Horizontal Part of the Duodenum as Side, Posterior View

Description

Running transversely from right to left, the third (horizontal, inferior) part of the duodenum is shown from a posterior perspective as it crosses the anterior surface of the L3 vertebral body, often extending from the right of midline toward the left psoas region before ascending into the duodenojejunal flexure. Superior to it lies the head of the pancreas, while inferiorly the root of the mesentery begins its oblique course across the posterior abdominal wall. Medially, the duodenum approaches the aorta, and just to its right the inferior vena cava tracks vertically. A retroperitoneal segment. This angle matters because the horizontal duodenum is the segment classically compressed between the superior mesenteric artery anteriorly and the aorta posteriorly, the anatomic basis of superior mesenteric artery syndrome with postprandial pain and bilious vomiting. It is also the portion mobilized during a Kocher maneuver when exposure of the pancreatic head, distal common bile duct, or retrocaval structures is required, and it helps orient surgeons to the plane where duodenal hematoma or perforation can track posteriorly. Radiologists and endoscopists also use this segment’s fixed retroperitoneal position to interpret narrowing on contrast studies and to localize obstruction relative to the ligament of Treitz. Ideal for gross anatomy and gastrointestinal blocks when teaching duodenal parts and their relationships to major vessels and lumbar vertebrae, and for surgical texts discussing mesenteric ischemia workup, SMA syndrome, or posterior approaches to the pancreaticoduodenal region. Suitable for labeling in atlases, board-style questions, and patient-facing explanations of vascular compression. Anatomical accuracy verified by SciePro's Medical Advisory Board.