are often used to treat inflammatory conditions, immune-mediated disease, and the uncontrolled, abnormal growth of cells or tissues (neoplastic conditions).

Although they tend to work well in the short-term, they also have complications including:

• glucocorticoid hepatopathy (steroid related liver disease)
• elevated liver enzymes, including alkaline phosphatase
• changes in liver function (histopathologic hepatic changes)
• lethargy
• panting
• gastrointestinal issues including ulceration
• blood clots
• urinary tract infections
• pyometra in intact female dogs

7. Progestational Therapy

Some drugs used to treat sexually driven behavior problems in dogs can have side-effects that may indirectly contribute to gallbladder mucocele in dogs. For example, more serious side-effects can trigger diabetes and decreased thyroid function, both of which can lead to gallbladder problems.

8. Cystic Mucinous Hyperplasia

This is a tumor-like lesion of the gallbladder that can lead to gallbladder mucocele in dogs.

9. Gallbladder Disease

Gallbladder disease affects the way the gallbladder works and can include inflammation, infection, stones, or blockages.

10. Age

Gallbladder mucocele tends to occur in middle-aged and older dogs. The average age for gallbladder mucocele development is nine years old.

11. Dog Size

The condition appears more frequently in small to medium-sized dogs.

12. Dog Breed

Breeds most vulnerable include:

• Shetland Sheepdogs
• Miniature Schnauzers
• Cocker Spaniels

It may also be seen in other breeds like Pomeranians and Chihuahuas as well as mixed breeds.

13. Cushing’s Disease

Cushing’s is a serious disease that occurs when the adrenal glands produce too much cortisol (cortisone). Too much cortisol in the body can cause complications, including the development of kidney disease, high blood pressure, blood clots, and diabetes.

A low-dose dexamethasone suppression test can be used to screen for Cushing’s disease.

14. High Fat Diet & High Cholesterol

Dogs who have high fat diets are at risk of developing gallstones, which can lead to gallbladder inflammation.

15. Pancreatitis

Pancreatitis refers to inflammation of the pancreas. It can either be chronic or acute. Chronic pancreatitis can cause obstructions in the common bile duct and the proximal pancreatic duct.

Any type of blockage in this area will impact the gallbladder, potentially resulting in the development of mucocele.

16. Gallbladder Cyst Formation

Cysts or tumors that develop in the gallbladder can lead to an obstruction.

17. Inflammatory Bowel Disease

An inflammatory bowel disease like Crohn’s, for example, can lead to inflammation in the small intestine. If the small intestine is inflamed, it’s not able to easily absorb bile salts. Without enough bile salts, cholesterol can collect in the gallbladder.

This leads to the formation of gallstones.

Diagnosis Gallbladder Mucocele in Dogs

In order to make an appropriate diagnosis, the veterinarian may do a few things, including:

Physical Examination

The veterinarian will palpate the dog’s abdomen to detect signs of pain and distention. If the gallbladder has ruptured there may be evidence of shock including tachycardia, pale mucous membranes, and slow capillary refill time.

Blood Tests

Blood work will show if there is an elevation of liver enzymes. Elevated white blood cell counts are also supportive of active inflammation.

Abdominal Ultrasound

Ultrasound is considered the “gold standard” for diagnosing problems with the gallbladder. If the gallbladder is ruptured, the dog will require emergency surgery.

Cholecystocentesis

If this test is required, it involves the use of an ultrasound-guided laparoscopy to collect gallbladder bile. The bile is then tested for bacterial infections.

Treating Gallbladder Mucocele Formation in Dogs

Surgical intervention is vital for survival if the dog’s gallbladder has ruptured or is at immediate risk of rupturing.

If the clinical signs are mild, and the dog is otherwise in good health, the veterinarian may recommend a wait-and-see approach to try and resolve the problem medically. In an ideal situation, a low-fat diet and ursodiol, a drug that breaks up gallstones, will be helpful.

Antibiotics are also recommended.

A wait-and-see approach might help avoid risky surgery, but it can also leave the dog vulnerable to sudden complications, including a ruptured gallbladder.

You may be asked to monitor your dog at home for signs of digestive problems, pain, or discomfort. In addition, your dog may need an ultrasound of the abdomen and gallbladder every 3 to 6 months.

Surgical Intervention

Unfortunately, medical management often isn’t enough. Although surgical removal (cholecystectomy) of the gallbladder is risky, it’s sometimes the only option for the best potential outcome.

Complications that can arise after surgery include:

• Vomiting
• Unwillingness to eat
• Lethargy
• Pain

Medications may be prescribed post-surgery to aid in the recovery process. These may include antacids, anti-nausea and pain medication. In some cases, medications that support liver function are also prescribed.

Prognosis

According to the American College of Veterinary Surgeons, “overall mortality rates are reported to be between 20–39%”. Although that may sound bleak, it’s important to note that mortality rates can be significantly reduced if the condition is diagnosed and treated early, before rupture occurs.

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Summary

Gallbladder mucocele simply refers to the distension of the gallbladder because of excessive mucus buildup.

The potential causes and risk factors, however, are much more complicated. You may not be able to prevent your dog from developing gallbladder problems, but there are some proactive things you can do to keep your dog as healthy as possible, for as long as possible.

Regular wellness checks with a licensed veterinarian are a great way to stay on top of your dog’s health. Of course, a lot can happen between yearly visits, which is why it’s important to remain alert to any changes in your dog’s health.

Vomiting, a a poor appetite, lethargy, and diarrhea could point to any number of conditions. Its not unusual for dogs to have minor digestive upset from time to time.

However, if these signs persist, develop quickly and are associated with abdominal pain, jaundice, or fever, it could be a sign of gallbladder rupture which is often deadly.

Works Cited

CENTER.SHARON. “Canine Gallbladder Mucocele – Digestive System – Merck Veterinary Manual.” Merck Veterinary Manual, www.merckvetmanual.com/digestive-system/hepatic-disease-in-small-animals/canine-gallbladder-mucocele. Accessed 7 Dec. 2022.

“Gall Bladder Mucocele | Nashville Veterinary Specialists.” Gall Bladder Mucocele | Nashville Veterinary Specialists, www.nashvillevetspecialists.com/articles/gall-bladder-mucocele. Accessed 7 Dec. 2022.

“Hypothyroidism in Dogs.” Veterinary Teaching Hospital, 28 June 2021, hospital.vetmed.wsu.edu/2021/06/28/hypothyroidism-in-dogs.

Dog Gallstones Symptoms – Gallstones Treatments for Dogs | PetMD. (n.d.). Dog Gallstones Symptoms – Gallstones Treatments for Dogs | PetMD. Retrieved December 11, 2022, from https://www.petmd.com/dog/conditions/digestive/c_multi_cholelithiasis

Medroxyprogesterone Acetate | VCA Animal Hospital. (n.d.). Vca. Retrieved December 11, 2022, from https://vcahospitals.com/know-your-pet/medroxy—progesterone

Lisa Theriault