Compartments of the peritoneal cavity
Supramesocolic compartment (upper floor) extends from the diaphragm inferiorly to the transverse mesocolon. It is conventionally divided into interconnected right and left divisions. The right division includes the perihepatic space and the lesser sac (omental bursa). The perihepatic space itself comprises the phrenic recess (above the liver) and the subhepatic recess (between the liver and the right kidney, known as Morison's pouch). The lesser sac has superior and inferior recesses; the superior recess communicates with the subhepatic space via the epiploic foramen (foramen of Winslow).
The left division is more complex and consists of four recesses. The anterior perihepatic and anterior subphrenic spaces lie anteriorly, while the posterior ones (including the hepatogastric recess and perisplenic space) lie posterior to the stomach and the left lobe of the liver.
Inframesocolic compartment (lower floor) lies inferior to the transverse mesocolon and extends to the pelvic inlet. The broad root of the small-bowel mesentery divides it into right and left spaces. Flanking the ascending and descending colon are the right and left paracolic gutters. Through the right gutter, fluid can flow freely into the pelvic peritoneal cavity.
Mesenteries and their role
Mesenteries are massive two-layered duplicatures (folds) of the peritoneum. They envelop segments of the intestine and securely anchor them to the posterior abdominal wall. Within the adipose tissue of the mesenteries run blood vessels, lymphatic pathways, lymph nodes, and nerves.
- Small-bowel mesentery (small-bowel mesentery) has a broad fan-shaped configuration, suspending the jejunum and ileum. Its root begins at the duodenojejunal flexure and descends to the ileocecal junction. With a root length of only 15 cm, the intestinal border reaches 6–8 meters, which accounts for the corrugated appearance of the bowel.
- Transverse mesocolon serves as an important dividing barrier between the compartments, but also acts as a pathway for the spread of disease. On CT, it appears as a fat plane extending from the pancreas.
- Sigmoid mesocolon has the shape of an inverted letter "V" with its apex at the bifurcation of the left common iliac artery.
Omenta
The omentum consists of specialized broad folds of the peritoneum.
Greater omentum (greater omentum) is a large four-layered structure. It descends from the greater curvature of the stomach inferiorly, covering the loops of the intestine, and then reflects back to the transverse colon. Its clinical significance is immense: it is capable of localizing foci of infection (e.g., in localized peritonitis) and sealing intestinal injuries. The omentum includes the gastrocolic, gastrosplenic, and phrenicocolic ligaments.
Lesser omentum (lesser omentum) is stretched between the lesser curvature of the stomach and the fissure for the ligamentum venosum of the liver. Its base is the hepatogastric ligament, which transmits the left gastric artery and coronary vein. The inferior margin of the lesser omentum forms the hepatoduodenal ligament. This is a critically important zone, as it encloses the common hepatic and common bile ducts, the hepatic artery, and the portal vein.
Anomalies and pathologies: hernias and cysts
Knowledge of normal anatomy is essential for identifying congenital malformations such as malrotation — an arrest of the normal rotation of the midgut around the superior mesenteric artery. On CT, this often manifests as an inversion of the positions of the artery and vein.
Also encountered are internal hernias — displacement of organs into natural peritoneal recesses. Over 50% of these are paraduodenal hernias. Left-sided hernias form through Landzert's fossa, with bowel loops accumulating posterior to the stomach. Right-sided ones exit through Waldeyer's fossa. Transmesenteric hernias occur through defects in the mesentery and carry a high risk of volvulus.
Cysts may form within the mesenteries. The most common is lymphangioma, presenting as a thin-walled multilocular mass. Unlike inflammatory fluid collections in peritonitis or ascites, a lymphangioma has internal septations and does not dependently pool in the gravity-dependent recesses of the peritoneal cavity.
Briefly: answers to topical questions
What are the anterior, posterior, superior, and inferior boundaries of the epiploic foramen (foramen of Winslow)?
The epiploic foramen (foramen epiploicum) is bounded by ligaments, peritoneum, a lobe of the liver, and a part of the duodenum.
- Anteriorly — hepatoduodenal ligament (lig. hepatoduodenale).
- Posteriorly — parietal peritoneum covering the inferior vena cava, and the hepatorenal ligament (lig. hepatorenale).
- Superiorly — caudate lobe of the liver.
- Inferiorly — duodenorenal ligament (lig. duodenorenale) and superior part of duodenum.
What anatomical structures form the walls of the lesser sac?
The walls of the lesser sac are formed by internal organs, ligaments, and peritoneal folds.
- Anterior wall — lesser omentum (lig. hepatogastricum and lig. hepatoduodenale), posterior wall of the stomach, gastrocolic ligament (part of the greater omentum).
- Posterior wall — parietal layer of peritoneum covering the pancreas, aorta, inferior vena cava, left adrenal gland, left kidney, and nerve plexuses.
- Superior wall — caudate lobe of the liver and partially the diaphragm.
- Inferior wall — transverse colon and its mesocolon.
- Left wall — spleen and its ligaments (gastrosplenic and phrenicosplenic ligaments).
Which abdominal organs have a mesoperitoneal coverage?
The following abdominal organs are covered mesoperitoneally (on three sides):
- Ascending colon (colon ascendens) — in 70.8% of cases.
- Descending colon (colon descendens) — in 55% of cases.
- Liver (hepar).
- Urinary bladder — when distended.
- Right and left colic flexures (right colic flexure and left colic flexure) — in 42.7% and 28.2% of cases, respectively.
- Cecum — in cases where the posterior surface is applied to the iliac fossa and devoid of peritoneum.
Which ligaments form the lesser omentum?
The lesser omentum (omentum minus) is formed by two ligaments stretched between the porta hepatis, the lesser curvature of the stomach, and the superior part of the duodenum.
- Hepatogastric ligament (lig. hepatogastricum) — extends from the lesser curvature of the stomach deep into the fissure for the ligamentum venosum.
- Hepatoduodenal ligament (lig. hepatoduodenale) — forms the inferior margin of the hepatogastric ligament and connects the superior duodenal flexure to the porta hepatis.
Class and exam questions
What is Morison's pouch and why is it important?
This is the right subhepatic space located between the liver and the right kidney. Fluid frequently accumulates here during gallbladder infections or following surgical interventions.
How does the lesser sac communicate with the main peritoneal cavity?
The lesser sac communicates with the right subhepatic space via the epiploic foramen (foramen of Winslow), located in the region of the superior lesser recess.
What distinguishes mesenteric lymphangioma from standard ascites on imaging?
In lymphangioma, septations are visualized, the cyst compresses adjacent bowel loops, and the fluid itself is localized and does not pool in the gravity-dependent recesses of the peritoneal cavity.
What else to study on this topic
- Cross-sectional imaging anatomy of the peritoneal cavity on CT scans
- Detailed structure of the recesses of the left supramesocolic compartment
- Transmesenteric hernias and surgical risks of intestinal volvulus
- Formation and boundaries of the pelvic peritoneal cavity in males and females
- Signs of intestinal malrotation on axial slices
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