Anatomy: Peritoneum Detail

Anatomy: Peritoneum in Detail

Peritoneal Compartments

The peritoneal cavity is divided by the transverse mesocolon into supracolic and infracolic compartments. The supracolic compartment (above the transverse mesocolon) contains the liver, stomach, and spleen. The infracolic compartment (below) contains the small bowel mesentery, ascending, descending, and sigmoid colon. The transverse mesocolon connects the transverse colon to the posterior abdominal wall.

The paracolic gutters (lateral channels between the ascending/descending colon and the lateral abdominal wall) allow communication between the supracolic and infracolic compartments: fluid from a perforated peptic ulcer can track down the right paracolic gutter to the right iliac fossa, simulating appendicitis. The right paracolic gutter is deeper (communicates more freely with the right subphrenic space and pelvis) than the left (blocked by the phrenocolic ligament at the splenic flexure).

Lesser Sac (Omental Bursa)

The lesser sac (omental bursa) is a pouch of the peritoneal cavity posterior to the stomach and lesser omentum. It communicates with the greater sac only through the epiploic foramen (foramen of Winslow). Its boundaries: anteriorly (posterior surface of stomach + lesser omentum), posteriorly (anterior surface of pancreas, left adrenal, left kidney), superiorly (undersurface of liver), inferiorly (transverse mesocolon). Pancreatitis can cause fluid accumulation in the lesser sac (pancreatic pseudocyst).

Mesenteries and Peritoneal Folds

Small bowel mesentery: fan-shaped, attaches from duodenojejunal flexure (L2, left of midline) to ileocaecal junction (R iliac fossa). Contains SMA branches, lymphatics, fat. Transverse mesocolon: connects transverse colon to posterior abdominal wall; root passes anterior to the pancreas. Sigmoid mesocolon: inverted V-shaped; at the apex, the left ureter crosses (surgical landmark). Appendicular mesentery: triangular, contains appendicular artery.

Surgical Recesses and Hernias

Important recesses: right/left subphrenic recesses (between liver/spleen and diaphragm), hepatorenal recess (Morrison's pouch), paravesical recesses (around the bladder). Internal hernias can occur through these recesses or through defects in mesenteries.

Retroperitoneal Structures

Primary retroperitoneal (never had a mesentery): kidneys, ureters, adrenal glands, aorta, IVC, oesophagus (thoracic), rectum. Secondary retroperitoneal (lost mesentery during development): duodenum 2nd–4th parts, ascending colon, descending colon, pancreas body/head. The SADPUCKER mnemonic: Suprarenal glands, Aorta/IVC, Duodenum, Pancreas, Ureters, Colon (ascending/descending), Kidneys, Rectum.