Greater Omentum

Definition and Overview

Structure

• It is a four-layered peritoneal fold (as described in Grainger & Allison's diagnostic radiology) - descending from the greater curvature of the stomach, then turning superiorly to insert into the anterosuperior aspect of the transverse colon.
• Usually a thin membrane, but always contains some amount of fat - which may become substantial in obese individuals.
• In an adult, it lies between the abdominal wall and the hollow viscera, usually extending down into the pelvis.

Ligamentous Extensions

• Schwartz's Principles of Surgery, p. 1585

Blood Supply

• Derived from the right and left gastroepiploic (gastro-omental) arteries, which run between the double peritoneal layers just inferior to the greater curvature of the stomach.
• Venous drainage parallels the arterial supply and ultimately drains into the portal system.
• Gray's Anatomy for Students, p. 367; Schwartz's Principles of Surgery, p. 1585

Lymphatic Drainage

• Lymphatics drain via the subpyloric nodes (right side) or splenic nodes (left side), ultimately converging at the celiac nodes and then the thoracic duct.
• Schwartz's Principles of Surgery, p. 1585

The "Policeman of the Abdomen"

1. When bowel becomes inflamed, it ceases peristalsis (local paralytic ileus). The adjacent motile bowel "massages" the omentum toward the static, inflamed area.
2. The omentum migrates to the site and adheres, walling off the infection.
3. It forms fibrin adhesions at sites of inflammation, preventing diffuse peritonitis.
4. It expresses chemotactic, inflammatory, and hemostatic factors to promote tissue repair.
5. A fibrin bridge forms between the omentum and an injured site, allowing passage of immune cells.

• An acutely inflamed appendix is often found wrapped in omentum, protecting the patient from diffuse peritonitis.
• The omentum often plugs hernial sacs, preventing bowel strangulation.
• The Graham patch repair of a perforated peptic ulcer exploits the omentum's inflammatory/healing properties to improve leak rates.
• Bailey and Love's Short Practice of Surgery, 28th Ed.; Schwartz's Principles of Surgery, p. 1585-1586

Metabolic Functions

• Increased omental fat is an independent risk factor for insulin resistance and hypertriglyceridemia.
• Omental adipose tissue secretes adipokines (cell-signaling molecules) that act on peripheral tissues.
• Visceral inflammation in intra-abdominal obesity contributes to systemic metabolic dysfunction.
• Schwartz's Principles of Surgery, p. 1586

Clinical / Surgical Relevance

Omental Cake

Omental Infarction

• A rare cause of acute abdominal pain.
• Primary causes: torsion from sudden movements, thrombosis, vasculitis, or venous outflow obstruction.
• Secondary causes: hernias, tumors, or adhesions.
• More common in male, obese patients.
• Mimics appendicitis, cholecystitis, or diverticulitis.
• CT shows a "streaking whirling pattern" of fatty tissue in the anterior abdomen.
• Treatment: laparoscopic resection of the infarcted tissue.

Omental Cysts

• Rare; thought to form from degeneration or inclusion of lymphatic structures.
• Present as vague abdominal pain, nausea, or vomiting - or found incidentally on imaging.
• Can serve as a lead point for omental torsion.
• CT and US reveal a well-circumscribed cystic lesion. Small malignant transformation risk.
• Usually resected if symptomatic.

Omental Neoplasms

• Most are metastatic in origin.
• Ovarian cancer is the most common primary to involve the omentum.
• Others: GI tract tumors, melanoma, endometrial cancer, kidney cancer.
• Schwartz's Principles of Surgery, pp. 1585-1587

First Structure Seen at Laparotomy

• Gray's Anatomy for Students, p. 368; Berek & Novak's Gynecology

• Gray's Anatomy for Students (pp. 367-368)
• Schwartz's Principles of Surgery, 11th Ed. (pp. 1585-1587)
• Bailey and Love's Short Practice of Surgery, 28th Ed. (Ch. 65)
• Berek & Novak's Gynecology
• Grainger & Allison's Diagnostic Radiology