| Greater omentum | |
|---|---|
 The greater omentum and corresponding vasculature is visible covering the intestines (dissection image with liver held out of the way). Label at bottom. | |
| Details | |
| Precursor | Dorsal mesentery |
| Artery | Right gastroepiploic artery |
| Identifiers | |
| Latin | omentum majus |
| TA98 | A10.1.02.201 |
| TA2 | 3757 |
| FMA | 9580 |
| Anatomical terminology | |
Thegreater omentum (also thegreat omentum,omentum majus,gastrocolic omentum,epiploon, or, especially in non-human animals,caul) is a large apron-like fold ofvisceral peritoneum that hangs down from the stomach. It extends from thegreater curvature of thestomach, passes in front of the small intestines, and doubles back to ascend to thetransverse colon before reaching to the posteriorabdominal wall. The greater omentum is larger than thelesser omentum, which hangs down from theliver to thelesser curvature. 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).[1]
The greater omentum is the larger of the twoperitoneal folds. It consists of a double sheet of peritoneum, folded on itself so that it has four layers.[2]
The two layers of the greater omentum descend from the greater curvature of the stomach and the beginning of theduodenum.[2] They pass in front of thesmall intestines, sometimes as low as thepelvis, before turning on themselves, and ascending as far as thetransverse colon, where they separate and enclose that part of theintestine.[2]
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 thegastrosplenic ligament; its right border extends as far as the beginning of theduodenum.
The greater omentum is usually thin, and has aperforated appearance. It contains someadipose tissue, which can accumulate considerably inobese people. It is highlyvascularised.[3]
The greater omentum is often defined to encompass a variety of structures. Most sources include the following three:[4][5]
Thesplenorenal ligament (orlienorenal ligament) (from the leftkidney to thespleen) is occasionally considered part of the greater omentum.[6][7] It is derived from theperitoneum, where the wall of the general peritoneal cavity comes into contact with thelesser sac between the leftkidney and thespleen; thesplenic artery andvein pass between its two layers. It contains the tail of thepancreas, the only intraperitoneal portion of the pancreas, and splenic vessels.
One or more of the preceding sentences incorporates text in thepublic domain from the 20th edition ofGray's Anatomy (1918)
Thephrenosplenic ligament (lienophrenic ligament orphrenicolienal ligament) is a double fold ofperitoneum that connects thethoracic diaphragm andspleen.[8]
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.[8]
The right and leftgastroepiploic arteries (also known as gastroomental) provide the sole blood supply to the greater omentum. Both are branches of theceliac trunk. The right gastroepiploic artery is a branch of thegastroduodenal artery, which is a branch of thecommon hepatic artery, which is a branch of the celiac trunk. The left gastroepiploic artery is the largest branch of thesplenic 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.
The greater omentum develops from thedorsal mesentery that connects thestomach 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 thefrontal 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 thelesser 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.
The functions of the greater omentum are:
Omentectomy refers to the surgical removal of the omentum, a relatively simple procedure with no documented major side effects, that is performed in cases where there is concern that there may be spread of cancerous tissue into the omentum. Examples for this areovarian cancer and advanced or aggressiveendometrial cancer as well asintestinal cancer and alsoappendix cancer. The procedure is generally done as an add-on when the primary lesion is removed.
The greater omentum may be surgically harvested for reconstruction of thethoracic wall.[3] It has also been used experimentally to reinforce bioengineered tissues transplanted to the surface of the heart for cardiac regeneration.[10]
The greater omentum may be surgically harvested to provide revascularization of brain tissue after a stroke.[11]
The greater omentum is also known as the great omentum, the omentum majus, the gastrocolic omentum, the epiploon, and the caul.
In 1906, the greater omentum was described as the "abdominal policeman" by the surgeonJames Rutherford Morrison.[12] This is due to its immunological function, whereby omental tissue seems to "surveil" the abdomen for infection and cover areas of infection when found - walling it off with immunologically active tissue.
The omentum helps to restore tissue integrity in the peritoneum by connecting tissue repair with immunological defense. Upon intraperitoneal immunization, follicles and germinal centers can be formed.
