Biliary Myeloid Sarcoma Mimicking Cholangiocarcinoma: A Diagnostic Pitfall

A 53-year-old man presented with a three-day history of jaundice and anorexia.Laboratory tests showed markedly elevated liver enzymes and bilirubin, consistent with obstructive jaundice.Computed tomography (CT) and magnetic resonance cholangiopancreatography (MRCP) demonstrated marked thickening and enhancement of the extrahepatic bile duct from the hepatic confluence to the ampulla, with intrahepatic ductal dilatation and no clear involvement of the right or left hepatic ducts.Hilar cholangiocarcinoma (Bismuth-Corlette type II) was strongly suspected, and a multidisciplinary tumor board proposed an extended left hepatectomy with bile duct resection.The patient first underwent percutaneous biliary drainage and left portal vein embolization.Intraoperative biopsies of the right and left hepatic ducts showed no evidence of adenocarcinoma, and surgery was completed without complications.Final pathology revealed myeloid sarcoma of the extrahepatic bile ducts, with architectural effacement by a diffuse proliferation of intermediate-sized cells with scant cytoplasm and monotonous round nuclei.The cells were diffusely positive for myeloperoxidase and multifocally positive for CD117, and negative for pancytokeratin, B-cell markers, T-cell markers, CD138, CD34, and CD163, excluding an epithelial neoplasm and lymphoma.Bone marrow involvement was subsequently identified, and the patient is awaiting chemotherapy followed by allogeneic stem cell transplantation.Many inflammatory and neoplastic biliary conditions mimic cholangiocarcinoma on imaging.Biopsy or cytology is therefore recommended before surgery.Myeloid sarcoma, a tumor of extramedullary myeloid blasts, is equivalent to a diagnosis of acute myeloid leukemia.Primary biliary involvement is exceedingly rare and may be misdiagnosed as cholangitis or cholangiocarcinoma.