Perivascular spaces and brain waste clearance systems: relevance for neurodegenerative and cerebrovascular pathology

Enlarged perivascular spaces and clinical outcome of acute ischemic stroke patients receiving intravenous thrombolysis

BACKGROUND

Enlarged perivascular spaces (EPVS) is one of the main imaging features of cerebral small vessel disease (CSVD). Previous studies have shown that hypertension and advanced age were important risk factors for the occurrence and development of EPVS. We aim to explore the correlation between the severity of EPVS at centrum semiovale and basal ganglia and the early and long-term outcome of acute ischemic stroke (AIS) patients receiving intravenous thrombolysis.

METHODS

AIS who received intravenous thrombolysis at the First Affiliated Hospital of Kunming Medical University were retrospectively collected. Demographic data, stroke risk factors, laboratory test results and head imaging data were collected. The number of EPVS in centrum semiovale and basal ganglia of patients in cranial magnetic resonance imaging (MRI) was counted by visual quantification method. Logistic regression analysis was used to evaluate the independent risk factors affecting the prognosis.

RESULTS

A total of 196 subjects were included in this study. The proportion of patients with poor clinical outcome at 90 days was higher in patients with moderate-to-severe centrum semiovale EPVS than in those with no-to-mild EPVS (42.9 % vs 18.7 %, P=0.031). Similarly, patients with moderate-to-severe EPVS in the basal ganglia region had a significantly poor clinical outcome at 90 days (51.7 % vs 18.3 %, P=0.001). Moderate to severe basal ganglia EPVS (OR=2.661, 95 %CI: 1.070-6.618, P=0.035), hyperlipidemia (OR=3.011, 95 %CI: 1.147-7.902, P=0.025) and a higher baseline NIHSS score before thrombolysis (OR=1.194, 95 %CI: 1.071-1.331, P=0.001) were independent risk factors for poor clinical outcome at 90 days. Early neurological improvement (OR=0.220, 95 %CI 0.093-0.520, P=0.001) was associated with a reduced risk of poor clinical outcomes at 90 days.

CONCLUSIONS

Moderate-to-severe EPVS in basal ganglia were an independent risk factor for poor clinical outcome at 90 days in AIS patients with intravenous thrombolysis. Therefore, the severity of EPVS in the basal ganglia region can serve as an imaging marker to predict the 90-day clinical outcome of AIS patients treated with intravenous thrombolysis.

The causal relationship between enlarged perivascular spaces and intracerebral hemorrhage: A 2-sample Mendelian randomization study

The genetic prediction of the causal relationship between enlarged perivascular spaces (PVS) and intracerebral hemorrhage (ICH). We performed a 2-sample Mendelian randomization (MR) study that used published data from genome-wide association studies on ICH and PVS. We primarily utilized the inverse variance weighted (IVW), MR-Egger, weighted median and weighted mode method. Sensitivity analyses included Cochran Q test, MR-Egger regression, MR-PRESSO global test and leave-one-out analysis. IVW analysis showed no statistical association between genetically predicted enlargement of hippocampal PVS (OR = 0.74, 95% CI = 0.23-2.35, P = .605), basal ganglia PVS (OR = 1.59, 95% CI = 0.64-3.95, P = .318), or white matter PVS (OR = 1.59, 95% CI = 0.64-3.95, P = .318) with the risk of ICH. The results of MR-Egger regression, Weighted Median, and Weighted Mode methods were consistent with those of the IVW method. The sensitivity analyses did not reveal any pleiotropy or heterogeneity. The leave-one-out plots did not found any single mutation that might influence the results. Our findings indicate that there is no causal relationship between PVS enlargement and the development of ICH at the genetic level. Using PVS as a diagnostic marker might lack specificity, needed for the planning of timely diagnostic procedures in the risk populations.

Relation of MRI visible perivascular spaces with global and regional brain structural connectivity measures: The Framingham Heart Study (FHS)

MRI visible perivascular spaces (PVS) are associated with cognitive impairment and dementia, which are also associated with disrupted network connectivity. PVS may relate to dementia risk through disruption in brain connectivity. We studied the relation between PVS grade and global and regional structural connectivity in Framingham Heart Study participants free of stroke and dementia. PVS were rated on axial T2 sequences in the basal ganglia (BG) and centrum semiovale (CSO). We assessed structural global and regional network architecture using global efficiency, local efficiency and modularity. Analysis of covariance was used to relate PVS grades with structural network measures. Models adjusted for age, sex (model 1), and vascular risk factors (model 2). Effect modification on the associations by age, sex, hypertension and APOE-ɛ4 status was assessed. Among 2525 participants (mean age 54 ± 13 years, 53 % female), significant associations were observed between grade III and IV PVS in the BG and CSO with reduced global efficiency. Grade III (β -0.0030; 95 % confidence interval [CI] -0.0041, -0.0019) and IV (β -0.0033, CI -0.0060, -0.0007) PVS in the BG and grade IV (β -0.0015; CI -0.0024, -0.0007) PVS in the CSO were associated with reduced local efficiency. We observed shared and different strength of association by age, hypertension, sex and APOE-ɛ4 in the relationship between high burden PVS in the BG and CSO with structural network measures. Findings suggest that higher grade PVS are associated with disruption of global and regional structural brain networks.

Lipidopathy disrupts peripheral and central amyloid clearance in Alzheimer's disease: Where are our knowledge

Amyloid-beta (Aβ) production is a normal physiological process, essential for neuronal function. However, an imbalance in Aβ production and clearance is the central pathological feature of Alzheimer's disease (AD), leading to the accumulation of Aβ plaques in the brain. Low-density lipoprotein receptor-related protein 1 (LRP1) plays a critical role in both the central clearance of Aβ from the brain and its peripheral transport to visceral organs. Disruptions in these processes contribute to the accumulation of Aβ in the central nervous system (CNS) and the progression of AD. Recent research emphasizes the need for a broader focus on the systemic effects of organs outside the brain, particularly in the context of AD prevention and treatment. The contribution of peripheral systems, such as the liver, in Aβ clearance, is vital, given that Aβ levels in the plasma correlate closely with those in the brain. Consequently, targeting systemic processes, rather than focusing solely on the CNS, may offer promising therapeutic approaches. Furthermore, high-density lipoprotein (HDL) facilitates the formation of lipoprotein-amyloid complexes, which are important for Aβ transport and clearance, using proteins such as apolipoproteins E and J (ApoE and ApoJ) to form complexes that help manage Aβ accumulation. On the other hand, low-density lipoprotein (LDL) facilitates Aβ efflux from the brain by binding to LRP1, promoting its clearance. Given the relationship between lipid profiles and Aβ levels, along with lipid-modifying drugs, may be effective in managing Aβ accumulation and mitigating AD progression.

Cerebral small vessel disease: The impact of glymphopathy and sleep disorders

The glymphatic system, a vital brain perivascular network for waste clearance, hinges on the functionality of the aquaporin 4 (AQP4) water channel. Alarmingly, AQP4 single nucleotide polymorphisms (SNPs) are linked to impaired glymphatic clearance, or glymphopathy, which contributes to sleep disturbances and various age-related neurodegenerative diseases. Despite the critical role of glymphopathy and sleep disturbances in cerebral small vessel disease (CSVD) - a silent precursor to age-related neurodegenerative disorders - their interplay remains underexplored. CSVD is a major cause of stroke and dementia, yet its pathogenesis is not fully understood. Emerging evidence implicates glymphopathy and sleep disorders as pivotal factors in age-related CSVD, exacerbating the condition by hindering waste removal and compromising blood-brain barrier (BBB) integrity. Advanced imaging techniques promise to enhance diagnosis and monitoring, while lifestyle modifications and personalised medicine present promising treatment avenues. This narrative review underscores the need for a multidisciplinary approach to understanding glymphopathy and sleep disorders in CSVD. By exploring their roles, emphasising the necessity for longitudinal studies, and discussing potential therapeutic interventions, this paper aims to pave the way for new research and therapeutic directions in CSVD management.

The role of Ergothioneine in cognition and age-related neurodegenerative disease: a systematic review

Ergothioneine (ET) is an under recognised diet-derived compound which has the potential to be a "longevity vitamin". It was found to be beneficial for cognitive function and age-related neurodegenerative disorder (ARND). Thus, this study was conducted to synthesise the existing evidence of ET's effects on cognition and ARND, emphasizing its potential as a micronutrient for healthy aging. This study also highlights the future prospects of the research regarding ET's effects on cognition and ARND that are suggested in existing literature. Three databases (Pubmed, Scopus, and Web of Science) were used to search for the studies that meet the inclusion and exclusion criteria. A total of 19 studies were included after screening in this review. The risk of bias of each study was assessed using the Office of Health Assessment and Translation (OHAT) risk of bias rating tool. All studies' characteristics and main findings were tabulated according to their type of study. Mechanisms of ET in improving cognitive function and preventing ARND were found to be through its antioxidative, anti-inflammatory and antisenescence properties. Its role in neurotransmission and neuroprotection also contributed to improving cognition and preventing ARND. In conclusion, ET is a potential compound to be explored as its role in cognition and ARND have been discovered through several studies.

