Imaging anatomy of peritoneum

peritoneum and peritoneal cavity

1. Imaging anatomy of peritoneum Nagaraju.B

2. Peritoneum The peritoneum is a thin, translucent, serous membrane and is the largest and most complexly arranged serous membrane in the body The peritoneum that lines the abdominal wall is called the parietal peritoneum whereas the peritoneum that covers a viscus or an organ is called a visceral peritoneum

3. Both types of peritoneum consist of a single layer of simple low-cuboidal epithelium called a mesothelium A capillary film of serous fluid (approximately 50–100 mL) separates the parietal and visceral layers of peritoneum from one another and lubricates the peritoneal surfaces

4. Peritoneal cavity The peritoneal cavity is a potential space between the parietal peritoneum, which lines the abdominal wall, and the visceral peritoneum, which envelopes the abdominal organs In men, the peritoneal cavity is closed, but in women, it communicates with the extraperitoneal pelvis exteriorly through the fallopian tubes

5. Normal Peritoneal Anatomy The peritoneal spaces are potential spaces that are not normally visualized unless they are distended with fluid or the fascia is thick Folds of peritoneum, called ligaments , connect and provide support for structures within this cavity Knowledge of the anatomic spaces is critical for the diagnosis, staging, and treatment of fluid collections by either surgical or radiologic methods

6. Various imaging modalities Plain radiography has been superseded by crosssectional imaging techniques and the peritoneal cavity is visualized only via contrast herniography . US Ultrasound is widely used to detect intraperitoneal collections, but is limited by bowel gas and body habitus .

7. CT/MRI Contrast-enhanced CT (with or without oral contrast medium) is the method of choice to evaluate the peritoneal spaces, reflections and their contents. MRI provides good visualization of the peritoneal spacesand reflections; however, bowel peristalsis and respiratory movement can degrade the images.

8. Peritoneal spaces The two main peritoneal compartments are separated by the transverse mesocolon . Supramesocolic compartment Divided arbitrarily into right and left supramesocolic peritoneal spaces, which can be further subdivided into a number of subspaces that are in communication.

9. Right supramesocolic space Three subspaces Right subphrenic space extends over the diaphragmatic surface of the right lobe of the liver to the right coronary ligament posteroinferiorly and the falciform ligament medially (which separates it from the left subphrenic space) Right subhepatic space Anterior right subhepatic space is limited inferiorly by the transverse colon and its mesentery

10. P osterior right subhepatic space ( hepatorenal fossa or Morison’s pouch) Extends posteriorly to the peritoneum overlying the right kidney Bounded superiorly by the inferior surface of the right lobe of the liver Communicates freely with the right subphrenic space and the right paracolic gutter

11. Coronal image of the anterior abdomen in a patient with dilute contrast material injected into the Peritoneum The right subphrenic space (RSP ) extends from the falciform ligament (F) laterally between the abdominal wall and the liver This space then communicates with the right pericolic space ( RC) and the right subhepatic space (RS ). The left subphrenic space (LSP ) communicates with the left subhepatic space ( lsh ).

12. Lesser sac Posterior to the lesser omentum , stomach, duodenal bulb and gastrocolic ligament; anterior to the pancreas Communicates with the rest of the peritoneal cavity through the epiploic foramen (of Winslow), which lies between the inferior vena cava and the free margin of the hepatoduodenal ligament Lesser sac divided into two recesses by the pancreatogastric fold (peritoneal fold over the left gastric artery ):

13. Smaller superior recess completely encloses the caudate lobe of the liver and lies posterior to the portal vein at the porta hepatis . superiorly, it extends deep into the fissure for the ligamentum venosum and posteriorly lies adjacent to the right diaphragmatic crus. Larger inferior recess lies between the stomach and the pancreas; it is bounded inferiorly by the transverse colon and its mesentery, but can extend for a variable distance with in the greater omentum ; to the left it is bounded by the gastrosplenic and splenorenal ligaments

14. The anatomic boundaries of the lesser sac are noted. The sac (L) is anterior to the pancreas (P) and extends posteriorly behind the stomach (ST) as the splenic recess (SR) The margin of the foramen of Winslow (w) contains the portal vein, the hepatic artery, and the common bile duct

15. This level demonstrates the attachment of the coronary ligaments of the right lobe of the liver (straight arrows) The recesses of the lesser sac, the superior recess (S) adjacent to the vena cava (v), and the splenic recess (SP) behind the stomach are seen.

