Fluid-attenuated inversion recovery evolution within 12 hours from stroke onset: a reliable tissue clock?

BACKGROUND AND PURPOSE It has recently been proposed that fluid-attenuated inversion recovery (FLAIR) imaging may serve as a surrogate marker for time of symptom onset after stroke. We assessed the hypothesis that FLAIR imaging could be used to decide if an MRI was performed within 4.5 hours from symptom onset or later. METHODS All consecutive patients with presumed stroke who underwent an MRI within 12 hours after known symptom onset were included regardless of stroke subtype and severity between May 2008 and May 2009. Blinded to time of symptom onset, 2 raters judged the visibility of lesions on FLAIR. Apparent diffusion coefficient values, lesion volume on diffusion-weighted imaging, and relative signal intensity of FLAIR lesions were determined. RESULTS In 94 consecutive patients with stroke, we found that median time from symptom onset for FLAIR-positive patients (189 minutes; interquartile range, 110 to 369 minutes) was significantly longer compared with FLAIR-negative patients (103 minutes; interquartile range, 75 to 183 minutes; P=0.011). Negative FLAIR had a sensitivity of 46% and a specificity of 79% for allocating patients to a time window of less than 4.5 hours. FLAIR positivity increased with diffusion-weighted imaging lesion volume (P<0.001) but showed no correlation with apparent diffusion coefficient values (P=0.795). There was no significant correlation between relative signal intensity and time from symptom onset (Spearman correlation coefficient -0.152, P=0.128). CONCLUSIONS Based on our findings, we cannot recommend the use of FLAIR visibility as an estimate of time from symptom onset within the first 4.5 hours.