Differential tissue and cellular distribution of chemokine C-C motif ligand 2 in grey/white matters of healthy and simian immunodeficiency virus infected monkey

Previous studies have shown that CCL2 concentration is higher in cerebrospinal fluid than in plasma of health and human immunodeficiency virus (HIV) infected individuals, suggesting an extra source of CCL2 in brain. Brain cellular CCL2 has been broadly studied in cultured cells and its in-vivo cellular distribution has been investigated in rodent experimental autoimmune encephalomyelitis model. However, its cellular distribution in grey and white matter (GM, WM) remains elusive. We explored this issue using healthy and simian immunodeficiency virus (SIV) infected monkeys and found: 1) Neurons were a major source of CCL2-like immunoreactivity (CCL2-ir) in normal GM, and corpus callosum (CC) ependyma showed high density of CCL2-ir. 2) Upon SIV infection, CCL2-ir was strikingly raised in GM neurons, and in CC ependyma. 3) Brain vascular-perivascular cells were a large source of CCL2-ir in normal GM and WM, which was relatively larger in CC WM than in GM. 4) Vascular-perivascular CCL2-ir proportional areas were significantly enhanced by SIV infection in both GM and CC WM. 5) Microglia seemed not to express CCL2 in healthy brain. Microglia-marker and CCL2-ir co-labeled cells were significantly increased by SIV infection. 6) A vast of macrophage-like cells were situated along infected CC ependyma, suggesting a large number of monocytes be crossing ependyma, which may be related to establishment of viral reservoir. In conclusion, our study provides valuable insights into the cellular sources and alterations of CCL2 in the monkey brain under normal and SIV-infected conditions, which may promote better understanding of CCL2 in related neurological processes.

Enlarging and shrinking focal perivascular spaces

Background and PurposePerivascular spaces (PVS) are interstitial fluid-filled spaces surrounding blood vessels traversing the deep gray nuclei and white matter of the brain. These are commonly encountered on CT and MR imaging and are generally asymptomatic and of no clinical significance. However, occasional changes in the size of focal PVS, for example, when enlarging, may mimic pathologies including neoplasms and infections, hence potentially confounding radiological interpretation. Given these potential diagnostic issues, we sought to better characterize common clinical and imaging features of focal PVS demonstrating size fluctuations.Materials and MethodsUpon institutional approval, we retrospectively identified 4 cases demonstrating PVS with size changes at our institution. To supplement our cases, we also performed a literature review, which identified an additional 14 cases. Their clinical and imaging data were analyzed to identify characteristic features.ResultsOf the 18 total cases (including the 4 institutional cases), 10 cases increased and 8 decreased in size. These focal PVS ranged from 0.4-4.5 cm in size. Whereas a decrease in size did not represent a diagnostic issue, focal increase in size of PVS led to concerning differential diagnoses in at least 30% of the radiology reports. These enlarging PVS were most found in the basal ganglia and temporal lobe, and in patients with previous brain radiation treatment.ConclusionFocal size change of PVS can occur, especially years after brain radiation treatment. Being cognizant of this benign finding is important to consider in the differential diagnosis to avoid undue patient anxiety or unnecessary medical intervention.

Cerebrovascular burden and neurodegeneration linked to 15-year odor identification decline in older adults

Background

The mechanisms underlying olfactory decline in aging need further investigation. Noticeably, the longitudinal relationship of biological markers with olfaction remains underexplored. We investigated whether baseline levels and progression of microvascular lesions and brain atrophy are associated with odor identification (OID) decline.

Methods

The association between structural MRI markers and OID decline was examined in participants from the SNAC-K MRI study who were free from dementia at baseline (n = 401, mean age = 70.2 years, 60% females). OID was repeatedly assessed over 15 years. Presence of lacunes, white matter hyperintensities (WMH), perivascular spaces (PVS), and lateral ventricular, hippocampal, amygdalar, and total gray matter (GM) volumes were assessed up to 6 years, concurrent with the first 6 years of olfactory assessments.

Results

Higher PVS count and lower hippocampal and GM volumes at baseline were associated with accelerated OID decline (pFWE  < 0.05). Longitudinally (n = 225), presence of lacunes at follow-up, faster WMH volume and PVS count increases, faster lateral ventricular enlargement, and faster hippocampal, amygdalar, and GM atrophy were associated with accelerated OID decline (p FWE < 0.05).

Conclusion

Olfactory decline is related to both increased cerebrovascular burden and accelerated brain atrophy over time.

The Dysregulation of the Glymphatic System in Patients with Psychosis Spectrum Disorders Minimally Exposed to Antipsychotics: La dérégulation du système glymphatique en présence de troubles psychotiques chez des patients peu exposés à des antipsychotiques

OBJECTIVE

The pathophysiological mechanisms influencing psychosis spectrum disorders are largely unknown. The glymphatic system, which is a brain waste clearance pathway, has recently been implicated in its pathophysiology and has also been shown to be disrupted in various neurodegenerative and vascular diseases. Initial studies examining the glymphatic system in psychosis spectrum disorders have reported disruptions, but the findings have been confounded by medication effects as they included antipsychotic-treated patients. In this study, we used diffusion tensor imaging analysis along the perivascular space (DTI-ALPS) as a technique to measure the functionality of the glymphatic system in a sample of antipsychotic-minimally exposed patients with psychosis spectrum disorders and healthy controls.

METHODS

The study included 13 antipsychotic-minimally exposed (2 weeks antipsychotic exposure in the past 3 months/lifetime) patients with psychosis spectrum disorders and 114 healthy controls. We quantified water diffusion metrics along the x-, y-, and z-axes in both projection and association fibres to derive the DTI-ALPS index, a proxy for glymphatic activity. Between-group differences were analyzed using two-way ANCOVA controlling for age and sex. Partial correlations were used to assess the association between the ALPS index and clinical variables.

RESULTS

Analyses revealed that antipsychotic-minimally exposed psychosis spectrum disorder patients had a lower DTI-ALPS index value than healthy controls in both hemispheres and the whole brain (all P < 0.005). Significant differences were also observed between the x and y projections/associations between patients and healthy controls (P < 0.001). Furthermore, we did not find any significant correlations (all P > 0.05) between the DTI-ALPS index with age, body mass index, symptomatology, and metabolic parameters.

CONCLUSION

This study shows that the glymphatic system is dysregulated in antipsychotic-minimally exposed patients with psychosis spectrum disorders. Understanding the mechanisms that influence the glymphatic system may help to understand the pathophysiology of psychosis spectrum disorders as proper waste clearance is needed for normal brain functioning.

Perivascular enhancement pattern: Identification, diagnostic spectrum and practical approach - A pictorial review

Perivascular spaces (PVS) are fluid-filled structures that form the immediate peripheral environment of small cerebral vessels. They are a central component of the glymphatic system, which plays a crucial role in maintaining cerebral homeostasis. Their involvement in central nervous system diseases is currently a major focus of research, particularly in neuroimaging. Pathological enhancement of PVS on post-contrast MRI sequences creates a distinctive pattern due to their topography. As with other intracranial enhancement patterns, a differential diagnosis approach can be applied to perivascular enhancement (PVE). However, it is particularly challenging due to the rarity and complexity of the conditions involved. This article aims to facilitate the recognition of PVE pattern, to highlight the various causal conditions and to propose a practical diagnostic approach.

Enlarged perivascular spaces correlate with blood-brain barrier leakage and cognitive impairment in Alzheimer's disease

BackgroundThe clinical significance of enlarged perivascular spaces (EPVS) in Alzheimer' s disease (AD) was ambiguous.ObjectiveTo investigate whether EPVS contribute to blood-brain barrier (BBB) leakage and cognition in AD.MethodsThe study included a total of 64 participants (26 healthy controls and 38 patients with AD). The evaluation of EPVS and BBB permeability was performed in specific anatomical locations: the centrum semiovale (CSO), basal ganglia, and hippocampus. The EPVS ratings were performed according to Potter's instructions. BBB permeability was evaluated using dynamic contrast-enhanced-MRI. The relationship between EPVS and global cognition (Mini-Mental State Examination and Montreal Cognitive Assessment), cognitive subdomains, and BBB permeability were examined in both groups. Finally, the relationship between CSO BBB permeability and cognition in AD patients was investigated.ResultsHigh-grade CSO EPVS was found associated with AD (OR: 3.40, 95% CI: 1.11-11.90, p = 0.04). In the AD group, a significant correlation was observed between high-grade CSO EPVS and lower MMSE score (r = -0.36, p = 0.03) and verbal fluency (r = -0.44, p = 0.01). High-grade CSO EPVS positively correlated with BBB leakage (r = 0.58, p < 0.001). The BBB permeability of CSO negatively correlated with verbal fluency (r = -0.52, p < 0.001) and attention (r = -0.40, p = 0.01).ConclusionsHigh-grade CSO EPVS is related to BBB leakage, which contributes to cognitive impairment in AD patients, especially verbal frequency. CSO EPVS can function as a convenient AD marker for intervention and therapy.

