Horizontal Segment of the Male Duodenum, Posterior View

Description

Posteriorly oriented anatomy of the duodenum centers on the pars horizontalis (inferior, third part), running transversely from right to left at approximately the L3 level. The segment crosses anterior to the abdominal aorta and inferior vena cava, with the superior mesenteric artery and vein descending anterior to it as they leave the root of the mesentery. Medially, the duodenojejunal junction approaches the left side near the aorta, while laterally the loop returns toward the head of the pancreas. This is a tight corridor. That posterior relationship is why the horizontal duodenum is a classic compression site in superior mesenteric artery syndrome, where reduced aortomesenteric angle can trap the bowel between the SMA anteriorly and the aorta posteriorly. Surgeons also care about this plane during pancreaticoduodenectomy and vascular exposure, because mobilization with a Kocher maneuver brings the duodenum off the retroperitoneum and can reveal the inferior vena cava and right renal vessels immediately posterior to the second and third parts. Injury risk is not theoretical. Use this artwork in gross anatomy and gastrointestinal modules to teach duodenal parts and their retroperitoneal relationships, or in radiology and surgical texts when correlating CT axial slices with the third part crossing the great vessels. It also fits patient education or lecture slides on proximal obstruction syndromes and postoperative anatomy after pancreatic head surgery. Anatomical accuracy verified by SciePro's Medical Advisory Board.