Surgical Approach to the Lesser Sac
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Direct answer
Three routes lead a surgeon into the omental bursa, and each exploits a different window in its walls. The gastrocolic route opens the gastrocolic ligament along the greater curvature, the standard approach to the body and tail of the pancreas; the hepatogastric route breaches an avascular window of the lesser omentum; and the transmesocolic route pierces the transverse mesocolon, risking the middle colic vessels. Choosing between them is pure wall-anatomy: enter where the wall is thin and vessels are avoidable, because the bursa is wrapped around the pancreas precisely where the abdomen's most treacherous vessels run.
What you must remember
- Gastrocolic route: divide the gastrocolic ligament between the greater curvature and the transverse colon, outside the gastroepiploic arcade — the workhorse approach to the pancreas.
- Hepatogastric route: open the avascular window of the lesser omentum between the liver and lesser curvature — fast, but it may contain a replaced or accessory left hepatic artery from the left gastric.
- Transmesocolic route: a window in an avascular part of the transverse mesocolon, used for draining collections, with the middle colic vessels the constant danger.
- Kocherisation: mobilising the second part of the duodenum and head of the pancreas off the vena cava — exposure of the pancreatic head, not strictly a lesser sac entry.
- Gastroepiploic arcade: the right and left gastroepiploic vessels anastomose along the greater curvature; stay below it or outside it to enter cleanly.
- Cystogastrostomy: a matured pseudocyst is drained through the adherent posterior gastric wall — the lesser sac operation every MBBS student must explain.
Working through a gastrocolic entry
Take a patient planned for drainage of pancreatic necrosis. The surgeon lifts the greater omentum and identifies the fusion plane between the gastrocolic ligament above and the transverse mesocolon below — an embryo logically two separate double sheets, fused after birth, which is why a clean plane exists at all. Entry is made through the gastrocolic ligament at the midpoint of the greater curvature, avoiding the gastroepiploic vessels hugging the curve and the middle colic artery in the mesocolon. One is now standing in the inferior recess of the lesser sac, staring directly at the pancreas.
From there the whole posterior wall is available: the body and tail towards the spleen, the head with kocherisation of the duodenum, and the splenic artery crawling along the upper border. The common error — entering too low and tearing the middle colic arcade — produces brisk bleeding exactly where visibility is worst, which is why the anatomy is taught before the surgery. In laparoscopic work the same window is used, with the camera entering the hepatogastric window sometimes as an alternative when the gastrocolic plane is fused by previous inflammation.
Where students slip
The hepatogastric window is called "avascular" and treated as safe. It is avascular in most people, but a replaced or accessory left hepatic artery runs in the lesser omentum in a sizeable minority, and dividing it silently devascularises left lobe segments; a proper answer names that risk. The second slip is calling kocherisation a lesser sac approach — it opens the retroperitoneum behind the duodenum and pancreatic head. The third is forgetting that in the adult the inferior recess is partly obliterated by fusion of the gastrocolic ligament with the transverse mesocolon and greater omentum, so the bursa of the cadaver is smaller than the diagram suggests.
Frequently asked questions
Which is the standard surgical approach to the lesser sac?
The gastrocolic approach, dividing the gastrocolic ligament along the greater curvature outside the gastroepiploic arcade, entering the inferior recess to expose the pancreas.
What is the danger of the hepatogastric route?
A replaced or accessory left hepatic artery arising from the left gastric artery may run in the lesser omentum and can be injured in the supposedly avascular window.
Why must the transmesocolic route be made carefully?
The middle colic vessels run in the transverse mesocolon; an incision in the wrong plane lacerates them, endangering the blood supply of the transverse colon.
What is kocherisation?
Incision of the peritoneum lateral to the second part of the duodenum and mobilisation of the duodenum and pancreatic head medially, exposing the inferior vena cava behind.
How is a pancreatic pseudocyst drained using lesser sac anatomy?
The cyst, occupying the bursa, adheres to the posterior gastric wall; a cystogastrostomy opens it through the stomach without entering the general peritoneal cavity.