Omental foramen [Epiploic foramen]

The omental foramen (Epiploic foramen; foramen of Winslow) is an opening that allows passage between the greater sac (general peritoneal cavity) and the lesser sac (omental bursa). It lies dorsally to the lesser omentum, posterior to the stomach, and anterior to the caudal vena cava.

2. Boundaries of the Omental Foramen

• Dorsally: Caudal vena cava, which ascends to the liver from the abdomen.

• Ventrally : Portal vein, enclosed in the hepatoduodenal ligament (a portion of the lesser omentum).

• Cranially : Caudate process of the caudate lobe of the liver, which covers the foramen from above.

• Caudally : First part of the duodenum (cranial duodenal flexure) and hepatic artery.

3. Structures Associated Through the Foramen

The hepatoduodenal ligament, which passes through the foramen, contains the following vital structures (the portal triad):

• Portal vein

• Hepatic artery

• Common bile duct

4. Species-Specific Notes

• Horse: The omental bursa and foramen are relatively large. Horses are particularly prone to internal hernias through this foramen.

• Ruminants (e.g., cattle): The omental structures are massive, with the superficial and deep leaves of the greater omentum forming a large omental sling. This anatomy restricts herniation through the foramen.

• Dogs and cats: Though smaller, the foramen is still a relevant structure, especially in procedures involving the portal system.

5. Developmental and Functional Aspects

Embryologically, the omental foramen forms as part of the rotation of the stomach and the formation of the lesser sac. Functionally, it provides:

• Pathway for fluids or infection to spread between peritoneal compartments.

• A channel for surgical exploration in minimally invasive procedures.