Greater Omentum

Overview

The greater omentum is a large, apron-like fold of peritoneum that hangs down from the greater curvature of the stomach and drapes over the intestines. It plays a critical role in immune defense, fat storage, infection containment, and maintaining abdominal organ stability. Although it is not directly involved in digestion, it is vital for protecting and supporting abdominal viscera.

Location

The greater omentum is located in the anterior abdominal cavity. It:

• Arises from the greater curvature of the stomach and the proximal duodenum

• Hangs down like an apron in front of the small intestines (especially the jejunum and ileum)

• Loops back and attaches to the transverse colon and its associated mesocolon

It occupies the space between the anterior abdominal wall and the underlying intestinal loops.

Structure

The greater omentum is composed of:

• Four layers of peritoneum: Two anterior and two posterior layers that fuse during development

• Fat tissue: Variable amounts of adipose tissue stored between the peritoneal layers

• Blood vessels: Supplied primarily by the right and left gastroepiploic arteries and veins

• Lymphatics: Numerous lymph nodes embedded in the fat for immune surveillance

The omentum is highly mobile and can migrate toward sites of infection or injury in the peritoneal cavity, earning it the nickname "policeman of the abdomen."

Function

The greater omentum serves several important functions:

• Immune surveillance: Contains macrophages and lymphocytes that monitor and respond to infection or inflammation

• Fat storage: Acts as a depot for energy storage and insulation

• Protection: Cushions the abdominal organs from trauma

• Infection containment: Physically walls off areas of infection or perforation (e.g., in appendicitis or diverticulitis)

Physiological Role(s)

Though not directly digestive, the greater omentum contributes to abdominal physiology by:

• Immune modulation: Lymphoid aggregates in the omentum help regulate peritoneal immune responses

• Vascular support: Provides collateral blood flow to the stomach and colon through its arterial network

• Tissue repair: Aids in healing damaged or inflamed peritoneal tissues

• Peritoneal fluid absorption: Assists in maintaining fluid balance within the peritoneal cavity

Clinical Significance

The greater omentum is involved in several clinical contexts:

• Omental infarction: A rare condition where omental tissue becomes ischemic due to torsion or vascular compromise, mimicking appendicitis

• Adhesions and omental wrapping: The omentum may adhere to inflamed organs, sometimes protecting them but also contributing to postoperative adhesions

• Tumor spread (omentum cake): Metastatic cancer, particularly from ovarian, gastric, or colon cancer, can spread to and thicken the omentum, creating a radiologic sign called an “omental cake”

• Omentectomy: Surgical removal of the omentum, often performed in oncologic surgeries to remove metastatic deposits

• Transplantation and grafting: Due to its rich vascular and immune properties, the omentum has been used experimentally in grafting procedures to promote healing

Imaging techniques like ultrasound, CT scan, and laparoscopy can be used to visualize the greater omentum, especially in cases of inflammation, tumors, or fluid accumulation.