Interactive Transcript
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We've seen several examples of CT,
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CTA, and CT perfusion of stroke.
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We've seen examples of diffusion-weighted
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MRI, MRA, and MR perfusion of stroke.
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What I'd like to do is to make sure that we are all
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comfortable with the non-contrast CT findings of stroke,
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because that's the first scan that you're gonna see.
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So on these two images,
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we see the demonstration of the hyperdense blood
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vessel, in this case at the distal internal carotid
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artery, going into the proximal M1 segment. The dense
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MCA sign on the image to the right is a more subtle
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finding but one that you should learn to recognize.
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This is the insular ribbon sign.
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This is the normal side, the right side,
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where the insula is slightly hyperdense. The gray
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matter of the peri-insular tissue is slightly
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hyperdense compared to the adjacent underlying white
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matter. On the left side, which is the abnormal side,
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the insula is not bright.
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It's actually low in signal intensity.
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You can see that probably best right here,
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and it doesn't have the bright insular ribbon.
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This is more an example of gray matter
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that's kind of bright, whereas we've lost that.
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These are two findings of early acute stroke
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on a non-contrast CT scan.
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Here is a little bit more dramatic example of a dense
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MCA on a non-contrast CT—a big clot here in the MCA.
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And here we see an additional
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finding, which is loss of the
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distinction between the basal
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ganglia tissue for an acute stroke.
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Notice that the caudate nucleus is low in signal
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intensity on the left side compared to the
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right, and the distinction between the caudate
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nucleus, the anterior rim of the internal capsule,
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and the subglobus pallidum has been lost.
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On the left side, you'll also note the
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insula on the right side is nice and bright.
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Notice that the insula on the left side has lost its
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normal brightness and is low in signal intensity.
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So this is the basal ganglia sign as
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well as the insular ribbon sign, as well
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as the dense MCA sign for acute stroke.
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So in looking for stroke on CT, there are lots
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of different things that we would look at:
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dense MCA, perfusion deficit (if we have CT
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perfusion), gray-white matter blurring in the
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insular ribbon, and in the basal ganglia, low
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density, which we can also see, and also mass effect.
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What we're also looking for is hemorrhage.
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So these are the things that would be, in
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general, very important to look at to
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determine whether or not the patient should
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go on for thrombolysis or thrombectomy.
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If the stroke is greater than one-third of the middle
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cerebral artery distribution, that patient has a poor
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prognosis and would probably not benefit very much
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from thrombectomy and thrombolysis,
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even if there was a perfusion mismatch.
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The presence of hemorrhage is obviously very important.
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It contraindicates, in most situations,
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thrombolysis. The presence of herniation,
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obviously, is another situation where intervention
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would be emergent to prevent the patient
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from herniating and dying on that basis.
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As far as the dense MCA sign goes, it's
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seen in not the majority of patients who
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have a middle cerebral artery stroke.
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It's only in about 35 to 50%, but it
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does suggest that there is likely going
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to be a large volume of infarction.
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Now, just the M1 segment, as you know, is where
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the lenticulostriate branches will come off.
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So you may see deep gray matter,
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basal ganglionic infarctions
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from the clot in the M1 segment.
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If the patient has great collaterals for the
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peripheral portions of the middle cerebral artery,
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it is not a contraindication for treatment, although
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it does imply that the patient may do worse.
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This is an interesting graph that I think is important
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with respect to reporting on the size of the clot.
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The probability for successful recanalization
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of occluded vessels by intravenous
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thrombolysis depends on thrombus length.
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If it's a three-millimeter clot, as
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you can see, the success rate of
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recanalization is way up here at about 85%.
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Here's 90%, whereas if it's a five-millimeter
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clot, and again, we're just measuring
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across the distance of the bright density.
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You're around a 50% probability of recanalization.
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If it's eight millimeters, we're way down here at
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less than a 10% chance that the patient is going to
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have recanalization using intravenous thrombolysis.
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So the options are, alright, well,
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we're not gonna be successful.
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Do we just treat the patient medically
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and expectantly without thrombolysis?
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Or do we suggest this is a good patient
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for thrombectomy rather than thrombolysis?
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Because a lot of times they're able to pull
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out the clot, even if you can't dissolve
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it with intravenous thrombolysis.
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Additional CT findings—low density—usually means
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that the stroke is older.
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Here's one where it's isodense, so it's
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not an old stroke. Loss of the interface in
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the basal ganglia we talked about before.
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This is the same image.
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What I want to emphasize is that it is important
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that when you are looking for strokes, you
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manipulate the window and level on the CT scan because
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narrow windows and levels will highlight an area
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of low density and make it more apparent to you.
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So you should have stroke windows preassigned
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that are more like this—very kind of grainy,
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high contrast—but it will show that this
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caudate nucleus on the left is lower density
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than the normal caudate nucleus on the right.
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That's something that if you use your
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standard windows might not be as obvious.
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Here is another example of a patient who has
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an infarct where you have loss of gray-white
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differentiation in the entire middle cerebral
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artery distribution on the image to the left, and
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more FLAIR in the parietal lobe on the right side,
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on the right-hand image.
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