Primary Extrahepatic Biliary Mucinous Cystic Neoplasm Suspected Preoperatively and Treated by Robotic...

Biliary mucinous cystic neoplasm (MCN) is a cystic tumor characterized by ovarian-like stroma and is recognized as a neoplasm with the potential for invasive carcinoma. While MCNs predominantly occur in the pancreas, primary occurrence in the extrahepatic bile duct is exceedingly rare. Most reported cases are diagnosed postoperatively due to the lack of specific clinical symptoms, the difficulty in preoperative differentiation from other cystic diseases, such as intraductal papillary neoplasm of the bile duct, and the strict requirement of pathological evaluation for definitive diagnosis. Here, we report a case of primary extrahepatic biliary MCN that was strongly suspected preoperatively using multimodal imaging and treated with robotic surgery.

A 48-year-old woman presented to a previous hospital with jaundice and abdominal pain. CT revealed a 40-mm cystic lesion in the common bile duct. Despite biliary stenting for obstructive jaundice, she experienced recurrent cholangitis and was referred to our hospital for further investigation and treatment. Detailed imaging evaluation, including endoscopic ultrasound (EUS), identified characteristic findings of MCN, such as a thick capsule and a cyst-in-cyst appearance. The absence of continuity with the pancreas led to the preoperative clinical suspicion of MCN originating from the bile duct wall. As the tumor extended into the intrapancreatic bile duct and was suspected to be benign or low-grade, we performed robotic pylorus-preserving pancreaticoduodenectomy aiming to balance radicality with minimal invasiveness. Histopathology confirmed primary extrahepatic biliary MCN with low-grade dysplasia. The patient was discharged on POD 8 and remains recurrence-free at 6 months' follow-up.

Although primary extrahepatic biliary MCN is an extremely rare entity, this case suggests that detailed multimodal imaging, particularly EUS, may help with preoperative suspicion of biliary MCN by identifying characteristic features. The characteristic findings presented herein will serve as a valuable reference for the preoperative differentiation of this rare disease. While complete surgical resection is mandatory, our experience suggests that robotic surgery can serve as a minimally invasive approach capable of achieving this. To the best of our knowledge, this is the first reported case of primary extrahepatic biliary MCN treated by robotic surgery, representing a feasible therapeutic option.