Gallbladder Mucocele (GBM)
A biliary mucocele is the distention of a bile containing structure or cavity by an inappropriate accumulation of mucus.
Gallbladder mucoceles have recently received much attention in the veterinary literature and have been perceived as a relatively new disease; however, many surgeons, internists, and pathologists agree that gallbladder mucoceles are not a new disease or condition, but instead develop along the continuum of progressive gallbladder disease, somewhere between acute cholecystitis and chronic necrotizing cholecystitis with rupture.
Biliary stasis, decreased gallbladder motility, and altered absorption of water from the gallbladder lumen are predisposing factors to biliary sludge. Biliary sludge may be a precipitating factor for the development of canine biliary mucoceles but it is more likely to be a small part of a complex disease process involving inflammation of the gallbladder wall and secondary changes to the lining of the gallbladder changing the consistency of its secretions. Obstruction of the ducts with stones, cancer, or inflammation of the pancreas does not appear to play a primary role in the formation of gallbladder mucoceles.
The underlying lesion has been described as cystic mucosal hyperplasia Hypersecretion of mucus leads to an accumulation of thick gelatinous bile within the gall bladder. Increased viscosity over a period of weeks or months leads to thick gelatinous material eventually occupying the entire lumen of the gallbladder and in some cases also being present in the ducts. Predisposing factors to mucocele formation include older age, hyperlipidemia and hypercholesterolemia, and motility disturbances. The inciting cause of mucus hypersecretion is unknown and is likely multifactorial and recent evidence has linked GBM to certain diseases (Cushing’s disease, hypothyroidism, and inflammatory bowel disease). Certain genetic predispositions may play a role as Shetland Sheepdogs were recently shown to be predisposed to gallbladder disease albeit not specifically to GBM formation.
Signs and Symptoms:
Clinical signs associated with gallbladder mucocele are often nonspecific and vague and, in some cases, a mucocele is discovered incidentally. Decreased appetite, anorexia, lethargy, vomiting, diarrhea, and abdominal pain or splinting have all been associated with gallbladder mucocele.
Exam, Screening Tests, and Imaging:
Diagnosis of the gallbladder mucoceles relies on physical examination by a veterinarian and blood work combined with imaging modalities, like abdominal ultrasonography. Abdominal ultrasound is incredibly useful early in the disease process and should be considered in any animal with clinical signs related to gastrointestinal upset. Up to half of patients with gallbladder mucoceles have a gallbladder rupture at the time of diagnosis and this number can be greatly reduced with early diagnostic intervention.
Complications Caused by the Condition:
The presence and progression of gelatinous material in the gallbladder may lead to a life threatening obstruction of the bile duct or the inflammatory changes to the wall of the gallbladder can lead to rupture and spillage of bile contents into the abdomen.
There have been some sporadic case reports regarding the medical dissolution and resolution of gallbladder mucoceles using special diets and nutraceuticals. However, a proactive course is recommended in most patients with gallbladder mucoceles and patients with an incidental mucocele or “premucocele” on ultrasound should be considered as a cholecystectomy candidate. A current trend is to wait to perform a cholecystectomy on these patients until they have failed medical management, have become systemically ill, or the gallbladder has ruptured. This “wait and see” philosophy has yielded mortality rates of 20-30% in dogs with gallbladder mucoceles. Many surgeons are now recommending that a cholecystectomy be performed in patients with gallbladder mucoceles at initial presentation or if found as an incidental finding on abdominal ultrasound. Routine open or laparoscopic cholecystectomy in the clinically unaffected gallbladder mucocele patient has been found to have an excellent outcome and rapid return to normal function in the small number of cases reported.
When to Seek Veterinary Surgical Advice:
The surgical treatment of choice for gallbladder mucocele is cholecystectomy, or surgical removal of the gallbladder. Given this is a disease of the gallbladder and that many of the gallbladders submitted for histopathology have evidence of necrosis, it is advised not to perform a cholecystotomy or cholecystoenteric anastamosis or any other procedure that involves sparing the gallbladder. Before removing the gallbladder, the surgeon should assess the bile duct to be certain there is no obstruction. An irresolvable obstruction of the common bile duct would preclude the removal of the gallbladder.
Potential Complications Following Treatment:
As with any surgical procedure, there are risks associated with general anesthesia. Preoperative bloodwork and imaging, and correction of fluid and electrolyte imbalances will help your veterinarian to minimize the anesthetic risk. Biliary surgery has inherent risks, including bleeding, and leakage of bile into the abdominal cavity, which can cause peritonitis.
Dogs with biliary mucoceles that undergo cholecystectomy and survive the immediate perioperative period have an excellent long term prognosis. Overall mortality rates are reported to be between 20-39% for this disease, however, early surgical intervention may significantly reduce mortality rates. The resected gallbladder and a small piece of liver may be submitted for histopathology and microbiologic testing by your veterinary surgeon.
Figure 1: Abdominal ultrasound images of a dog with a gallbladder mucocele demonstrating the typical kiwi (or strawberry in this case) or stellate pattern. Courtesy of Dr. Jennifer Bouma.
Figure 2: A large mucobiliary plug that was removed from the common bile duct of a dog with a gallbladder mucocele. This plug was removed by a choledochotomy incision.
Figure 3: An intraoperative image of a dog with a gallbladder mucocele. Flushing of the biliary tract with sterile saline is being performed retrograde via catheterization of the major duodenal papilla from a duodenotomy incision.
—Steve J. Mehler, DVM