16. Left supramesocolic space ; Four arbitrary subspaces, which are in communication with each other in normal individuals : Anterior left perihepatic space Bounded medially by the falciform ligament, posteriorly by the liver surface and left coronary ligament, and anteriorly by the diaphragm Communicates superiorly and to the left with the left anterior subphrenic space, and inferiorly with the greater peritoneal cavity over the surface of the transverse mesocolon

17. Posterior left perihepatic space ( gastrohepatic recess ): Surrounds the lateral segment of the left hepatic lobe extending into the fissure for the ligamentum venosum on the right anterior to the main portal vein Posteriorly , the lesser omentum separates this space from the superior recess of the lesser sac . Bounded on the left by the lesser curvature of the stomach Communicates anteroinferiorly with the anterior left perihepatic space

18. Anterior left subphrenic space This lies between the stomach and the left hemidiaphragm Communicates on the right with the left anterior perihepatic space, and posteriorly with the posterior subphrenic ( perisplenic ) space Posterior left subphrenic ( perisplenic ) space Superior to gastric fundus and spleen Covers the superior and inferolateral surfaces of the spleen

19. L imited inferiorly by the splenorenal and phrenicocolic ligaments, and more superiorly by the gastrosplenic ligament Partially separated from the rest of the peritoneal cavity by the phrenicocolic ligament which extends from the splenic flexure to the diaphragm

20. Sagittal image close to midline. The liver (LL) and adjacent structures are seen, including the anterior left subphrenic space ( alsp ), the superior recess of the lesser sac (small angled arrow), and the “bare area” of the liver (horizontal arrow).

21. Inframesocolic compartment Divided into two unequal spaces posteriorly by the root of the small bowel mesentery Right inframesocolic space Bounded by the transverse mesocolon superiorly and to right , and by the root of the small bowel mesentery inferiorly and to left Left inframesocolic space In free communication with the pelvis to the right of the midline Sigmoid mesocolon forms a partial barrier to the left of the midline

22. Paracolic gutters Peritoneal recesses on the posterior abdominal wall lateral to the ascending and descending colon Right paracolic gutter : continuous superiorly with the right subhepatic and subphrenic spaces; larger than the left L eft paracolic gutter : partially separated from the left subphrenic spaces by the phrenicocolic ligament. Both paracolic spaces are in continuity with the pelvic peritoneal spaces.

23. Pelvic peritoneal spaces Inferiorly the peritoneum is reflected over the dome of the bladder, the anterior and posterior surface of the uterus and upper posterior vagina in females, and on to the front of the rectum at the junction of its middle and lower thirds The urinary bladder subdivides the pelvis into right and left paravesical spaces

24. In men, there is only one potential space for fluid collection posterior to the bladder, the rectovesical pouch . In women there are two potential spaces: posterior to the bladder , the uterovesical pouch and , posterior to the uterus, the deeper rectouterine pouch (of Douglas ). The layers of peritoneum on the anterior and posterior surfaces of the uterus are reflected laterally to the pelvic side walls as the broad ligaments, containing the fallopian tubes.

25. Terminology peritoneal reflections

26. 1 . Right coronary ligament Formed by the reflection of the peritoneum from the diaphragm to the posterior surface of the right lobe of the liver The triangular area of liver enclosed by these layers is the bare area devoid of peritoneal covering and is continuous with the anterior pararenal space 2 . Left coronary ligament ( left triangular ligament ): Fimsy structure formed by apposition of the peritoneal reflections between the left lobe of liverand diaphragm Little clinical signifcance Peritoneal ligaments

27. 3 . Gastrosplenic ligament Extends from the greater curve of the stomach to the spleen Continuous with the greater omentum Contains the left gastroepiploic and short gastric vessels 4 . Falciform ligament Extends from the anterosuperior surface of the liver to the diaphragm and anterior abdominal wall, carrying the ligamentum teres (obliterated left umbilical vein) in its free edge, in continuity with the fissure for the ligamentum venosum and coronary ligaments

28. 5 . Phrenicocolic ligament Extends from the splenic flexure to the diaphragm at the level of the eleventh rib Continuous with the transverse mesocolon and splenorenal ligament Supports the spleen Potential barrier to the spread of infected fluid from the pelvis and left paracolic gutter to the left subphrenic space

29. 6 . Splenorenal ligament Extends from the tip of the pancreatic tail to the splenic hilum , carrying the splenic vessels Continuous with the gastrosplenic ligament, forming the lef lateral boundary of the lesser sac

