The asymmetry of glymphatic system dysfunction in patients with temporal lobe epilepsy: A DTI-ALPS study

Age-related change of glymphatic function in normative children assessed using diffusion tensor imaging-analysis along the perivascular space

BACKGROUND

The glymphatic system, crucial for brain waste removal and homeostasis, has an underexplored developmental trajectory in children. This study describes changes in glymphatic function during childhood via diffusion tensor imaging-analysis along the perivascular space (DTI-ALPS).

METHODS

We retrospectively studied DTI MR images of 72 pediatric participants (mean age = 92.37 months; 0-19.8 years; 50 % females), all showing normal MRI findings from 2019 to 2022. Imaging utilized 3 T scanners with a DTI sequence of 21 diffusion-encoded gradients, focusing on the ALPS index to assess glymphatic function. Clinical outcomes were determined using the Pediatric Cerebral Performance Category Scale and medical records within two weeks post-MRI. Regions-of-interest on diffusion maps were selected manually, guided by fractional anisotropy maps, for automatic ALPS computation. Pearson correlation and multiple linear regression analyzed the relationship between ALPS indices, age, and clinical scores, with a paired t-test comparing bilateral ALPS indices. Significance was set at P < 0.05.

RESULTS

Significant positive correlations between age and both left (R = 0.510, P < 0.001) and right (R = 0.688, P < 0.001) DTI-ALPS indices were observed, indicating developmental changes in glymphatic function. Age alone significantly predicted the DTI-ALPS indices (left ALPS: adjusted R2 = 0.235; right ALPS: adjusted R2 = 0.460), underscoring its developmental trajectory. The study found no significant differences between left and right DTI-ALPS indices, suggesting symmetrical glymphatic function during childhood.

CONCLUSION

This study reveals developmental changes in the glymphatic system across childhood, demonstrating an age-related increase in glymphatic function and bilateral symmetry.

Effects of sleep on the glymphatic functioning and multimodal human brain network affecting memory in older adults

Understanding how sleep affects the glymphatic system and human brain networks is crucial for elucidating the neurophysiological mechanism underpinning aging-related memory declines. We analyzed a multimodal dataset collected through magnetic resonance imaging (MRI) and polysomnographic recording from 72 older adults. A proxy of the glymphatic functioning was obtained from the Diffusion Tensor Image Analysis along the Perivascular Space (DTI-ALPS) index. Structural and functional brain networks were constructed based on MRI data, and coupling between the two networks (SC-FC coupling) was also calculated. Correlation analyses revealed that DTI-ALPS was negatively correlated with sleep quality measures [e.g., Pittsburgh Sleep Quality Index (PSQI) and apnea-hypopnea index]. Regarding human brain networks, DTI-ALPS was associated with the strength of both functional connectivity (FC) and structural connectivity (SC) involving regions such as the middle temporal gyrus and parahippocampal gyrus, as well as with the SC-FC coupling of rich-club connections. Furthermore, we found that DTI-ALPS positively mediated the association between sleep quality and rich-club SC-FC coupling. The rich-club SC-FC coupling further mediated the association between DTI-ALPS and memory function in good sleepers but not in poor sleepers. The results suggest a disrupted glymphatic-brain relationship in poor sleepers, which underlies memory decline. Our findings add important evidence that sleep quality affects cognitive health through the underlying neural relationships and the interplay between the glymphatic system and multimodal brain networks.

Enlarged perivascular space in the temporal lobe as a prognostic marker in temporal lobe epilepsy with hippocampal sclerosis

OBJECTIVE

This study was undertaken to investigate the regional burden of enlarged perivascular spaces (EPVSs) in patients with temporal lobe epilepsy with hippocampal sclerosis (TLE-HS) and explore its prognostic relevance.

METHODS

In this retrospective observational study, EPVSs in the temporal lobe (T-EPVS), centrum semiovale (CS-EPVS), basal ganglia (BG-EPVS), midbrain, and hippocampus were visually rated in 68 treatment-naïve patients with TLE-HS. Regional EPVS burden was dichotomized into high and low degrees (cutoff: >10 for BG-EPVS/T-EPVS; >20 for CS-EPVS). Cox proportional hazards models were used to determine the potential predictors of seizure freedom (SF; no seizure for >1 year) and delayed SF (SF achieved >6 months after initiating antiseizure medication [ASM]). Multivariate logistic regression using stepwise variable selection based on the Akaike information criterion was performed to investigate whether EPVS burden was associated with medical refractoriness (never achieving SF).

