Regional Ischemic Vulnerability of the Brain to Hypoperfusion

Abstract

Purpose To characterize the spatial pattern of cerebral ischemic vulnerability to hypoperfusion in stroke patients. Methods We included 90 patients who underwent admission CT perfusion (CTP) and MRI within 12 hours of ischemic stroke onset. Infarcted brain lesions (“core”) were segmented from admission diffusion-weighted-imaging (DWI), and - along with the CTP parameter maps - coregistered onto MNI-152 brain space, which was parcellated into 125 mirror cortical and subcortical regions per hemisphere. We tested the hypothesis that the percent infarction increment per unit relative cerebral blood flow (rCBF) reduction differs statistically between regions using regression analysis to assess the interaction between regional rCBF and region variables. Next, for each patient, a “vulnerability index” (VI) map was constructed with voxel values equaling the product of that voxel’s rCBF and infarction probability (derived from the MNI-152-transformed, binary, segmented DWI lesions). Voxel-based rCBF threshold for core was determined within the upper 20th percentile of VI map voxel values. Results Different regions had different percent infarction increase per unit rCBF reduction (p=0.001). The caudate body, putamen, insular ribbon, paracentral lobule, precentral, middle and inferior frontal gyri had the highest ischemic vulnerability to hypoperfusion. A voxel-based rCBF threshold of <0.42 optimally distinguished infarct core in the highly-vulnerable regions, whereas rCBF <0.16 distinguished core in the remainder of the brain. Conclusion We demonstrated regional ischemic vulnerability of the brain to hypoperfusion in acute stroke patients. Location specific - rather than whole-brain - rCBF thresholds may provide a more accurate metric for estimating infarct core using CTP maps.

Percentage Insula Ribbon Infarction of >50% Identifies Patients Likely to Have Poor Clinical Outcome Despite Small DWI Infarct Volume

“…14 The association between insula infarct involvement and worsened tissue and clinical outcome may be 2-fold: 1) Insula infarcts may serve as a marker for poor collateral flow throughout the greater MCA territory, and 2) infarcts of the insula may lead to autonomic system alterations that may contribute to adverse tissue outcome. The insula is supplied almost exclusively by M2 segment MCA branches, with a small contribution from M1 insular branches in some individuals.…”

Location-weighted CTP analysis predicts early motor improvement in stroke

“…The insula is highly sensitive to hypoperfusion. 13 Severe insular ribbon ischemia is not only associated with a low probability of aphasia improvement, 5 but also a high probability of infarct growth. 14 We therefore speculate that severe admission hypoperfusion of the insula may be a "canary in the coal mine" for poor global stroke outcome.…”

Cerebral regions preserved by successful endovascular recanalization of acute M1 segment occlusions: a voxel based analysis

“…The binary infarct lesion masks were affine registered to the standard MNI-152 space using the FLIRT tool included in the FSL software (Oxford Centre for Functional MRI of the Brain, University of Oxford, Oxford, UK). 16,17 Separate infarct lesion summation maps were created for patients with and without successful recanalization. Each voxel in summation maps represented the total number of patients with infarct involving that particular voxel coordinate ( Figure 1).…”

“…The median NIHSS score at presentation was 20 (interquartile: [15][16][17][18][19][20][21][22][23]. The average onsetto-catheterization time was 4.9 6 2.5 h; and 25 (53%) had left M1 segment occlusion.…”