Ultrasound abdomen general

Indication/Technique

This course provides general information about ultrasound examination of the abdomen, with details on how it can and cannot be used.

Primary indications: 

• Abdominal pain (including appendicitis, bile stones, kidney stones), herniation, umbilical hernia, inguinal hernia. 
• Ascites
• Abdominal aneurysm 
• Abnormal blood test results (liver and renal impairment)
• Unexplained fever
• Trauma (internal bleeding screening)
• Oncology (liver metastases screening)

Technique

The Ultrasound Technique course provides a basic understanding of ultrasound technique; it is recommended to read this course also.
By way of repetition: location and direction of the transducer on the patient's skin determine anterior/posterior and left/right in the image.

As a general rule, in the transversal plane:

• The top of the ultrasound image is the anterior (ventral) side and the bottom is the posterior (dorsal) side. 
• Left on the image is actually right and vice versa. The body is seen from below as it were (as in a transversal section of a CT scan).
• As a general rule, in the sagittal plane:
  • The top of the ultrasound image is the anterior side and the bottom is the posterior side. 
  • Right on the image is towards the feet (= caudal) and left is towards the head (= cranial).
    
  • Orientation tip during examination: up is always the skin side, irrespective of position and tipping.
    As a general rule, each organ and each abnormality is imaged in two directions; in most cases the transversal and sagittal directions.
    Posterior sound transmission and acoustic shadowing are ultrasound characteristics that are frequently used in abdominal ultrasound examinations. See also the Ultrasound Technique course under Artefacts.
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    Normal anatomy

    The normal anatomy or organs imaged in a standard abdominal examination is explained below.
    Note: for the sake of brevity, the various organs will be not discussed in detail.

    Liver

    The liver allows for effective ultrasound imaging. A healthy liver has a homogeneous echo reflection pattern and smooth contours. The echo reflection pattern of the liver is similar to or slightly higher than that of the renal cortex. The echo reflection pattern and smooth contours of the liver are best evaluated by imaging the right kidney and the right liver lobe together (see fig. 2).
    
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    .    The main branch of the portal vein can be seen clearly in the hepatic hilum. The portal vein can be identified by its echogenic fibrous wall and has a left and right branch at the center of the liver.
    The direction of flow in the portal vein is into the liver (= hepatopetal) with a monophasic Doppler signal (fig. 4).
    
  • 2.    The hepatic artery carries oxygen-rich blood to the liver. The main arterial branch is also located in the hepatic hilum. There it (in most cases) passes between the portal vein (anterior) and choledochal duct (posterior) and then branches into the left and right hepatic arteries (fig. 5).
    The direction of flow is into the liver (=hepatopetal) with a triphasic Doppler signal.
    
  • 3.    The hepatic veins originate in the inferior caval vein and normally have three main branches: right, middle and left branch. The hepatic veins have hypoechogenic walls, making them easily distinguishable from the portal vessels (fig. 6).
    The direction of flow is out of the liver (= hepatofugal) with a triphasic Doppler signal.
    
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  • Gallbladder/bile ducts

    The gallbladder is best evaluated when the patient is in the fasting state, when the gallbladder is filled with hypoechogenic bile. The gallbladder wall thickness is usually < 2 mm. When the patient inhales deeply, the gallbladder will appear from under the rib cage (fig. 7a). The gallbladder now lies against the abdominal wall, enabling you to use your echo transducer to push into the gallbladder and evaluate its compressibility. A filled gallbladder will be partially compressible when you push against it (fig. 7b)
    
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    The choledochal duct is located in the liver hilum.  Here it passes anterior/ventral of the portal vein (fig. 8). The choledochal duct usually has a diameter < 7 mm. The diameter may increase in elderly patients or patients who are stable after cholecystectomy.
    
  • The intrahepatic bile ducts are too small for ultrasound evaluation. However, dilated intrahepatic bile ducts (in bile duct obstruction) will become visible (see Pathology section). 

    Kidneys

    The right kidney can be imaged effectively using the right liver lobe as acoustic window (fig. 9/10). For the left kidney, the spleen can act (partially) as acoustic window. When the patient inhales deeply, the kidneys will move in the caudal direction, which may facilitate evaluation of the kidneys.