RESULTS

Of the 68 patients, 20 were classified into the refractory group (29.4%). The high T-EPVS group had an older epilepsy onset (37.3 ± 12.3 vs. 26.5 ± 13.0 years, p = .005), higher pretreatment seizure density (median = 12.0, interquartile range [IQR] = 5.0-20.0 vs. 4.0, IQR = 2.0-10.5, p = .008), and lower focal to bilateral tonic-clonic seizure prevalence (13.3% vs. 73.6%, p < .001) than the low T-EPVS group. High T-EPVS burden (odds ratio [OR] = 10.908, 95% confidence interval [CI] = 1.895-62.789) was an independent predictor of medial refractoriness, along with female sex (OR = 12.906, 95% CI = 2.214-75.220) and ASM treatment duration (OR = .985, 95% CI = .971-.999). The low T-EPVS group had higher probability of achieving delayed SF than the high T-EPVS group (pLog-rank = .030, pCox regression = .038), whereas the probability of achieving SF was comparable between the two groups (pLog-rank = .053, pCox regression = .146).

SIGNIFICANCE

Increased T-EPVS burden may serve as an imaging marker of unfavorable prognosis in patients with TLE-HS, underscoring the potential role of perivascular dysfunction in diminished ASM response.

Analysis of the glymphatic system function in high-grade glioma patients using diffusion tensor imaging along perivascular spaces

OBJECTIVES

This study seeks to determine if patients with high-grade glioma (HGG) demonstrate glymphatic system (GS) impairments using Diffusion Tensor Imaging Along Perivascular Spaces (DTI-ALPS). Additionally, it aims to examine the factors affecting GS performance and their implications for HGG prognosis.

METHODS

The study enrolled fifty HGG patients alongside fifty age- and sex-matched healthy individuals. Each participant underwent diffusion tensor imaging with a Philips 3.0T MRI scanner to assess and compute the ALPS index within perivascular spaces. Variables such as gender, grade, location, volume, peritumoral edema volume, mass-edema index (peritumoral edema volume/tumor volume) and ALPS index were recorded. The Student's t-test and rank sum test compared the ALPS indices between HGG patients and healthy controls to evaluate hemispheric differences. Linear and multivariate Cox regression analyses were utilized to discern factors influencing the ALPS index and to establish independent prognostic markers for HGG, respectively.

RESULTS

The ALPS indices in both hemispheres were significantly lower in HGG patients, with the ipsilateral hemisphere exhibiting further reduced levels than the contralateral (P < 0.001). In comparisons involving tumor and edema volumes, no significant variations were observed between the hemispheres within HGG patients harboring larger tumors (P = 0.079) or lesser edema volumes (P = 0.24). A decrease in postoperative ALPS indices compared to preoperative figures was noted (P < 0.001). Univariate linear regression indicated a negative relationship between the ipsilateral ALPS index and peritumoral edema volume (P = 0.0392). Kaplan-Meier analysis demonstrated shorter survival times in patients with lower ALPS indices. Moreover, multivariate Cox regression highlighted tumor grade (HR = 1.548, P = 0.023) and ipsilateral ALPS index (HR = 0.040, P = 0.003) as crucial prognostic indicators.

CONCLUSION

In patients with HGG, there is impaired GS function in both hemispheres of the brain. Additionally, the impaired GS function in the tumor-side hemisphere is associated with tumor-associated edema. Following surgery, further damage to GS function is observed in both hemispheres of the brain in HGG patients. Poor GS function in the tumor-side hemisphere is correlated with a worse prognosis in HGG patients.

Intrinsic brain network stability during kainic acid-induced epileptogenesis

OBJECTIVE

Altered intrinsic brain networks have been revealed in patients with epilepsy and are strongly associated with network reorganization in the latent period. However, the development and reliability of intrinsic brain networks in the early period of epileptogenesis are not well understood. The current study aims to fill this gap by investigating the test-retest reliability of intrinsic brain networks in the early stage of epileptogenesis.

