Duodenal duplication cyst of the ampulla of Vater.

A 35-year-old man presented with the complaint of epigastric discomfort. Gastrointestinal endoscopy and endoscopic ultrasonography revealed a cystic lesion 20 mm in size at the ampulla of Vater. Endoscopic retrograde cholangiopancreatography (ERCP) revealed that the cystic lesion communicated with both the common bile duct and pancreatic duct via the common channel. Choledochocele was ruled out by close examination of the ERCP findings. The cystic lesion was surgically resected. Since histological findings revealed that the mucosa inside the lesion was duodenum-like and contained a layer of smooth muscle, the lesion was diagnosed as a congenital duplication cyst of the duodenum.