Is white matter more prone to diffusion lesion reversal after thrombolysis?

Background and Purpose: In acute ischemic stroke, white matter (WM) is considered more resistant to infarction than gray matter (GM). To test this hypothesis, we compared the fate of WM and GM voxels belonging to the acute diffusion-weighted imaging (DWI) lesion, expecting WM voxels to be more prone to reversal after thrombolysis.
Methods: Reversible acute DWI (RAD) lesion was defined voxel-wise as an acute lesion on initial DWI (DWI1) with no visible lesion on 24-hour DWI (DWI2). Only patients with RAD lesions >10 mL and >10% of DWI1 from our previously reported cohort were eligible. The core was defined as voxels hyperintense on DWI1 and DWI2. Semiautomated segmentation of DWI1, core, and RAD lesions, normalization into standard space, and WM/GM segmentation allowed calculations of WM/GM proportions in each region of interest using a voxel-counting algorithm.
Results: Thirty patients were eligible (RAD lesion median volume [interquartile range], 23.3 mL [19.1-35.0 mL]; onset-to-treatment time, 134 minutes [105-185 minutes]). WM voxels fraction was greater in RAD lesions than in the core (59.4% [52.8%-68.9%] versus 49.6% [43.0%-57.5%]; P=0.011). The proportion of reversibility was greater for WM than for GM voxels (60.8% [25.5%-88.7%] versus 53.5% [21.1%-77.3%]; P=0.02). The percentage of RAD lesions increased with the proportion of WM present in the acute DWI lesion (P<0.0001; R=0.67).
Conclusions: Acute DWI lesions predominantly involving WM may be more prone to reversal and, hence, to respond to therapy than their GM counterparts.