FLAIR can estimate the onset time in acute ischemic stroke patients

Background and purpose: Although thrombolysis can be performed for acute ischemic stroke (AIS) within 6h of onset, patients with an unknown onset time cannot receive this treatment. The aim of the present study is to investigate a method for determining the onset time of stroke in AIS patients within 24 hours (h) of onset.

Methods: AIS patients with onset time clearly defined within 24h were enrolled. All patients were examined using diffusion-weighted imaging (DWI) and fluid-attenuated inversion recovery (FLAIR). We investigated the utility of FLAIR in estimating the onset time of stroke.

Results: We enrolled 333 consecutive patients (median age, 74 years [interquartile range, 63-81]; males, 207 [62%]). Fifty-three patients underwent multiple MRI examinations; thus, a total of 389 MRI studies were analyzed. When the MRI findings were DWI-positive and FLAIR-negative (DWI+/FLAIR-), the interval between onset and imaging time was estimated to be within 3h with sensitivity of 0.83, specificity of 0.71, positive predictive value (PPV) of 0.64, and negative predictive value (NPV) of 0.87; to be within 4.5h with sensitivity of 0.74, specificity of 0.85, PPV of 0.87, and NPV of 0.70; and to be within 6h with sensitivity of 0.69, specificity of 0.91, PPV of 0.94, and NPV of 0.59. When patients with infra-tentorial lesions, lacunar stroke on imaging, and mild neurological deficit were excluded, DWI+/FLAIR- estimated that the onset time was within 3h with sensitivity of 0.93 and PPV of 0.77; within 4.5h with sensitivity of 0.77 and PPV of 0.96; and within 6h with sensitivity of 0.74 and PPV of 1.00.

Conclusion: FLAIR can estimate the onset time of stroke in AIS within 24h of onset.