Chapter 289: Diseases of the Gallbladder and Extrahepatic Biliary System

Gallbladder Anatomy

• Gallbladder sits between right medial and quadrate liver lobes
• Bile formed in hepatocyte and actively secreted into bile canaliculi
• Bile flows into intralobular ducts, then lobar ducts, then left and right hepatic ducts
• Hepatic ducts give rise to cystic duct, which travels toward the gallbladder
• Cystic duct separates hepatic ducts from more distal common bile duct

Bile Composition and Function

• Bile composed of cholesterol, lecithin, phospholipids, bile salts
• Bile emulsifies fats
• Gallbladder contraction releases bile into common bile duct, which enters duodenum through sphincter of Oddi
• In dogs, common bile duct joins minor pancreatic duct and both empty at major duodenal papilla
• In cats, common bile duct fuses with major pancreatic duct before entering duodenum

Cholelithiasis and Choledocholithiasis

• Older female dogs predisposed, especially Miniature Schnauzer and Miniature Poodle breeds
• Cholesterol, bilirubin, and mixed stones common in dogs
• Feline choleliths composed of cholesterol, bilirubin, or calcium salts
• Abnormalities promoting cholelith formation include gallbladder dyskinesia, hypercholesterolemia, hypertriglyceridemia, hyperbilirubinemia, endocrine disease
• Choledocholiths are stones in common bile duct specifically
• Often animals are asymptomatic; in other cases, there may be obstruction of common bile duct and/or biliary rupture with bile peritonitis

Biliary Stenting

• Choledochal stenting for treatment of extrahepatic biliary duct obstruction
• Plastic (polyurethane) stents facilitate patency and drainage of biliary tree; dislodge on their own or can be removed endoscopically
• Self-expanding metallic stents more permanent, for treatment of recurrent disease or malignancy
• Endoscopic retrograde cholangiopancreatography uses combo of endoscopy and fluoroscopy to evaluate biliary tree

Cholecystitis

• Inflammatory conditions of the gallbladder
• Predisposing factors include bile stasis, gallbladder mucocele, ascending bacterial or parasitic infection, neoplasia
• In cats, bacterial infection thought to be secondary to inflammation rather than inciting cause
• May be acute or chronic, mild or severe
• Most clinicopathologic changes consistent with cholestasis or posthepatic biliary disease
• Ultrasound reliably demonstrates gallbladder sediment, thickened gallbladder wall, choleliths, and evidence of extrahepatic bile duct obstruction

Emphysematous Cholecystitis

• Rare manifestation of acute cholecystitis complicated by gas-producing organisms
• Gas accumulates in lumen, wall, or pericholecystic tissues
• Radiographically, disease characterized by spherical to ovoid gas opacity superimposed over hepatic silhouette
• Anaerobes are most commonly isolated, including E. coli and Clostridium perfringens

Biliary Neoplasia

• Biliary cystadenomas occur regularly in older cats and rarely in dogs
• Most commonly from intrahepatic bile ducts
• Biliary carcinomas (cholangiocarcinomas) most common malignant, primary feline hepatobiliary tumor, second most common in dogs
• Labradors at increased risk
• Locally invasive tumors with high likelihood of metastasis at time of diagnosis

Parasitic Disease of the Biliary System

• Some species of flukes infect the hepatobiliary tree of cats (Platynosomum species)
• Causes bacterial cholangitis, cholangiohepatitis, ductal fibrosis, EHBDO, and liver failure
• Elevated liver enzymes and hyperbilirubinemia common
• Ultrasound may show ductal dilation, hepatic cysts, biliary obstruction

Gallbladder Mucocele

• Defined as presence of bile-laden semisolid to immobile mucoid material within the gallbladder
• Predisposing factors include dyslipidemias, dysmotility of the gallbladder, endocrine disease, and exogenous steroid administration
• Breed predispositions include Shetland Sheepdogs, Cocker Spaniels, and Miniature Schnauzers
• Complications include extrahepatic bile duct obstruction, cholecystitis, necrotizing cholecystitis, bile peritonitis, and pancreatitis
• Proposed etiologies include hyperadrenocorticism, exogenous steroids, and hypothyroidism