New insights on gallbladder mucocele formation in dogs

Incidences of canine gallbladder mucoceles are on the rise, despite not existing 20 years ago. Learn more from mulocele expert, Dr. Jody Gookin.

Since the first gallbladder mucoceles were first described just over 20 years ago, the incidence of this disease has been on the rise. What was once an uncommon diagnosis is now one of the most frequently diagnosed gallbladder diseases in dogs. Despite increasing frequency and awareness, the disease is poorly understood. Add controversy over treatment into the mix and you have a headache for practitioners and dog owners facing this disease.

Incidence and predisposing factors for gallbladder mucocele development

Although an exact incidence rate is unknown, experts agree that the overall incidence of gallbladder mucoceles is increasing. Older, small or middle-sized dogs are most commonly affected. There is no sex predilection, but several breeds are predisposed to gallbladder mucocele formation. At-risk breeds include cocker spaniels, Shetland sheepdogs, border terriers and miniature schnauzers. Reported risk factors for the disease are hyperadrenocorticism, hypothyroidism and imidacloprid use, but many dogs can develop mucoceles and have no risk factors.

Digging deep on how mucoceles form

The gallbladder is a storage site for bile, for subsequent delivery into the intestine to aid in fat digestion. Although this is its primary function, the gallbladder is not a passive bag of fluid. The epithelium of the gallbladder actively transports molecules to maintain hydration of mucosal membranes. The gallbladder epithelium also secretes mucus and depends on adequate hydration to maintain health.

Recent research suggests that attributing mucocele formation just to excess mucus secretion is overly simplistic. Studies show that the composition of mucus in dogs with this disease is very thick and rubbery, possibly secondary to abnormalities in transport of electrolytes that are needed to hydrate the mucus and prevent it from becoming overly tenacious.

As the mucus accumulates, it fills the gallbladder, can cause pressure necrosis, and ultimately gallbladder rupture.

Clinical signs, diagnosis and treatment

Dogs with gallbladder mucoceles can exhibit a wide range of clinical signs from no apparent signs to lethargy, vomiting, icterus, abdominal pain and inappetence. In some cases, gallbladder mucoceles are found incidentally during abdominal ultrasound.

In cases where the gallbladder ruptures secondary to mucocele formation, clinical signs reflect bile peritonitis and are serious emergencies.

Although bloodwork and urinalysis are useful in the diagnosis of co-morbidities, there is nothing specific on routine bloodwork that is pathognomonic for gallbladder mucocele.

Gallbladder mucoceles have a characteristic appearance on abdominal ultrasound and this diagnostic modality remains one of the best ways to establish a diagnosis.

Once a diagnosis is made, treatment depends on the presence or absence of other disease as well as the severity of signs exhibited by the patient.

In patients with stable or mild clinical signs, treatment of any underlying disease is important. Specific medical therapy for gallbladder mucoceles includes starting the patient on a low-fat diet and beginning ursodiol therapy. Serial ultrasound monitoring every three months is crucial in patients managed with medical therapy.

Unfortunately, many patients don’t respond to medical therapy alone. Surgery remains the definitive treatment for this condition, but is associated with a 25% perioperative mortality rate, with a reported range of 7% to a staggering 45% mortality. However, in patients that survive the immediate post-operative period, long-term survival is very good.

In cases of gallbladder rupture, emergency surgery is required to remove the gallbladder and address peritonitis. Prognosis for these patients is grave.

Current research and future directions

Morris Animal Foundation has invested in several studies on gallbladder mucoceles conducted by Dr. Jody Gookin, a professor and veterinary internist at North Carolina State University. Dr. Gookin recently appeared on the Foundation’s Fresh Scoop podcast to discuss her research on this serious and growing problem.

Dr. Gookin was alarmed by the sudden appearance of this disease in dogs along with the high mortality rate and coupled with lack of treatment options beyond surgery. She decided to start by looking at the gallbladder epithelium itself to learn more about control of secretion and mucus formation in tandem with genetic studies.

“When you think about breed-associated diseases, you think about puppies and kittens and animals showing something at a young age,” said Dr. Gookin. “But here is a disease that actually manifests later in life. My idea is that sometime 20 years ago, there’s emergence of an environmental exposure to which certain breeds of dog are genetically predisposed to reacting in this unusual way.”

Dr. Gookin’s research has zeroed in on a few candidate genes that could be interacting with something in the environment that ultimately results in mucocele formation in genetically susceptible dogs. Her team is working on applying xenobiotics to cultured gallbladder epithelial cells and monitoring the effect on the cells’ mucus production. Her hope is to identify the environmental exposures involved in triggering mucocele formation.

To learn more about gallbladder mucoceles, listen to Morris Animal Foundation’s podcast with Dr. Gookin discussing her studies on this serious disease and considering future therapies.

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