Horizontal Part of the Duodenum Viewed Through an Anterior Section

Description

Seen through an anterior section, the pars horizontalis duodeni (D3) runs transversely from right to left at the level of L3, with its lumen and mucosal folds visible along the inner wall. Superior and anterior to this segment lies the superior mesenteric artery as it emerges from the aorta and crosses the third part of the duodenum, while the superior mesenteric vein typically sits just to the right of the artery. Posteriorly, D3 is related to the abdominal aorta and inferior vena cava, and the uncinate process of the pancreas approaches it superiorly and medially. A tight anatomic corridor. This sectional perspective matters because D3 is the classic site of vascular compression in superior mesenteric artery syndrome, where loss of the mesenteric fat pad narrows the aortomesenteric angle and traps the horizontal duodenum, producing postprandial pain and bilious vomiting. It is also a practical orientation for pancreatic head surgery, since mobilization of the duodenum (Kocher maneuver) and identification of the uncinate process hinge on understanding where D3 sits relative to the superior mesenteric vessels. Use this illustration in gross anatomy and gastrointestinal block teaching to anchor the three-dimensional course of the duodenum, and in surgical texts discussing duodenal obstruction, SMA syndrome, or pancreaticoduodenectomy anatomy, where the artery-over-duodenum relationship must be stated without ambiguity. Radiology educators will also find it aligns cleanly with axial CT reasoning about the aortomesenteric angle and D3 caliber. Anatomical accuracy verified by SciePro's Medical Advisory Board.