The celiac trunk is closely flanked by the median arcuate ligament of the aortic hiatus above and the superior border of the pancreas below (Fig. 10-2). Viewed from an anterior perspective, the celiac trunk lies beneath the overlapping edges of the liver and stomach. On separating these two organs, the connecting gastrohepatic ligament, which forms the anterior wall of the omental bursa, is seen overlying the celiac trunk. Inside the omental bursa lies a final covering membrane, the posterior parietal peritoneum. Beneath the peritoneum, the celiac trunk is surrounded by lymphatic and nerve plexuses.

The celiac trunk is almost perpendicular to the aorta. The three branches of the celiac trunk most often form a trifurcation (see variations, Chapter 19). One significant vein, the left gastric (or coronary) vein, crosses over the celiac trunk in its course from the lesser curve of the stomach to the portal vein.

The hepatic artery passes to the right beneath the posterior peritoneum of the omental bursa, enters the hepatoduodenal ligament just cephalad to the pylorus, and ascends to the hilum of the liver on the left side of the common bile duct. The terminal branching of the hepatic artery is highly variable, and alternate origins of hepatic artery branches are not uncommon.

The splenic artery descends beneath the peritoneum to undulate along the cephalad border of the pancreas where it gives off a significant dorsal pancreatic branch and a few smaller branches. After dividing into four to five branches near the hilum of the spleen, it gives off short gastric branches and the left gastroepiploic artery that run in the gastrosplenic ligament and the gastrocolic ligament, respectively (Fig. 10-3).

The left gastric artery ascends a short distance beneath the peritoneum to reach the lesser curve of the stomach at the gastroesophageal junction. It is accompanied by the left gastric (coronary) vein and the celiac branch of the posterior vagus nerve. When the esophagus is mobilized, the left gastric artery limits the surgeon from sliding a finger further down the posterior wall of the stomach.

The origin of the superior mesenteric artery from the aorta forms a sharp caudal angle. The left renal vein is wedged into the acute angle. The first part of the superior mesenteric is crossed by the neck of the pancreas and the splenic vein. Behind the neck of the pancreas, the artery converges with the superior mesenteric vein so that the two structures are side by side at the lower margin of the pancreatic neck (Fig. 10-4). The vessels then pass over the uncinate process of the pancreas and the third portion of the duodenum to enter the root of the small bowel mesentery.

As soon as the superior mesenteric artery emerges below the pancreas, it sends the middle colic artery into the overlying root of transverse mesocolon. At the level of the uncinate process, the superior mesenteric artery also gives rise to the inferior pancreaticoduodenal artery, which makes a potentially important connection with the celiac circulation through the pancreaticoduodenal arcade.

The continuation of the superior mesenteric artery gives rise to two named branches and numerous vessels supplying the small bowel. Shortly after crossing the duodenum, the superior mesenteric gives off the right colic artery, which lies within the fused mesentery of the right colon. The ileocolic branch arises in common with or distal to the right colic and descends toward the cecum. The root of the small bowel mesentery passes from midline to the right lower quadrant, allowing mobilization of
this mesentery to the right for exposure of the aorta (Fig. 10-5).

The inferior mesenteric artery emerges near the lower border of the third portion of the duodenum where the latter crosses the aorta (Fig. 10-1). It is closely applied to the aorta as it passes to the left into the fused mesentery of the left colon. Within 5 cm of its origin, the artery first gives off a left colic branch and then several sigmoidal branches into the mobile sigmoid mesentery and finally terminates as the superior rectal branch. The latter crosses over the left iliac vessels to reach the posterior wall of the upper rectum (Fig. 10-1). In some cases of superior mesenteric occlusive disease, mesenteric channels between the left colic and middle colic arteries hypertrophy to form a meandering mesenteric artery (described by Riolan, see below),
which supplements the deficient superior mesenteric system.

Major communications among the three levels of visceral vessels provide collateral circulation in case of segmental occlusion (Fig. 10-6). The pancreaticoduodenal arcade connects the celiac and superior mesenteric circulations. The marginal artery (of Drummond) is composed of the left branch of the middle colic artery and the ascending branch of the left colic artery. If complete across the splenic flexure, the marginal artery may be adequate to maintain visceral perfusion between the superior and inferior mesenteric circulations when one or the other is occluded. Some individuals develop an enlarged accessory collateral between the inferior and superior mesenteric circulations. This so-called meandering mesenteric artery (of Riolan) is named for its tortuous appearance within the transverse mesocolon owing to extensive hypertrophy in patients with occlusive disease of the superior or inferior mesenteric branches. The inferior mesenteric circulation is also supported by collaterals between the superior rectal artery and the inferior rectal branches of the internal iliac artery.