Lesser Omentum

The lesser omentum is a double-layered fold of peritoneum that extends from the liver to the lesser curvature of the stomach and the first part of the duodenum. It forms part of the anterior wall of the lesser sac and serves as a conduit for vital structures traveling between the liver and the gastrointestinal tract. Despite its thin and transparent appearance, the lesser omentum plays a crucial anatomical and surgical role due to the structures it encloses and its relationship with the portal triad. It contrasts with the thicker, fat-filled greater omentum both in position and function.

Structure

The lesser omentum is composed of two closely apposed layers of visceral peritoneum. It arises from the visceral peritoneum covering the liver and extends to the stomach and duodenum.

Attachments

• Superior attachment: Porta hepatis of the liver
• Inferior attachment: Lesser curvature of the stomach and the first 2–3 cm of the duodenum

The space between the two layers encloses important neurovascular and lymphatic structures that are part of the hepatoduodenal ligament.

Subdivisions

The lesser omentum is traditionally divided into two named ligaments based on its attachments:

1. Hepatogastric Ligament

• Connects the liver to the lesser curvature of the stomach
• Forms the thin, membranous portion of the lesser omentum
• Contains small gastric vessels (right and left gastric arteries and veins)

2. Hepatoduodenal Ligament

• Connects the liver to the first part of the duodenum
• Thicker and more clinically important portion
• Contains the portal triad: hepatic artery proper, portal vein, and common bile duct

The hepatoduodenal ligament forms the anterior border of the epiploic (omental) foramen, which provides communication between the greater and lesser sacs of the peritoneal cavity.

Location and Boundaries

The lesser omentum lies in the upper abdomen, primarily in the epigastric and left hypochondriac regions. It forms part of the anterior wall of the lesser sac (omental bursa).

Boundary	Relation
Anteriorly	Liver and peritoneum
Posteriorly	Lesser sac and pancreas
Medially	Free edge at hepatoduodenal ligament
Laterally	Continuous with peritoneum of greater sac

Contents

The lesser omentum encloses several key structures, especially within the hepatoduodenal ligament. These include:

Hepatoduodenal Ligament Contents (Portal Triad)

• Hepatic artery proper: Supplies arterial blood to the liver
• Portal vein: Carries nutrient-rich blood from GI tract to liver
• Common bile duct: Carries bile from liver and gallbladder to duodenum

Additional Contents

• Right and left gastric arteries and veins (in hepatogastric ligament)
• Lymph nodes and lymphatics
• Nerve fibers from celiac plexus

Function

While structurally simple, the lesser omentum performs several important roles:

• Suspends the stomach and duodenum: Anchors these organs to the liver
• Conduit for portal triad: Transmits vital vessels and ducts between liver and gut
• Defines part of the lesser sac: Forms anterior boundary of this peritoneal compartment
• Barrier and passage: Acts as both a protective barrier and communication route between peritoneal compartments

Embryological Origin

The lesser omentum develops from the ventral mesogastrium in the embryo. As the stomach rotates during development, the ventral mesentery between the liver and the stomach becomes stretched and forms the lesser omentum. The dorsal mesogastrium, in contrast, gives rise to the greater omentum and structures like the splenorenal and gastrosplenic ligaments.

Clinical Significance

Pringle Maneuver

During hepatic surgery or trauma, the hepatoduodenal ligament can be clamped using the Pringle maneuver to temporarily stop inflow of blood to the liver. This compresses:

• Hepatic artery proper
• Portal vein

The common bile duct is also in the clamp area but typically not functionally obstructed by short-term compression.

Lesser Sac Access

• To access the posterior stomach or pancreas, surgeons may open the lesser omentum or enter through the gastrocolic ligament
• Rupture of gastric ulcers on the posterior wall may leak into the lesser sac, accessed behind the omentum

Portal Hypertension and Collaterals

Enlarged portal veins within the lesser omentum may be visualized on imaging in patients with portal hypertension. These can form part of portosystemic anastomoses.

Gastric and Liver Cancer Spread

• Tumors of the stomach or liver can spread along the peritoneal folds of the lesser omentum
• Involvement of omental lymph nodes may indicate advanced disease

Comparison: Lesser Omentum vs Greater Omentum

Feature	Lesser Omentum	Greater Omentum
Location	Between liver and lesser curvature of stomach	Hangs from greater curvature of stomach
Components	Hepatogastric and hepatoduodenal ligaments	Gastrocolic, gastrosplenic, gastrophrenic ligaments
Contents	Portal triad, gastric vessels	Fat, vessels, lymphatics, immune cells
Embryological origin	Ventral mesogastrium	Dorsal mesogastrium
Function	Suspends organs, transmits vital structures	Fat storage, immune response, organ protection