A 26 year-old man presents to his primary physician with complaints of intermittent crampy epigastric pain, nausea, and vomiting sholy after eating. He usually vomits undigested food and this relives the pain and nausea. He has preferred to eat soft foods his whole life, and he often relies on liquids. He is otherwise healthy and well developed upper gastrintesrinal barium study reveals a markedly narrowed second poion of the duodemun laboratory studies are unremarkable. Probable diagnosis is?

This patient has symptoms of gastric outlet obstruction or, as in this case, duodenal obstruction, Several of these diseases could result in duodenal obstruction. However, the fact that he is young, otherwise healthy, and has avoided solid foods all his life suggests he has a congenital problem. He does not describe symptoms of biliary colic nor does he have signs of cancer. Episodic pain is not typical during bouts of acute pancreatitis, and pancreas divisum does not cause duodenal obstruction. Annular pancreas fits best with his history, his constellation of presett symptoms, and his upper gastrointestinal study.