Relevant anatomy

The peritoneum is the largest and most complex serous membrane in the body. It forms a closed sac by lining the interior surfaces of the abdominal wall (anterior and lateral), by forming the boundary to the retroperitoneum (posterior), by covering the extraperitoneal structures in the pelvis (inferior), and by covering the undersurface of the diaphragm (superior). This parietal layer of the peritoneum reflects onto the abdominal visceral organs to form the visceral peritoneum. It thereby creates a potential space between the 2 layers (i.e., the peritoneal cavity).

The peritoneum consists of a signle layer of flattened mesothelial cells over loose areolar tissue. The loose connective tissue layer contains a rich network of vascular and lymphatic capillaries, nerve endings, and immune-competent cells, particularly lymphocytes and macrophages. The peritoneal surface cells are joined by junctional complexes, thus forming a dialyzing membrane that allows passage of fluid and certain small solutes. Pinocytotic activity of the mesothelial cells and phagocytosis by macrophages allow for clearance of macromolecules.

Normally, the amount of peritoneal fluid present is less than 50 mL, and only small volumes are transferred across the considerable surface region in a steady state each day.

The peritoneal fluid represents plasma ultrafiltrate, with electrolyte and solute concentrations similar to that of neighboring interstitial spaces and a protein content of less than 30 g/L, mainly albumin. In addition, peritoneal fluid contains small numbers of desquamated mesothelial cells and various numbers and morphologies of migrating immune cells (reference range is < 300 cells/mL, predominantly of mononuclear morphology).

The organs are divided into:

– intraperitoneal (stomach, small bowel, colon, sigmoid colon);

– mesoperitoneal (liver, ascending and descending colon);

– extraperitoneal.