CT ABDOMEN ANATOMY

Describes detailed cross sectional anatomy of abdomen CT scan and segmental liver anatomy and peritoneum and retroperitoneum anatomy .

1. CT DR SAKHER-ALKHADERI CONSULTANT RADIOLOGIST AMC CT ABDOMEN ANATOMY

2. Cross section anatomy of abdominal ct scan

3. Anatomy of the liver segments

4. Anatomy of the liver segments

5. Right hepatic vein  divides the right lobe into anterior and posterior segments. Middle hepatic vein  divides the liver into right and left lobes (or right and left hemiliver ). This plane runs from the inferior vena cava to the gallbladder fossa . The Falciform ligament  divides the left lobe into a medial- segment IV and a lateral part - segment II and III. The portal vein  divides the liver into upper and lower segments. The left and right portal veins branch superiorly and inferiorly to project into the center of each segment. Anatomy of liver segments

6. segment I :   is the caudate lobe situated posteriorly around the IVC and different to the other 7 segments. It may receive its supply from both the right and the left portal vein and is drained directly into the  IVC  by one or more small hepatic veins The remainder of the segments (II to VIII) are numbered in a clockwise fashion starting superiorly in the left hemiliver : segments II and III  : are lateral to the left hepatic vein and  falciform ligament  with II superior and III inferior to the portal plane segment IV   : lies medial to the falciform ligament, between the left and middle hepatic veins. It is subdivided into  IVa  (superior) and  IVb  (inferior) subsegments . Easy tip: IV a a bove and IV b b elow the portal plane. Segment IV includes the quadrate lobe. Segment V to VIII make up the right hemiliver and are easier to describe: segment V   : is located below the portal plane between the middle and right hepatic veins segment VI  : is located below the portal plane lateral to the right hepatic vein segment VII :  is located above the portal plane lateral to the right hepatic vein segment VIII  : is located above the portal plane between the middle and right hepatic veins

7. CT PERITONEUM ANATOMY

8. Peritoneum

9. Mesoappendix

10. Inflammed mesosigmoid in diverticulitis

11. Mesenteries True mesenteries all connect to the posterior peritoneal wall.  These are: The small bowel mesentery The transverse mesocolon The sigmoid mesentery (or mesosigmoid ) Specialized mesenteries do not connect to the posterior peritoneal wall.  These are: The greater omentum : connects the stomach to the colon The lesser omentum : connects the stomach to the liver The mesoappendix : connects the appendix to the ileum

12. 1-The lesser omentum 2-Transverse mesocolon 3-Small bowel mesentery 4-Sigmoid mesentery Mesenteries

13. The falciform ligament is the remnant of the most ventral part of the ventral mesentery and contains the obliterated umbilical vein. It is a relative (incomplete) barrier to the transfer of fluid from the right subphrenic space to the left subphrenic space

14. The transverse mesocolon divides the peritoneum into the supramesocolic and inframesocolic spaces; Left Supramesocolic Spaces: Includes   left subphrenic , and perisplenic spaces Right Supramesocolic Spaces : include the right subphrenic ( subdiaphragmatic ) space, the Morison pouch ( subhepatic or hepatorenal space), and the lesser sac ( omental bursa). -The right subhepatic space is an important site of fluid collections resulting from liver injuries because it is the most gravity-dependent space at this site Peritoneal spaces

15. Peritoneal spaces Morison pouch ( subhepatic or hepatorenal space),

16. Right and Left Inframesocolic Spaces The right and left inframesocolic spaces are separated from the supramesocolic spaces by the transverse mesocolon and from the paracolic gutters laterally by the ascending or descending colon. The smaller right inframesocolic space is limited inferiorly by the attachment of the small bowel mesentery to the cecum ; collections in this space generally do not extend into the pelvis However, the larger left inframesocolic space communicates freely with the pelvis. Peritoneal spaces

17. Peritoneal spaces

18. Lesser sac

19. Lesser sac

20. Pelvic peritoneal space The  pelvic peritoneal space  is the inferior reflection of the  peritoneum  over the fundus of the  urinary bladder  and the front of the  rectum  at the junction of its middle and lower thirds. In females, the reflection is also over the anterior and posterior surface of the  uterus  and the upper posterior  vagina . In males there is only one potential space for fluid collection posterior to the bladder, the r ectovesical pouch . In females there are two potential spaces posterior to the bladder, the  uterovesical pouch , and posterior to the uterus the deeper  rectouterine pouch  (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 .

21. Pelvic peritoneal space

22. Retroperitoneum The  retroperitoneum  is the part of the  abdominal cavity  that lies between the posterior parietal  peritoneum  and anterior to the  transversalis fascia . It is divided into three spaces by the  perirenal fascia  and is best visualised using CT or MRI. The three spaces are: anterior pararenal space perirenal space posterior pararenal space A fourth space, the  great vessel space , is defined in the recent literature

23. Retroperitoneal Spaces

24. Retroperitoneal Spaces

25. Retroperitoneal Spaces

26. S  = Suprarenal (adrenal) Glands A  = Aorta/IVC D  =Duodenum (except the duodenal cap- first 2cm) P  = Pancreas (except the tail) U  = Ureters C  = Colon (ascending and descending parts) K  = Kidneys E  = (O)esophagus R  = Rectum Retroperitoneal organs

27. THE END