The peritoneum is the serous membrane forming the lining of the abdominal cavity or coelom in amniotes and some invertebrates, such as annelids.

The peritoneum is one continuous sheet, forming two layers and a potential space between them: the peritoneal cavity.

[1] The tunica vaginalis, the serous membrane covering the male testis, is derived from the vaginal process, an outpouching of the parietal peritoneum.

[3] Peritoneal folds are omentums, mesenteries and ligaments; they connect organs to each other or to the abdominal wall.

In addition, in the pelvic cavity there are several structures that are usually named not for the peritoneum, but for the areas defined by the peritoneal folds: The structures in the abdomen are classified as intraperitoneal, mesoperitoneal, retroperitoneal or infraperitoneal depending on whether they are covered with visceral peritoneum and whether they are attached by mesenteries (mensentery, mesocolon).

MRI scan is also increasingly used to visualise peritoneal diseases, but requires long scan time (30 to 45 minutes) and prone to motion artifacts due to respiration and peristalsis and chemical shift artifacts at the bowel-mesentery interface.

Those with peritoneal carcinomatosis, acute pancreatitis, and intraabdominal sepsis may not tolerate prolonged MRI scan.

The fluid is left there for a prescribed amount of time to absorb waste products, and then removed through the tube.

It can also be provoked by the presence of fluids that produce chemical irritation, such as gastric acid or pancreatic juice.