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Omental bursa (lesser sac)

Bursa omentalis

Also known as: lesser sac, omental foramen, epiploic foramen, foramen of Winslow

The omental bursa (lesser sac) is the part of the peritoneal cavity behind the stomach and lesser omentum. It communicates with the greater sac only through the omental (epiploic) foramen.

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Overview

The lesser sac lets the stomach glide freely over the structures behind it. In front lie the lesser omentum, the posterior surface of the stomach and the gastrocolic ligament. Behind, covered by parietal peritoneum, lie the pancreas, left kidney and suprarenal, aorta and coeliac trunk. The sac has several recesses. The superior recess extends up behind the caudate lobe to the diaphragm. The inferior recess lies between the layers of the greater omentum and is usually obliterated in adults. The splenic recess reaches the splenic hilum between the gastrosplenic and splenorenal ligaments.

The omental (epiploic) foramen, of Winslow, is the only natural opening. It admits about one finger. Its boundaries are: anterior, the free edge of the hepatoduodenal ligament (portal triad); posterior, the IVC and right crus; superior, the caudate process of the liver; inferior, the 1st part of the duodenum.

Location

Behind the stomach and lesser omentum, in front of the pancreas and left kidney. It opens to the greater sac at the omental foramen, behind the free edge of the lesser omentum.

Parts & subdivisions

  1. Omental foramen
    Boundaries: hepatoduodenal ligament (anterior), IVC (posterior), caudate process (superior), 1st part of the duodenum (inferior).
  2. Superior, inferior and splenic recesses
    Extensions of the lesser sac towards the diaphragm, into the greater omentum and to the spleen.

Anatomy

Development

Formed when the stomach rotates and the dorsal mesogastrium grows to the left, creating a space behind the stomach.

Function

  • Allows free movement of the stomach.

Clinical significance

Pancreatic pseudocyst

Inflammatory fluid from acute pancreatitis collects in the lesser sac. After about 4 weeks it can mature into a walled pseudocyst behind the stomach, causing early satiety or obstruction.

Posterior perforation and internal hernia

A perforated ulcer on the posterior wall of the stomach leaks into the lesser sac and may initially produce only localised signs. Bowel can rarely herniate through the omental foramen.

Mnemonics

Boundaries of the omental foramen

Front: the "portal triad" (hepatoduodenal ligament). Back: the "big vein" (IVC). Roof: the caudate lobe. Floor: the duodenum (1st part).

Compiled from standard anatomy and physiology references — see the Digestive System sources. For education only; not medical advice.