The Peritoneal Cavity
- 1 Subdivisions of the Peritoneal Cavity
- 2 Structure of the Peritoneal Cavity in the Pelvis
- 3 Clinical Relevance: Sampling of Peritoneal Fluid
- 4 Clinical Relevance: Disorders of the Peritoneal Cavity
The peritoneal cavity is a potential space between the parietal and visceral peritoneum.
It contains only a thin film of peritoneal fluid, which consists of water, electrolytes, leukocytes and antibodies.
The fluid serves two main functions:
- It acts as a lubricant, enabling free movement of the abdominal viscera.
- The antibodies fight infection.
Ordinarily, the peritoneal cavity is only of capillary thinness; however, it is referred to as a potential space because excess fluid can accumulate in the peritoneal cavity resulting in the clinical condition of ascites (see clinical applications).
Subdivisions of the Peritoneal Cavity
The peritoneal cavity can be divided into the greater and lesser peritoneal sacs. The greater sac comprises the majority of the peritoneal cavity. The lesser sac (also known as the omental bursa) is smaller and lies posterior to the stomach and lesser omentum.
The Greater Sac
The greater sac is the larger portion of the peritoneal cavity. It is further divided into two compartments by the mesentery of the transverse colon (known as the transverse mesocolon):
- The supracolic compartment lies above the transverse mesocolon and contains the stomach, liver and spleen.
- The infracolic compartment lies below the transverse mesocolon and contains the small intestine, ascending and descending colon. The infracolic compartment is further divided into left and right infracolic spaces by the mesentery of the small intestine.
The supracolic and infracolic compartments are connected by the paracolic gutters which lie between the posterolateral abdominal wall and the lateral aspect of the ascending or descending colon.
Clinical Relevance: Subphrenic Abscesses
The subphrenic spaces are recesses in the greater sac of the peritoneal cavity between the anterosuperior diaphragmatic surface of the liver and the diaphragm. They are separated into right and left subphrenic spaces by the falciform ligament of the liver.
Subphrenic abscesses generally occur as a result of the accumulation of pus in the left or right subphrenic space as a consequence of peritonitis. They are more common on the right side due to the increased frequency of appendicitis and ruptured duodenal ulcers.
Lesser Sac (Omental Bursa)
The omental bursa lies posterior to the stomach and lesser omentum. It allows the stomach to move freely against the structures posterior and inferior to it.
The omental bursa is connected with the greater sac through an opening in in the omental bursa, the epiploic foramen.
The epiploic foramen is situated posterior to the free edge of the lesser omentum (the hepatoduodenal ligament).
Structure of the Peritoneal Cavity in the Pelvis
Due to the different pelvic organs, the peritoneal cavity differs in structure between the sexes. This is the most distal portion of the cavity, and so any infected fluid is likely to collect here. Thus, it is clinically important to be aware of the differences between males and females.
In females, the rectouterine pouch (pouch of Douglas) is a double folded extension of the peritoneum between the rectum and the posterior wall of the uterus. The vesicouterine pouch is a double fold of peritoneum between the anterior surface of the uterus and the bladder.
The peritoneal cavity is not completely closed in females. The abdominal ostia of the uterine tubes open into the peritoneal cavity, providing a potential pathway between the female genital tract and the abdominal cavity.
Clinically, this means that infections of the vagina, uterus and uterine tubes may result in infection and inflammation of the peritoneum (peritonitis). This is, however, rare due to the presence of a mucous plug in the external os (opening) of the uterus which prevents the passage of pathogens but allows sperm to enter the uterus.
Clinical Relevance: Sampling of Peritoneal Fluid
Culdocentesis involves the extraction of fluid from the rectouterine pouch (pouch of Douglas) through a needle inserted through the posterior fornix of the vagina. It can be used to extract fluid from the peritoneal cavity or to drain a pelvic abscess in the rectouterine pouch.
Paracentesis is a procedure used to drain fluid from the peritoneal cavity. A needle is inserted through the anterolateral abdominal wall into the peritoneal cavity. The needle must be inserted superior to the urinary bladder and the clinician must take care to avoid the inferior epigastric artery.
It is used to drain ascitic fluid, diagnose the cause of ascites and to check for certain types of cancer which may metastasise via the peritoneum, e.g. liver cancer.
Clinical Relevance: Disorders of the Peritoneal Cavity
Ascites refers to an accumulation of excess fluid in the peritoneal cavity. It can occur in conjunction with infection and peritonitis, however it is more commonly caused by portal hypertension secondary to cirrhosis of the liver.
Other causes include; malignancies of the GI tract, malnutrition, heart failure, and mechanical injuries which result in internal bleeding. Patients present with a distended abdomen, discomfort, nausea, and dyspnoea.
The paracolic gutters provide a route for the flow ascitic fluid, and for the spread of intraperitoneal infections and cancer metastases. Patients with peritonitis are often positioned in a sitting position (at least a 45° angle) to encourage the flow of ascitic fluid into the pelvis where toxins are absorbed more slowly.
Peritonitis refers to infection and inflammation of the peritoneum. It can occur as a result of bacterial contamination during a laparotomy (open surgical incision of the peritoneum) or it can occur secondary to an infection elsewhere in the GI tract, for example a burst appendix, acute pancreatitis or a gastric ulcer eroding through the wall of the stomach. Exudation of fluid into the peritoneal cavity occurs.
The patient experiences pain and tenderness of the overlying skin and the anterolateral abdominal muscles contract to protect the viscera (known as guarding). Other symptoms include; fever, nausea, vomiting, and constipation. Patients may lie with their knees flexed in an effort to relax the anterolateral abdominal wall muscles. Generalised peritonitis (when peritonitis is widespread in the abdominal cavity) can result in sepsis and thus must be treated as an emergency or it can be fatal.