Greater omentum

The common anatomical term "epiploic" derives from "epiploon", from Greek epipleein 'to float or sail on', since the greater omentum appears to float on the surface of the intestines. It is the first structure observed when the abdominal cavity is opened anteriorly (from the front).

Structure

The greater omentum is the larger of the two peritoneal folds. It consists of a double sheet of peritoneum, folded on itself so that it has four layers.

The two layers of the greater omentum descend from the greater curvature of the stomach and the beginning of the duodenum. They pass in front of the small intestines, sometimes as low as the pelvis, before turning on themselves, and ascending as far as the transverse colon, where they separate and enclose that part of the intestine.

These individual layers are easily seen in the young, but in the adult they are more or less inseparably blended.

The left border of the greater omentum is continuous with the gastrosplenic ligament; its right border extends as far as the beginning of the duodenum.

The greater omentum is usually thin, and has a perforated appearance. It contains some adipose tissue, which can accumulate considerably in obese people. It is highly vascularised, which means that if it is unintentionally damaged during surgery, it can cause internal bleeding.

Subdivisions

The greater omentum is often defined to encompass a variety of structures. Most sources include the following three:

• Gastrophrenic ligament—extends to the underside of the left dome of the diaphragm
• Gastrocolic ligament (occasionally on its own considered synonymous with "greater omentum")—extends to the transverse colon
• Gastrosplenic (or Gastrolineal) ligament—extends to the spleen, overlying the kidney

The splenorenal ligament (or lienorenal ligament) (from the left kidney to the spleen) is occasionally considered part of the greater omentum. It is derived from the peritoneum, where the wall of the general peritoneal cavity comes into contact with the lesser sac between the left kidney and the spleen; the splenic artery and vein pass between its two layers. It contains the tail of the pancreas, the only intraperitoneal portion of the pancreas, and splenic vessels. One or more of the preceding sentences incorporates text in the public domain from the 20th edition of Gray's Anatomy (1918)

Phrenicosplenic ligament

The phrenosplenic ligament (lienophrenic ligament or phrenicolienal ligament) is a double fold of peritoneum that connects the thoracic diaphragm and spleen.

The phrenicosplenic ligament is part of the greater omentum. Distinctions between the phrenicosplenic ligament and adjacent ligaments, such as the gastrophrenic, gastrosplenic and splenorenal ligaments, which are all part of the same mesenteric sheet, are often nebulous.

Blood supply

The right and left gastroepiploic arteries (also known as gastroomental) provide the sole blood supply to the greater omentum. Both are branches of the celiac trunk. The right gastroepiploic artery is a branch of the gastroduodenal artery, which is a branch of the common hepatic artery, which is a branch of the celiac trunk. The left gastroepiploic artery is the largest branch of the splenic artery, which is a branch of the celiac trunk. The right and left gastroepiploic arteries anastomose within the two layers of the anterior greater omentum along the greater curvature of the stomach.

Development

The greater omentum develops from the dorsal mesentery that connects the stomach to the posterior abdominal wall. During its development, the stomach undergoes its first 90° rotation along the axis of the embryo, so that posterior structures are moved to the left and structures anterior to the stomach are shifted to the right. As a result, the dorsal mesentery folds over on itself, forming a pouch with its blind end on the left side of the embryo. A second approximately 90° rotation of the stomach, this time in the frontal plane, moves structures inferior if they were originally to the left of the stomach, and superior if they were originally to the stomach's right. Consequently, the blind-ended sac (also called the lesser sac) formed by the dorsal mesentery is brought inferiorly, where it assumes its final position as the greater omentum. It grows to the point that it covers the majority of the small and large intestine.