Diffusion-weighted image and fluid-attenuated inversion recovery image mismatch: unclear-onset versus clear-onset stroke.

Background and Purpose: Mismatch in lesion visibility between diffusion-weighted image and fluid-attenuated inversion recovery image (DWI-FLAIR mismatch) has been proposed as a biomarker for the estimation of ischemic lesion age. The actual onset in some patients with unclear-onset stroke (UnCOS) may be close to the first-found abnormal time. We hypothesized that patients with UnCOS within a particular time window might have a similar DWI-FLAIR mismatch profile with patients with clear-onset stroke (COS).
Methods: Patients who underwent MRI within 6 hours from first-found abnormal time were recruited retrospectively. Clinical characteristics and the proportion of DWI-FLAIR and perfusion-weighted image-DWI mismatch in each time window were compared between UnCOS and COS.
Results: The final analysis included 259 patients (114 with UnCOS and 145 with COS). Patients with UnCOS were older and had more severe stroke at baseline. Risk factors, stroke subtypes, and perfusion-weighted image-DWI mismatch did not differ between the 2 groups. The proportion of patients with DWI-FLAIR mismatch in UnCOS did not differ from COS within 2 hours of first-found abnormal time (50.0% versus 51.5%; P=0.92), but it was significantly lower in UnCOS than in COS at 2 to 3 hours (16.1% versus 44.4%; P=0.02), 3 to 4 hours (13.8% versus 36.4%; P=0.04), and 4 to 5 hours (5.6% versus 29.6%; P=0.05).
Conclusions: The proportion of DWI-FLAIR mismatch in UnCOS within the first 2 hours from first-found abnormal time was similar with COS, but it sharply decreased beyond 2 hours. These data suggest that patients with UnCOS within 2 hours of symptom detection may be good candidates for multimodal imaging-based thrombolysis.