Increased corticospinal tract fractional anisotropy can discriminate stroke onset within the first 4.5 hours.

BACKGROUND AND PURPOSE The role of diffusion tensor imaging in determining stroke age remains unclear. We tested the ability of diffusion tensor imaging metrics to discriminate ischemic stroke <4.5 hours of onset. METHODS We enrolled 60 consecutive patients for multimodal 1.5 T MRI within 12 hours of middle cerebral artery ischemic stroke onset. We measured fractional anisotropy (FA), mean diffusivity (MD), apparent diffusion coefficient (ADC), and T2-weighted signal intensity in affected ipsilateral and unaffected contralateral deep gray matter, cortical gray matter, deep white matter in the corticospinal tract (CST), and subcortical white matter and calculated ipsilateral-to-contralateral ratios (r). Hyperintensity in infarcted tissue was considered fluid-attenuated inversion recovery-positive. RESULTS We analyzed the 48 patients (17 women; mean age, 68 ± 14 years) with known onset. In 25 (52.1%) patients, onset was ≤ 4.5 hours (mean, 182.3 ± 65.6 minutes). Variables differing significantly between infarcts <4.5 hours and >4.5 hours were rFA CST (P = 0.001), rMD cortical gray matter (P = 0.036), rADC cortical gray matter (P = 0.009), rT2 CST (P = 0.006), and fluid-attenuated inversion recovery (P<0.001). rFA at CST was the most reliable to discriminate infarcts <4.5 hours (Goodman-Kruskal = 0.76). The sensitivity, specificity, and positive and negative predictive values for infarct <4.5 hours of onset by rFA at CST >0.970 were 93.8%, 84.6%, 88.2%, and 91.7%, respectively. CONCLUSIONS These preliminary results suggest rFA at CST may be a surrogate marker of acute stroke age.