Omental Bursa and Its Recesses
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Direct answer
Behind the stomach lies the omental bursa or lesser sac, the largest fully enclosed recess of the peritoneal cavity, communicating with the greater sac only through the epiploic foramen of Winslow. Its walls are the stomach and lesser omentum in front, the pancreas, left suprarenal, left kidney and transverse mesocolon behind, and the gastrosplenic and splenorenal ligaments to the left. Three named recesses — superior, splenic and inferior — extend towards the oesophageal hiatus, the splenic hilum and below the greater curvature, and in disease the bursa fills first: a pancreatic pseudocyst is essentially an omental bursa distended by fluid.
What you must remember
- Only communication: the epiploic foramen of Winslow, big enough for two fingers, between the free edge of the lesser omentum in front and the inferior vena cava behind.
- Foramen boundaries: anterior — hepatoduodenal ligament with the portal triad; posterior — inferior vena cava; superior — caudate lobe of liver; inferior — first part of the duodenum.
- Anterior wall: caudate lobe and lesser omentum above, stomach and gastrocolic ligament below.
- Posterior wall: pancreas, left suprarenal gland, left kidney above, and the transverse mesocolon below — largely the "stomach bed".
- Superior recess: passes behind the lesser omentum towards the oesophageal hiatus; splenic recess extends to the left between gastrosplenic and splenorenal ligaments; inferior recess lies between the gastrocolic ligament and the transverse mesocolon.
- Clinical filling: pancreatitis fluid, posterior gastric ulcer perforation and trauma blood collect in the bursa; a pseudocyst bulges the stomach forwards.
- Development: the bursa forms from the right pneumatoenteric recess rotated by gastric growth — an intestinally derived cavity, not a split in the mesentery.
A worked example: the pseudocyst
A man with severe acute pancreatitis is readmitted four weeks later with a sense of fullness and a smooth, rounded epigastric swelling; ultrasound shows a 10 cm collection behind the stomach. The anatomy now writes the treatment. The bursa lies immediately behind the stomach's posterior wall, separated from it by peritoneum alone, so the pseudocyst matures, adheres to the posterior gastric wall, and a cystogastrostomy — an incision through the anterior and posterior gastric walls into the cavity — drains it without ever crossing the peritoneal cavity. That single operation is the payoff of knowing the bursa's anterior wall.
The same relations explain his pain. A posterior gastric or duodenal ulcer perforates into the bursa rather than the greater sac, so peritonitis is late and muted, and erosion backwards threatens the splenic artery on the pancreas, giving back pain instead of a board-like abdomen. Fluid from the bursa can escape through the foramen of Winslow into the greater sac and track down the right paracolic gutter, which is why pancreatic ascites can follow a disrupted duct.
Where students slip
The foramen's posterior boundary is the inferior vena cava, not the aorta — a favourite one-mark MCQ — and its inferior boundary is the first part of the duodenum, which is why a duodenal perforation can gush into the lesser sac. The caudate lobe, being embryologically part of the left lobe, lies in the superior recess and forms the roof of the foramen; students send it to the right lobe. Finally, the splenic recess explains spleen surgery: the gastrosplenic and splenorenal ligaments are literally the left wall of the bursa, so short gastric vessel ligation opens into it.
Frequently asked questions
How does the omental bursa communicate with the greater sac?
Only through the epiploic foramen of Winslow, bounded by the hepatoduodenal ligament in front, the inferior vena cava behind, the caudate lobe above and the first part of the duodenum below.
What are the three recesses of the omental bursa?
The superior recess behind the lesser omentum near the oesophageal hiatus, the splenic recess towards the splenic hilum, and the inferior recess between the gastrocolic ligament and the transverse mesocolon.
Why is a pancreatic pseudocyst an omental bursa problem?
The pancreas forms the posterior wall of the bursa, so fluid from a disrupted duct collects in it and pushes the stomach forwards, allowing drainage by cystogastrostomy.
What happens when a posterior gastric ulcer perforates?
It ruptures into the lesser sac, so generalized peritonitis is delayed; erosion of the splenic artery or pancreas produces back pain and haemorrhage.
Which structures form the posterior wall of the bursa?
From above downwards, the left suprarenal gland, upper part of the left kidney, the pancreas and the transverse mesocolon — collectively the stomach bed.