Diagnostic challenges in biliary cytology of biliary inflammatory pseudotumor of the liver: A case report and a review of the literature.

Biliary inflammatory pseudotumor (IPT) of the liver is a rare benign tumor of which radiographic images, such as biliary stricture and dilatation, resemble those of cholangiocarcinoma (CC). Although repeated biliary cytology via endoscopic nasobiliary drainage (ENBD) is performed for differential diagnosis, a correct diagnosis remains difficult. The present study describes the case of a 76-year-old female patient with chronic liver disease. During surveillance, intrahepatic CC was suspected by imaging analyses; however, the carcinoembryonic antigen and CA19-9 levels were within normal ranges. Percutaneous core needle biopsy was not performed due to technical reasons; however, a left lobectomy was performed based on the diagnosis of malignancy by ENBD bile cytology. A pathological examination of the resected liver demonstrated biliary IPT. Reflecting on the cytological diagnosis of this case, a multi-reviewer re-evaluation of the biliary cytology of this IPT case and 2 cases of well-differentiated CC was then performed, which demonstrated difficulty in distinguishing between them. On the whole, ENBD cytology can play a limited role in differentiation between benign and malignant bile strictures. Surgical indication should be carefully determined and percutaneous core needle biopsy may be warranted in patients with normal tumor marker levels.