DWI predicts malignant MCA infarction
MedWire News: Measuring stroke lesion volume on diffusion-weighted magnetic resonance imaging (DWI) helps to predict risk for a malignant course in patients with middle cerebral artery (MCA) infarction, say researchers.
Götz Thomalla (Universitätsklinikum Hamburg-Eppendorf, Germany) and colleagues report that the risk for a space-occupying "malignant" infarct in patients with MCA stroke is increased if they have an infarct larger than 82 ml.
Their findings, which appear in the Annals of Neurology, are based on data on 140 patients with acute ischemic stroke and MCA occlusion who underwent imaging within 6 hours of onset. Of these, 19% developed malignant infarction.
The risk for malignant infarction was increased 4% by each 1-ml increase in DWI lesion volume, 5.38-fold by the presence of combined MCA and internal carotid artery occlusion, and 16% by each 1-point increase in admission National Institutes of Health Stroke Scale score.
The prespecified DWI lesion volume cutoff of 82 ml had a high positive and negative predictive value for malignant infarction, at 88% and 90%, respectively, meaning that cases identified were mostly true positives and those excluded were mostly true negatives.
It was highly specific, at 98%, but had low sensitivity, at 52% - in other words, it detected very few false-positive cases, but missed many true cases.
The researchers say this is due to the "remarkable number" of patients with small lesions at presentation who later developed malignant infarction, and put it down to the early timing of brain imaging.
They note that using a lower lesion volume cutoff would increase sensitivity, but maintain that higher specificity is more useful for guiding clinical decision-making.
"Of note, using the dichotomized parameter of a DWI lesion volume of >82 ml alone resulted in a higher rate of correct classifications as compared to the multivariate prediction model tested," say Thomalla et al.
"It appears unlikely that it will be possible to reach better predictive values by combining different predictors in this very early time window.
"More likely, only clinical course and follow-up imaging will help identify patients developing malignant MCA infarction that are misclassified using acute DWI lesion volume."
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By Eleanor McDermid