30. 7. Hepatoduodenal ligament Represents the thickened free right edge of the lesser omentum ( gastrohepatic ligament) Extends from the flexure between the first and second parts of the duodenum to the porta hepatis Carries the portal triad (hepatic artery, portal vein and common bile duct)& anterior margin of the epiploic foramen (of Winslow)

31. 8. Duodenocolic ligament Extends from the hepatic flexure to the descending duodenum Continuous with the transverse mesocolon Carries the lymphatic drainage of the right-sided colon to the central superior mesenteric nodes

32. 1 . Greater omentum ( gastrocolic ligament) Largest peritoneal fold consisting of a double sheet folded on itself (i.e. made up of four layers) Two layers of peritoneum descend from the greater curve of the stomach and proximal duodenum passing inferiorly, anterior to the small bowel for a variable distance, and then turn superiorly again to insert into the anterosuperior aspect of the transverse colon Omenta

33. The left border is continuous with the gastrosplenic ligament The right border extends to the origin of the duodenum Contains adipose tissue which is easily identifed on CT anterior to the transverse colon superiorly and loops of small bowel inferiorly

34. 2. Lesser omentum ( gastrohepatic ligament ) Extends from the lesser curvature of the stomach and proximal 2 cm of the duodenum to the liver ( attached to the fissures for the porta hepatis and ligamentum venosum ) Forms the anterior surface of the lesser sac The free edge forms the hepatoduodenal ligament

35. Generally wedge-shaped and contains adipose tissue, the gastric artery, the coronary vein, and the left gastric nodal chain Identifed on cross-sectional imaging by finding the fissure for the ligamentum venosum immediately inferior to the gastro- oesophageal junction

36. 1. Small bowel mesentery Contains fat, the jejunal and ileal branches of the superior mesenteric arteries and their accompanying veins , nerves and lymphatics Suspends 20–25 feet of jejunum and ileum Connected to the posterior abdominal wall by an oblique 15 cm root extending from the duodenojejunal flexure to the ileocaecal valve Mesentries

37. The root is a bare area continuous with the left anterior pararenal space superiorly and the right anterior pararenal space inferiorly; it passes in front of the horizontal part of the duodenum ( where the superior mesenteric vessels enter the mesentery ), abdominal aorta, inferior vena cava, right ureter and right psoas muscle as it travels from left to right

38. 2. Transverse mesocolon Connects the transverse colon to the posterior abdominal wall Formed by two layers passing from the anterior surface of the head and the anterior border of the body of the pancreas to the posterior surface of the transverse colon, where they separate to surround the bowel The upper layer is adherent to, but separable from, the greater omentum

39. Carries the middle colic vessels, autonomic nerves, and lymphatics which supply the transverse colon Becomes confluent with the root of the small bowel mesentery near the uncinate process of the pancreas

40. 3. Sigmoid mesocolon Attaches the sigmoid colon to the pelvic wall in an inverted V, the apex of which lies anterior to the left common iliac artery bifurcation and left ureter; the left limb descends medially to the left psoas muscle; the right limb descends into the pelvis and ends in the midline anterior to S3 Carries the sigmoid and superior rectal vessels

41. 4. Mesoappendix Surrounds the vermiform appendix and attaches to the lower end of the small bowel mesentery close to the ileocaecal junction Usually extends to the tip of the appendix and sometimes suspends the caecum

42. In the normal abdomen without intraperitoneal disease, there is a small amount of peritoneal fluid that continuously circulates . The movement of fluid in this circulatory pathway is produced by the movement of the diaphragm and peristalsis of bowel. It predominantly flows up the right paracolic gutter which is deeper and wider than the left and is partially cleared by the subphrenic lymphatics. Peritoneal circulation

43. There are watershed regions in the peritoneal cavity that are areas of fluid stasis: Ileocolic region Root of the sigmoid mesentery Pouch of Douglas When you are staging a patient for gastrointestinal malignancy you have to look for disease in these areas of stasis. 90 % of peritoneal fluid is cleared at the subphrenic space by the submesothelial lymphatics. These lymphatics are connected with lymphatics at the other side of the diaphragm.

44. The peritoneum is continuous in the male pelvis. In women the peritoneum is discontinuous at the ostia of the oviducts. Through this opening disease can spread from the extraperitoneal pelvis into the peritoneal cavity.  For example, pelvic inflammatory disease (PID).