Occasionally, the entral segment deelops around the duodenum rather than behind it, creating a loop (annular pancreas) that could deelop an extrinsic constricture of the first segment of the duodenum.

• 如果，腹侧段围绕十二指肠发育形成环状（环状胰腺）而不是在它的背侧，将导致十二指肠的第一段外在狭窄。