Carcinoid tumor of gallbladder in a dog

A 7-year-old female mixed-breed dog was presented to a veterinary clinic for pyometra. During abdominal ultrasonography, an abnormal finding was noted in the gallbladder. A cholecystectomy was performed. Grossly, the gallbladder wall was thickened with a polypoid nodular projection into the lumen. Microscopically, the polyp consisted of a solid sheet of round to polygonal-shaped cells that formed small packets with fibrovascular septa. The neoplastic cells contained abundant cytoplasmic eosinophilic granules. Immunohistochemically, the neoplastic cells were positive to chromogranin A and neuron-specific enolase, whereas they were negative to vimentin and cytokeratin. This case was diagnosed as a primary gallbladder carcinoid tumor.