[A case of mucosa-associated lymphoid tissue lymphoma of the bile duct diagnosed using intraductal ultrasonography and transpapillary investigation of the bile duct].

A 78-year-old woman with a chief complaint of mammary tumor was referred to our hospital and was diagnosed with mucosa-associated lymphoid tissue (MALT) lymphoma using needle biopsies. She presented with MALT lymphoma lesions in the stomach, duodenum, and intraperitoneal lymph nodes. Abdominal ultrasonography revealed thickened internal layer of the bile duct.