Lesser Omentum

Overview

The lesser omentum is a double-layered fold of peritoneum that connects the lesser curvature of the stomach and the proximal duodenum to the liver. Though smaller than the greater omentum, it plays a crucial role in supporting key structures such as blood vessels, lymphatics, and ducts entering or leaving the liver. It also contributes to the organization of the upper abdominal cavity and provides a pathway for neurovascular communication.

Location

The lesser omentum is located in the upper abdomen, forming part of the anterior boundary of the lesser sac (omental bursa). It:

• Extends from the liver (porta hepatis) to the lesser curvature of the stomach and the first part of the duodenum

• Forms the anterior wall of the epiploic (omental) foramen, which connects the lesser sac to the greater sac

• Is suspended vertically between the liver and the stomach/duodenum

Structure

The lesser omentum is composed of two main parts:

• Hepatogastric ligament: Connects the liver to the lesser curvature of the stomach; thinner and more membranous

• Hepatoduodenal ligament: Thicker portion that connects the liver to the first part of the duodenum; contains the portal triad

The portal triad, enclosed within the hepatoduodenal ligament, includes:

• Hepatic artery proper

• Portal vein

• Common bile duct

The lesser omentum is covered by visceral peritoneum on both surfaces, with a thin layer of connective tissue in between.

Function

Though primarily structural, the lesser omentum serves several key functions:

• Suspends and stabilizes: Anchors the stomach and proximal duodenum to the liver

• Conduit for vessels and ducts: Allows passage of vital structures such as the portal triad between the liver and digestive tract

• Partitioning of peritoneal cavities: Helps separate the greater sac from the lesser sac of the peritoneal cavity

Physiological Role(s)

Beyond structural support, the lesser omentum contributes to digestive and hepatic physiology:

• Facilitates bile transport: The bile duct housed within the hepatoduodenal ligament carries bile from the liver and gallbladder to the duodenum for fat emulsification

• Delivers oxygenated blood: The hepatic artery proper supplies arterial blood to the liver

• Returns nutrient-rich blood: The portal vein brings venous blood from the gastrointestinal tract to the liver for filtration and metabolic processing

• Immune function: Though less immunologically active than the greater omentum, it may still assist in limiting localized infection spread within the upper abdomen

Clinical Significance

The lesser omentum is important in several clinical and surgical contexts:

• Portal triad clamping (Pringle maneuver): During liver surgery or trauma, clamping the hepatoduodenal ligament temporarily controls bleeding from the hepatic artery and portal vein

• Access to the lesser sac: Surgeons must reflect the lesser omentum to access the posterior stomach, pancreas, and omental bursa during procedures like pancreatic resections

• Peritonitis spread: The lesser omentum may be a route for infectious or inflammatory material to spread between compartments

• Hepatogastric ligament involvement: May be invaded or thickened in cases of gastric or hepatic cancer, and can be assessed during staging laparoscopy

• Lymphatic drainage and metastasis: Lymph nodes within or near the lesser omentum may harbor metastatic disease from gastric or hepatic primaries

Imaging techniques like CT or laparoscopy can help visualize the lesser omentum and its contents, especially in the context of cancer staging or surgical planning.