of Liver, Bile ducts, Pancreas and Spleen






LIVER


Functional Segmental Liver Anatomy


based on distribution of 3 major hepatic veins:


(a)  middle hepatic vein


divides liver into right and left lobe;


also separated by main portal vein scissura


(Rex-Cantlie line = extrapolated line from posthepatic IVC to long axis of gallbladder demarcating on liver surface anteriorly the right and left parts of liver)


(b)  left hepatic vein


divides left lobe into medial + lateral sectors


(c)  right hepatic vein


divides right lobe into anterior + posterior sectors


Each of the four sections is further divided:


by an imaginary transverse line drawn through the right + left portal vein into anterior + posterior segments; the segments are numbered counterclockwise from IVC


Portal Vein Anatomy (Akgul Classification)


Type A  Normal anatomy: bifurcation of MPV and RPV (79–86%)


◊  Posterior branch of RPV as 1st portal vein branch (13%) = most common variant


N.B.:   unintended devascularization of hepatic segments V + VIII during left trisegment-ectomy (resection of segments II, III, IV) / harvest of left lobe for liver transplantation if unrecognized


Type B  Trifurcation of MPV (9–15%)


Type C  Right anterior portal vein from LPV (1–4%)


Type D  LPV from right anterior portal vein (0.3–1.2%)


Type E  Right anterior portal vein from MPV (1–3%)


Maximum Cross-sectional Diameter of Portal Vein


(a)  child < 10 years of age:  8.5 mm


(b)  10–20 years of age:  10.0 mm


(c)  adult:  13.0 mm





Embryology of Portal Vein


Time:  4th–12th week of GA


›  paired vitelline veins around duodenum → form 3 major side-to-side anastomoses (cranioventral + caudoventral + dorsal) → pierce septum transversum (primitive liver) → broken up into sinusoids → drain into sinus venosus (of primitive heart)


›  selective involution of caudal part of right vitelline vein + cranial part of left vitelline vein:


»  regression of caudoventral anastomosis


»  dorsal anastomosis → main portal vein


»  cranioventral anastomosis → left portal vein


»  caudal right vitelline vein → superior mesenteric vein


»  caudal left vitelline vein → splenic vein


Major Anatomic Variants of Portal Vein (rare)


1.   Duplication of portal vein


2.   Congenital portosystemic shunt


3.   Congenital absence of portal vein


4.   Absent branching of portal vein


5.   Preduodenal portal vein


Hepatic Artery Anatomy (Michels classification)


Type 1 (55–60%):


›  celiac trunk trifurcates into common hepatic artery (CHA) + left gastric artery (LGA) + splenic artery (SpA)


›  CHA divides into


Location:   CHA courses to right along superior ridge of pancreas branching at lower end of epiploic foramen


(a)  proper hepatic artery (PHA)


Location:   PHA courses right + upward along anterior border of epiploic foramen


(b)  gastroduodenal artery (GDA)


›  right hepatic artery (RHA) + left hepatic artery (LHA) arise from PHA


›  middle hepatic a. (supplying caudate lobe) arises from:


(a)  LHA / RHA


(b)  PHA (in 10%)


Type 2 (4–10%):


›  CHA divides into RHA + GDA


›  LHA replaced to LGA


›  middle hepatic artery from RHA


Type 3 (8–11%):


›  CHA divides into GDA + LHA


›  RHA replaced to SMA


›  middle hepatic artery from LHA


Type 4 (2–4%):


›  CHA divides into middle hepatic artery + GDA


›  RHA + LHA are both replaced


Type 5 (9–16%):


›  accessory L hepatic a. arises from LGA


Type 6 (1–7%):


›  accessory R hepatic artery arises from SMA


Type 7 (1%):


›  accessory R + L hepatic arteries


Type 8 (2–3%):


›  combinations of accessory + replaced hepatic arteries


Type 9 (1–3%):


›  hepatic trunk replaced to SMA


Type 10 (0.5%):


›  hepatic trunk replaced to LGA



The presence of a portal branch without corresponding artery indicates a replaced or accessory vascular anatomy or transhepatic hepatofugal collateral vessels.