Increased burden of enlarged perivascular spaces in patients with patent foramen ovale

INTRODUCTION

Patent foramen ovale (PFO) patients may experience states of hypoxia and hypoperfusion, which may increase the burden of enlarged perivascular spaces (EPVS). However, to our knowledge, no data are available regarding EPVS in PFO patients. This study sought to investigate if patients with PFO exhibit a heightened burden of EPVS and to identify the mediating factors between PFO and EPVS.

METHODS

A total of 108 consecutive PFO patients (PFO group) and 110 healthy controls (HC group) from January 2022 to February 2024 were enrolled. The differences in centrum semiovale EPVS (CSO-EPVS) and basal ganglia EPVS (BG-EPVS) scores between PFO and HC groups were compared. The correlations among PFO diameters, laboratory indexes, and EPVS burdens were analyzed. The relationships among them were obtained using mediation analysis.

RESULTS

Mean age of PFO and HC group was 47.68 ± 14.47 and 48.14 ± 12.84 years. The CSO-EPVS and BG-EPVS scores were higher in PFO group than HC group (P < 0.001). The CSO-EPVS and BG-EPVS scores for PFO group were concentrated in the ranges 1-3 and 1-2 points, while for HC group were concentrated in the range 0-1 points. A positive correlation among PFO diameters and CSO-EPVS score (r = 0.62, P < 0.001), BG-EPVS score (r = 0.63, P < 0.001), and homocysteine (HCY)(r = 0.21, P = 0.03) was observed. Mediation analysis indicated that higher HCY significantly mediated the relationship between PFO diameter and BG-EPVS burden in PFO patients (P < 0.05).

CONCLUSION

These findings revealed the presence of glymphatic dysfunction in patients with PFO. HCY may mediate the impact of PFO diameter on glymphatic function.

Atypical Lesions in Virchow-Robin Spaces: A Case Report

The differentiation between benign and malignant brain lesions remains a fundamental challenge in modern neuroimaging. This case highlights a rare presentation of ectatic Virchow-Robin spaces (VRS), which mimicked tumefactive brain lesions and required a comprehensive diagnostic evaluation to exclude neoplastic, infectious, and inflammatory processes. A 37-year-old female presented with progressive headache, cognitive impairment, and facial pain. Magnetic resonance imaging revealed a multiloculated subcortical cystic lesion, initially raising suspicions of a dysembryoplastic neuroepithelial tumor or neurocysticercosis. Advanced imaging modalities, including MR spectroscopy and MR angiography, played a crucial role in confirming the benign nature of the lesion. This report underscores the critical role of a multidisciplinary diagnostic approach, integrating clinical presentation, imaging characteristics, and laboratory findings, to address the diagnostic overlap between benign dilated VRS and pathological conditions such as tumors or infections. Additionally, the case emphasizes the importance of recognizing atypical presentations of VRS to avoid unnecessary interventions and to guide patient-centered management.

Angiotensin-converting enzyme inhibitors: a therapeutic option for controlling blood pressure associated with delayed cognitive processing speed

Antihypertensive treatment (AT) is essential for preventing hypertension-related cognitive decline. The goals of this observational study were to compare cognitive performance (CP) between non-hypertensive (NH) volunteers and hypertensive patients and to evaluate the correlation between CP and antihypertensive drugs (AHD). Three groups were constituted: NH (n = 30) [group 1], hypertensive with systolic blood pressure (SBP) < 140 mmHg and diastolic blood pressure (DBP) < 90 mmHg (n = 54) [group 2] and hypertensive with SBP ≥ 140 or DBP ≥ 90 (n = 31) [group 3]. To analyze the cognitive domains, a neuropsychological battery was applied and the raw performance values in these tests were transformed into z-scores. The domain was considered impaired if it presented a z-score below -1.5 SD. Compared to group 1, both groups of hypertensive were older (51 [ ± 12] years) and showed a worse CP in episodic memory (p = 0.014), language (p = 0.003) and processing speed (PS) [p = 0.05]. Angiotensin-converting enzyme inhibitors (ACEi) and angiotensin receptor blockers (ARB) were the most used AHD (46.3%, p = 0.01 [group 2] and 64.5%, p = 0.005 [group 3]) and showed correlations with PS. Linear regression models revealed a negative association of PS with the use of ACEi (β = -0.230, p = 0.004), but not with the use of ARB (β = 0.208, p = 0.008). The effect of AT on cognition appears to go beyond the search for lower blood pressure targets and also includes the mechanism of action of AHD on the brain, so that additional benefits may possibly be achieved with simple adaptations in the treatment regimen, particularly in patients without clinically manifest cognitive impairment.

Drug delivery in leptomeningeal disease: Navigating barriers and beyond

Leptomeningeal disease (LMD) refers to the infiltration of cancer cells into the leptomeningeal compartment. Leptomeninges are the two membranous layers, called the arachnoid membrane and pia mater. The diffuse nature of LMD poses a challenge to its effective diagnosis and successful management. Furthermore, the predominant phenotype; solid masses or freely floating cells, has altering implications on the effectiveness of drug delivery systems. The standard of care is the intrathecal delivery of chemotherapy drugs but it is associated with increased instances of treatment-related complications, low patient compliance, and suboptimal drug distribution. An alternative involves administering the drugs systemically, after which they must traverse fluid barriers to arrive at their destination within the leptomeningeal space. However, this route is known to cause off-target effects as well as produce subtherapeutic drug concentrations at the target site within the central nervous system. The development of new drug delivery systems such as liposomal cytarabine has improved drug delivery in leptomeningeal metastatic disease, but much still needs to be done to effectively target this challenging condition. In this review, we discuss about the anatomy of leptomeninges relevant for drug penetration, the conventional and advanced drug delivery methods for LMD. We also discuss the future directions being set by different clinical trials.

Vascular Cognitive Impairment

OBJECTIVE

Vascular cognitive impairment is a major contributor to age-associated cognitive decline, both independently and as a contributor to mixed dementia syndromes. This article reviews the current understanding of how vascular dysfunction contributes to cognitive impairment and dementia risk in older individuals and includes updated diagnostic criteria and treatment recommendations.

LATEST DEVELOPMENTS

Clinical and research criteria have been evolving to more accurately determine the full prevalence of vascular cognitive impairment. The Boston Criteria version 2.0 for cerebral amyloid angiopathy now includes multiple punctate MRI T2 white matter hyperintensities and MR-visible perivascular spaces in addition to previously described T2* hemorrhagic signatures. MR-visible perivascular spaces are associated with both vascular cognitive impairment and Alzheimer disease, potentially linking cerebrovascular dysfunction to neurodegenerative disorders through its role in brain waste clearance. The American Heart Association's goal for cardiovascular health promotion, "Life's Essential 8," has been updated to include sleep health and acknowledges psychological well-being and social determinants of health as fundamental components necessary to achieve optimal cardiovascular health for all adults.

ESSENTIAL POINTS

Vascular cognitive impairment is a common and often underrecognized contributor to cognitive impairment in older individuals, with heterogeneous etiologies requiring individualized treatment strategies. Effective cerebrovascular disease risk factor modification starting in midlife is critical to reducing the risk of Alzheimer disease and related dementias, with the goal of preventing vascular brain injury and maintaining cognitive reserve in the presence of nonvascular age-related brain pathologies.

Evaluation of the Glymphatic System in Schizophrenia Spectrum Disorder Using Proton Magnetic Resonance Spectroscopy Measurement of Brain Macromolecule and Diffusion Tensor Image Analysis Along the Perivascular Space Index

BACKGROUND AND HYPOTHESIS

The glymphatic system (GS), a brain waste clearance pathway, is disrupted in various neurodegenerative and vascular diseases. As schizophrenia shares clinical characteristics with these conditions, we hypothesized GS disruptions in patients with schizophrenia spectrum disorder (SCZ-SD), reflected in increased brain macromolecule (MM) and decreased diffusion-tensor-image-analysis along the perivascular space (DTI-ALPS) index.

