Background: Components critical to cerebral perfusion have been noted to oscillate over a 24-h cycle. We previously reported that ischemic core volume has a diurnal relationship with stroke onset time when examined as dichotomized epochs (i.e. Day, Evening, Night) in a cohort of over 1,500 large vessel occlusion (LVO) patients. In this follow-up analysis, our goal was to explore if there is a sinusoidal relationship between ischemic core, collateral status (as measured by HIR), and stroke onset time.

Methods: We retrospectively examined collection of LVO patients with baseline perfusion imaging performed within 24 h of stroke onset from four international comprehensive stroke centers. Both ischemic core volume and HIR, were utilized as the primary radiographic parameters. To evaluate for differences in these parameters over a continuous 24-h cycle, we conducted a sinusoidal regression analysis after linearly regressing out the confounders age and time to imaging.

Results: A total of 1506 LVO cases were included, with a median ischemic core volume of 13.0 cc (IQR: 0.0-42.0) and median HIR of 0.4 (IQR: 0.2-0.6). Ischemic core volume varied by stroke onset time in the unadjusted (p = 0.001) and adjusted (p = 0.003) sinusoidal regression analysis with a peak in core volume around 7:45PM. HIR similarly varied by stroke onset time in the unadjusted (p = 0.004) and adjusted (p = 0.002) models with a peak in HIR values at around 8:18PM.

Conclusion: The results suggest that critical factors to the development of the ischemic core vary by stroke onset time and peak around 8PM. When placed in the context of prior studies, strongly suggest a diurnal component to the development of the ischemic core.