Impact of white matter hyperintensities on structural connectivity and cognition in cognitively intact ADNI participants

We used indirect brain mapping with virtual lesion tractography to test the hypothesis that the extent of white matter tract disconnection due to white matter hyperintensities (WMH) is associated with corresponding tract-specific cognitive performance decrements. To estimate tract disconnection, WMH masks were extracted from FLAIR MRI data of 481 cognitively intact participants in the Alzheimer's Disease Neuroimaging Initiative (ADNI) and used as regions of avoidance for fiber tracking in diffusion MRI data from 50 healthy young participants from the Human Connectome Project. Estimated tract disconnection in the right inferior fronto-occipital fasciculus, right frontal aslant tract, and right superior longitudinal fasciculus mediated the effects of WMH volume on executive function. Estimated tract disconnection in the left uncinate fasciculus mediated the effects of WMH volume on memory and in the right frontal aslant tract on language. In a subset of ADNI control participants with amyloid data, positive status increased the probability of periventricular WMH and moderated the relationship between WMH burden and tract disconnection in executive function performance.

White matter hyperintensity burden and functional outcomes in acute ischemic stroke patients after mechanical thrombectomy: A systematic review and meta-analysis

BACKGROUND

The influence of white matter hyperintensity (WMH) on clinical outcomes in acute ischemic stroke (AIS) patients treated with mechanical thrombectomy (MT) remains controversial. We performed a systematic review and meta-analysis to examine whether WMH burden is associated with clinical outcomes in AIS patients after MT.

METHODS

PubMed, Embase, and Web of Science were searched from inception to Sep 03, 2023. The registration number for PROSPERO is CRD42022340568. Studies reporting an association between the burden of WMH in AIS patients and clinical outcomes after MT were included in the meta-analysis. A random-effects model was used for meta-analysis. The quality of the included studies was assessed using the Newcastle-Ottawa Scale. Additionally, the presence of imprecise-study effects was evaluated using Egger's test and funnel plot.

RESULTS

Fifteen studies with 3,456 patients were enrolled in this meta-analysis. Among AIS patients who underwent MT, moderate/severe WMH had higher odds of 90-day unfavorable functional outcomes (odds ratio [OR] 2.72, 95% confidence interval [CI] 2.14-3.44; I2 = 0.0%; 95% CI 0.0%-42.7%), 90-day mortality (OR 1.94, 95% CI 1.45-2.60; I2 = 19.5%; 95% CI 0.0%-65.2%) and futile recanalization (OR 2.99, 95% CI 1.42-6.28; I2 = 69.7%; 95% CI 0.0%-91.0%) compared with none/mild WMH. However, the two groups had no significant difference in successful recanalization, symptomatic hemorrhagic transformation, and hemorrhagic transformation. A subset analysis of patients from 3 articles showed that WMH volume was not significantly associated with these outcomes. A notable limitation is that this meta-analysis lacks direct adjustment for imbalances in important baseline covariates.

CONCLUSIONS

Patients with moderate/severe WMH on baseline imaging are associated with substantially increased odds of 90-day unfavorable outcomes, futile recanalization, and 90-day mortality after MT. This association suggests that moderate/severe WMH may contribute to the prediction of clinical outcomes in AIS patients after MT.

Distinct effects of cholesterol profile components on amyloid and vascular burdens

BACKGROUND

Cholesterol plays important roles in β-amyloid (Aβ) metabolism and atherosclerosis. However, the relationships of plasma cholesterol levels with Aβ and cerebral small vessel disease (CSVD) burdens are not fully understood in Asians. Herein, we investigated the relationships between plasma cholesterol profile components and Aβ and CSVD burdens in a large, non-demented Korean cohort.

METHODS

We enrolled 1,175 non-demented participants (456 with unimpaired cognition [CU] and 719 with mild cognitive impairment [MCI]) aged ≥ 45 years who underwent Aβ PET at the Samsung Medical Center in Korea. We performed linear regression analyses with each cholesterol (low-density lipoprotein cholesterol [LDL-c], high-density lipoprotein cholesterol [HDL-c], and triglyceride) level as a predictor and each image marker (Aβ uptake on PET, white matter hyperintensity [WMH] volume, and hippocampal volume) as an outcome after controlling for potential confounders.

RESULTS

Increased LDL-c levels (β = 0.014 to 0.115, p = 0.013) were associated with greater Aβ uptake, independent of the APOE e4 allele genotype and lipid-lowering medication. Decreased HDL-c levels (β =  - 0.133 to - 0.006, p = 0.032) were predictive of higher WMH volumes. Increased LDL-c levels were also associated with decreased hippocampal volume (direct effect β =  - 0.053, p = 0.040), which was partially mediated by Aβ uptake (indirect effect β =  - 0.018, p = 0.006).

CONCLUSIONS

Our findings highlight that increased LDL-c and decreased HDL-c levels are important risk factors for Aβ and CSVD burdens, respectively. Furthermore, considering that plasma cholesterol profile components are potentially modified by diet, exercise, and pharmacological agents, our results provide evidence that regulating LDL-c and HDL-c levels is a potential strategy to prevent dementia.