METHODS

We used the rat intrahippocampal kainic acid model of mesial temporal lobe epilepsy. Three sessions of resting-state functional magnetic resonance imaging (rs-fMRI) data were acquired over a 2-week period from 9 sham control rats and 12 rats that later developed spontaneous epilepsy (KA). A group independent component analysis (GICA) approach was used to identify the intrinsic brain networks. Both within and between networks were identified, and test-retest reliability was assessed using the intraclass correlation coefficient (ICC).

RESULTS

Our results showed good-to-excellent within-network stability of resting-state functional brain connectivity in most intrinsic brain networks in sham control rats and in the KA group, except for frontal cortex (FCN) and hippocampal networks (HPN). Further analysis of the between networks showed an increase in variation in the KA brain compared to the sham controls.

SIGNIFICANCE

Overall, our study demonstrated a "moderately stable" phase of the intrinsic brain network in a 2-week latent period window, with an altered between- and within-network connectome feature.

PLAIN LANGUAGE SUMMARY

This fMRI study explored how brain connectivity changes in healthy animals compared to animals in the latent period of epilepsy. We found that functional connectivity increased during the latent period compared to the control group, and this increase persisted across all tested sessions. Additionally, brain networks became less stable in the epilepsy group, particularly in the frontal cortex and hippocampus. These observations provide further insight into how brain networks change and persist during the early stages of epileptogenesis.

Perivascular space and white matter hyperintensities in Alzheimer's disease: associations with disease progression and cognitive function

BACKGROUND

Alzheimer's disease (AD) is the leading cause of dementia, characterized by the accumulation of amyloid-beta (Aβ) and neurofibrillary tangles. Recent studies emphasize the role of vascular factors, including the glymphatic system, in AD pathogenesis, particularly in Aβ clearance. The diffusion tensor image analysis along the perivascular space (DTI-ALPS; ALPS-Index) has emerged as a novel, non-invasive method to evaluate the glymphatic system in vivo, showing glymphatic insufficiency in AD. This study aimed to investigate alterations in the function of the glymphatic system in individuals with AD versus healthy controls (HC), and to explore its association with Aβ, cerebrovascular disease (CVD), white matter hyperintensities (WMH), and cognitive function.

METHODS

DTI MRI data from three independent study cohorts (ActiGliA: AD n = 16, Controls n = 18; DELCODE: AD n = 54, Controls n = 67; ADNI: AD n = 43, Controls n = 49) were used to evaluate the perivascular space (PVS) integrity; a potential biomarker for glymphatic activity. The DTI-Along the Perivascular Space technique was used to measure water diffusion along PVS providing an index to assess the efficiency of the glymphatic system's waste clearance function. WMH load was quantified in FLAIR MRI using the lesion segmentation tool. We quantified WMHs volume within our defined region of interest (ROI) and excluded participants with any WMHs to avoid confounding the ALPS-Index. Associations with cerebrospinal fluid (CSF) AD hallmark biomarkers, cognitive performance (MMSE) and clinical severity (CDR) were assessed.

RESULTS

AD patients had a significantly lower ALPS-Index vs. healthy controls (ActiGliA: AD: mean = 1.22, SD = 0.12; Controls: mean = 1.36, SD = 0.14, p = 0.004; DELCODE: AD: mean = 1.26, SD = 0.18; Controls: mean = 1.34, SD = 0.2, p = 0.035; ADNI: AD: mean = 1.08, SD = 0.24; Controls: mean = 1.19, SD = 0.13, p = 0.008). The ALPS-Index was associated with CSF Aβ concentration, WMH number and MMSE and CDR. WMH, found in the ROIs correlated negatively with the ALPS-Index.

CONCLUSIONS

This study highlights the potential of the DTI-ALPS-Index as a biomarker for glymphatic dysfunction in AD. It underscores the importance of considering vascular factors and the glymphatic system in the pathogenesis and diagnosis of AD as WMHs in the ROI could cause disturbances and inaccurate indices.

Association between glymphatic system function and cognitive impairment in elderly patients with late-onset epilepsy

PURPOSE

Recent studies have shown that late-onset epilepsy (LOE) is accompanied with cognitive decline and increased risk of dementia, particularly Alzheimer's disease (AD). However, the pathophysiological mechanism underlying the cognitive decline in LOE remains unclear. The aim of current study was to evaluate the relationship between glymphatic system (GS) function and cognitive decline in LOE patients using the diffusion tensor imaging (DTI) analysis along the perivascular space (DTI-ALPS).

