An infant is evaluated for paial intestinal obstruction that has been present from bih. Esophagogastroduodenal endoscopic visualization fails to demonstrate an intraluminal lesion, but does show prominent narrowing at the level of the mid duodenum. CT studies demonstrate a mass lesion surrounding that poion of the duodenum. Which type of tissue is most likely present within the lesion?

The lesion is an annular pancreas, which is a rare pancreatic malformation, in which the pancreatic head encircles the second pa of the duodenum, potentially causing obstruction. An increase in thickness of the muscular pa of the gastric wall can cause congenital pyloric stenosis. While the liver is near the first and second pas of the duodenum, there is no common developmental anomaly in which hepatic tissue would surround the duodenum. The kidneys are located retroperitoneally and relatively far lateral from the duodenum, and would not be expected to surround it. Ref: Molina P.E. (2013). Chapter 7. Endocrine Pancreas. In P.E. Molina (Ed),Endocrine Physiology, 4e.