Week One: Your First Scanning Experience<br />Thanks to the U.S. National Archives’ for the flicker image.No known copyright restrictions.<br />
Sonographic Appearance of the Liver <br />The liver is described as having a medium level homogenous echo-texture. Portal and hepatic veins can be seen scattered throughout the entire liver parenchyma. Because vessels are fluid filled, they will appear anechoic (without echo). When the vessels appear “tubular”, they are in their longest cross section and when the vessels appear “round” they are in their shortest cross section. <br />No matter what cross section a vessel is in, long or short, they will always appear anechoic. <br />
Figure 1. Sagittal cross section of the liver <br />Typical sonographic appearance of the liver.<br /><ul><li>The liver demonstrates a uniform medium level echogenicity with an overall homogeneous echotexture.
The bright reflective line demonstrates the diaphragm that divides the liver from the lungs; it appears echogenic.
The shape of the diaphragm helps to differentiate that this is a sagittal cross section.
A few small vessels can be seen scattered throughout the liver, these represent hepatic and portal veins (two small arrows). These small vessels are not major landmarks for the portal or hepatic systems.</li></ul>Diaphragm<br />
Figure 2. Sagittal cross section of the liver. <br />Sonographic Appearance of the Liver with hepatic and portal vessels.<br /><ul><li>This sagittal cross section of the liver was acquired while angling the transducer lateral, toward the right side of the patient (right lateral).
The shape of the diaphragm helps to differentiate this image as a sagittal cross section. The diaphragm is seen as rounded in a sagittal cross section.
Both the portal and hepatic veins can be seen as anechic structures, some long and tubular and others short and circular. </li></ul>Portal Vein<br />Hepatic Vein<br />
Portal and Hepatic Veins<br />The easiest way to differentiate between the portal and hepatic veins is to determine where the vessels are leading.<br /><ul><li>The many hepatic veins travel towards the diaphragm as they empty blood from the liver into the IVC. At they get closer to the IVC they form three larger veins; right, left and middle hepatic veins.
Portal veins enter the liver at the portahepatis. The main portal vein is the confluence of three smaller veins; spleen, IMV and SMV. </li></ul>In a transverse cross section the long lengths (tubular appearance) of both the larger hepatic and portal veins, are more typically seen. <br />
Figure 3. Transverse Superior Cross Section of the Liver<br />When you see the right, middle, and left hepatic veins draining into the IVC (as demonstrated in this image), you will have demonstrated the correct landmark to indicate that you are in a superior transverse cross section of the of the liver (make sure to document this image).<br />IVC<br />IVC<br />
Figure 4. Transverse Mid Cross section of the Liver<br />The portal vein is seen entering the liver at the mid section of the liver, which is considered the level of the portahepatis (where the portal vein and hepatic artery enter the liver).<br />Note: The transverse mid liver cross section is one cross sectional level below the transverse superior liver cross section (as see on figure 3).<br />Portal vein<br />
Portal and Hepatic Veins<br />Another way to distinguish between portal and hepatic veins is to look at the echogenicity of their walls.<br /><ul><li>Hepatic veins typically do not have echogenic walls.
Portal veins usually have echogenic walls. </li></ul>Differentiating between hepatic and portal wall echogenicity is another sonographic characteristic that will help you determine which vessels you are evaluating. <br />
Figure 5. Transverse Mid Cross section of the Liver<br />You can differentiate between the hepatic and portal veins by the echogenicity of their walls. <br /><ul><li>Portal veins have more echogenic walls compared to the hepatic veins, as demonstrated in this image.</li></ul>Portal vein<br />Hepatic vein<br />
Figure 6. Transverse superior cross section of the Liver<br />Scanning the liver in a transverse cross section, when angling superior, toward the patient’s head, you will encounter the right, middle and left hepatic veins (RHV, MHV, LHV) as they drain into the inferior vena cava (IVC). <br />Note: The hepatic veins do not typically have echogenic walls, however if the ultrasound beam hits a hepatic vein at a 90 degree (as seen in this image) only that portion of the hepatic vein will appear to have an echogenic wall, this is due to the difference in interface of the two tissue structures at 90 degrees to the transducer.<br />LHV<br />MHV<br />RHV<br />Echogenic<br />Hepatic vein<br />wall<br />IVC<br />