MRI Assessment of Ischemic Lesion Evolution within White and Gray Matter

BACKGROUND: In acute ischemic stroke (AIS), gray matter (GM) and white matter (WM) have different vulnerabilities to ischemia. Thus, we compared the evolution of ischemic lesions within WM and GM using MRI.

METHODS: From a European multicenter prospective database (I-KNOW), available T1-weighted images were identified for 50 patients presenting with an anterior AIS and a perfusion weighted imaging (PWI)/diffusion weighted imaging (DWI) mismatch ratio of 1.2 or more. Six lesion compartments were outlined: initial DWI (b = 1,000 s/mm2) lesion, initial PWI-DWI mismatch (Tmax >4 s and DWI-negative), final infarct mapped on 1-month fluid-attenuated inversion recovery (FLAIR) imaging, lesion growth between acute DWI and 1-month FLAIR, DWI lesion reversal at 1 month and salvaged mismatch. The WM and GM were segmented on T1-weighted images, and all images were co-registered within subjects to the baseline MRI. WM and GM proportions were calculated for each compartment.

RESULTS: Fifty patients were eligible for the study. Median delay between symptom onset and baseline MRI was 140 min. The percentage of WM was significantly greater in the following compartments: initial mismatch (52.5 vs. 47.5%, p = 0.003), final infarct (56.7 vs. 43.3%, p < 0.001) and lesion growth (58.9 vs. 41.2%, p < 0.001). No significant difference was found between GM and WM percentages within the initial DWI lesion, DWI reversal and salvaged mismatch compartments.

CONCLUSIONS: Ischemic lesions may extend preferentially within the WM. Specific therapeutic strategies targeting WM ischemic processes may deserve further investigation.