Lateral Profile of the Ascending Part of the Male Duodenum

Description

Viewed in lateral profile, the ascending (fourth) part of the duodenum rises from the inferior duodenal flexure to the duodenojejunal flexure, crossing from a more right-sided position toward the left of the midline as it approaches the root of the mesentery. Its posterior relations are dominated by the left psoas major and the bodies of the upper lumbar vertebrae, while the anterior surface lies deep to the transverse mesocolon and adjacent jejunal loops. Superiorly, the duodenojejunal junction sits just inferior to the pancreas and near the ligament of Treitz. A fixed retroperitoneal segment. This lateral orientation matters because the ascending duodenum marks the transition from relatively immobile duodenum to mobile jejunum, a junction surgeons and endoscopists use as a landmark when orienting within the proximal small bowel. Proximity to the superior mesenteric artery and aorta is not academic: loss of mesenteric fat can narrow the aortomesenteric angle and compress the third part of the duodenum, and mobilization around the ligament of Treitz is a standard step in exposure for procedures ranging from trauma evaluation to pancreatic and small-bowel surgery. Malrotation also alters the expected position of the duodenojejunal flexure, and this profile helps teach the normal relationship. Use this illustration in gross anatomy and gastrointestinal block teaching to clarify duodenal parts, flexures, and retroperitoneal fixation, or in operative manuals discussing mobilization of the duodenojejunal flexure and adjacent vascular landmarks. It also suits radiology education when correlating upper GI contrast studies or CT with the expected location of the duodenojejunal junction in an adult male. Anatomical accuracy verified by SciePro's Medical Advisory Board.