STUDY DESIGN

Forty-seven healthy controls (HCs) and 103 patients with SCZ-SD were studied. Data included 135 proton magnetic resonance spectroscopy (1H-MRS) sets, 96 DTI sets, with 79 participants contributing both. MM levels were quantified in the dorsal-anterior cingulate cortex (dACC), dorsolateral prefrontal cortex, and dorsal caudate (point resolved spectroscopy, echo-time = 35ms). Diffusivities in the projection and association fibers near the lateral ventricle were measured to calculate DTI-ALPS indices. General linear models were performed, adjusting for age, sex, and smoking. Correlation analyses examined relationships with age, illness duration, and symptoms severity.

STUDY RESULTS

MM levels were not different between patients and HCs. However, left, right, and bilateral DTI-ALPS indices were lower in patients compared with HCs (P < .001). In HCs, age was positively correlated with dACC MM and negatively correlated with left, right, and bilateral DTI-ALPS indices (P < .001). In patients, illness duration was positively correlated with dACC MM and negatively correlated with the right DTI-ALPS index (P < .05). In the entire population, dACC MM and DTI-ALPS indices showed an inverse correlation (P < .01).

CONCLUSIONS

Our results suggest potential disruptions in the GS of patients with SCZ-SD. Improving brain's waste clearance may offer a potential therapeutic approach for patients with SCZ-SD.

Enlarged perivascular spaces in the basal ganglia are associated with arteries not veins

Enlarged perivascular spaces (EPVS) are common in cerebral small vessel disease (CSVD) and have been identified as a marker of dysfunctional brain clearance. However, it remains unknown if the enlargement occurs predominantly around arteries or veins. We combined in vivo ultra-high-resolution MRI and histopathology to investigate the spatial relationship of veins and arteries with EPVS within the basal ganglia (BG). Furthermore, we assessed the relationship between the EPVS and measures of blood-flow (blood-flow velocity, pulsatility index) in the small arteries of the BG. Twenty-four healthy controls, twelve non-CAA CSVD patients, and five probable CAA patients underwent a 3 tesla [T] and 7T MRI-scan, and EPVS, arteries, and veins within the BG were manually segmented. Furthermore, the scans were co-registered. Six autopsy-cases were also assessed. In the BG, EPVS were significantly closer to and overlapped more frequently with arteries than with veins. Histological analysis showed a higher proportion of BG EPVS surrounding arteries than veins. Finally, the pulsatility index of BG arteries correlated with EPVS volume. Our results are in line with previous works and establish a pathophysiological relationship between arteries and EPVS, contributing to elucidating perivascular clearance routes in the human brain.

Spaceflight associated neuro-ocular syndrome: connections with terrestrial eye and brain disorders

Spaceflight Associated Neuro-ocular Syndrome (SANS) is a series of findings found in astronauts who have experienced long-duration spaceflight. It is characterized by neuro-ocular changes that may irreversibly alter vision and increase the risk for the development of terrestrial eye and brain disorders. Theories regarding its etiology and countermeasures to combat the findings seen continue to evolve. There is currently no direct treatment for SANS. Traditional Chinese Medicine (TCM) modalities have been used to treat eye and brain disorders on Earth that are pathogenically similar to SANS, therefore, TCM may be able to target corresponding pathology in astronauts, prevent and mitigate SANS findings, and decrease the risk for future development of disorders. This paper intends to discuss pathological similarities between SANS and terrestrial eye and brain disorders and how TCM has been used to treat those disorders.

Transcranial focused ultrasound stimulation enhances cerebrospinal fluid movement: Real-time in vivo two-photon and widefield imaging evidence

BACKGROUND

Cerebrospinal fluid (CSF) flow is crucial for brain homeostasis and its dysfunction is highly associated with neurodegenerative diseases. Restoring CSF circulation is proposed as a key strategy for the treatment of the diseases. Among the methods to improve CSF circulation, focused ultrasound (FUS) stimulation has emerged as a promising non-invasive brain stimulation technique, with effectiveness evidenced by ex vivo studies. However, due to technical disturbances in in vivo imaging combined with FUS, direct evidence of real-time in vivo CSF flow enhancement by FUS remains elusive.

OBJECTIVE

To investigate whether FUS administered through the skull base can enhance CSF influx in living animals with various real-time imaging techniques.

METHODS

We demonstrate a novel method of applying FUS through the skull base, facilitating cortical CSF influx, evidenced by diverse in vivo imaging techniques. Acoustic simulation confirmed effective sonication of our approach through the skull base. After injecting fluorescent CSF tracers into cisterna magna, FUS was administered at the midline of the jaw through the skull base for 30 min, during which imaging was performed concurrently.

RESULTS

Enhanced CSF influx was observed in macroscopic imaging, demonstrated by the influx area and intensity of the fluorescent dyes after FUS. In two-photon imaging, increased fluorescence was observed in the perivascular space (PVS) after stimulation. Moreover, particle tracking of microspheres showed more microspheres entering the imaging field, with increased mean speed after FUS.

CONCLUSION

Our findings provide direct real-time in vivo imaging evidence that FUS promotes CSF influx and flow in the PVS.

Stroke studies in large animals: Prospects of mitochondrial transplantation and enhancing efficiency using hydrogels and nanoparticle-assisted delivery

One of the most frequent reasons for mortality and disability today is acute ischemic stroke, which occurs by an abrupt disruption of cerebral circulation. The intricate damage mechanism involves several factors, such as inflammatory response, disturbance of ion balance, loss of energy production, excessive reactive oxygen species and glutamate release, and finally, neuronal death. Stroke research is now carried out using several experimental models and potential therapeutics. Furthermore, studies are being conducted to address the shortcomings of clinical care. A great deal of research is being done on novel pharmacological drugs, mitochondria targeting compounds, and different approaches including brain cooling and new technologies. Still, there are many unanswered questions about disease modeling and treatment strategies. Before these new approaches may be used in therapeutic settings, they must first be tested on large animals, as most of them have been done on rodents. However, there are several limitations to large animal stroke models used for research. In this review, the damage mechanisms in acute ischemic stroke and experimental acute ischemic stroke models are addressed. The current treatment approaches and promising experimental methods such as mitochondrial transplantation, hydrogel-based interventions, and strategies like mitochondria encapsulation and chemical modification, are also examined in this work.

Genetic Determinants of Vascular Dementia

Vascular dementia (VaD) is a prevalent form of cognitive impairment with underlying vascular etiology. In this review, we examine recent genetic advancements in our understanding of VaD, encompassing a range of methodologies including genome-wide association studies, polygenic risk scores, heritability estimates, and family studies for monogenic disorders revealing the complex and heterogeneous nature of the disease. We report well known genetic associations and highlight potential pathways and mechanisms implicated in VaD and its pathological risk factors, including stroke, cerebral small vessel disease, and cerebral amyloid angiopathy. Moreover, we discuss important modifiable risk factors such as hypertension, diabetes, and dyslipidemia, emphasizing the importance of a multifactorial approach in prevention, treatment, and understanding the genetic basis of VaD. Last, we outline several areas of scientific advancements to improve clinical care, highlighting that large-scale collaborative efforts, together with an integromics approach can enhance the robustness of genetic discoveries. Indeed, understanding the genetics of VaD and its pathophysiological risk factors hold the potential to redefine VaD on the basis of molecular mechanisms and to generate novel diagnostic, prognostic, and therapeutic tools.

Repetitive Head Impacts and Perivascular Space Volume in Former American Football Players

Importance

Exposure to repetitive head impacts (RHI) is associated with increased risk for neurodegeneration. Accumulation of toxic proteins due to impaired brain clearance is suspected to play a role.

Objective

To investigate whether perivascular space (PVS) volume is associated with lifetime exposure to RHI in individuals at risk for RHI-associated neurodegeneration.

Design, Setting, and Participants

This cross-sectional study was part of the Diagnostics, Imaging, and Genetics Network for the Objective Study and Evaluation of Chronic Traumatic Encephalopathy (DIAGNOSE CTE) Research Project, a 7-year multicenter study consisting of 4 US study sites. Data were collected from September 2016 to February 2020 and analyses were performed between May 2021 and October 2023. After controlling for magnetic resonance image (MRI) and processing quality, former American football players and unexposed asymptomatic control participants were included in analyses.

Exposure

Prior exposure to RHI while participating in American football was estimated using the 3 cumulative head impact indices (CHII-G, linear acceleration; CHII-R, rotational acceleration; and CHII, number of head impacts).

Main Outcomes and Measures

Individual PVS volume was calculated in the white matter of structural MRI. Cognitive impairment was based on neuropsychological assessment. Linear regression models were used to assess associations of PVS volume with neuropsychological assessments in former American football players. All analyses were adjusted for confounders associated with PVS volume.

