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How to Scan the GB

The GB may be difficult to find as it is only tethered at the GB neck. The rest of the GB may be flopping in any direction. Thus the best way to find it is to start imaging at the porta hepatis which contains the CBD. The common bile duct is formed by the joining of the cystic duct from the GB and the hepatic duct from the liver. The neck of the GB is not too far away from all this. 

With the patient supine, begin scanning in the right hypochondrium, midclavicular line, transducer perpendicular to the lowest rib, probe marker cranial. 

In this position, you will visualise the portal vein in transverse with the CBD superiorly on the left of screen and the hepatic artery on the right of screen. This is the Mickey Mouse Sign.

Usually you seen an anechoic round or oval structure close by and this is the GB. 

If you can't visualise the GB at all, look for an acoustic shadow which may give you a clue to the location of a GB full of stones.

GB in transverse, a large stone obscuring most of it. the dense acoustic shadow provides. clue

 When there is no fluid in the GB and just the large stone against the gall bladder wall, this is called the wall echo shadow complex.

GB wall not well defined here. GB wall maybe calcified

TROUBLESHOOTING

1. Roll the patient to right lateral decubitus so the bowel gas moves out of the way

2. Held inspiration to move the abdominal sturctures inferiorly

3. Try imaging from the axilla through the intercostal spaces

Once you visulaise the GB, slide or sweep the transducer so the GB is in the middle of the screen and then rotate until you get a longitudinal image of the GB with the portal vein in transverse at the neck: giving the classic exclamation mark sign.

In bedside US, it's not really necessary to measure the GB length. However if it appears enlarged put a numerical value on it. >10cm long is abnormal. Unless the GB is parallel with the transducer, I do not measure the wall thickness here as the wall won't be perpendicular with the beam leading to error. 

With your best longitudinal view of the GB in the middle of the screen, rotate the transducer 90 degrees to image the GB in transverse. Ensure the transverse view of the GB is a round as possible with bright hyperechoic walls because then you know you are perpendicular to the organ. The transverse diameter of the normal GB is <5cm.

Look for pericholecystic fluid, gall stones and pain on transducer pressure on the abdomen when imaging the GB.

GB trans

GB WALL THICKNESS

I usually measure wall thickness in transverse because it is easiest to get the GB wall perpendicular to the US beam in this view. Always measure the anterior wall because the posterior wall is affected by posterior acoustic enhancement and may appear thicker than it is. 

The normal GB wall is <3mm.

CBD

Common bile duct measurement is not necessary for the bedside diagnosis of cholecystitis. But a dilated CBD will alert you to masses at the porta hepatis, CBD stone and ascending cholangitis. 

To image the CBD start at the right hypochondrium MCL, probe marker cranial. You will see the portal vein in transverse with the CBD and hepatic artery superior to it (Mickey Mouse sign). 

Put the colour doppler box onto the vessels. The structure with no colour will be the CBD. 

Now rotate the the transducer until this round duct is seen longitudinally. Measure the inner wall to inner wall. The normal CBD is <6-7mm and normally about 3-4mm.

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REFERENCES

Yarmenitis SD. Ultrasound of the gallbladder and the biliary tree. Eur Radiol. 2002 Feb;12(2):270-82.