The peritoneal cavity is a potential space between the parietal and visceral peritoneum.
It normally contains only a thin film of peritoneal fluid, which consists of water, electrolytes, leukocytes and antibodies. This fluid acts as a lubricant, enabling free movement of the abdominal viscera, and the antibodies in the fluid fight infection.
While the peritoneal cavity is ordinarily filled with only a thin film of fluid, it is referred to as a potential space because excess fluid can accumulate in it, resulting in the clinical condition of ascites (see clinical applications).
In this article, we shall look at the anatomy of the peritoneal cavity – its subdivisions, structure and clinical correlations.
Fig 1
The peritoneal cavity is a potential space between the parietal and visceral peritoneum.
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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.
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):
- Supracolic compartment – lies above the transverse mesocolon and contains the stomach, liver and spleen.
- 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.
Fig 2
The greater sac can be subdivided into the supracolic and infracolic compartments.
Clinical Relevance
Subphrenic Abscesses
The subphrenic recesses are potential spaces in the supracolic compartment of the greater sac. They are located between the diaphragm and the liver. There are left and right subphrenic spaces, separated by the falciform ligament of the liver.
Subphrenic abscesses refer to an accumulation of pus in the left or right subphrenic space. They are more common on the right side due to the increased frequency of appendicitis and ruptured duodenal ulcers (pus from the appendix can track up to the subphrenic space via the right paracolic gutter).
Lesser Sac (Omental Bursa)
The lesser sac 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 the omental bursa – the epiploic foramen (of Winslow).
The epiploic foramen is situated posterior to the free edge of the lesser omentum (the hepatoduodenal ligament).
Fig 4
The lesser omentum removed to show the epiploic foramen of Winslow.
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Structure of the Peritoneal Cavity in the Pelvis
Due to the presence of different pelvic organs, the peritoneal cavity differs in structure between the sexes. The primary difference in structure is the location of the most distal portion of the cavity.
When humans stand or sit upright, any superfluous fluid (which could be blood, pus, or infected fluid) is likely to collect in the most inferior portion of the peritoneal cavity. Thus, it is clinically important to be aware of the differences between males and females.
Male
In males, the rectovesical pouch is a double folding of peritoneum located between the rectum and the bladder. The peritoneal cavity is completely closed in males.
Fig 5
The rectovesical pouch is the most distal portion of the peritoneal cavity in males.
Females
In females, there are two areas of note:
- Rectouterine pouch (of Douglas) – double folding of the peritoneum between the rectum and the posterior wall of the uterus.
- Vesicouterine pouch – double folding of peritoneum between the anterior surface of the uterus and the bladder.
The peritoneal cavity is not completely closed in females – 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, or uterine tubes may result in infection and inflammation of the peritoneum (peritonitis).
Actual passage of infectious material into the peritoneum, however, is 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
Culdocentesis involves the extraction of fluid from the rectouterine 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
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
Ascites refers to an accumulation of excess fluid within the peritoneal cavity. It is typically caused by portal hypertension (secondary to liver cirrhosis).
Other causes include malignancy of the GI tract, malnutrition, heart failure, and mechanical injuries which result in internal bleeding.
Clinical features of ascites include abdominal distension, abdominal discomfort, nausea, and dyspnoea due to pressure on the lungs from the enlarged abdominal cavity.
Fig 7
Ascites; an accumulation of excess fluid in the peritoneal cavity.
Peritonitis
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 ruptured appendix, acute pancreatitis or a gastric ulcer eroding through the wall of the stomach.
Exudation of fluid into the peritoneal cavity causes the cavity to expand, and due to the somatic innervation of the parietal peritoneum, results in pain
Clinical features include 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.