METHODS

Medical records and neuro-imaging data were obtained from 21 LOE patients with cognitive decline, 14 LOE patients without cognitive decline, and 20 age- and sex-matched healthy controls (HCs). Plasma biomarkers including Aβ42 and Aβ40 were examined using single-molecule array (Simoa) assays. The DTI-ALPS parameter was calculated and correlated with the clinical characteristics of LOE, including age, seizure frequency, duration of epilepsy, Mini-Mental State Examination (MMSE), and Aβ42/40. Regression models were used to evaluate the influencing factors of DTI-ALPS index.

RESULTS

LOE patients exhibited a decreased ALPS index and Aβ42/40 compared with the HCs. Post-hoc analysis indicated that the DTI-ALPS index and Aβ42/40 in LOE patients with cognitive decline was significantly lower in relative to LOE patients without cognitive decline and HCs. Spearman correlations showed a negative correlation between DTI-ALPS index and age, seizure frequency and disease duration while a positive correlations between the DTI-ALPS index and Aβ42/40 and MMSE scores in LOE patients. Linear regression analysis suggested that the DTI-ALPS index was independently related to age, Aβ42/40 and MMSE score after correcting for gender, education, and vascular risk factors.

CONCLUSION

Our findings using DTI-ALPS method found a positive correlation between cognitive decline and GS dysfunction in LOE patients, and may indicate a potential internal link between age-related LOEU and dementia formation. Therefore, the DTI-ALPS index may serve as a potential imaging marker for diagnosing and monitoring the GS function in LOE patients.

Diffusion tensor imaging changes along the perivascular spaces may serve as a prognostic factor for high-grade glioma

PURPOSE

To investigate the alteration of glymphatic activity in high-grade glioma (HGG) using the diffusion tensor image (DTI) analysis along perivascular spaces (ALPS) method and assess its prognostic performance.

METHODS

Data of HGG and volunteer were retrieved from The Cancer Imaging Archive and Consortium for Reliability and Reproducibility databases, respectively. Image features including multicenter, cystic change, tumor location, midline structure, lateral ventricle compression, and nerve fiber involvement were evaluated for HGG. The ALPS-index was calculated, and the difference of ALPS-index (D_ALPS), was defined to represent the difference of bilateral ALPS-index.

RESULTS

In total, 236 HGG and 61 volunteers were included. The ALPS-index of the tumor-side hemisphere was larger than that of the normal-side, but it was smaller than that of volunteers. The ALPS-index of the normal-side showed a decreasing trend for HGG cases presenting a compressed lateral ventricle, deviated midline structure, and peritumor edema-involved association and projection fibers, but increased in gross total resection. The D_ALPS increased for isocitrate dehydrogenase mutation. The normal-side ALPS-index negatively correlated with edema and tumor volume. The D_ALPS positively correlated with edema volume. Univariable and multivariable Cox analysis revealed smaller D_ALPS as independent factors for poor prognosis. Survival analysis showed that high D_ALPS corresponded to longer survival times compared to low D_ALPS.

CONCLUSIONS

The glymphatic activity in HGG individuals is lower compared with that of healthy volunteers, with a potential compensation in the tumor side. Many clinical-radiological characteristics affect the glymphatic activity. The defined D_ALPS shows potential as an independent prognostic factor in HGG.

Glymphatic system impairment in normal tension glaucoma evaluated by diffusion tensor image analysis along the perivascular space

Disruption of the glymphatic system plays a vital role in pathogenesis of neurodegeneration in normal tension glaucoma (NTG). We evaluated the impairment of glymphatic system of NTG patients by diffusion tensor image analysis along the perivascular space (DTI-ALPS), and explored the correlation between the ALPS index and dysfunction of visual cortices in resting state. DTI-ALPS was applied to 37 normal controls (NCs) and 37 NTG patients. Multidirectional diffusivity maps and fractional anisotropy (FA) maps were reconstructed to calculate ALPS index. The Amplitude of low-frequency fluctuation (ALFF) in visual cortices (V1-V5) were calculated using resting-state fMRI. Clinical data and ALPS indexes were compared between the groups. Lateralization of ALPS indexes and differences in visual field of two eyes were analyzed. Subsequently, regression analyses between ALPS indexes and mean deviation (MD) values of bilateral eyes and ALFF of visual cortices were performed. The bilateral ALPS indexes of NTG patients decreased significantly. In NCs and NTG patients, ALPS indexes in right hemisphere were lower than that in left hemisphere. The right ALPS indexes of NTG patients were positively correlated with the MD values of the left eyes. In NTG patients, decreased ALFF was detected in right V1 and bilateral V2-5, and the left ALPS indexes were positively correlated with ALFF in bilateral V1, V2, V5, and right V3V area. The ALPS index decreased in NTG patients, correlated with visual defects and ALFF, indicating impairment of the glymphatic system and the potential to be a biomarker in the future.

