Interactive Transcript
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Sometimes you see a CT scan which has areas of
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low density, and you don't know whether those
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areas of low density represent acute infarctions,
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subacute infarctions, or chronic infarctions.
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Again, to make that determination, it often is
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worthwhile to recommend an MRI scan because, remember,
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that DWI (diffusion-weighted imaging) on an MRI scan is our
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gold standard for identifying acute infarctions.
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This is just that certain case.
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I'm showing you the diffusion-weighted imaging
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in a patient who had multiple areas of low density
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on the CT scan. Here, on the diffusion-weighted imaging,
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we see almost immediately that there is a
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focal area of bright signal intensity in the left
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posterior cerebellum. As we scroll up,
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some of this is just susceptibility artifact at the
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junction between the temporal bone and the brain
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tissue, but we also are able to identify that there
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are bright areas in the frontal lobes bilaterally.
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Small dots of bright signal intensity
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on the diffusion-weighted imaging.
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Naturally, we would want to see this
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side by side with our ADC map in order to
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ensure that what we're seeing is restricted
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diffusion rather than T2 shine-through.
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So if we look at this with the ADC map, here's
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our ADC map, and what we're looking for is dark
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signal intensity, which indeed we see corresponding
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to the areas of the bright signal intensity
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on the diffusion-weighted imaging (DWI) package.
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So what about this area?
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So here is an area of encephalomalacia.
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You notice that it is not bright on the DWI
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sequence and is not dark on the ADC map.
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So this is an old injury.
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So you can see how diffusion-
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weighted imaging is very helpful
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in distinguishing an acute infarction, which
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is going to have restricted diffusion and
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low ADC, versus an old infarction, which is not
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going to be bright on the DWI but is going to
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show bright signal intensity on the ADC map.
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We can also confirm this by looking at the T2
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weighted sequence because, on the T2-weighted
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sequence, we can see that there is encephalomalacia
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associated with this old area of infarction.
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So what to do about these multiple little
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bright areas, however, bilaterally?
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By virtue of seeing bilateral disease in
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the middle cerebral artery distribution, right and
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left, as well as an area of restricted diffusion
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in the cerebellum, we would suggest that these
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are occurring in multiple vascular distributions—
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right and left internal carotid artery, as
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well as the left vertebral artery distribution.
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This tells us that the source of the
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stroke is more likely to be from the heart,
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rather than a carotid bifurcation.
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It doesn't make sense—
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it's bilateral disease, and it also
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includes the vertebral arteries.
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So this is a patient who likely has atrial
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fibrillation or an atrial clot, or a left
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ventricular clot, or potentially even a
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hypercoagulable state where they're creating
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multiple clots because of a, uh, coagulation problem.
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So it not only gives us a sense of whether
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or not this patient needs thrombectomy—no.
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This also gives us a sense of where the
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source of the embolic phenomenon
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is occurring—most likely in the heart.
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Remember that after looking at the DWI and giving a call
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to the clinician that it's positive, you would normally
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also look at your susceptibility-weighted imaging.
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So here is our SWI sequence. On the SWI
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sequence—susceptibility-weighted imaging—
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blood products are dark.
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So the susceptibility—the blood products are dark.
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Here is that old stroke, and what we see are
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areas of dark signal intensity representing
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hemosiderin—old blood products—in the
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right posterior frontal and parietal lobe.
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There's also blood products elsewhere in this patient.
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You can see here another area where there is
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an area of encephalomalacia. This
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little bright area around the periphery—
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we would have to look at the ADC map.
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It turned out that this was not dark on the ADC.
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This again represented T2 shine
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through of vasogenic edema and gliosis.
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So these are older areas of infarction where
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hemorrhage has been deposited, and that also is
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typical of a patient who, for example, might have
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atrial fibrillation and is on anticoagulants.
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So patients who have atrial fibrillation, in order
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to prevent clots from forming, will often be on
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warfarin or antiplatelet drugs, and they
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may have a propensity for peripheral
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hemorrhage in their infarction.
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So in summary, although there are areas of focal
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restricted diffusion representing an acute
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infarction, this is superimposed on multiple areas of
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older infarction in multiple vascular
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distributions associated with hemorrhage, most
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likely secondary to cardioembolic phenomenon
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in a patient who is on anticoagulation.
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