Editorial for “Diaschisis Profiles in the Cerebellar Response to Hemodynamic Stimuli: Insights From Dynamic Measurement of Cerebrovascular Reactivity to Identify Occult and Transient Maxima”

Editorial for “Diaschisis Profiles in the Cerebellar Response to Hemodynamic Stimuli: Insights From Dynamic Measurement of Cerebrovascular Reactivity to Identify Occult and Transient Maxima” Crossed cerebellar diaschisis (CCD) is phenomenon characterized by remote reduction of blood flow and metabolic activity in the undamaged cerebellum contralateral to injured functionally linked injured cerebral cortex. It is crossed because the affected cortex is metabolically and vascularly linked to the contralateral cerebellar hemisphere. The underlying relationship between cerebellar blood flow and reduced cerebellar metabolism was first characterized with positron emission scanning in the 1980s. The concept underlying cerebellar diaschisis was first proposed by CharlesEdouard Brown-Séquard in the late 1800s, but the term “diaschisis” was first coined by Constantin von Monakow in 1914. The observed cerebellar effects are hypothesized to be mediated by possible “interruption of the cortico-pontocerebellar connections by the infarct causing differentiation and transneural metabolic depression” in the hemisphere of the cerebellum functionally linked to affected cortex. Cerebellar diaschisis is seen in many central nervous system disorders such as carotid stenosis, ischemic stroke, Glioma’s, uncontrolled seizures, and radiation necrosis. Recently, approaches to measure CCD in the setting of ongoing carotid occlusion using the differences in cerebrovascular reactivity (CVR) between the affected cortical region and its metabolically and vascular linked contralateral cerebellum, has become a potential tool for assessing the risk of ischemia in the setting of carotid stenosis. These techniques may have a clinical role in forming the timing of carotid revascularization for atherosclerotic carotid stenosis in patients at risk for cerebral ischemia. In this setting, changes in the contralateral cerebellar blood flow detected by changes in CVR in the affected cerebral cortex and the linked cerebellum can be used to assess the clinical effects of reduced blood flow to the associated cerebral cortex and may grant insight into when surgical revascularization may be necessary. Cerebrovascular reactivity (CVR) and time-shift (TS) using BOLD and resting-state MRI techniques reflect individual subclinical hemodynamic changes in stroke patients with vascular lesions in the anterior circulation. It has recently been reported in JMRI that CCD is associated with hemodynamic impairment in the ipsilateral MCA territory in symptomatic unilateral anterior circulation strokes as measured by changes in CVR. Additionally, CVR and TS are vascularrelated parameters associated with the risk of stroke in patients with asymptomatic carotid artery stenosis. Determining CCD through measurement of altered perfusion and CVR in the cerebellum and affected cerebrum can possibly be used to determine the future risk of ischemia in patients with carotid stenosis in the anterior circulation. In this issue of the Journal of Magnetic Resonance Imaging in an article entitled; “Diaschisis Profiles in the Cerebellar Response to Hemodynamic Stimuli: Insights from Dynamic Measurement of Cerebrovascular Reactivity to Identify Occult and Transient Maxima”, the authors report new data about the association between diaschisis and CVR. In this retrospective study 23 previously enrolled patients with unilateral chronic steno-occlusive disease underwent 32 ACZ-BOLD exams using a custom denoising pipeline to generate BOLD-CVR time signals. This allowed for denoised BOLD-CVR values per-voxel, per-TR extraction. The CVR at end (CVRend) value was established using the last minute BOLD response relative to the first minute baseline. CVR at maximum (CVRmax) was determined as the maximum CVR detected. Bothe CVRmax and CVRend were calculated for bilateral cerebral and cerebellar hemispheres in the setting of reduced ipsilateral blood flow from carotid stenosis. The authors found that correlation between CVR in affected cerebral hemispheres and their contralateral healthy cerebellar hemispheres was stronger for CVRmax than for CVRend because of reduced tendency for false underestimation of CVR in both regions for CVRmax as compared to CVRend. From these data, it appears that conventional CVRend underestimates CVR and exaggerates CCD due to