How is the zone of ischemia quantified in stroke imaging?

Updated: Nov 30, 2018
  • Author: Andrew Danziger; Chief Editor: L Gill Naul, MD  more...
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Noncontrast CT scanning can be used to estimate the area of ischemic tissue in order to guide therapy. This concept is postulated on evidence-based guidelines that state that larger infarcts, specifically greater than one third of the MCA distribution, are more likely to hemorrhage following thrombolytic therapy. [13, 25, 58]

One classification system, the Alberta Stroke Programme Early CT Score (ASPECTS) uses a 10-point scoring system to quantify acute ischemia on noncontrast CT based upon degree of involvement of the MCA territory. The ASPECTS system divides the MCA territory into 10 regions and deducts a point for each region involved. Thus, a normal MCA territory would receive a score of 10, and diffuse MCA involvement would receive a score of 0. Lower scores correlate with worse stroke severity and higher risk of symptomatic hemorrhage (see the images below). [59, 60, 61, 62]

ASPECTS quantitative stroke scoring system: For AS ASPECTS quantitative stroke scoring system: For ASPECTS scoring, the middle cerebral artery (MCA) territory is allotted 1 point for each of 10 separate regions: M1, M2, M3, M4, M5, M6, the caudate nucleus (C), lentiform nucleus (L), insular cortex (I), and internal capsule (IC). Scoring is based on a section at the level of the basal ganglia and thalami and another section above the level at the basal ganglia. One point is subtracted for each area demonstrating signs of early ischemic change, such as focal parenchymal hypoattenuation or edema. A normal scan would be scored a 10, and diffuse edema involving all points would be scored 0.
Noncontrast CT scan performed in a 60-year-old mal Noncontrast CT scan performed in a 60-year-old male who presented with acute stroke demonstrates the use of the ASPECTS. Diffuse hypodensity is noted throughout the middle cerebral artery (MCA) distribution involving the M1-M6 regions and insula. Seven points are then subtracting from the 10-point ASPECTS, yielding a score of 3. C = caudate nucleus, L = lentiform nucleus, I = insular cortex, and IC = internal capsule.

Another classification instrument, the Boston Acute Stroke Imaging Scale (BASIS), can also help predict patient outcome. BASIS uses data about the patency of vasculature on CTA or MRA and presence of early ischemic parenchymal changes on noncontrast CT or MRI to classify stroke as major or minor. Large vessel occlusions or significant ischemic changes are classified as major stroke; if both changes are absent, the stroke is classified as minor. Survivors of major stroke, as classified by BASIS, have been found to have significantly longer hospital stays and are subsequently much more likely to be discharged to a rehabilitation facility rather than home. [63]

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