Is diffusion imaging appearance an independent predictor of outcome after ischemic stroke?

Background: MR diffusion-weighted imaging (DWI) in ischemic stroke can be quantified by calculating the apparent diffusion coefficient (ADC) or measuring lesion volume. Objective: To clarify the association between DWI lesion parameters, clinical stroke severity at baseline, and the relationship with functional outcome. Methods: Consecutive patients with stroke were categorized for stroke type (Oxford Community Stroke Project Classification [OCSP]) and severity (Canadian Neurologic Scale [CN Scale]) before DWI. The ratio of the trace of the apparent diffusion tensor in the ischemic lesion to the mirror image area in the contralateral hemisphere was calculated (<ADC>r). The volume of the visible lesion on DWI was measured. Any visible lesion on T2-weighted imaging (T2WI) was noted. All assessments were blind to all other information. A blinded observer obtained a 6-month Rankin score. Univariate and multivariate analyses were performed to test for independent associations with outcome. Results: In 108 patients, those with lower (i.e., more abnormal) <ADC>r values had more severe strokes according to the CN Scale (p = 0.01) and the OCSP stroke type (p 0.002), a large lesion on DWI (p = 0.05), a visible lesion on T2WI (p = 0.001), and poor 6-month functional outcome (p 0.009). However, on logistic regression, neither <ADC>r nor DWI lesion volume were independent predictors of 6-month outcome over and above age and stroke severity. Conclusion: The <ADC>r is associated with functional outcome, but that is because it and DWI lesion volume are also associated with stroke severity. Although DWI lesion features are univariate surrogate outcome predictors, the authors were unable to show that they were independent outcome predictors in the current study. Differences between these and other results may be due to differences in study design, sample size, and case mix.