Results

Analyses included 224 participants (median [IQR] age, 57 [51-65] years), with 170 male former football players (114 former professional athletes, 56 former collegiate athletes) and 54 male unexposed control participants. Former football players had larger PVS volume compared with the unexposed group (mean difference, 0.28 [95% CI, 0.00-0.56]; P = .05). Within the football group, PVS volume was associated with higher CHII-R (β = 2.71 × 10-8 [95% CI, 0.50 × 10-8 to 4.93 × 10-8]; P = .03) and CHII-G (β = 2.24 × 10-6 [95% CI, 0.35 × 10-6 to 4.13 × 10-6]; P = .03). Larger PVS volume was also associated with worse performance on cognitive functioning in former American football players (β = -0.74 [95% CI, -1.35 to -0.13]; P = .04).

Conclusions and Relevance

These findings suggest that impaired perivascular brain clearance, as indicated by larger PVS volume, may contribute to the association observed between RHI exposure and neurodegeneration.

The Spectrum of Cerebral Small Vessel Disease: Emerging Pathophysiologic Constructs and Management Strategies

Cerebral small vessel disease (CSVD) is a spectrum of disorders that affect small arterioles, venules, cortical and leptomeningeal vessels, perivascular spaces, and the integrity of neurovascular unit, blood brain barrier, and surrounding glia and neurons. CSVD is an important cause of lacunar ischemic stroke and sporadic hemorrhagic stroke, as well as dementia-which will constitute some of the most substantive population and public health challenges over the next century. This article provides an overview of updated pathophysiologic frameworks of CSVD; discusses common and underappreciated clinical and neuroimaging manifestations of CSVD; and reviews emerging genetic risk factors linked to sporadic CSVD.

The Role of Astrocytes in Migraine with Cortical Spreading Depression: Protagonists or Bystanders? A Narrative Review

Cortical spreading depression (CSD) is a slow wave of cortical depolarization closely associated with migraines with an aura. Previously, it was thought that CSD depolarization was mainly driven by neurons, with characteristic changes in neuronal swelling and increased extracellular potassium (K+) and glutamate. However, the role of astrocytes, a member of the neurovascular unit, in migraine with CSD has recently received increasing attention. In the early stages of CSD, astrocytes provide neurons with energy support and clear K+ and glutamate from synaptic gaps. However, in the late stages of CSD, astrocytes release large amounts of lactic acid to exacerbate hypoxia when the energy demand exceeds the astrocytes' compensatory capacity. Astrocyte endfoot swelling is a characteristic of CSD, and neurons are not similarly altered. It is primarily due to K+ influx and abnormally active calcium (Ca2+) signaling. Aquaporin 4 (AQP-4) only mediates K+ influx and has little role as an aquaporin. Astrocytes endfoot swelling causes perivascular space closure, slowing the glymphatic system flow and exacerbating neuroinflammation, leading to persistent CSD. Astrocytes are double-edged swords in migraine with CSD and may be potential targets for CSD interventions.

Visualization of Cerebrospinal Fluid Outflow and Egress along the Nerve Roots of the Lumbar Spine

Intrinsic cerebrospinal fluid (CSF) dynamics in the brain have been extensively studied, particularly the egress sites of tagged intrinsic CSF in the meninges. Although spinal CSF recirculates within the central nervous system (CNS), we hypothesized that CSF outflows from the lumbar spinal canal. We aimed to visualize and semi-quantify the outflow using non-contrast MRI techniques. We utilized a 3 Tesla clinical MRI with a 16-channel spine coil, employing time-spatial labeling inversion (Time-SLIP) with tag-on and tag-off acquisitions, T2-weighted coronal 2D fluid-attenuated inversion recovery (FLAIR) and T2-weighted coronal 3D centric ky-kz single-shot FSE (cSSFSE). Images were acquired using time-spatial labeling inversion pulse (Time-SLIP) with tag-on and tag-off acquisitions with varying TI periods. Ten healthy volunteers with no known spinal diseases participated. Variations in tagged CSF outflow were observed across different thoracolumbar nerve root segments in all participants. We quantified CSF outflow at all lumbar levels and the psoas region. There was no significant difference among the ROIs for signal intensity. The tagged CSF outflow from the spinal canal is small but demonstrates egress to surrounding tissues. This finding may pave the way for exploring intrathecal drug delivery, understanding of CSF-related pathologies and its potential as a biomarker for peripheral neuropathy and radiculopathy.

Association between enlarged perivascular spaces in basal ganglia and cerebral perfusion in elderly people

Background and objective

Enlarged perivascular spaces in basal ganglia (BG-EPVS) are considered an imaging marker of cerebral small vessel disease (CSVD), but its pathogenesis and pathophysiological process remain unclear. While decreased cerebral perfusion is linked to other CSVD markers, the relationship between BG-EPVS and cerebral perfusion remains ambiguous. This study aimed to explore this association.

Methods

Elderly individuals with severe BG-EPVS (n = 77) and age/sex-matched controls (n = 89) underwent head CT perfusion imaging. The cerebral perfusion parameters including mean transit time (MTT), time to maximum (TMAX), cerebral blood flow (CBF), and cerebral blood volume (CBV) were quantitatively measured by symmetric regions of interest plotted in the basal ganglia region. Point-biserial correlation and logistics regression analysis were performed to investigate the association between BG-EPVS and cerebral perfusion.

Results

There were no significant differences in MTT, TMAX, or CBF between BG-EPVS group and control group. CBV was significantly lower in the BG-EPVS group (p = 0.035). Point-biserial correlation analysis showed a negative correlation between BG-EPVS and CBV (r = -0.198, p = 0.011). BG-EPVS group and control group as the dependent variable, binary logistics regression analysis showed that CBV was not an independent risk factor for severe BG-EPVS (p = 0.448). All enrolled patients were divided into four groups according to the interquartile interval of CBV. The ordered logistic regression analysis showed severe BG-EPVS was an independent risk factor for decreased CBV after adjusting for confounding factors (OR = 2.142, 95%CI: 1.211-3.788, p = 0.009).

Conclusion

Severe BG-EPVS is an independent risk factor for decreased CBV in the elderly, however, the formation of BG-EPVS is not solely dependent on changes in CBV in this region. This finding provides information about the pathophysiological consequence caused by severe BG-EPVS.

Enlarged perivascular spaces and their association with motor, cognition, MRI markers and cerebrovascular risk factors in male fragile X premutation carriers

FMR1 premutation carriers (55-200 CGG repeats) are at risk of developing fragile X-associated tremor/ataxia syndrome (FXTAS), a neurodegenerative disorder associated with motor and cognitive impairment. Bilateral hyperintensities of the middle cerebellar peduncles (MCP sign) are the major radiological hallmarks of FXTAS. In the general population, enlarged perivascular spaces (PVS) are biomarkers of small vessel disease and glymphatic dysfunction and are associated with cognitive decline. Our aim was to determine if premutation carriers show higher ratings of PVS than controls and whether enlarged PVS are associated with motor and cognitive impairment, MRI features of neurodegeneration, cerebrovascular risk factors and CGG repeat length. We evaluated 655 MRIs (1-10 visits/participant) from 229 carriers (164 with FXTAS and 65 without FXTAS) and 133 controls. PVS in the basal ganglia (BG-EPVS), centrum semiovale, and midbrain were evaluated with a semiquantitative scale. Mixed-effects models were used for statistical analysis adjusting for age. In carriers with FXTAS, we revealed that (1) BG-PVS ratings were higher than those of controls and carriers without FXTAS; (2) BG-PVS severity was associated with brain atrophy, white matter hyperintensities, enlarged ventricles, FXTAS stage and abnormal gait; (3) age-related increase in BG-PVS was associated with cognitive dysfunction; and (4) PVS ratings of all three regions showed robust associations with CGG repeat length and were higher in carriers with the MCP sign than carriers without the sign. This study demonstrates clinical relevance of PVS in FXTAS especially in the basal ganglia region and suggests microangiopathy and dysfunctional cerebrospinal fluid circulation in FXTAS physiopathology.

Pericyte derivation and transplantation for blood-CNS barrier reconstitution in CNS disorders

Disruption of the blood-central nervous system barrier (BCB) is increasingly recognized as a pathological factor in diseases and trauma of the central nervous system. Despite the neuropathological impact, current treatment modalities do not target the BCB; strategies to reconstitute the impaired BCB have been restricted to nutritional and dietary remedies. As an integral cell type in the neurovascular unit, pericytes are crucial to the development, maintenance, and repair of the BCB. As such, pericytes are well poised as cellular agents for reconstitution of the impaired BCB. Here, we summarize recent revelations regarding the role of BCB disruption in diseases and trauma of the central nervous system and highlight how pericytes are harnessed to provide targeted therapeutic effect in each case. This review will also address how recent advances in pericyte derivation strategies can serve to overcome practical hurdles in the clinical use of pericytes.

