Epiploic Foramen (of Winslow)

The epiploic foramen, also known as the foramen of Winslow, is a narrow anatomical passage that connects the greater sac with the lesser sac (omental bursa) of the peritoneal cavity. Located in the upper right quadrant of the abdomen, it lies posterior to the free edge of the lesser omentum and is bordered by critical vascular structures. Despite its small size, the epiploic foramen plays a central role in internal abdominal communication, surgical access, and the pathophysiology of hernias and fluid spread.

Location

The foramen is found deep in the upper abdomen, just posterior to the hepatoduodenal ligament, which contains the portal triad. It opens from the greater sac into the posteriorly located lesser sac and lies just inferior to the caudate lobe of the liver.

Surface Landmark

• Located approximately at the level of vertebral body T12–L1
• Behind the free edge of the lesser omentum (hepatoduodenal ligament)

Boundaries of the Epiploic Foramen

Boundary	Structure
Anterior	Hepatoduodenal ligament (portal triad)
Posterior	Inferior vena cava and right crus of diaphragm
Superior	Caudate lobe of the liver
Inferior	First part of the duodenum

Structures in the Anterior Boundary (Portal Triad)

Contained within the hepatoduodenal ligament, these three structures are arranged in a specific orientation:

• Common bile duct: Most lateral and anterior
• Hepatic artery proper: Medial and anterior
• Portal vein: Posterior and central

Function

The epiploic foramen functions as the only natural communication between the greater sac and lesser sac of the peritoneal cavity. Its roles include:

• Fluid communication: Allows peritoneal fluid, blood, or infection to pass between compartments
• Surgical access route: Used to reach the lesser sac and posterior stomach or pancreas
• Landmark for hepatic inflow control: Access point for the Pringle maneuver

Clinical Significance

Pringle Maneuver

This is a life-saving technique used in trauma or liver surgery to temporarily stop hepatic blood inflow. A finger or clamp is inserted through the epiploic foramen to compress the portal triad within the hepatoduodenal ligament.

• Stops bleeding: From hepatic artery or portal vein injury
• Spares hepatic veins: Which lie posterior and are not affected by the maneuver

Internal Herniation

A rare but serious condition, internal hernia through the epiploic foramen can occur when loops of small intestine become trapped in the lesser sac.

• Can cause bowel obstruction and ischemia
• Difficult to diagnose; may require exploratory surgery

Infection and Fluid Spread

Peritoneal infections, hemorrhages, or pancreatic fluid collections can migrate from the greater sac into the lesser sac through this foramen, especially when the patient is supine.

Embryological Background

The epiploic foramen forms as a natural defect between peritoneal folds during rotation of the stomach and formation of the lesser sac. The liver grows into the septum transversum and the stomach rotates to the left, forming the lesser omentum and isolating the lesser sac posteriorly. The connection between the two sacs persists as the epiploic foramen.

Applied Anatomy and Surgical Relevance

• Right index finger landmark: During open surgery, the epiploic foramen can be palpated with the surgeon’s index finger placed behind the hepatoduodenal ligament
• Laparoscopic access: Surgeons may approach the lesser sac through the gastrocolic ligament or identify the foramen to control bleeding
• Avoid injury: The close relationship with the portal vein and inferior vena cava makes this region high-risk during dissection

Comparison: Epiploic Foramen vs Other Openings

Feature	Epiploic Foramen	Inguinal Canal	Femoral Canal
Location	Upper abdomen, between liver and duodenum	Lower anterior abdominal wall	Upper thigh, under inguinal ligament
Function	Connects greater and lesser peritoneal sacs	Passage for spermatic cord / round ligament	Contains lymphatics, site of femoral hernia
Clinical Issue	Internal hernia, Pringle maneuver site	Inguinal hernia	Femoral hernia
Contains major vessels?	Yes – portal triad in anterior boundary	No major vessels inside canal	Femoral vein and artery nearby