Review Article
Diffusion-weighted Imaging–Fluid Attenuated Inversion Recovery Mismatch in Nocturnal Stroke Patients with Unknown Time of Onset

https://doi.org/10.1016/j.jstrokecerebrovasdis.2012.01.004Get rights and content

Background

More than a quarter of patients with ischemic stroke (IS) are excluded from thrombolysis because of an unknown time of symptom onset. Recent evidence suggests that a mismatch between diffusion-weighted imaging (DWI) and fluid attenuated inversion recovery (FLAIR) imaging could be used as a surrogate for the time of stroke onset. We compared used the DWI–FLAIR mismatch and the FLAIR/DWI ratio to estimate the time of onset in a group of patients with nocturnal strokes and unknown time of onset.

Methods

We used a prospectively collected acute IS patient database with MRI as the initial imaging modality. Nineteen selected nocturnal stroke patients with unknown time of onset were compared with 22 patients who had an MRI scan within 6 hours from stroke onset (control A) and 19 patients who had an MRI scan between 6 and 12 hours (control B). DWI and FLAIR signal was rated as normal or abnormal. FLAIR/DWI ratio was calculated from independent DWI and FLAIR ischemic lesion volumes using semiautomatic software.

Results

The DWI–FLAIR mismatch was different among groups (unknown 43.7%; control A 63.6%; control B 10.5%; Fisher-Freeman-Halton test; P = .001). There were significant differences in FLAIR/DWI ratio among the 3 groups (unknown 0.05 ± 0.12; control A 0.17 ± 0.15; control B 0.04 ± 0.06; Kruskal–Wallis test; P < .0001). Post-hoc pairwise comparisons revealed that FLAIR/DWI ratio from the unknown group was significantly different from the control B group (P = .0045) but not different from the control A group. DWI volumes were not different among the 3 groups.

Conclusions

A large proportion of patients with nocturnal IS and an unknown time of stroke initiation have a DWI–FLAIR mismatch, suggesting a recent onset of stroke.

Section snippets

Patients

A prospectively collected imaging database of patients with AIS who presented within 12 hours of the stroke onset was screened for patients who had undergone MRI as the initial brain imaging modality. We chose a group of patients with unknown time of onset who had a high probability of having their stroke while they were asleep. The selection criteria for these patients included presenting with AIS symptoms, unknown time of stroke onset, last seen normal >6 hours ago, with an arrival to the

Results

There were 22 nocturnal stroke patients with unknown time of onset, 19 patients in the control A group, and 22 patients in the control B group. The National Institutes of Health Stroke Scale score at admission was higher in the control A group (11.2 ± 9.3 vs 17.1 ± 8.3 vs 11.7 ± 6.7; P = .028), and hypertension was more prevalent in the control B group (81.8% vs 59.1% vs 36.8%; P = .012). All other baseline characteristics were similar among groups (Table 1).

Discussion

In this study, >40% of patients in whom the time of stroke onset was uncertain had a DWI–FLAIR mismatch, and nearly half had a negative FLAIR image for AIS. These findings were similar to those seen in patients whose stroke onset time was <6 hours. In patients with unknown time of stroke onset, this criterion might identify those in whom thrombolytic therapies might be considered. Intriguingly, we found that the mismatch and the FLAIR/DWI ratio within the unknown group were not different from

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    Supported by the National Institutes of Health (K23NS054084 and P50NS044378) to Dr. Liebeskind and an educational National Institutes of Health grant to the University of California, San Diego Stroke Center (3P50 NSO44148-07S2).

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    Copyright © 2013 National Stroke Association. Published by Elsevier Inc. All rights reserved.