Pathology of cholangiocellular adenoma: A benign tumour mimicking the malignant neoplasm in a dog

An incidental finding of cholangicellular adenoma in a non-descript dog was described. A seven-year old non-descript dog carcass was presented for necropsy. Liver showed single to multiple aggregated cyst-like structures in the left and right lobes protruding slightly above the capsule. Microscopically, these structures revealed an irregularly circumscribed sub-capsular lesion characterized by hyperplastic bile ducts forming irregular tubules. Hyperplastic bile duct tubules formed inter-anastomosing locules separated by thin non-collagenous stroma. Few locules contained bile increments, cell debris and erythrocytes. Locular content showed positive for neutral mucin with Alcian blue-PAS stain whereas, modified Foucher’s stain showed emerald green bile pigments. Tubules were penetrating into the hepatic parenchyma causing isolation and pressure atrophy of hepatic cords. Histochemical profile differentiated CCA from Von Meyenberg complexes as an origin from postnatal life. Margin of the lesion revealed atypical neoplastic cells characterized by anisocytosis, anisokaryosis, few mitotic figures and slightly vacuolated biliary duct epithelium. Although the cause was obscure till date, hepatic injury/disease predispose for CCA as of now. Evidence of splenic infarct, enteritis, interstitial nephritis, pancreatitis in the present case substantiate the possible hepatic injury to be the cause for the CCA. Hence the lesion was diagnosed as CCA with malignancy features in a dog.