Differential Pathophysiological Mechanisms of Stroke Evolution between New Lesions and Lesion Growth: Perfusion-Weighted Imaging Study

Background: Stroke evolution frequently occurs during the first week after stroke. However, the association between the type of stroke evolution and baseline perfusion severity has not been investigated. Methods: We analyzed clinical and serial MRI data on patients with acute middle cerebral artery infarcts. Multimodal MRIs were acquired before treatment and on day 7. Time to peak (Tmax) perfusion lesion maps were then generated, and changes in the day 7 diffusion-weighted imaging (DWI) were classified; new lesions were defined as new DWI lesions not contiguous with initial abnormalities, and infarct growth as enlargement of DWI lesions. Results: Among 74 patients (mean age 64.2 years), 51 received recanalization therapy. The day 7 DWI revealed the presence of new lesions in 39 cases (52.7%) and infarct growth (mean ± SD 20.0 ± 4.3 ml) in 52. No correlation was observed between new lesion and infarct growth (r = 0.029, p = 0.805). Most new lesions were multiple and small, located in cortical/superficial areas and within the mild perfusion delay (2 ≤ Tmax < 4 s) regions, whereas infarct growth generally occurred within the severer perfusion delay regions. Multiple regression analysis revealed that large mild perfusion delay was independently associated with new lesions, whereas large initial DWI lesions and a severer perfusion delay (4 ≤ Tmax < 8 s) were associated with infarct growth. In terms of treatment, endovascular therapy was associated with new lesions, whereas the degree of angiographic recanalization was inversely associated with infarct growth. Conclusions: The types of stroke evolution differed depending on the baseline hypoperfusion severity, and the mode and effect of recanalization therapy. A poor correlation was observed between new lesions and infarct growth.