Infarct - acute, evolving, chronic
Acute, evolving, or chronic? Easy to tell on MRI, but harder to tell on CT. Here's a quick reminder of features that distinguish acute versus chronic infarct.
CT Head
acute infarct, less than 2 hrs
- Normal appearance.
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Head CT is ordered in suspected acute infarct to detect acute bleeds that would contraindicate thrombolytics. A radiology report indicating no loss of grey-white differentiation does not exclude infarct.
acute or evolving, more than 2hrs
- loss of grey-white differentiation - vascular territory, hypodensity that is higher density than CSF
- mass effect - narrowing of adjacent sulci, narrowing of adjacent CSF (ventricles, basal cisterns)
- new relative to studies within the past month
chronic infarct, months to years
- loss of grey-white differentiation - vascular territory, hypodensity that is close to CSF
- volume loss - widening of adjacent sulci, ex vacuo dilatation of adjacent CSF (ventricles, basal cisterns)
- unchanged relative to studies within the past month
MRI Brain
< 6 hours from onset
- vascular territory
- high DWI or B1000
- low ADC
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MRI can detect acute infarct within minutes of onset. Run both axial and coronal DWI for added sensitivity to small infarcts in the brainstem. Focused protocols can scan a patient in less than 5 minutes.
6 hours - 14 days
- vascular territory
- high DWI or B1000
- low ADC
- high FLAIR (if >6 hours old)
14 days-30 days
- vascular territory
- high DWI or B1000
- normal ADC
- high FLAIR
- ring enhancement
>30 days
- vascular territory
- normal DWI or B1000, and normal ADC
- high FLAIR