An unusual presentation of a hepatic ductal malformation in a Boxer dog

Abstract

An 11‐year‐old male neutered Boxer presented for evaluation of an external ear canal mass, postoperatively diagnosed as a benign inflammatory lesion. Preoperative staging of the ear mass identified a 10‐cm mass affecting the majority of the left lateral hepatic lobe, with inconclusive cytology. A left lateral liver lobectomy was performed. Histopathology revealed the hepatic parenchyma was largely effaced and replaced by a myriad of small calibre tubules lined by well‐differentiated biliary epithelium (cytokeratin19 and cytokeratin7 positive (CK19+, CK7+) supported by abundant fibrosis. Small cords and islands of hepatocytes (hepatocyte paraffin1 positive) (HepPar1+) were entrapped throughout these bile ducts. Analysis of the proliferation index via antigen KI‐67 (Ki67) immunohistochemistry confirmed lack of proliferative activity. Histological and immunohistochemical features were consistent with a ductal plate malformation (DPM). This is the first time a DPM of this size has been described on a computed tomography (CT) scan.