Background: To investigate the effect of early (<6 h) versus delayed (>6 h) recanalization on infarct pattern in acute middle cerebral artery (MCA) occlusion. Methods: 35 patients with acute MCA occlusion (M1 segment; symptom onset <6 h) were analyzed. Stroke MRI was performed immediately after admission (day 0), and on days 1 and 7. In addition, vessel status was assessed within 6 h, at 24 h and on day 7. Patients were grouped according to early (≤6 h, n = 10), delayed (6–24 h, n = 8) or no recanalization within 24 h (n = 17). Infarct patterns between the three subgroups were compared on normalized day 1 diffusion-weighted imaging (DWI) data. Lesion plots were generated for the three subgroups depicting voxel by voxel the relative frequency of infarction. Results: Lesion growth was significantly larger in the group without recanalization (125 ± 100 cm3; mean ± SD) compared to patients with early (41 ± 42 cm3; p = 0.02) or delayed (47 ± 45 cm3; p < 0.05) recanalization. The analysis of infarct patterns revealed extensive sparing of peripheral cortical regions in both the early and delayed recanalization groups compared to the persistent occlusion group. In the early/delayed recanalization groups, cortical involvement was often limited to the central MCA territory (i.e. insular region and adjacent cortex, in addition to the basal ganglia). The final infarct volume was 80 ± 71 cm3 in patients with early, 93 ± 62 cm3 in those with delayed, and 194 ± 156 cm3 in those without recanalization. Conclusions: Delayed recanalization significantly limits DWI lesion expansion in patients with proximal MCA occlusion and selectively saves peripheral cortical regions. Collateral supply to the peripheral MCA territory may be sufficient for an extended period of time.

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