The omental bursa, also known as the lesser sac, is a significant anatomical structure within the abdominal cavity. It is part of the peritoneal cavity, which is the space within the abdomen that contains the stomach, liver, and other abdominal organs.
Location
The omental bursa is situated behind the stomach and the lesser omentum (a double layer of peritoneum extending from the liver to the lesser curvature of the stomach). It lies in front of the pancreas and posterior to the stomach, creating a large recess or pocket within the abdomen. The greater omentum, which is a large apron-like fold of visceral peritoneum, hangs down from the greater curvature of the stomach and covers the intestines, forming the anterior border of the omental bursa.
Structure and Appearance
The omental bursa is like a large, flattened sac. Its structure is defined by several boundaries:
- Anteriorly: It is bounded by the stomach and the lesser omentum, which contain the liver, stomach, and duodenum.
- Posteriorly: It is bordered by the pancreas, the transverse mesocolon (the peritoneum that attaches the colon to the posterior abdominal wall), and the posterior abdominal wall.
- Superiorly: The bursa extends upward to the diaphragm.
- Inferiorly: It extends downward between the layers of the greater omentum.
Inside, the omental bursa is a slit-like space, and its size can vary depending on the distension of the surrounding organs, particularly the stomach. Typically, it is collapsed since the visceral and parietal layers of the peritoneum lie against each other. However, it can expand significantly if filled with fluid, air, or if a disease process is present.
The omental bursa is connected to the greater peritoneal sac (the main part of the peritoneal cavity) by a narrow opening called the epiploic foramen (also known as the foramen of Winslow). This foramen allows the passage between the two parts of the peritoneal cavity.
Function
The omental bursa, also known as the lesser sac, plays several important roles in the abdominal cavity, despite primarily being considered a potential space. Its main functions include:
- Facilitating Organ Movement: It allows the stomach and other adjacent organs to move smoothly against each other. This is crucial for the normal mobility and function of the stomach and intestines, facilitating the process of digestion and the movement of food through the gastrointestinal tract.
- Infection and Fluid Spread: The omental bursa can act as a conduit for the spread of infections or fluids within the abdomen. Because it is a relatively encapsulated space, infections that enter the lesser sac can become localized there, potentially leading to localized abscesses. Conversely, this characteristic can also help limit the spread of infections to other parts of the peritoneal cavity.
- Storage of Fat: The greater omentum, which forms part of the anterior boundary of the omental bursa, is a significant fat storage area. This fat can serve as an energy reserve, insulation to maintain body temperature, and protection for abdominal organs against injury.
- Immune Response: The omentum, closely associated with the omental bursa, contains milky spots which are rich in macrophages and lymphocytes. These cells play a role in the body’s immune response, helping to identify and react to pathogens that enter the abdominal cavity.
- Pathway for Surgical and Therapeutic Interventions: In certain medical conditions, such as ascites (the accumulation of fluid in the peritoneal cavity), the omental bursa’s space can be utilized for therapeutic interventions. For example, surgeons may create a pathway between the bursa and the peritoneal cavity to manage ascites or to access organs during abdominal surgeries.
Clinical significance
The omental bursa, while primarily a structural feature, has notable clinical significance in various medical contexts:
- Disease Spread and Localization: The omental bursa can act as a pathway or barrier for the spread of diseases within the abdomen. In conditions like pancreatitis, an inflammation of the pancreas, or perforation of a peptic ulcer, infection and inflammation can extend into the omental bursa. Conversely, because it is somewhat isolated, it can also serve to localize infections or malignant cells, preventing them from spreading throughout the peritoneal cavity.
- Surgical Access and Complications: During abdominal surgeries, particularly those involving the stomach, pancreas, or liver, knowledge of the omental bursa’s anatomy is crucial. Surgeons may need to access the bursa to remove diseased tissue, drain abscesses, or perform biopsies. However, unintended entry into the omental bursa can lead to complications, including the spread of infection or the accidental injury to nearby structures.
- Fluid Collections: The omental bursa can accumulate fluid in various pathological conditions, such as ascites, internal bleeding, or infection (abscess formation). These fluid collections can be symptomatic and may require diagnostic imaging for confirmation. In some cases, drainage or surgical intervention may be necessary to resolve the issue.
- Cancer Metastasis: The omental bursa is a potential site for the metastasis of cancers from nearby organs, such as the stomach, colon, pancreas, or liver. Tumors can spread into the bursa directly or through lymphatic or peritoneal dissemination. The presence of cancer cells in the omental bursa can affect the staging, treatment planning, and prognosis of abdominal cancers.
- Diagnostic Imaging: The omental bursa is often examined in diagnostic imaging studies, such as CT scans, MRI, or ultrasounds, especially when abdominal disease is suspected. Abnormalities in the size, shape, or contents of the bursa can provide valuable clues to the presence and nature of various diseases.
- Immune Function: The greater omentum, closely related to the omental bursa, plays a role in immune response, harboring collections of immune cells that can help fight infections and facilitate wound healing in the abdominal cavity. This immunological function has implications for the body’s response to abdominal infections and inflammation.
