Remnant cystic duct cancer with gradual enlargement over two years of follow-up: a case report and literature review.

Remnant cystic duct cancer is a rare disease, with only a few reported cases. We report a case of remnant cystic duct cancer that gradually increased in size. A 78-year-old woman with a history of cholecystectomy presented with a gradually enlarging mass at the porta hepatis after laparoscopic liver resection for hepatocellular carcinoma. Diagnostic imaging, including computed tomography and magnetic resonance imaging, showed a mass at the porta hepatis near a surgical staple, which gradually increased in size over two years. Endoscopic ultrasonography revealed a mass in the cystic duct enhanced with perfluorobutane. Resection of the extrahepatic bile duct with choledochojejunostomy was performed. Histopathological examination revealed a well-differentiated adenocarcinoma at the site where the cystic duct protrudes into the common bile duct opening. The patient remains alive two years after surgery without recurrence or metastasis. Remnant cystic duct cancer is extremely rare and often presents at an advanced stage. This case demonstrated a slow, asymptomatic progression, offering new insight into its natural history.