What Is Peritoneum?
The peritoneum (Greek peritonaion = stretched across) is an abdominal membrane consisting of two sheets: the parietal peritoneum (Latin parietalis = belonging to walls) that covers the inner side of the abdominal wall and the visceral peritoneum (Latin viscera = internal organs) that covers certain abdominal organs.
Picture of peritoneal cavity, parietal and visceral peritoneum
Peritoneal Cavity, Intraperitoneal and Retroperitoneal Organs
Abdominal organs that are totally surrounded by visceral peritoneum are called intraperitoneal organs and include: the liver, spleen, stomach, gallbladder, a part of the duodenum, small intestine, transverse and sigmoid colon, uterus, Fallopian tubes and ovaries.
Abdominal and pelvic organs lying behind or below the parietal peritoneum, and only partly covered by it, are called retroperitoneal organs and include: both kidneys, adrenal glands and ureters, the pancreas, aorta, inferior vena cava, a part of the duodenum, ascending and descending colon, rectum, urinary bladder, prostate and vagina.
The thin space between the parietal and visceral peritoneum is called peritoneal cavity; it contains a small amount of fluid.
Video 1. Peritoneum and its parts
Structure and Function of the Peritoneum
The peritoneum is a sheet of connective tissue, covered by a layer of mesothelial cells, called mesothelium. Mesothelium secretes fluid into peritoneal cavity thus preventing friction between both peritoneal sheets.
Mesentery and Omentum
Mesentery (Greek mesos = in the middle; enteron = bowel) is the part of the peritoneum that connects the bowel to the back abdominal wall. Omentum is the peritoneal fold that connects the stomach with other abdominal organs. See Video 1 for details.
Function of the Peritoneum
Peritoneum connects intraperitoneal abdominal organs with the abdominal wall, holds and protects them, but allows them to move freely. Retroperitoneal organs, like kidneys or rectum, are less movable. Peritoneal sheets also serve as conduit for abdominal blood and lymph vessels and nerves.
Peritoneal dialysis is a method of removing waste products from the blood in patients with chronic kidney failure. Dialysis solution in the form of infusion is introduced into the peritoneal cavity through a permanent tube. Certain substances from the solution and the blood are exchanged by spontaneous diffusion across the peritoneal membrane and the resulting intraperitoneal fluid is flushed out; the process is repeated every day.
Ascites is an accumulation of fluid within the peritoneal cavity. Main symptom is distended abdomen; a common cause is liver cirrhosis. Disorder commonly recur. Untreated ascites may be fatal.
It is important to know, that bleeding from intraperitoneal organs, like stomach or bowel, regularly results in collection of the blood in the abdominal cavity, and can be often detected by an ultrasound or CT, and seen during the exploratory surgery, while blood from injured retroperitoneal organs, like kidneys or aorta, usually stays localized in small areas behind the peritoneum and thus hard to detect with imaging investigations and even during surgery, if not expected in advance.
Peritonitis is an inflammation (with or without infection) of the peritoneum, caused by ruptured appendix, stomach ulcer or bowel, pancreatitis, trauma, tuberculosis, infection during peritoneal dialysis, etc. Abdominal pain and tenderness are main symptoms, but nausea, fever or diarrhea also commonly occur. Diagnosis is by peritoneal fluid analysis and blood tests. Treatment is with antibiotics, but often a surgery is needed. Without prompt treatment, acute peritonitis may be fatal.
Peritoneal Inclusion Cyst
Peritoneal inclusion cyst is a fluid filled benign tumor of peritoneal lining (mesothelium) that almost exclusively occur in women before menopause as a reaction to abdominal surgery, pelvic inflammatory disease, Crohn’s disease, endometriosis, trauma, etc. The cyst usually causes abdominal pain or visible or palpable abdominal mass. Diagnosis is with ultrasound, MRI or laparoscopy. Treatment is with surgical removal of the cyst. Cysts commonly recur.
Peritoneal Carcinoma – Mesothelioma
Peritoneal mesothelioma is an aggressive primary peritoneal cancer, caused by asbestos exposure. Symptoms may include abdominal pain or swelling, palpable lumps under the abdominal skin, change of bowel habit and unexplained weight loss. CT may not always show a mesothelioma in an early stage. Diagnosis is by pathological investigation of a sample of the peritoneum, obtained by peritoneal biopsy during laparoscopy or open surgery. Treatment is with surgery, chemotherapy or irradiation. Mesothelioma in advanced stage has a bad prognosis.
Peritoneal carcinomatosis refers to spread of abdominal cancer over the peritoneum; it often has a bad prognosis. Cancerous tissue, in a form of peritoneal implants, can be sometimes detected by ultrasound, CT, MRI or laparoscopy. In some cases, depending on the type of original cancer, a combination of extensive surgery and intraperitoneal chemotherapy can be successful (1).
Peritoneal adhesions, bands of connective tissue binding parts of the peritoneum together and causing chronic abdominal pain, nausea, vomiting or constipation, may develop within few days to several years after a surgery, infection, like tuberculosis, ascites episode, Crohn’s disease, abdominal cancer, endometriosis, trauma, etc.
Peritoneal Fluid Analysis
Peritoneal fluid analyzis can be done to find out the cause of unexplained abdominal swelling, or to confirm peritonieal infection, mesothelioma or carcinomatosis. A peritoneal fluid is obtained by inserting a needle into peritoneal cavity (paracentesis).
When metastasis of abdominal tumor into peritoneum is suspected, a salt solution can be introduced into the peritoneal cavity, removed by suction and examined under the microscope for cancerous cells. The procedure is called peritoneal washing or peritoneal lavage.
- Right Upper (RUQ) Abdominal Pain
- Left Upper (LUQ) Abdominal Pain
- Right Lower (RLQ) Abdominal Pain
- Left Lower (LLQ) Abdominal Pain
- Peritoneal carcinomatosis (oxforjournals.org)