Aberrant Hepatic Artery


=  hepatic artery coursing between IVC + portal vein


1.   Replaced right hepatic artery (50%)


2.   Right hepatic artery with early bifurcation of common hepatic artery into right + left hepatic arteries (20%)


3.   Accessory right hepatic artery (15%)


4.   Replacement of entire hepatic trunk to SMA (15%)


Left Hepatic Artery


=  usually arises from proper hepatic artery (PHA)


Location:   from hepatic hilum to umbilical portion of left portal vein (usually to its right) coursing up- and leftward


Accessory LHAs:     from LGA / celiac trunk / aorta


Division (arteriographic description):


after forming an arch overriding the portal vein


›  A2 branches: course to left corner of liver, usually superior to A3


›  A3 branches: course ventral + caudal along left side of umbilical portion of PV and then toward left


Right Hepatic Artery


=  usually arises from PHA / SMA when replaced


Accessory RHAs:   from SMA / celiac trunk / aorta


Division (arteriographic description):


›  anterior branch: straight right + upward course


›  posterior branch: proximally meandering course


A6: inferolateral course to lower corner of liver


A7: compact complex meandering course superiorly (on frontal projection)



The RHA forms anterior and posterior branches characterized by a straight right upward course and by a meandering proximal portion, respectively.


Caudate Lobe


=  located behind liver hilum + wrapping around IVC, supplied by multiple small branches from LHA + RHA


Variations (arteriographic description):


›  RHA + LHA (53%)


›  RHA only (35%)


Location:   courses posteromedially mainly supplying the lateral (= paracaval portion and papillary process) of S1


›  LHA only (12%)


Location:   courses posteriorly mainly supplying medial portion (= caudate process, Spiegel lobe) of S1




Hepatic Vein Drainage Pattern of Right Hepatic Lobe (Nakamura Classification)


Type 1  Large right hepatic vein (RHV) drains extensive area of right lateral sector + part of right paramedian sector; small short hepatic vein drains small area of right lateral sector (occasionally absent) (39–57%)


Type 2  Right hepatic vein of medium size; one thick short hepatic vein of 5–10 mm in diameter (= middle / inferior hepatic vein) drains right lateral sector concomitantly directly into IVC (29–37%)


Type 3  Right lobe drainage allocated to a short RHV that drains superior part of right lateral sector and large middle hepatic vein (MHV) + inferior right hepatic vein that drains inferior part of right lateral sector (15–24%)



It is important to identify any variation in the middle hepatic vein because the hepatectomy plane in living donors is about 1 cm to the right of the middle hepatic vein along the gallbladder fossa.


Third Inflow to Liver


=  aberrant veins supplying small areas of liver tissue + communicating with intrahepatic portal vein branches


Effect:  focal decrease of portal vein perfusion resulting in areas of fat-sparing / fat accumulation


1.   Cholecystic veins


›  directly entering liver segments 4 + 5


›  veins joining the parabiliary veins via triangle of Calot


2.   Parabiliary venous system


=  venous network within hepatoduodenal ligament anterior to main portal vein


Tributaries:


›  cholecystic vein through triangle of Calot


[Jean-François Calot (1861–1944), French surgeon]


›  pancreaticoduodenal vein


›  right gastric / pyloric vein


√  pseudolesion at dorsal aspect of segment 4


3.   Epigastric-paraumbilical venous system


=  small veins around falciform ligament draining anterior part of abdominal wall directly into liver


Subgroups:


(a)  superior vein of Sappey


[Marie Philibert Constant Sappey (1810–1896), professor of anatomy and president of the Académie Nationale de Médecine, Paris, France]


›  drains upper portion of falciform ligament + medial part of diaphragm


›  enters peripheral left portal vein branches


›  communicates with superior epigastric + internal thoracic veins


(b)  inferior vein of Sappey


›  drains lower portion of falciform ligament


›  enters peripheral left portal vein branches


›  communicates with branches of inferior epigastric vein around the umbilicus


(c)  vein of Burow


›  terminates in middle part of collapsed umbilical v.


›  communicates with branches of inferior epigastric vein around the umbilicus


(d)  intercalary veins


›  interconnect vein of Burow + inferior vein of Sappey


Normal Hemodynamic Parameters of Liver


Portal vein velocity:   > 11 (range, 16–40) cm/sec


Portal vein cross-section:   0.99 ± 0.28 cm2


Congestion index:   0.070 ± 0.09 cm•sec


(= cross-sectional area of portal vein divided by average velocity)


Hepatic artery resistive index:   0.60–0.64 ± 0.06




Hepatic Fissures


1.   Fissure for ligamentum teres = umbilical fissure


=  invagination of ligamentum teres = embryologic remnant of obliterated umbilical vein connecting placental venous blood with left portal vein


›  located at dorsal free margin of falciform ligament


›  runs into liver with visceral peritoneum


›  divides left hepatic lobe into medial + lateral segments (divides subsegment 3 from 4)


