Scanning Considerations
It is no secret that hepatobiliary scanning is one of the tougher scans for an emergency physician to learn. Body habitus, quirky locations of the gallbladder and bowel gas all play a role in thwarting the sonographer from obtaining optimal scans.
Consider these few recommendations in locating the
1. Gallblader
2. Measuring the gallbladder wall
3. Measuring the common bile duct (CBD) thickness
to ease your scanning woe with difficult patients.
Begin under the right costal margin about 4-5 cm from the xiphoid in the longitudinal (sagittal) plane and start looking. If you think of your ultrasound probe as a very thin paintbrush, try to "paint" the liver with your very thin bristles to locate a cystic, hypoechoic structure which is the gallbladder. Rotate, tilt and move the probe gently; millimeter to centimeter adjustments will fan through the liver well. Careful though, the inferior vena cava (IVC) in different planes may appear similar to gallbladder. Confirm that there is no flow through the gallbladder with color and pulse wave doppler to be sure of your location. If the cystic structure is "bouncing" with respiration ---> it's likely that you're looking at IVC.
Still having trouble? Rotate the patient into the left lateral decubitus position or have them take a deep breath and hold it (hold yours too, so as not to asphyxiate the patient.) Be sure to scan all the way through the GB in both transverse and longitudinal planes so as not to miss any stones. Pay particular attention to the neck of the gallbladder.
Once you've located the gallbladder the trick will be to position the gallbladder in the right upper quadrant of your screen. By doing this, in most patients the portal vein will become visible in the center of your screen. The portal vein (PV) and its associated vasculature has a brightly echogenic coat around it that distinguishes it from the hepatic vasculature. It will be in cross section if you've made your gallbladder appear like this:
The common bile duct runs along the longitudinal axis of the portal vein in nearly all patients. You may see the CBD as at tiny pea on top of the PV in transverse section, or as a thin tube coursing along the top of the portal vein in a longitudinal axis.
Measurements to remember:
| Structure |
Size |
Comments |
| GB wall thickness upper limit (outside diameter) |
>4mm abnormal |
Measured anteriorly to avert false increase in diameter due to posterior acoustic enhancement |
| CBD (inside diameter) |
>1cm, or > a mm per decade is abnormal |
Varies with prandial state |
On to Pathology!
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