Role of Noncontrast CT in Stroke Imaging & ASPECTS Grading
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So, first we'll talk about non-contrast CT.
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So, the three classic findings are loss
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of gray-white differentiation, the insular
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ribbon sign, and the hyperdense vessel sign.
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I'm going to show you examples
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of those on the upcoming cases.
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Hypodensity on non-contrast CT is highly
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specific for in part core, which means
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hypodensity, that tissue is already dead.
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The problem is detection requires a
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substantial increase in tissue water.
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That takes time.
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So the sensitivity in the first
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six hours is not very good.
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It's only 45%.
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You usually can't see small infarctions.
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It improves with narrow windows.
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Non-contrast CT is helpful for excluding other
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causes of acute neurologic deficit, tumor, other
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mass lesions, hemorrhage, vasogenic edema, etc.
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It's also important for identifying
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contraindications to IV thrombolysis.
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So.
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The major contraindication is
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detection of intracranial hemorrhage.
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It used to be that greater than one
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third of the MCA region hypodensity was
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a contraindication because that meant a
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large infarction, but it's no longer a
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contraindication based on a number of trials.
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Now, the problem with non-contrast
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CT is the findings are subtle.
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And so you can't really measure the
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volume of tissue that's dead on arrival.
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So people use the ASPECT score and normal ASPECT
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score is 10 and you take away one point or areas
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of hyperdensity and they look at the CAUTI.
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It went from nucleus, internal capsule,
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insula, as well as the antere of temporal
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lobe and the more posterior temporal lobe,
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and then the anterior, more superior frontal
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lobe, the frontal lobe in the region of
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the motor strip, and, um, The parietal
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lobe and the region of the sensory strip.
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So for every abnormality,
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you take away one point.
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So patients who have an ASPECT score of
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above six, six to eight or nine to 10
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in this example have a better outcome
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if they receive intra-arterial therapy.
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Patients with a score of zero to five,
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meaning they have a pretty big stroke in
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this meta-analysis of five intra-arterial
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trials did not show benefit of treatment.
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It depends on the age of the
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patient, the comorbidities.
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This is just a guideline, but it really
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depends on the individual patient when
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the interventionists are making decisions.
Pamela W Schaefer, MD, FACR
Professor of Radiology, Vice Chair of Education
Massachusetts General Hospital
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