2.   Fissure for ligamentum venosum


=  invagination of obliterated ductus venosus


=  embryologic connection of left portal vein with left hepatic vein


›  separates caudate lobe from left lobe of liver


›  lesser omentum within fissure separates the greater sac anteriorly from lesser sac posteriorly


3.   Fissure for gallbladder (GB)


=  shallow peritoneal invagination containing the GB


›  divides right from left lobe of liver


4.   Transverse fissure


=  invagination of hepatic pedicle into liver


›  contains horizontal portion of left + right portal veins


5.   Accessory fissures


(a)  Right inferior accessory fissure = from gallbladder fossa / just inferior to it → to lateroinferior margin of liver


(b)  Others (rare)




Size of Liver


A.  YOUNG INFANT


right hepatic lobe should not extend > 1 cm below right costal margin


B.  CHILD


right hepatic lobe should not extend below right costal margin


C.  ADULT


(a)  midclavicular line (vertical / craniocaudad axis):




















< 13 cm = normal
13.0–15.5 cm = indeterminate (in 25%)
> 15.5 cm = hepatomegaly (87% accuracy)

(b)  preaortic line < 10 cm


(c)  prerenal line < 14 cm


Liver Capsule


=  2 adherent layers:


(a)  thick, fibrous inner layer = Glisson capsule


(b)  outer serous layer derived from peritoneum excluding


›  bare area near diaphragm


›  porta hepatis


›  gallbladder attachment


Liver Echogenicity & Attenuation


US:     pancreatic > splenic ≥ hepatic > renal echogenicity


CT:     50–65 HU (precontrast)


   CECT:   early arterial phase (20 sec), late arterial phase (30–40 sec), portal venous phase (60–70 sec); maximal enhancement at 45–60 sec


Enzymatic Liver Tests


A.  Alkaline phosphatase (AP)


Formation:   bone, liver, intestine, placenta


High increase:


cholestasis with extrahepatic biliary obstruction (confirmed by rise in γGT), drugs, granulomatous disease (sarcoidosis), primary biliary cirrhosis, primary + secondary malignancy of liver


Mild increase:   all forms of liver disease, heart failure


B.  Gamma-glutamyl transpeptidase (γGT)


very sensitive in almost all forms of liver disease


Utility:   confirms hepatic source of elevated AP, may indicate significant alcohol use


C.  Transaminases


High increase:   viral / toxin-induced acute hepatitis


(a)  aspartate aminotransferase (AST; formerly serum glutamic oxaloacetic transaminase [SGOT])


Formation:   liver, muscle, kidney, pancreas, RBCs


(b)  alanine aminotransferase (ALT; formerly serum glutamic pyruvic transaminase [SGPT])


Formation:   primarily in liver


•  rather specific elevation in liver disease


D.  Bilirubin


helps differentiate between various causes of jaundice


(a)  unconjugated / indirect bilirubin = insoluble in water


Formation:   breakdown of senescent RBCs


Metabolism:   tightly bound to albumin in vessels, actively taken up by liver, cannot be excreted by kidneys


(b)  conjugated / direct bilirubin = water-soluble


Formation:   conjugation in liver cells


Metabolism:   excretion into bile; NOT reabsorbed by intestinal mucosa; excreted in feces


Elevation:


›  ↑ production: hemolytic anemia, resorption of hematoma, multiple transfusions


›  ↓ hepatic uptake: drugs, sepsis


›  ↓ conjugation: Gilbert syndrome, neonatal jaundice, hepatitis, cirrhosis, sepsis


›  ↓ excretion into bile: hepatitis, cirrhosis, drug-induced cholestasis, sepsis, extrahepatic biliary obstruction


E.  Lactic dehydrogenase (LDH)


nonspecific and therefore not helpful


high increase:   primary or metastatic liver involvement


F.  Alpha-fetoprotein (AFP)


> 400 ng/mL   strongly suggests that a focal mass represents a hepatocellular carcinoma


PORTA HEPATIS


=  LIVER HILUM


=  deep short transverse fissure that passes across left posterior aspect of undersurface of right lobe of liver separating caudate lobe from quadrate lobe


Contents:


(a)  portal triad:


1.   Main portal vein (MPV)


2.   Proper hepatic artery: left anterior to MPV


3.   Common hepatic duct: right anterior to MPV


(b)  nerves: left vagal trunk + sympathetic hepatic plexus


(c)  lymphatics



Within the porta hepatis, the common bile duct and proper hepatic artery typically are located anterior to the portal vein, with the common bile duct to the right and the proper hepatic artery to the left.

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Jun 29, 2017 | Posted by in GENERAL RADIOLOGY | Comments Off on of Liver, Bile ducts, Pancreas and Spleen

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