Peritoneal anatomy www.afrad.org Dr. Hidayatullah Hamidi 2nd year radiology resident , FMIC 17/11/2014 www.afrad.org

Peritoneum Large, complex serous membrane consists of two parietal and visceral layers. Normally <1 mm thick Not visualized in imaging unless thickened by disease/surrounded by fluid.

Peritoneal cavity Potential space between parietal and visceral layers Visualized on imaging when filled with abnormal fluid or gas Divided into two regions: Greater sac and lesser sac

Peritoneal Ligaments Two layers of peritoneum supporting structures within peritoneal cavity. Named according to structures it connects.

Mesentery Double layer of peritoneum that suspends bowel from posterior abdominal wall. Conduit for neurovascular and lymphatic structures. True Mesenteries: Connect to posterior wall. Small bowel mesentery Transverse mesocolon Sigmoid mesentery Specialized: Not connected to posterior wall.  Greater omentum: Stomach to colon Lesser omentum: Stomach to liver Mesoappendix: Appendix to ileum

Cut-surface of mesenteries After remove intraperitoneal bowel Lesser omentum Transverse mesocolon Small bowel mesentery Sigmoid mesentery

Omentum Double-layered peritoneum joining stomach and proximal duodenum to adjacent structures. Greater omentum: Greater curvature to the liver. (Made of 4 layers) Lesser omentum: lesser curvature to liver

Relation to abdominal organs Intraperitoneal organs: Stomach Liver Spleen Retroperitoneal organs: Duodenum Kidneys Pancreas Part of rectum.

Peritoneal spaces Peritoneal ligaments, mesenteries and omenta divide Peritoneal cavity into interconnecting spaces. Dictate location and direction of spread diseases.

Suspensory Ligaments of Liver Triangular Falciform ligaments.

Triangular Ligaments Left: Short and does not divide left sub phrenic space. Right: long and separates right subphrenic space from right subhepatic space.

Falciform Ligament Contains obliterated umbilical vein. Incomplete barrier between right and left sub phrenic spaces. Tumor spread within it may mimic liver metastasis.

Falciform Ligament 49-year-old woman with metastatic ovarian cancer Metastases on surface of liver Other metastasis in falciform ligament that appears to be in liver.

Ligaments of Stomach Lesser omentum Greater omentum Gastrospleenic

Lesser Omentum Gastrohepatic ligament: Lesser curve to liver contains left gastric artery and vein Hepatoduodenal ligament: Duodenum to liver Contains portal vein, hepatic art, common hepatic ducts, part of cystic duct Route for spread of pancreatic disease to portahepatis and liver

Greater Omentum May become visible if it is diseased or if ascites is present. 75-year-old woman with ovarian carcinoma, Abnormal omental metastases along greater curvature and transverse colon

Gastrosplenic Ligament Frequent route for sub peritoneal spread of pancreatitis-related fluid Contains the short gastric vessels (Arrow) Fluid within GSL is often mistaken for a lesser sac collection 51-year-old man, dialysate solution outlining (GSL)

70-year-old man: Free fluid within LSP and LPC spaces and outlining GSL Arrowhead = phrenicocolic ligament.

Splenorenal Ligament Contains the pancreatic tail and Splenorenal collateral vessels in patients with portal hypertension. 58-year-old man with cirrhosis Tortuous splenorenal shunt arising from left renal vein and coursing within SRL to splenic hilum Coronal T2WI

Transverse Mesocolon Attaches transverse colon to retroperitoneum Contains middle colic vessels In patients with pancreatic head cancer, it is important possible source of local extension Because of its numerous vessels, vascular control is difficult, and extension into mesocolon renders pancreatic cancer inoperable. 56-years old man: Pancreatic cancer with transverse mesocolon metastasis. The tumor was deemed unresectable due to invasion and many small vessels (arrow) that make vascular control difficult Axial CT image

Small Bowel Mesentery (SBM) Attaches small bowel to retro peritoneum. Extends from ligament of Treitz to ileocecal valve. Contains SMVs and their branches. Rarely, its rotational and fusion anomalies may lead to volvulus or internal hernia.

Sigmoid Mesocolon Attaches the sigmoid colon to posterior pelvic wall. Contains the hemorrhoidal and sigmoid vessels. Most common pathology involving it is acute diverticulitis. Perforated cancer and Crohn disease also may cause its inflammation.

Peritoneal spaces Supramesocolic Inframesocolic pelvic cavity.

Supramesocolic compartment Is Above transverse colon. Contains: stomach, liver, and spleen. Subphrenic spaces (Right and left – falciform Lig) Sub hepatic lesser sac (via the epiploic foramen)

Rt & Lt SPS RSPS Falciform Lig LSPS

Left Supramesocolic Spaces LSPS freely communicates with left paracolic space (LPC).

Right Supramesocolic Spaces Include RSPS, Morison pouch and lesser sac Is separated from the left perihepatic space by the falciform ligament. Lesser sac: Superior recess and a larger inferior recess. (left gastric artery)

Right and Left Inframesocolic Spaces Separated from paracolic gutters by ascending or descending colon. Smaller right space is limited inferiorly by small bowel mesentery. Collections in space generally do not extend into pelvis (Fig 10). Larger left space communicates freely with pelvis. 61-year-old man: Underwent heart transplantation and subsequently developed retroperitoneal hemorrhage, shows LIMCs and RIMCs, which are separated by SBM (white arrow). LIMCs, RPCs and LPCs communicate with pelvis (black arrows), RIMCs space does not. TM = transverse mesocolon. Coronal CT image

Paracolic Spaces Lateral left and right colon. RPC gutter > left. RPCs communicates freely with RSPs. LPCs --- LSPs (phrenicocolic ligament) Both communicate with pelvic spaces.

Free communication between LSPs LPCs is prevented by phrenicocolic Lig.

Pelvic Spaces The most gravity-dependent site for fluid accumulation: Men: Rectovesical space. Women: retrouterine space Anteriorly, the medial umbilical folds, which contain the obliterated umbilical arteries, divide the pelvic spaces into lateral and medial compartments. On each side, the inferior epigastric artery divides the lateral pelvic compartments into lateral and medial inguinal fossae, the sites of direct and indirect inguinal hernias, respectively.

Female pelvis Peritoneum has communication with extra peritoneum by fallopian tubes. Disease spread from extraperitoneal pelvis into peritoneal cavity (PID).

Peritoneal fluid circulation Normally contains about 100 ml. Continually produced, circulated and resorbed. Mechanism: Diaphragmatic movement and bowel peristalsis. Predominantly RPCs which is deeper and wider than left and is partially cleared by subphrenic lymphatics. 90% of fluid is cleared at subphrenic.

References R.R. Patel, K. Planche. Applied peritoneal anatomy. Clinical Radiology 68 (2013) 509-520. Peritoneum and Mesentery - part I: Anatomy: www.radiologyassistant.nl Temel Tirkes, MD. Peritoneal and Retroperitoneal Anatomy and Its Relevance for Cross­ Sectional Imaging, RadioGraphics 2012;32:437–451 Ashish P. Wasnik, Primary and secondary disease of the peritoneum and mesentery: review of anatomy and imaging features. Abdom Imaging (2014)

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