DUODENAL FOSSAE AND LIGAMENT OF TREITZ
The duodenojejunal flexure lies left of the midline at the level of the first and second lumbar vertebrae. The suspensory muscle of the duodenum (ligament of Treitz, suspensory ligament of the duodenum) is a flat, fibromuscular ligament arising from the right crus of the diaphragm near the aortic hiatus. It passes, with individual variations, inferior to the left of the celiac trunk and superior mesenteric artery, posterior to the pancreas, to reach the duodenojejunal flexure. The smooth muscle cells of the ligament are largely continuous with the musculature of the celiac and superior mesenteric arteries; at the intestinal attachment they are connected with the longitudinal muscular layer of the gut, some extending as far as the mesentery of the small intestine. The attachment of the ligament to the duodenum may be quite narrow or it may extend over a considerable portion of the third part of the duodenum. If the suspensory ligament of the duodenum is short, the duodenojejunal flexure is high; if it is long, the flexure may lie so low that the terminal duodenal segment does not take the usual ascending course.
Several peritoneal recesses exist to the left of the ascending portion of the duodenum. These result from secondary fixation of the mesentery of the descending colon to the posterior abdominal wall; they vary greatly in depth and size between individuals. The most important are those arising from the superior duodenal fold and the inferior duodenal fold. These originate from the point of attachment of the descending mesocolon and run archlike from left to right, the superior to reach the duodenojejunal flexure and the inferior to the ascending portion of the duodenum. The superior fold is inferiorly concave and forms the aperture of the superior duodenal fossa, whereas the inferior fold is superiorly concave and forms the aperture of the inferior duodenal fossa. These fossae may be clinically significant as sites of intraperitoneal herniation. They are bounded anteriorly by the superior and inferior duodenal folds, respectively, and on the left by the ascending portion of the duodenum or the duodenojejunal flexure. Both fossae are bounded on the right by the parietal peritoneum and extend behind the posterior duodenal wall, which is covered by visceral peritoneum. Near the insertion of the superior duodenal fold is the inferior mesenteric vein, ascending to reach the splenic vein. At the corresponding position in the inferior fold is the ascending branch of the left colic artery. The left ureter can be found immediately posterior to the inferior duodenal fossa.
Several rarer types of fossae may also be found in this region, such as the paraduodenal recess bounded by the inferior mesenteric vein and the ascending branch of the left colic artery. In this case, a somewhat longitudinal peritoneal fold, the paraduodenal fold, slightly concave to the right, occasionally gives rise to a so-called left duodenal hernia (of Moynihan). This fossa can sometimes be separated into two partial folds; the more ventral and superficial fold rises above the ascending branch of the left colic artery, whereas the deeper or more posterior fold is bordered by the inferior mesenteric vein.
On very rare occasions a duodenojejunal fossa (not illustrated) extends cranially from the duodenojejunal flexure under the root of the transverse mesocolon, or a retroduodenal recess runs superiorly between the aorta and the ascending portion of the duodenum. The mesentericoparietal fossa, invariably present in the fetus, occasionally forms the enclosing sac for a right paraduodenal hernia. It is bounded anteriorly by the superior mesenteric vessels as they enter the mesentery of the small intestine, and posteriorly by the parietal peritoneum over the right side of the aorta.