Choroid plexus calcifications are not associated with putative markers of glymphatic dysfunction: A population study in middle-aged and older adults

BACKGROUND AND PURPOSE

Recent studies have suggested an association between dysfunction of the choroid plexus and the glymphatic system. However, information is inconclusive. Following a population-based study design, we aimed to assess the association between choroid plexus calcifications (CPCs)-as a surrogate of choroid plexus dysfunction-and severity and progression of putative markers of glymphatic dysfunction, including white matter hyperintensities (WMH) of presumed vascular origin and abnormally enlarged basal ganglia perivascular spaces (BG-PVS).

METHODS

This study recruited community-dwellers aged ≥40 years living in neighboring Ecuadorian villages. Participants who had baseline head CTs and brain MRIs were included in cross-sectional analyses and those who additional had follow-up MRIs (after a mean of 6.4 ± 1.5 years) were included in longitudinal analyses. Logistic and Poisson regression models, adjusted for demographics and cardiovascular risk factors, were fitted to assess associations between CPCs and WMH and enlarged BG-PVS severity and progression.

RESULTS

A total of 590 individuals were included in the cross-sectional component of the study, and 215 in the longitudinal component. At baseline, 25% of participants had moderate-to-severe WMH and 27% had abnormally enlarged BG-PVS. At follow-up, 36% and 20% of participants had WMH and enlarged BG-PVS progression, respectively. Logistic regression models showed no significant differences between CPCs volumes stratified in quartiles and severity of WMH and enlarged BG-PVS. Poisson regression models showed no association between the exposure and WMH and enlarged BG-PVS progression. Baseline age remained significant in these models.

CONCLUSIONS

Choroid plexus calcifications are not associated with putative markers of glymphatic system dysfunction.

A pathway linking pulse pressure to dementia in adults with Down syndrome

Adults with Down syndrome are less likely to have hypertension than neurotypical adults. However, whether blood pressure measures are associated with brain health and clinical outcomes in this population has not been studied in detail. Here, we assessed whether pulse pressure is associated with markers of cerebrovascular disease and is linked to a diagnosis of dementia in adults with Down syndrome via structural imaging markers of cerebrovascular disease and atrophy. The study included participants with Down syndrome from the Alzheimer's Disease - Down Syndrome study (n = 195, age = 50.6 ± 7.2 years, 44% women, 18% diagnosed with dementia). Higher pulse pressure was associated with greater global, parietal and occipital white matter hyperintensity volume but not with enlarged perivascular spaces, microbleeds or infarcts. Using a structural equation model, we found that pulse pressure was associated with greater white matter hyperintensity volume, which in turn was related to increased neurodegeneration, and subsequent dementia diagnosis. Pulse pressure is an important determinant of brain health and clinical outcomes in individuals with Down syndrome despite the low likelihood of frank hypertension.

The glymphatic system in migraine and other headaches

Glymphatic system is an emerging pathway of removing metabolic waste products and toxic solutes from the brain tissue. It is made of a network of perivascular spaces, filled in cerebrospinal and interstitial fluid, encompassing penetrating and pial vessels and communicating with the subarachnoid space. It is separated from vessels by the blood brain barrier and from brain tissue by the endfeet of the astrocytes rich in aquaporin 4, a membrane protein which controls the water flow along the perivascular space. Animal models and magnetic resonance (MR) studies allowed to characterize the glymphatic system function and determine how its impairment could lead to numerous neurological disorders (e.g. Alzheimer's disease, stroke, sleep disturbances, migraine, idiopathic normal pressure hydrocephalus). This review aims to summarize the role of the glymphatic system in the pathophysiology of migraine in order to provide new ways of approaching to this disease and to its therapy.

The glymphatic system and Amyotrophic lateral sclerosis

The glymphatic system and the meningeal lymphatic vessels provide a pathway for transport of solutes and clearance of toxic material from the brain. Of specific relevance to ALS, this is applicable for TDP-43 and glutamate, both major elements in disease pathogenesis. Flow is propelled by arterial pulsation, respiration, posture, as well as the positioning and proportion of aquaporin-4 channels (AQP4). Non-REM slow wave sleep is the is key to glymphatic drainage which discontinues during wakefulness. In Parkinson's disease and Alzheimer's disease, sleep impairment is known to predate the development of characteristic clinical features by several years and is associated with progressive accumulation of toxic proteinaceous products. While sleep issues are well described in ALS, consideration of preclinical sleep impairment or the potential of a failing glymphatic system in ALS has rarely been considered. Here we review how the glymphatic system may impact ALS. Preclinical sleep impairment as an unrecognized major risk factor for ALS is considered, while potential therapeutic options to improve glymphatic flow are explored.

Evaluation of glymphatic system activity by diffusion tensor image analysis along the perivascular space in presbycusis

PURPOSE

Previous studies have suggested that presbycusis (age-related hearing loss) is accompanied with cognitive decline and dementia. However, the neural mechanism underlying the cognitive decline in presbycusis remains unclear. This study aimed to evaluate the glymphatic system function in presbycusis patients compared to healthy controls using diffusion tensor imaging (DTI) with the perivascular space (DTI-ALPS) method.

METHODS

DTI scans were obtained from 30 presbycusis patients with cognitive decline (PCD), 30 presbycusis patients with no cognitive decline (PNCD) and 40 age-, gender-, and education-matched healthy controls (HCs). The DTI-ALPS index was calculated for each group. We evaluated the differences in the DTI-ALPS index among PCD, PNCD and HCs. In addition, we conducted a correlation analysis between the DTI-ALPS index and cognitive performance.

RESULTS

There were significant differences of the DTI-ALPS index among three groups. Post-hoc analysis suggested that the DTI-ALPS index in PCD was significantly lower patients in relative to PNCD and HCs (1.49147 vs. 1.57441 vs. 1.62020, p < 0.001). After correcting for age, gender, and education, the DTI-ALPS index is positively correlated with the MoCA scores (rho = 0.426, p = 0.026).

CONCLUSION

Presbycusis patients with cognitive impairment exhibited decreased glymphatic activity than those without cognitive impairment and HCs. The DTI-ALPS index may provide useful disease progression or treatment biomarkers for patients with presbycusis as an indicator of modulation of glymphatic activity.

Enlarged perivascular spaces predict malignant cerebral edema after acute large hemispheric infarction

INTRODUCTION

Enlarged perivascular spaces (EPVS) are considered early manifestations of impaired clearance mechanisms in the brain; however, it is unclear whether EPVS they are associated with the development of malignant cerebral edema (MCE) after large hemispheric infarction (LHI). Therefore, we investigated the predictive value of EPVS in predicting MCE in LHI.

METHODS

Patients suffering from acute LHI were consecutively enrolled. EPVS were rated after the stroke with validated rating scales from magnetic resonance imagess. Patients were divided into two groups according to the occurrence of MCE. Logistic regression was used to analyze the relationship between EPVS and MCE in the basal ganglia (BG) and centrum semiovale (CS) regions. Receiver operating characteristic (ROC) curves assessed the ability of EPVS individually and with other factors in predicting MCE.

RESULTS

We included a total of 255 patients, of whom 98 were MCE patients (58 [59.2%] males, aged 70 [range=61.75-78] years) and found that atrial fibrillation, National Institutes of Health Stroke Scale score, infarct volume, neutrophil-lymphocyte ratio, and moderate-to-severe CS-EPVS were positively associated with MCE. After adjusting for confounds, moderate-to-severe CS-EPVS remained independent risk factor of MCE (odds ratio=16.212, p＜0.001). According to the ROC analysis, MCE was highly suspected when CS-EPVS > 14 (sensitivity=0.82, specificity=0.48), and the guiding value were higher when CS-EPVS combined with other MCE predictors (area under the curve=0.90, sensitivity=0.74, specificity=0.90).

CONCLUSION

CS-EPVS were important risk factor for MEC in patients with acute LHI and can help identify patients at risk for MCE.

Blood-Brain Barrier Disruption and Perivascular Spaces in Small Vessel Disease and Neurodegenerative Diseases: A Review on MRI Methods and Insights

Perivascular spaces (PVS) and blood-brain barrier (BBB) disruption are two key features of cerebral small vessel disease (cSVD) and neurodegenerative diseases that have been linked to cognitive impairment and are involved in the cerebral waste clearance system. Magnetic resonance imaging (MRI) offers the possibility to study these pathophysiological processes noninvasively in vivo. This educational review provides an overview of the MRI techniques used to assess PVS functionality and BBB disruption. MRI-visible PVS can be scored on structural images by either (subjectively) counting or (automatically) delineating the PVS. We highlight emerging (diffusion) techniques to measure proxies of perivascular fluid and its movement, which may provide a more comprehensive understanding of the role of PVS in diseases. For the measurement of BBB disruption, we explain the most commonly used MRI technique, dynamic contrast-enhanced (DCE) MRI, as well as a more recently developed technique based on arterial spin labeling (ASL). DCE MRI and ASL are thought to measure complementary characteristics of the BBB. Furthermore, we describe clinical studies that have utilized these MRI techniques in cSVD and neurodegenerative diseases, particularly Alzheimer's disease (AD). These studies demonstrate the role of PVS and BBB dysfunction in these diseases and provide insight into the large overlap, but also into the differences between cSVD and AD. Overall, MRI techniques may provide valuable insights into the pathophysiological mechanisms underlying these diseases and have the potential to be used as markers for disease progression and treatment response. LEVEL OF EVIDENCE: 3 TECHNICAL EFFICACY: Stage 2.

