CT

DR SAKHER-ALKHADERICONSULTANT RADIOLOGIST AMC

CT ABDOMEN ANATOMY

Cross section anatomy of abdominal ct scan

Anatomy of the liver segments

Anatomy of the liver segments

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

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 veinsThe 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 planesegment 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: IVa above and IVb below 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 veinssegment VI  : is located below the portal plane lateral to the right hepatic veinsegment VII :  is located above the portal plane lateral to the right hepatic veinsegment VIII : is located above the portal plane between the middle and right hepatic veins

CT

PERITONEUM ANATOMY

Peritoneum

Mesoappendix

Inflammed mesosigmoid in diverticulitis

Mesenteries

True mesenteries all connect to the posterior peritoneal wall. These are:The small bowel mesenteryThe transverse mesocolonThe sigmoid mesentery (or mesosigmoid)

Specialized mesenteries do not connect to the posterior peritoneal wall. These are:The greater omentum: connects the stomach to the colonThe lesser omentum: connects the stomach to the liverThe mesoappendix: connects the appendix to the ileum

1-The lesser omentum2-Transverse mesocolon3-Small bowel mesentery4-Sigmoid mesentery

Mesenteries

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

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

Peritoneal spaces

Morison pouch (subhepatic or hepatorenal space),

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

Peritoneal spaces

Lesser sac

Lesser sac

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 rectovesical 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 thefallopian tubes.

Pelvic peritoneal space

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 spaceperirenal spaceposterior pararenal spaceA fourth space, the great vessel space, is defined in the recent literature

Retroperitoneal Spaces

Retroperitoneal Spaces

Retroperitoneal Spaces

S = Suprarenal (adrenal) GlandsA = Aorta/IVCD =Duodenum (except the duodenal cap- first 2cm)P = Pancreas (except the tail)U = UretersC = Colon (ascending and descending parts)K = KidneysE = (O)esophagusR = Rectum

Retroperitoneal organs

THE END