Glymphatic system dysfunction in epilepsy related to focal cortical dysplasia and its relationship with antiseizure medication response

PURPOSE

Glymphatic function has not been explored in patients with focal cortical dysplasia (FCD)-related epilepsy. This study aimed to investigate the glymphatic system's involvement in these patients and to evaluate its correlation with response patterns to different antiseizure medications (ASMs) using diffusion tensor imaging along the perivascular space (DTI-ALPS).

METHODS

Fifty-two patients with FCD-related epilepsy (10 with drug-responsive epilepsy and 42 with drug-resistant epilepsy) and 24 healthy controls (HC) were included. Bilateral DTI-ALPS index were calculated and compared among drug-responsive epilepsy, drug-resistant epilepsy, and HC groups. Additionally, we analyzed correlations between the DTI-ALPS index and clinical characteristics.

RESULTS

Compared to HC, patients with FCD-related epilepsy showed significantly lower DTI-ALPS index in the bilateral hemispheres (p < 0.001). Notably, a significant decrease in the DTI-ALPS index was noted in the hemisphere ipsilateral to the epileptogenic foci, compared to the contralateral hemisphere (p < 0.001). Further analysis revealed that, in patients with drug-resistant epilepsy, the ipsilateral DTI-ALPS index was significantly lower than the contralateral DTI-ALPS index (p < 0.001), whereas patients with drug-responsive epilepsy did not show a significant difference between ipsilateral and contralateral DTI-ALPS index. No significant correlations were found between the DTI-ALPS index and clinical characteristics such as age and duration of epilepsy.

CONCLUSION

Our findings suggest a correlation between glymphatic system dysfunction and patients with FCD-related epilepsy, particularly in drug-resistant patients.

Unraveling the Diffusion MRI-Based Glymphatic System Alterations in Children with Rolandic Epilepsy

RATIONALE AND OBJECTIVES

Although dysfunction of the glymphatic system in adult epilepsy has been extensively studied, there is a lack of research on the changes in this system during childhood development, particularly in children with Rolandic epilepsy (RE). This study aimed to investigate the changes in diffusion MRI measures related to the glymphatic function in children with RE.

MATERIALS AND METHODS

A total of thirty-eight children with RE and thirty-six demographically matched healthy children were enrolled in the study. All participants performed structural and diffusion MRI using a 3.0 T MRI scanner, and children with RE also underwent intellectual assessment. Diffusion MRI measures, including fractional volume of free water in white matter (FW-WM) and diffusion tensor imaging-along the perivascular space (DTI-ALPS) indices, were calculated and compared between the two groups. Spearman correlation were employed to assess the associations of the MRI indices with epilepsy age and intelligence quotients.

RESULTS

Children with RE had significantly higher cerebral FW-WM (0.227 vs. 0.210; p < 0.001) and lower ALPS index (1.482 vs. 1.667; p < 0.001) than controls. The higher cerebral FW-WM was negatively correlated with full-scale IQ (r ＝ -0.389, p ＝ 0.021), while the lower ALPS index was positively correlated with age (r ＝ 0.529, p ＝ 0.001).

CONCLUSION

Children with RE exhibited altered diffusion MRI measures, which could be triggered by impairment of the glymphatic system. Additionally, our findings also indicate the associations of diffusion MRI measures with epilepsy age and lower intelligence levels.