Sex differences in risk factors for white matter hyperintensities in non-demented older individuals

White matter hyperintensities (WMH) are generally considered to be associated with cerebral small vessel disease, especially, in older age. Although significant sex differences have been reported in the severity of WMH, it is not yet known if the risk factors for WMH differ in men and women. In this study, magnetic resonance imaging brain scans from 2 Australian cohorts were analyzed to extract WMH volumes. The objective of this study is to examine the moderation effect by sex in the association between known risk factors and WMH. The burden of WMH was significantly higher in women compared to men, especially in the deep WMH (DWMH). In the generalized linear model that included the interaction between sex and body mass index (BMI), there was a differential association of BMI with DWMH in men and women in the exploratory sample, that is, the Sydney Memory and Aging Study, n = 432, aged between 70 and 90. The finding of a higher BMI associated with a higher DWMH in men compared to women was replicated in the Older Australian Twins Study sample, n = 179, aged between 65 and 90. The risk factors of WMH pathology are suggested to have a different impact on the aging brains of men and women.

Severe asymptomatic carotid stenosis is associated with robust reductions in homotopic functional connectivity

Severe (>70% narrowing) asymptomatic carotid stenosis (SACS) is associated with cognitive impairment and future strokes, and connectivity basis for the remote brain consequences is poorly understood. Here we explored homotopic connectivity and parenchymal lesions measured by multimodal magnetic resonance imaging (MRI) parameters in patients with SACS. Twenty-four patients with SACS (19 males/5 females; 64.25 ± 7.18 years), 24 comorbidities-matched controls (19 males/5 females; 67.16 ± 6.10 years), and an independent sample of elderly healthy controls (39 females/45 males; 57.92 ± 4.94 years) were included. Homotopic functional connectivity (FC) of resting-state functional MRI and structural connectivity (SC) of deterministic tractography were assessed. Arterial spin labeling based cerebral perfusion, susceptibility weighted imaging based microhemorrhagic lesions, and T2-weighted white matter hyperintensities were also quantified. Significant and robust homotopic reductions (validated by the independent dataset and support vector machine-based machine learning) were identified in the Perisylvian fissure in patients with SACS (false discovery rate corrected, voxel p < 0.05). These involved regions span across several large-scale brain systems, which include the somatomotor, salience, dorsal attention, and orbitofrontal-limbic networks. This significantly reduced homotopic FC can be partially explained by the corrected white matter hyperintensity size. Further association analyses suggest that the decreased homotopic FC in these brain regions is most closely associated with delayed memory recall, sensorimotor processing, and other simple cognitive functions. Together, these results suggest that SACS predominately affects the lower-order brain systems, while higher-order systems, especially the topographies of default mode network, are least impacted initially, but may serve as a hallmark precursor to vascular dementia. Thus, assessment of homotopic FC may provide a means of noninvasively tracking the progression of downstream brain damage following asymptomatic carotid stenosis.

Characterizing the white matter hyperintensity penumbra with cerebral blood flow measures

Objective

White matter hyperintensities (WMHs) are common with age, grow over time, and are associated with cognitive and motor impairments. Mechanisms underlying WMH growth are unclear. We aimed to determine the presence and extent of decreased normal appearing white matter (NAWM) cerebral blood flow (CBF) surrounding WMHs to identify ‘WM at risk’, or the WMH CBF penumbra. We aimed to further validate cross-sectional finding by determining whether the baseline WMH penumbra CBF predicts the development of new WMHs at follow-up.

Methods

Sixty-one cognitively intact elderly subjects received 3 T MPRAGE, FLAIR, and pulsed arterial spin labeling (PASL). Twenty-four subjects returned for follow-up MRI. The inter-scan interval was 18 months. A NAWM layer mask, comprised of fifteen layers, 1 mm thick each surrounding WMHs, was generated for periventricular (PVWMH) and deep (DWMH) WMHs. Mean CBF for each layer was computed. New WMH and persistent NAWM voxels for each penumbra layer were defined from follow-up MRI.

Results

CBF in the area surrounding WMHs was significantly lower than the total brain NAWM, extending approximately 12 mm from both the established PVWMH and DWMH. Voxels with new WMH at follow-up had significantly lower baseline CBF than voxels that maintained NAWM, suggesting that baseline CBF can predict the development of new WMHs over time.

Conclusions

A CBF penumbra exists surrounding WMHs, which is associated with future WMH expansion. ASL MRI can be used to monitor interventions to increase white matter blood flow for the prevention of further WM damage and its cognitive and motor consequences.

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We examined cerebral blood flow (CBF) surrounding white matter hyperintensity (WMH) lesions.

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We examined whether low baseline CBF is associated with WMH expansion over time.

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WMH CBF penumbra exists, extending ~12 mm from both periventricular and deep WMH lesions.

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Baseline CBF can predict the development of new WMHs over time.

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ASL MRI can be used to monitor interventions to increase white matter blood flow.