lesser omentum

Vertical

disposition of the peritoneum. Main cavity, red; omental bursa, blue.

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Abdominal

cavity organs, with anterior margin of liver dragged to top. Lesser omentum in the middle, marked with bold text.

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An omentum is a double layer of peritoneum that attaches the stomach to another viscus:

the greater omentum hangs from the greater curvature of the stomach like an apron
the lesser omentum attaches the lesser curvature of the stomach to the liver superiorly

Gross anatomy

Greater omentum

The greater omentum is the largest peritoneal fold, consisting of a double sheet folded upon itself and thus made up of four layers. The two layers of peritoneum descend from the greater curve of the stomach and proximal duodenum passing inferiorly, anterior to the small bowel for a variable distance, and then turn superiorly again to insert into the anterosuperior aspect of the transverse colon. The left border is continuous with the gastrosplenic ligament; the right extends as far as the origin of the duodenum.

It is also known as the 'police of the abdomen' due to its rich vascular supply. During intra-abdominal sepsis/inflammation, it can move to the infected area and delivers lymphocytes to fight the infection.

Lesser omentum

The lesser omentum is the fold of peritoneum extending from the lesser curvature of the stomach and proximal 2 cm of the duodenum to the porta hepatis of the liver. It is formed by hepatogastric and hepatoduodenal ligaments.

It forms the anterior surface of the lesser sac. At its free edge, which extends to the porta hepatis, it forms the hepatoduodenal ligament. It is attached to its superior extent to the fissures for the porta hepatis and ligamentum venosum.