Microangiopathy in temporal lobe epilepsy with diffusion MRI alterations and cognitive decline

White matter microvascular alterations in temporal lobe epilepsy (TLE) may be relevant to acquired neurodegenerative processes and cognitive impairments associated with this condition. We quantified microvascular changes, myelin, axonal, glial and extracellular-matrix labelling in the gyral core and deep temporal lobe white matter regions in surgical resections from 44 TLE patients with or without hippocampal sclerosis. We compared this pathology data with in vivo pre-operative MRI diffusion measurements in co-registered regions and neuropsychological measures of cognitive impairment and decline. In resections, increased arteriolosclerosis was observed in TLE compared to non-epilepsy controls (greater sclerotic index, p < 0.001), independent of age. Microvascular changes included increased vascular densities in some regions but uniformly reduced mean vascular size (quantified with collagen-4, p < 0.05-0.0001), and increased pericyte coverage of small vessels and capillaries particularly in deep white matter (quantified with platelet-derived growth factor receptorβ and smooth muscle actin, p < 0.01) which was more marked the longer the duration of epilepsy (p < 0.05). We noted increased glial numbers (Olig2, Iba1) but reduced myelin (MAG, PLP) in TLE compared to controls, particularly prominent in deep white matter. Gene expression analysis showed a greater reduction of myelination genes in HS than non-HS cases and with age and correlation with diffusion MRI alterations. Glial densities and vascular size were increased with increased MRI diffusivity and vascular density with white matter abnormality quantified using fixel-based analysis. Increased perivascular space was associated with reduced fractional anisotropy as well as age-accelerated cognitive decline prior to surgery (p < 0.05). In summary, likely acquired microangiopathic changes in TLE, including vascular sclerosis, increased pericyte coverage and reduced small vessel size, may indicate a functional alteration in contractility of small vessels and haemodynamics that could impact on tissue perfusion. These morphological features correlate with white matter diffusion MRI alterations and might explain cognitive decline in TLE.

Evaluating the glymphatic system via magnetic resonance diffusion tensor imaging along the perivascular spaces in brain tumor patients

PURPOSE

To investigate glymphatic system function in patients with brain tumors, including both primary and secondary tumors, using diffusion tensor imaging along perivascular spaces (DTI-ALPS).

METHODS

We retrospectively analyzed the MR DTI of 24 patients with unilateral brain tumors and compared them with age and sex-matched controls. We compared the DTI-ALPS index of the ipsi- and contralateral brain hemispheres. The region of interest was placed in the periventricular vessels adjacent to the lateral ventricles. Differences between sex, age, and kind of tumor (primary or brain metastasis) were evaluated. Correlations between DTI-ALPS index and age and the tumor's apparent diffusion coefficient (ADC) were also investigated.

RESULTS

The DTI-ALPS index was significantly lower (p < 0.05) in the tumor-affected hemisphere (mean = 1.26 ± 0.24) than contralateral (mean = 1.43 ± 0.28). A comparison with healthy controls revealed no significant difference on the matched ipsilateral side. However, the DTI-ALPS index of the contralateral side of the patients was larger than the HC. Additionally, no statistically significant differences were found when analyzing the DTI-ALPS index vs. age, sex, and tumor entity. Additionally, we did not find a correlation between the DTI-ALPS index and patient age or tumor ADC.

CONCLUSION

The decreased DTI-ALPS index in the tumor-affected hemisphere may be related to impaired glymphatic system function. However, cancer is often a systemic disease; thus, the DTI-ALPS index from the contralateral brain hemisphere may not generally be considered as a normal control. Nonetheless, the DTI-ALPS index does not only reflect diffusion in the perivascular spaces but it can also be influenced by factors such as axonal degeneration. Therefore, it does not directly reflect brain waste clearance and changes in the index should be interpreted carefully.

Diffusion magnetic resonance imaging of cerebrospinal fluid dynamics: Current techniques and future advancements

Cerebrospinal fluid (CSF) plays a critical role in metabolic waste clearance from the brain, requiring its circulation throughout various brain pathways, including the ventricular system, subarachnoid spaces, para-arterial spaces, interstitial spaces, and para-venous spaces. The complexity of CSF circulation has posed a challenge in obtaining noninvasive measurements of CSF dynamics. The assessment of CSF dynamics throughout its various circulatory pathways is possible using diffusion magnetic resonance imaging (MRI) with optimized sensitivity to incoherent water movement across the brain. This review presents an overview of both established and emerging diffusion MRI techniques designed to measure CSF dynamics and their potential clinical applications. The discussion offers insights into the optimization of diffusion MRI acquisition parameters to enhance the sensitivity and specificity of diffusion metrics on underlying CSF dynamics. Lastly, we emphasize the importance of cautious interpretations of diffusion-based imaging, especially when differentiating between tissue- and fluid-related changes or elucidating structural versus functional alterations.