Overview of the Current Knowledge and Conventional MRI Characteristics of Peri- and Para-Vascular Spaces

Brain spaces around (perivascular spaces) and alongside (paravascular or Virchow-Robin spaces) vessels have gained significant attention in recent years due to the advancements of in vivo imaging tools and to their crucial role in maintaining brain health, contributing to the anatomic foundation of the glymphatic system. In fact, it is widely accepted that peri- and para-vascular spaces function as waste clearance pathways for the brain for materials such as ß-amyloid by allowing exchange between cerebrospinal fluid and interstitial fluid. Visible brain spaces on magnetic resonance imaging are often a normal finding, but they have also been associated with a wide range of neurological and systemic conditions, suggesting their potential as early indicators of intracranial pressure and neurofluid imbalance. Nonetheless, several aspects of these spaces are still controversial. This article offers an overview of the current knowledge and magnetic resonance imaging characteristics of peri- and para-vascular spaces, which can help in daily clinical practice image description and interpretation. This paper is organized into different sections, including the microscopic anatomy of peri- and para-vascular spaces, their associations with pathological and physiological events, and their differential diagnosis.

Late-Life High Blood Pressure and Enlarged Perivascular Spaces in the Putaminal Regions of Community-Dwelling Japanese Older Persons

BACKGROUND

Enlarged perivascular spaces (EPVS) of the brain may be involved in dementia, such as Alzheimer's disease and cerebral small vessel disease (CSVD). Hypertension has been reported to be a risk factor for dementia and CSVD, but the association between blood pressure (BP) and perivascular spaces is still unclear. The aim of this study was to determine the association between BP and EPVS volumes and to examine the interactions of relevant factors.

METHODS

A total of 9296 community-dwelling subjects aged ≥65 years participated in a brain magnetic resonance imaging and health status screening examination. Perivascular volume was measured using a software package based on deep learning that was developed in-house. The associations between BP and EPVS volumes were examined by analysis of covariance and multiple regression analysis.

RESULTS

Mean EPVS volumes increased significantly with rising systolic and diastolic BP levels (P for trend = .003, P for trend<.001, respectively). In addition, mean EPVS volumes increased significantly for every 1-mmHg-increment in systolic and diastolic BPs (both P values <.001). These significant associations were still observed in the sensitivity analysis after excluding subjects with dementia.

CONCLUSIONS

The present data suggest that higher systolic and diastolic BP levels are associated with greater EPVS volumes in cognitively normal older people.

Enlarged Perivascular Space in the Basal Ganglia is Associated with Cerebral Venous Reflux in Patients with Recent Small Subcortical Infarction

BACKGROUND

Research has linked enlarged perivascular spaces (EPVS) to cerebral venous reflux (CVR) in patients with hypertensive intracerebral hemorrhage, but it is unclear whether this association exists in recent small subcortical infarct (RSSI) patients.

OBJECTIVE

This study aimed to investigate the correlation between EPVS and CVR in patients with RSSI.

METHOD

This study included 297 patients, selected from patients with RSSI in the lenticulostriate artery admitted to the Department of Neurology of the First Affiliated Hospital of Zhengzhou University. CVR was assessed by time-of-flight magnetic resonance angiography (TOF-MRA). The relationship between EPVS and CVR was studied using multiple logistic regression analysis.

RESULTS

This study included patients with an average age of 59.84±12.27 years, including 201 males (67.7%). CVR was observed in 40 (13.5%) patients. Compared to the group without CVR, the proportions of male patients and patients with a history of smoking and drinking were higher in the CVR group. The proportions of high-grade EPVS in the centrum semiovale region [23 cases (57.5%) vs. 108 cases (42.0%), p =0.067] and the basal ganglia region [30 cases (75.0%) vs. 133 cases (51.8%), p =0.006] were higher in the CVR group. After multiple logistic regression analysis, high-grade EPVS in the basal ganglia region was still associated with CVR (OR, 2.68; 95% CI, 1.22-5.87;p=0.014).

CONCLUSION

In the population with RSSI, EPVS in basal ganglia is significantly associated with CVR, suggesting a close relationship between venous dysfunction and the formation of EPVS.

The elusive brain perivascular fibroblast: a potential role in vascular stability and homeostasis

In the brain, perivascular fibroblasts (PVFs) reside within the perivascular spaces (PVSs) of arterioles and large venules, however their physiological and pathophysiological roles remain largely unknown. PVFs express numerous extracellular matrix proteins that are found in the basement membrane and PVS surrounding large diameter vessels. PVFs are sandwiched between the mural cell layer and astrocytic endfeet, where they are poised to interact with mural cells, perivascular macrophages, and astrocytes. We draw connections between the more well-studied PVF pro-fibrotic response in ischemic injury and the less understood thickening of the vascular wall and enlargement of the PVS described in dementia and neurodegenerative diseases. We postulate that PVFs may be responsible for stability and homeostasis of the brain vasculature, and may also contribute to changes within the PVS during disease.

STAREE-Mind Imaging Study: a randomised placebo-controlled trial of atorvastatin for prevention of cerebrovascular decline and neurodegeneration in older individuals

Introduction

Cerebrovascular disease and neurodegeneration are causes of cognitive decline and dementia, for which primary prevention options are currently lacking. Statins are well-tolerated and widely available medications that potentially have neuroprotective effects. The STAREE-Mind Imaging Study is a randomised, double-blind, placebo-controlled clinical trial that will investigate the impact of atorvastatin on markers of neurovascular health and brain atrophy in a healthy, older population using MRI. This is a nested substudy of the 'Statins for Reducing Events in the Elderly' (STAREE) primary prevention trial.

Methods

Participants aged 70 years or older (n=340) will be randomised to atorvastatin or placebo. Comprehensive brain MRI assessment will be undertaken at baseline and up to 4 years follow-up, including structural, diffusion, perfusion and susceptibility imaging. The primary outcome measures will be change in brain free water fraction (a composite marker of vascular leakage, neuroinflammation and neurodegeneration) and white matter hyperintensity volume (small vessel disease). Secondary outcomes will include change in perivascular space volume (glymphatic drainage), cortical thickness, hippocampal volume, microbleeds and lacunae, prefrontal cerebral perfusion and white matter microstructure.

Ethics and dissemination

Academic publications from this work will address the current uncertainty regarding the impact of statins on brain structure and vascular integrity. This study will inform the utility of repurposing these well-tolerated, inexpensive and widely available drugs for primary prevention of neurological outcomes in older individuals. Ethics approval was given by Monash University Human Research Ethics Committee, Protocol 12206.

Trial registration number

ClinicalTrials.gov Identifier: NCT05586750.

Pathways linking pulse pressure to dementia in adults with Down syndrome

Individuals with Down syndrome (DS) are less likely to have hypertension than neurotypical adults. However, whether blood pressure measures are associated with brain health and clinical outcomes in this population has not been studied in detail. Here, we assessed whether pulse pressure is associated with markers of cerebrovascular disease, entorhinal cortical atrophy, and diagnosis of dementia in adults with DS. Participants with DS from the Biomarkers of Alzheimer's Disease in Adults with Down Syndrome study (ADDS; n=195, age=50.6±7.2 years, 44% women, 18% diagnosed with dementia) were included. Higher pulse pressure was associated with greater global, parietal, and occipital WMH volume. Pulse pressure was not related to enlarged PVS, microbleeds, infarcts, entorhinal cortical thickness, or dementia diagnosis. However, in a serial mediation model, we found that pulse pressure was indirectly related to dementia diagnosis through parieto-occipital WMH and, subsequently through entorhinal cortical thickness. Higher pulse pressure may be a risk factor for dementia in people with DS by promoting cerebrovascular disease, which in turn affects neurodegeneration. Pulse pressure is an important determinant of brain health and clinical outcomes in individuals with Down syndrome despite the low likelihood of frank hypertension.

Higher critical closing pressure is independently associated with enlarged basal ganglia perivascular spaces

Objective

This study aimed to explore the association between cerebral hemodynamic parameters focused on the critical closing pressure (CCP) and enlarged perivascular spaces (EPVS).

