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Okay, so this is about imaging gallstones

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on CT scan. As I told you, only about

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30% of gallstones are calcified.

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And here up in the right of our screen, you

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can see that these are beautifully calcified

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gallstones, but internally within the

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gallstones, you may see what looks like air.

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This is actually nitrogen, and that can occur within

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gallstones and can be kind of a funny, um, thing.

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The first time you see it, you may just see it

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floating alone within the gallbladder lumen.

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So you do not think of this as air in the setting of

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emphysematous cholecystitis.

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These little Mercedes-Benz of air-like density

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are really nitrogen, and that can occur within the

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gallstone itself as a result of, um, fissuring

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of the cholesterol and some resorptive, uh,

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oddities in that our body cannot really absorb

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nitrogen.

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That is why you will also see nitrogen

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within the intervertebral discs in a

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patient with vacuum disc phenomenon.

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It is a very similar principle, um, but something

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to be aware of so that you do not overcall

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this normal entity as an abnormal finding.

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There are other options for imaging

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gallstones that may be radiolucent on CT scan.

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If you are using dual-source imaging in

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your ER, you may have the opportunity to

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utilize the imaging to look for gallstone.

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So here is a gallbladder that is pretty distended

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at a hundred kV, and then we also image it

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at 90 kV, and that gives us the ability to do

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subtraction imaging to a virtual non-contrast.

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So it basically subtracts out all of the

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contrast in the patient, and now you can see

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these just increased densities within the

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dependent portion of that distended gallbladder.

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This patient also did

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receive an MRCP, so you can correlate

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the appearance of gallstones on an MRCP

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with those gallstones in the gallbladder.

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So if you have a patient who has right upper

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quadrant pain, you are unsure if they have gallstones.

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If you are using dual-source imaging, this is an

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opportunity for you to use the virtual non-contrast

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images to look for those gallstones, make the

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diagnosis, maybe save the patient 45 minutes of waiting

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for a right upper quadrant ultrasound or the like.