7.2: Normal anatomy and normal variant

7.2.1

CROSS SECTIONAL ANATOMY OF ABDOMEN

Satya Jha

Fig. 7.2.1.1Illustrated diagram showing division of liver into 8 segments.

Fig. 7.2.1.2Segments of liver. (A) Axial section of upper abdomen at the level of lung bases. (B) Axial section at the level of confluence of hepatic veins into IVC (*roman numbers denote superior segments of liver as divided by hepatic veins). (C) Axial section at the level of left portal vein (LPV). (D) Axial section at the level of right portal vein (RPV). (E) Axial section at the level of portosplenic confluence showing inferior hepatic segments.

Fig. 7.2.1.3(A) Axial section showing parts of stomach. (B) Axial section showing parts of stomach.

Fig. 7.2.1.4(A) Axial section at the level of kidneys and pancreas. (B) Axial section at the level of kidneys and pancreas (further lower section).

Fig. 7.2.1.5Axial section at the level of uncinate process of pancreas.

Fig. 7.2.1.6(A) Intrahepatic ductal anatomy in a patient with dilated right and left hepatic duct. (B) Further lower section showing confluence of right and left hepatic duct. (C) Further lower section showing common bile duct (CBD) and main pancreatic duct (MPD).

Fig. 7.2.1.8Axial section at the level of renal veins.

Fig. 7.2.1.9Serial axial sections showing parts of colon: (A) At the level of hepatic flexure and splenic flexure, (B) At the level of transverse colon, and (C) At the level of ileo cecal junction.

Fig. 7.2.1.10Axial section of pelvis below the level of aortic bifurcation showing bowel loops, vessels and muscles of abdominal wall.

Fig. 7.2.1.11Axial section of pelvis below the bifurcation of common iliac artery.

Fig. 7.2.1.12 Lower axial section of pelvis showing division of common iliac arteries.

Fig. 7.2.1.13 Axial section of female pelvis at the level of mid sacrum.

Fig. 7.2.1.14 (A) Axial sections of the male pelvis at the level of anorectum. (B) Axial sections of the male pelvis at the level of anal canal (further lower).

Fig. 7.2.1.15 (A) Axial section of pelvis at the level of lower sacrum. (B) Axial section of pelvis at the level of lowermost sacrum and hip joint. (C) Axial section of pelvis at the level of coccyx. (D) Axial section of pelvis at the level of pubic symphysis and ischium. (E) Axial section of pelvis at the level of inferior pubic ramus.

Fig. 7.2.1.16 (A) Axial sections of abdomen showing anatomy of major arteries. (B) Axial sections of abdomen showing anatomy of major arteries. (C) Mid sagittal section of abdomen (MIP) showing origin of celiac artery and superior mesenteric artery.

Fig. 7.2.1.17 (A) Coronal section of abdomen (MIP) showing branches of celiac axis origin of superior mesenteric artery. (B) Magnified coronal section of abdomen (MIP) showing branches of celiac axis and first branch of superior mesenteric artery. (C) Magnified coronal section of abdomen (MIP) showing origin, course and termination of gastroduodenal artery.

Fig. 7.2.1.18 Coronal section of abdomen (MIP) showing branches of superior mesenteric artery.

Fig. 7.2.1.19 Coronal section of abdomen (MIP) showing renal arteries arising from aorta and course of splenic artery along the pancreas splenic artery.

Fig. 7.2.1.20 VRT image of inferior mesenteric artery.

Fig. 7.2.1.21 (A) Coronal section of course of abdominal aorta and its bifurcation. (B) VRT image of abdominal aorta and its branches.

Fig. 7.2.1.22 (A) CT sections showing various peritoneal reflections and spaces: parts of lesser omentum – hepatoduodenal and gastroduodenal ligaments. (B–G) CT sections showing various peritoneal reflections and spaces. (H) Fluid collection of lesser sac.

Fig. 7.2.1.23 (A) Illustrated cross-section anatomy of the retroperitoneum. (B) CT sections showing parts of retro peritoneum.

7.2.2

NORMAL ANATOMY OF ABDOMEN AND PELVIS

Amandeep Singh

Liver

The two major surfaces:

• Superior/diaphragmatic surface
• Inferior/visceral surface

The anterior and posterior layers of the coronary ligament converge on bare area (not covered by peritoneum). Its right and left margins form the right and left triangular ligaments. The right triangular ligament extends toward the diaphragm and separates right subphrenic space from right subhepatic space. The left triangular ligament gives tracts extending to the diaphragm and falciform ligament and does not compartmentalize the left subphrenic space. Ligamentum teres or the obliterated umblical vein is contained in falciform ligament which attaches the liver to anterior abdominal wall. The main portal vein, the proper hepatic artery and the common bile duct are contained within investing peritoneal folds of hepatoduodenal ligament at the porta hepatis (Fig. 7.2.2.1).

