A 10-year-old, spayed, female mixed-breed dog was presented for weight loss and persistent vomiting. No abnormalities were noted on the physical examination. Serum biochemical abnormalities included increased levels of liver enzymes, including AST, ALT, LDH, and AP. Bilirubin levels were also elevated. The findings were consistent with hepatocellular damage and cholestasis. During the next 8 weeks, weight loss continued and the dog was lethargic and had an intermittent fever. Liver enzymes continued to increase. Radiographs demonstrated generalized hepatomegaly with abnormal calcification. Ultrasonographic examination identified gallbladder wall calcification and suggested cholelithiasis.

Cholecystectomy was performed 10 weeks after the initial presentation. The gallbladder was enlarged with a thickened wall. A 3-cm mass was found within the gallbladder and had a sessile attachment at the neck of the gallbladder, occluding most of the lumen. No other abdominal lesions were seen. The mass was determined to be a carcinoid tumor by various histologic features. In humans, carcinoid tumors can be malignant but usually grow slowly. Localized tumors are associated with a 5-year survival rate of 94%. This dog developed intermittent vomiting and diarrhea and was euthanized 8 months later. Necropsy was declined, so the origin of the tumor could not be confirmed, but it was suspected to originate in the gallbladder rather than being metastatic.

COMMENTARY: Adenomas and adenocarcinomas arising in the gallbladder mucosa have been reported previously in dogs. Carcinoid tumors should be included in the differential diagnosis when extrahepatic biliary masses are suspected.

A carcinoid tumor in the gallbladder of a dog. Morrell CN, Volk MV, Mankowski JL. Vet Pathol 39:756-758, 2002.