Lesser sac

Last revised by Dr Julius Rozmiarek on 22 Jan 2021

The lesser sac or omental bursa is a potential peritoneal space within the abdomen, part of the peritoneal cavity

The lesser sac may be conceptualized as the space posterior to the lesser omentum, between the posterior wall of the stomach and surface of peritoneum that covers the anterior surface of the left kidney 1.

The epiploic foramen (of Winslow) is the only natural communication between greater and lesser sac.

As the lesser sac is a peritoneal space, all of its boundaries are lined by visceral or parietal peritoneum.

  • anterior
    • lesser omentum
    • visceral peritoneum along posterior stomach
    • gastrocolic omentum (between greater curvature of stomach and transverse colon)
  • left lateral
    • gastrosplenic and splenorenal ligaments
  • right lateral
  • posterior
    • visceral/parietal peritoneum that covers diaphragm, pancreas, left kidney/adrenal gland, and duodenum
    • transverse mesocolon (between transverse colon and anterior surface of pancreas)
  • superior
    • peritoneum covering caudate lobe of the liver
  • Superior (hepatic) recess - between caudate lobe of liver and diaphragm
  • Splenic recess - between splenic ligaments and stomach
  • Inferior (omental) recess - between stomach and transverse colon

The lesser omentum is composed of two peritoneal ligaments that extend from the lesser curvature of the stomach and duodenal bulb to the liver, the gastrohepatic, and hepatoduodenal ligaments, respectively. During embryologic development, the rotation of the stomach relative to the liver causes redundancy in the mesentery about the stomach. 

As the greater curvature of the stomach rotates anterolaterally, a recess is formed between the redundant dorsal peritoneal ligament connecting greater curvature of the stomach to the dorsal abdominal wall. Simultaneously, the lesser curvature of the stomach rotates posteromedially, and the ventral peritoneal ligament between stomach and liver becomes the lesser omentum, an incomplete boundary separating the main peritoneal cavity (greater sac) from the posterior recess (lesser sac). 

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