Fig. 7.2.2.1 Diagram of anterior surface of the liver depicting hepatic ligaments.

The bismuth and couinaud classification of liver

Liver is divided into eight segments which are functionally independent and have their own vascular supply and biliary drainage.

• Right lobe of liver is divided into anterior and posterior segments by right hepatic vein.
• Left lobe is divided into medial and lateral segments by left hepatic vein.
• Liver is divided into left and right lobe by middle hepatic vein.
• Hepatic segments are divided into superior and inferior segments by left and right branches of left portal vein.

Couinaud	Traditional
Segment I	Caudate lobe
Segment II	Lateral superior segment of left lobe of liver
Segment III	Lateral inferior segment of left lobe of liver
Segment Iva	Medial superior segment of left lobe of liver
Segment IVb	Medial inferior segment of left lobe of liver
Segment V	Anterior inferior segment of right lobe of liver
Segment VI	Posterior inferior segment of right lobe of liver
Segment VII	Posterior superior segment of right lobe of liver
Segment VIII	Anterior superior segment of right lobe of liver

Arterial circulation: The branches of the hepatic artery accompanying the portal veins.

Hepatic venous system: The right, middle, and left hepatic veins draining into IVC (Figs. 7.2.2.2 and 7.2.2.3).

Fig. 7.2.2.2 Couinaud’s functional segmental anatomy. RHV, Right hepatic vein; MHV, middle hepatic vein; LHV, left hepatic vein; RPV, right portal vein; LPV, left portal vein; GB, gallbladder.

Fig. 7.2.2.3 Image shows sectional anatomy of liver on CT.

Gallbladder

Normal anatomy

The gallbladder is a blind pear-shaped muscular membranous sac which is an embryologic derivative of the foregut, is a pouch lying along the undersurface of the liver. The gallbladder fossa is located in the plane of the interlobar fissure, which lies between the right and left hepatic lobes. Its major function is to store and concentrate bile which is produced by the liver. It measures approximately 4 cm in diameter when it is normally distended.

Gallbladder is a smaller tubular structure in contracted state. The normal gallbladder wall thickness ranges from 1 to 3 mm. The gallbladder is divided into the fundus, body and neck. Infundibulum is present in the region of neck of the gallbladder, which is called the Hartmann pouch, where gallstones are usually impacted. Intrahepatic biliary radicles (IHBRs) scattered throughout the liver get confluent towards the hilum. They unite to form the right and left main hepatic ducts which further unite to form common hepatic duct (CHD) at the hilum. Common bile duct is formed by the union of cystic duct with common hepatic duct. The main pancreatic duct is joined with the common bile duct to form the ampulla of Vater at the major duodenal papilla (Figs. 7.2.2.4 and 7.2.2.5).

Fig. 7.2.2.4 Normal anatomy of gallbladder and biliary tree.

Fig. 7.2.2.5 Normal Gallbladder: (A) Distended (fasting), (B) Contracted (postprandial).

Pancreas

Normal anatomy and relationships of pancreas

Pancreas is located in anterior pararenal space of retroperitoneum anterior to perirenal (Gerota’s) fascia and posterior to parietal peritoneum. It is divided into head, uncinate process, neck, body and tail from right to left. Pancreas lies anterior to portal vein, which marks the point of transition between the body and neck. The region between head of pancreas and second and third parts of duodenum is known as the pancreatic groove. In postnephrectomy cases or with agenesis of kidney or ectopic kidney, pancreas moves posteriorly to partially fill in the empty renal fossa; its soft tissue density should not be mistaken for recurrent tumour.

Head

It is located in the pancreatic groove and is bounded superiorly by the duodenal bulb, laterally by second portion of duodenum, inferiorly by third portion of duodenum, medially by superior mesenteric vein and anterior to inferior vena cava.

Uncinate process

It is a wedge or wedge shaped lying posterior to superior mesenteric artery and vein.

Neck

It is an imaginary junction between the head and body and lies directly over the junction of the splenic vein and superior mesenteric vein.

Body

It is located posterior to the lesser sac and anterior to the aorta, left adrenal gland, left kidney, and renal vessels and runs obliquely upward to the left of the superior mesenteric vessels.

Tail

It is situated median to the colonic flexure and anterior to the left kidney. It is located in close proximity to the splenic hilum without a notable relation with the body of pancreas. It is seen anterior to the left kidney and median to the colonic flexure. The distal part of the tail passes between the peritoneal layers of the splenorenal ligament (Fig. 7.2.2.6 and 7.2.2.7).