Ultrasound of normal liver anatomy

Ultrasound of normal liver anatomy

 The normal ultrasound anatomy of the liver

we will discuss grayscale 

characteristics of the liver vascular supply of the liver and how to

differentiate between portal veins and 

hepatic veins.

We will discuss the segmental anatomy of 

the liver as well as threshold measurements for

the liver 

the liver lies in the right upper quadrant of the abdomen functionally it can be divided into

three lobes the right lobe 

the left lobe and caudate lobe the right lobe of the liver is separated

from the left lobe by the main lobar 

fissure which passes through the gallbladder fossa to the inferior vena cava the right lobe of the liver can be further divided into anterior and posterior segments the left intersegmental fissure divides the left lobe into medial and lateral segments the caudate lobe is situated on the posterior aspect of the liver with the inferior vena cava as its posterior border and the fissure for the ligamentum venosum as its anterior border renal slobe is a tongue-like extension of the inferior tip of the right lobe of the liver and this is frequently seen in thin women understanding vascular anatomy of the liver is essential to appreciate the relative positions of the hepatic segments the major hepatic veins course between the lobes and segments they are ideal segmental boundaries but visualized only when scanning the superior liver there are three hepatic veins right left and middle the right hepatic vein runs within the right intersegmental fissure and divides the right lobe into anterior and posterior segments in more caudal sections of the liver the right hepatic vein is no longer identified the middle hepatic vein courses within the main or fissure and separates the anterior segment of the right lobe from the medial segment of the left lobe the left hepatic vein courses between the medial and lateral segments of the left hepatic lobe in the left intersegmental fissure so as we just discussed the hepatic veins separate the hepatic segments they are intersegmental and interlobar and portal veins courses through segments intrasegmental the portal vein is formed by the union of all of the veins draining the intestine spleen pancreas and gall bladder it runs obliquely upward into the right and reaches the hilum of the liver accompanied by the hepatic artery and the common bile duct immediately after reaching the liver the portal vein divides in the porta hepatis into right and left portal veins the right portal vein divides into anterior and posterior branches the left portal vein divides into medial and lateral branches the left portal vein is in contact with the ligamentum teres the portal veins can be differentiated sonographically from the hepatic veins by the bright echogenic walls that surround them this is due to thick collagenous tissue in the portal vein walls the hepatic veins do not exhibit echogenic borders the branches of the portal vein are intrasegmental coursing within the segments of the liver while the branches of the hepatic veins are so going through evaluating more anatomy of the liver looking at the fissure for ligamentum venosum.

This is important to look for because it 

separates the caudate lobe from the lateral segment of the left lobe it is the anterior border of the caudate lobe with the ivc being the posterior border of the caudate lobe the ligamentum teres is an important landmark to identify and this courses between the medial and lateral segments of the left lobe as shown here as an echogenic structure the fibrous remnant of the umbilical a vein is within this ligament may be mistaken for focal lesion the main lobe fissure separates the right and left lobes but more importantly, it identified the location of the gallbladder fossa so if you have trouble finding the gall bladder if you can find the main lobar fissure it directs you to the gallbladder fossa coin odd anatomy because sonography allows evaluation of liver anatomy in multiple planes lesions can be localized to specific segments this can aid surgical planning and follow-up of lesions overtime coronated anatomy is now the universal nomenclature for hepatic lesion localization this description is based on portal segments and is a functional and importance each segment has its own blood supply lymphatics and biliary drainage thus the surgeon may resect a segment of a hepatic lobe providing the vascular supply to the remaining lobe is left intact each segment has a branch or branches of the portal vein at its center bounded by a hepatic vein there are eight segments the right middle and left hepatic veins

divide the liver longitudinally 

into four sections each of these sections are further divided transversely by an imaginary plane through the right main and left main portal branches segment one is the caudate lobe segments two and three are the left superior and inferior lateral segments respectively segment four which is further divided into four 4a and 4b is the medial segment of the left lobe the right lobe consists of segments 5 and 6 located caudal to the transverse plane and segments 7 and 8 which are cephalic to the transverse plane the caudate lobe segment one may receive branches of both the right and the left portal vein in contrast to the other segments segment one has one or several hepatic veins that drain directly into the ivc the echogenicity of the liver is homogeneous in echogenicity and it has fine low-level echoes when we are talking about echogenicity of a structure.

We are talking about it relative to 

other structures or adjacent structures

So when we are talking about the liver 

when compared to the pancreas it is hypoechoic or isoechoic to the pancreas it is hyperechoic or isoechoic relative to the right kidney

and it's always hypoechoic to the spleen 

so looking at images we get the liver adjacent to the right kidney and you can see the liver here is hyperechoic relative to the right kidney another example the liver and spleen as you can see in this image the liver is hypoechoic relative to the spleen

in some conditions the left lobe of  the 

liver can get large and wrap around the spleen called beaver tail because the liver is hypoechoic relative to the spleen sometimes it may be mistaken for subcapsular hematoma this can be easily differentiating by visualization of vessels within the liver and by putting color doppler on the length of the liver at the mid-clavicular line is the most commonly used measurement for evaluating the liver size various studies have found a range of the normal length of the liver variations in length can be due to different body types body mass index and gender here is an example of the length of the liver being measured in the midclavicular line in some studies found that the average length of the liver at mid-clavicular.

Line 

is 14 plus or minus 1.7 centimeters the mean length for men is 14.5 plus or

minus 1.7 centimeters 

and mean length for women is 13.5 plus or minus 1.7 centimeters

concluded that measurement of the liver at 

mid-clavicular line of 16 centimeters

or more is considered enlarged.