Annular pancreas is a rare condition in which the second part of the duodenum is surrounded by a ring of pancreatic tissue continuous with the head of the pancreas. This portion of the pancreas can constrict the duodenum and block or impair the flow of food to the rest of the intestines. Annular pancreas is caused by a birth defect. The developing pancreas does not form properly. The condition is caused by a ring of extra pancreatic tissue that covers the first part of your small intestine. Annular pancreas can be either complete or incomplete 1st complete annular pancreas: pancreatic parenchyma or annular duct is seen to completely surround the 2nd part of duodenum. incomplete annular pancreas: annulus does not surround the duodenum completely, giving a 'crocodile jaw' appearance.