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Bursa omentalis (lesser sac) is a vertical peritoneal cavity behind the stomach. It commu­nicates with the main peritoneal cavity (greater sac) through the foramen omentale, an opening located under the liver and posterior to the hepatoduodenal ligament. The anterior wall of the omental bursa is formed by the stomach and its double-layered peritoneal folds. The fold extending from the lesser curvature of the stomach and the superior part of the duodenum to the liver is called the lesser omentum (lat. omentum minus). Apart from this, another fold extends from the greater curvature to the diaphragm as the gastrophrenic ligament, to the left towards the spleen as the gastrosplenic ligament, and downwards to the transverse colon as the gastrocolic ligament. The posterior wall of the omental bursa is formed mainly by the parietal peritoneum, which covers the diaphragm, the aorta and its branches, the pancreas, the upper pole of the left kidney and the left suprarenal gland. On the left, the posterior wall is complemented by a peritoneal fold which extends from the posterior abdominal wall to the spleen hilum as the phrenicolienal and renolienal ligaments. Below, the posterior wall is formed by the mesocolon transversum. At the upper border, the parietal peritoneum of the posterior wall passes from the diaphragm to the liver as the coronary ligament and to the stomach fundus as the posterior layer of the gastrophrenic ligament. The spleen forms the left border of the omental bursa, while its bottom is created by the transverse colon. The space of the omental bursa can be divided into five compartments. Medially to the omental foramen is the vestibule, which extends upward between the inferior vena cava and the esophageal hiatus as the superior recess. Medially to the vestibule is the main compartment, which extends towards the spleen as the splenic recess and downwards between the stomach and the transverse colon as the inferior recess, the presence and size of which depend on the extent of adhesions in the layers of the greater omentum (lat. omentum majus).