In the article “BOLD cerebrovascular reactivity as a novel marker for crossed cerebellar diaschisis,” Sebök et al. reported similar sensitivity of blood oxygen level–dependent cerebrovascular reactivity (BOLD-CVR) in detecting crossed cerebellar diaschisis (CCD) as compared to (15O)-H2O-PET in 25 participants with symptomatic unilateral cerebrovascular steno-occlusive disease and reported that those with CCD had poorer baseline neurologic performance and 3-month neurologic outcome. In response, Reidler et al. question whether CCD was the cause of consequence of poor outcomes, noting that it may be an epiphenomenon of large-volume supratentorial strokes and citing conflicting evidence in the literature about independent association of CCD with post-stroke outcomes. They suggest accounting for lesion volume and distribution in the analyses. In their reply, Niftrik et al. agree that their finding of worse outcome in those with CCD should be cautiously interpreted and investigated in follow-up studies, but argue that supratentorial stroke volume is an inexact measurement, although stroke location would be helpful to examine. They clarify their finding of impaired supratentorial BOLD-CVR in the group with CCD and opine that hemodynamic changes may cause CCD rather than just functional disruption.

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