Survival free of second overt strokes in children with SCD while on transfusion therapy for secondary stroke prophylaxis. Participants with second overt strokes, stratified for the absence (solid line) or the presence (dashed line) of progressive cerebral vasculopathy while receiving chronic blood transfusion therapy. Vertical lines represent censored cases. Median second overt stroke–free interval was 7.6 years for those with progressive vasculopathy versus median stroke-free interval not reached for those without progressive vasculopathy (Mantel-Cox log-rank, P = .003).