Methods

Cerebral blood velocity in the middle cerebral artery (MCAv) and non-invasive continuous blood pressure (NIBP) were measured using a transcranial Doppler (TCD) and Finometer, followed by the calculation of cerebral hemodynamic parameters including CCP, resistance area product (RAP), pulsatility index (PI), and pulse pressure (PP). EPVS were graded separately in the basal ganglia (BG) and centrum semiovale (CSO), using a visual semiquantitative ordinal scale. Patients with EPVS >10 were classified into the severe BG-EPVS group and severe CSO-EPVS group, and the remainder into the mild BG-EPVS group and the mild CSO-EPVS group. Spearman's correlation and binary logistic regression analysis were performed to analyze the relationship between hemodynamic parameters and BG-EPVS and CSO-EPVS, respectively.

Results

Overall, 107 patients were enrolled. The severe BG-EPVS group had higher CCP, mean arterial blood pressure (MABP), systolic blood pressure (SBP), and diastolic blood pressure (DBP) than that in the mild BG-EPVS group (p < 0.05). There was no statistical difference in hemodynamic parameters between the severe CSO-EPVS group and the mild CSO-EPVS group. Spearman's correlation analysis showed that CCP was positively associated with BG-EPVS (rho = 0.331, p < 0.001) and CSO-EPVS (rho = 0.154, p = 0.044). The binary logistic regression analysis showed that CCP was independently associated with severe BG-EPVS (p < 0.05) and not with CSO-EPVS (p > 0.05) after adjusting for confounders.

Conclusion

CCP representing cerebrovascular tension was independently associated with BG-EPVS.

Military-related mild traumatic brain injury: clinical characteristics, advanced neuroimaging, and molecular mechanisms

Mild traumatic brain injury (mTBI) is a significant health burden among military service members. Although mTBI was once considered relatively benign compared to more severe TBIs, a growing body of evidence has demonstrated the devastating neurological consequences of mTBI, including chronic post-concussion symptoms and deficits in cognition, memory, sleep, vision, and hearing. The discovery of reliable biomarkers for mTBI has been challenging due to under-reporting and heterogeneity of military-related mTBI, unpredictability of pathological changes, and delay of post-injury clinical evaluations. Moreover, compared to more severe TBI, mTBI is especially difficult to diagnose due to the lack of overt clinical neuroimaging findings. Yet, advanced neuroimaging techniques using magnetic resonance imaging (MRI) hold promise in detecting microstructural aberrations following mTBI. Using different pulse sequences, MRI enables the evaluation of different tissue characteristics without risks associated with ionizing radiation inherent to other imaging modalities, such as X-ray-based studies or computerized tomography (CT). Accordingly, considering the high morbidity of mTBI in military populations, debilitating post-injury symptoms, and lack of robust neuroimaging biomarkers, this review (1) summarizes the nature and mechanisms of mTBI in military settings, (2) describes clinical characteristics of military-related mTBI and associated comorbidities, such as post-traumatic stress disorder (PTSD), (3) highlights advanced neuroimaging techniques used to study mTBI and the molecular mechanisms that can be inferred, and (4) discusses emerging frontiers in advanced neuroimaging for mTBI. We encourage multi-modal approaches combining neuropsychiatric, blood-based, and genetic data as well as the discovery and employment of new imaging techniques with big data analytics that enable accurate detection of post-injury pathologic aberrations related to tissue microstructure, glymphatic function, and neurodegeneration. Ultimately, this review provides a foundational overview of military-related mTBI and advanced neuroimaging techniques that merit further study for mTBI diagnosis, prognosis, and treatment monitoring.

Sex-Specific Patterns of Cerebral Atrophy and Enlarged Perivascular Spaces in Patients with Cerebral Amyloid Angiopathy and Dementia

BACKGROUND AND PURPOSE

Cerebral amyloid angiopathy is characterized by amyloid β deposition in leptomeningeal and superficial cortical vessels. Cognitive impairment is common and may occur independent of concomitant Alzheimer disease neuropathology. It is still unknown which neuroimaging findings are associated with dementia in cerebral amyloid angiopathy and whether they are modulated by sex. This study compared MR imaging markers in patients with cerebral amyloid angiopathy with dementia or mild cognitive impairment or who are cognitively unimpaired and explored sex-specific differences.

MATERIALS AND METHODS

We studied 58 patients with cerebral amyloid angiopathy selected from the cerebrovascular and memory outpatient clinics. Clinical characteristics were collected from clinical records. Cerebral amyloid angiopathy was diagnosed on MR imaging on the basis of the Boston criteria. Visual rating scores for atrophy and other imaging features were independently assessed by 2 senior neuroradiologists.

RESULTS

Medial temporal lobe atrophy was higher for those with cerebral amyloid angiopathy with dementia versus those cognitively unimpaired (P = .015), but not for those with mild cognitive impairment. This effect was mainly driven by higher atrophy in men with dementia, compared with women with and without dementia (P = .034, P = .012; respectively) and with men without dementia (P = .012). Enlarged perivascular spaces in the centrum semiovale were more frequent in women with dementia versus men with and without dementia (P = .021, P = .011; respectively) and women without dementia (P = .011).

CONCLUSIONS

Medial temporal lobe atrophy was more prominent in men with dementia, whereas women showed a higher number of enlarged perivascular spaces in the centrum semiovale. Overall, this finding suggests differential pathophysiologic mechanisms with sex-specific neuroimaging patterns in cerebral amyloid angiopathy.

Asymmetry of Lacunae between Brain Hemispheres Is Associated with Atherosclerotic Occlusions of Middle Cerebral Artery

Cerebral small vessel disease (CSVD) commonly coexists with intracranial atherosclerotic stenosis (ICAS). Previous studies have tried to evaluate the relationship between ICAS and CSVD; however, they have yielded varied conclusions. Furthermore, the methodology of these studies is not very rigorous, as they have evaluated the association between ICAS and CSVD of bilateral hemispheres rather than the affected hemisphere. Unilateral middle cerebral artery atherosclerotic occlusion (uni-MCAO) is a favorable model to solve this problem.

MATERIAL AND METHODS

Patients with uni-MCAO were retrospectively observed. Imaging characteristics, including lacunae, white matter hyperintensities (WMH), enlarged perivascular spaces (EPVS), and cerebral microbleeds (CMBs), were compared between the hemisphere ipsilateral to the MCAO and the contralateral hemisphere.

RESULTS

A total of 219 patients (median age 57 years; 156 males) were enrolled. Compared with the contralateral side, increased quality of lacunae (median, IQR, 0, 2 vs. 0, 1; p < 0.001) and elevated CSVD score (median, IQR, 0, 1 vs. 0, 1; p = 0.004) were found in the occluded hemisphere. No significant differences were shown for WMH, EPVS, and CMBs.

CONCLUSIONS

Uni-MCAO has a higher prevalence of lacunae in the ipsilateral hemisphere. However, no interhemispheric differences in WMH, EPVS, or CMBs were found.

The glymphatic system: a new perspective on brain diseases

The glymphatic system is a brain-wide perivascular pathway driven by aquaporin-4 on the endfeet of astrocytes, which can deliver nutrients and active substances to the brain parenchyma through periarterial cerebrospinal fluid (CSF) influx pathway and remove metabolic wastes through perivenous clearance routes. This paper summarizes the composition, overall fluid flow, solute transport, related diseases, affecting factors, and preclinical research methods of the glymphatic system. In doing so, we aim to provide direction and reference for more relevant researchers in the future.

Cerebral Amyloid Angiopathy

Cerebral amyloid angiopathy (CAA) is associated with deposition of amyloid proteins within the intracranial vessels. It is most frequently sporadic and risk increases with advancing age. Amyloid deposition is associated with increased risk of peripheral microhemorrhage, lobar hemorrhage, and/or repetitive subarachnoid hemorrhage. The presence of a peripherally located lobar hemorrhage on computed tomography in an elderly patient should raise concern for underlying CAA, as should multiple foci of peripheral susceptibility artifact or superficial siderosis on susceptibility-weighted imaging, the most sensitive modality for these findings. Newer PET radiotracers are also useful in detecting amyloid deposition.

Fluid dynamics in aging-related dementias

Recent human and animal model experimental studies revealed novel pathways for fluid movement, immune cell trafficking and metabolic waste clearance in CNS. These studies raise the intriguing possibility that the newly discovered pathways, including the glymphatic system, lymphatic meningeal vessels and skull-brain communication channels, are impaired in aging and neurovascular and neurodegenerative diseases associated with dementia, including Alzheimer's disease (AD) and AD-related dementia. We provide an overview of the glymphatic and dural meningeal lymphatic systems, review current methods and approaches used to study glymphatic flow in humans and animals, and discuss current evidence and controversies related to its role in CNS flow homeostasis under physiological and pathophysiological conditions. Non-invasive imaging approaches are needed to fully understand the mechanisms and pathways driving fluid movement in CNS and their roles across lifespan including healthy aging and aging-related dementia.