Introduction and hypothesis: In acute stroke patients the intensity of a FLAIR lesion in a region of diffusion restriction is associated with time from symptom onset. The DWI/FLAIR mismatch is currently used in trials for treatment of stroke patients with unknown onset time. However the accuracy of the DWI/FLAIR mismatch to predict symptom onset before 4.5h remains moderate. We hypothesized that collateral status, as assessed by the previously described hypoperfusion intensity ratio (HIR) could modify the association between time from stroke onset and FLAIR lesion intensity.
Methods: From the ‘Ax200 for ischemic stroke trial’ 141 patients were included. Quantitative FLAIR maps were calculated in a voxel-based manner. For each voxel the relative signal intensity (rSI) was determined by the ratio of the signal intensity in that voxel and the median of the signal intensity in a sphere with radius 15mm positioned in the homologue voxel in the other hemisphere. Lesion volumes based on diffusion-weighted imaging and perfusion-weighted imaging were determined using RAPID software. The HIR was defined as the proportion of a Tmax >6 s lesion volume with a Tmax >10 s delay. A previously defined HIR-threshold of ≤ 0.4 dichotomized good versus poor collaterals. We studied the interaction between collateral circulation and the association between time from symptom onset and FLAIR intensity.
Results: Time from symptom onset was associated with the mean FLAIR intensity in the region of non-reperfused core (b=1.05; 95%CI: 1.01-1.1). We identified an interaction between this association and collateral status (p=0.036). ROC analysis of FLAIR intensity to predict stroke onset before 4.5h showed an AUC of 0.66 (95% CI: 0. 49-0.83) for patients with good collaterals and 0.80 (95%CI: 0.71-0.90) for patients with poor collaterals.
Conclusions: Our findings suggest that the progression of FLAIR intensity with time varies depending on the quality of the collateral flow. Accordingly collateral circulation influences the accuracy of FLAIR lesion intensity to predict stroke onset before 4.5h. This could be of particular importance for clinical trials enrolling patients based on the DWI/FLAIR mismatch.