A case of malignant lymphoma of the extrahepatic bile duct diagnosed by detailed imaging examination and endoscopic ultrasound-guided fine needle aspiration.

A 70-year-old woman presented to our hospital with abdominal pain. Imaging examinations showed diffuse and extensive wall thickening at the perihilar bile duct; however, the degree of stricture was mild, and the mucosal epithelium was smooth. A transpapillary biopsy was performed considering cholangiocarcinoma and IgG4 sclerosing cholangitis as differential diagnoses; however, no pathologic diagnosis was obtained. Peroral cholangioscopy revealed a regular epithelium at the stricture, and endoscopic ultrasound-guided fine-needle aspiration (EUS-FNA) of the enlarged lymph node confirmed the diagnosis of diffuse large B-cell lymphoma. Multiagent chemotherapy was administered, which led to complete remission. Because primary bile duct malignant lymphomas are rare and specific, clinical, and imaging findings are lacking, and many of those reported so far have been diagnosed by postoperative pathology. As chemotherapy is the first-line treatment for malignant lymphoma, obtaining an accurate diagnosis is crucial. Our findings support that smooth and mild biliary strictures with mainly submucosal wall thickening may be characteristic imaging findings of primary bile duct malignant lymphoma, and that peroral cholangioscopy and EUS-FNA may be helpful for an accurate diagnosis.