Is White Matter More Prone to Diffusion Lesion Reversal After Thrombolysis?

Abstract

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 (DWI 1 ) with no visible lesion on 24-hour DWI (DWI 2 ). Only patients with RAD lesions >10 mL and >10% of DWI 1 from our previously reported cohort were eligible. The core was defined as voxels hyperintense on DWI 1 and DWI 2 . Semiautomated segmentation of DWI 1 , 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.

Does Diffusion Lesion Volume Above 70 mL Preclude Favorable Outcome Despite Post-Thrombolysis Recanalization?

“…22,26 Using voxel-based comparison of coregistered initial DWI and 24-hour DWI, reversible acute DWI lesion voxels were automatically determined as those initial DWI voxels that did not overlap with the coregistered 24-hour DWI, as previously described. 20,27 The relative reversal in each patient was expressed as percentage of DWI (Vol reversal /Vol baselineDWI ×100).…”

MRI Assessment of Ischemic Lesion Evolution within White and Gray Matter

“…In our study, the mismatch compartment had a significantly greater proportion of WM, suggesting that WM predominates within salvageable tissue. Previous studies using PET or MRI have also suggested that the amount of salvageable tissue is greater within WM [4][5][6] . This difference is likely due to different ischemic thresholds between GM and WM [1][2][3]21] as documented by lower CBV, CBF and ADC infarct thresholds in WM [1,3] .…”

“…Similarly, Koga et al [6] found an equal proportion of GM and WM salvaged at 3 months. Conversely, Tisserand et al [5] analyzed large reversal acute DWI (RAD) lesions (>10 ml) and showed that WM was more prone to early diffusion lesion reversal after thrombolysis. This difference might be explained by the smaller median RAD volume in our study and by the fact that the frequency and amount of DWI reversal are still unclear and remain a matter of debate [27,28] .…”

“…In most AIS studies, segmentation of the GM and WM is generally based on a probabilistic map [3-6, 21, 23] because T1-weighted images are not part of a standard stroke MRI protocol [5,6] . To the best of our knowledge, this is the first study to analyze the differences between GM and WM using T1-weighted images, which are considered the reference for anatomical tissue segmentation.…”

“…In stroke studies, brain tissue segmentation into GM or WM is usually based on probabilistic maps [3][4][5] , but this does not take into account the inter-individual variability. Furthermore, T1-weighted images are more appropriate for defining these 2 components [6] .…”