The reactivity penumbra as a novel metric of ischemic symptomatology in patients with intracranial cerebrovascular disease

Motivation: Quantitation of cerebrovascular reactivity (CVR) impairment from hypercapnic MRI stimuli is complicated by differences in imaging parameters, stimuli, and vendors. Goal(s): To evaluate if the volume of CVR impairment represents a reactivity penumbra that correlates directly with recent ischemic symptoms. Approach: Time-regression cerebrovascular reactivity analyses and subsequent area-under-the-curve analyses were applied separately in brain hemispheres of 91 moyamoya participants with versus without focal neurological symptoms in the past six months. Results: The parenchymal volumes of impaired reactivity were significantly higher in the flow territory of ischemic symptoms than in asymptomatic hemispheres. Impact: Cerebrovascular reactivity (CVR) metrics, assessed from fixed-inspired hypercapnic stimuli, differ in brain hemispheres with versus without recent ischemic symptoms; furthermore, the volume of CVR impairment, relative to asymptomatic hemispheres, and the CVR measurements themselves are related to recent ischemic symptomatology.