Association study of brain structure-function coupling and glymphatic system function in patients with mild cognitive impairment due to Alzheimer's disease

Background

Mild cognitive impairment (MCI) is a critical transitional phase from healthy cognitive aging to dementia, offering a unique opportunity for early intervention. However, few studies focus on the correlation of brain structure and functional activity in patients with MCI due to Alzheimer's disease (AD). Elucidating the complex interactions between structural-functional (SC-FC) brain connectivity and glymphatic system function is crucial for understanding this condition.

Method

The aims of this study were to explore the relationship among SC-FC coupling values, glymphatic system function and cognitive function. 23 MCI patients and 18 healthy controls (HC) underwent diffusion tensor imaging (DTI) and resting-state functional MRI (fMRI). DTI analysis along the perivascular space (DTI-ALPS) index and SC-FC coupling values were calculated using DTI and fMRI. Correlation analysis was conducted to assess the relationship between Mini-Mental State Examination (MMSE) scores, DTI-ALPS index, and coupling values. Receiver operating characteristic (ROC) curves was conducted on the SC-FC coupling between the whole brain and subnetworks. The correlation of coupling values with MMSE scores was also analyzed.

Result

MCI patients (67.74 ± 6.99 years of age) exhibited significantly lower coupling in the whole-brain network and subnetworks, such as the somatomotor network (SMN) and ventral attention network (VAN), than HCs (63.44 ± 6.92 years of age). Whole-brain network coupling was positively correlated with dorsal attention network (DAN), SMN, and visual network (VN) coupling. MMSE scores were significantly positively correlated with whole-brain coupling and SMN coupling. In MCI, whole-brain network demonstrated the highest performance, followed by the SMN and VAN, with the VN, DAN, limbic network (LN), frontoparietal network (FPN), and default mode network (DMN). Compared to HCs, lower DTI-ALPS index was observed in individuals with MCI. Additionally, the left DTI-ALPS index showed a significant positive correlation with MMSE scores and coupling values in the whole-brain network and SMN.

Conclusion

These findings reveal the critical role of SC-FC coupling values and the ALPS index in cognitive function of MCI. The positive correlations observed in the left DTI-ALPS and whole-brain and SMN coupling values provide a new insight for investigating the asymmetrical nature of cognitive impairments.

Glymphatic function and its influencing factors in different glucose metabolism states

BACKGROUND

Dysfunction of the glymphatic system in the brain in different stages of altered glucose metabolism and its influencing factors are not well characterized.

AIM

To investigate the function of the glymphatic system and its clinical correlates in patients with different glucose metabolism states, the present study employed diffusion tensor imaging along the perivascular space (DTI-ALPS) index.

METHODS

Sample size was calculated using the pwr package in R software. This cross-sectional study enrolled 22 patients with normal glucose metabolism (NGM), 20 patients with prediabetes, and 22 patients with type 2 diabetes mellitus (T2DM). A 3.0T magnetic resonance imaging was used to evaluate the function of the glymphatic system. The mini-mental state examination (MMSE) was used to assess general cognitive function. The DTI-ALPS index of bilateral basal ganglia and the mean DTI-ALPS index was calculated. Further, the correlation between DTI-ALPS and clinical features was assessed.

RESULTS

The left-side, right-side, and mean DTI-ALPS index in the T2DM group were significantly lower than that in the NGM group. The right-side DTI-ALPS and mean DTI-ALPS index in the T2DM group were significantly lower than those in the prediabetes group. DTI-ALPS index lateralization was not observed. The MMSE score in the T2DM group was significantly lower than that in the NGM and prediabetes group. After controlling for sex, the left-side DTI-ALPS and mean DTI-ALPS index in the prediabetes group were positively correlated with 2-hour postprandial blood glucose level; the left-side DTI-ALPS index was negatively correlated with total cholesterol and low-density lipoprotein level. The right-side DTI-ALPS and mean DTI-ALPS index were negatively correlated with the glycosylated hemoglobin level and waist-to-hip ratio in the prediabetes group. The left-side, right-side, and mean DTI-ALPS index in the T2DM group were positively correlated with height. The left-side and mean DTI-ALPS index in the T2DM group were negatively correlated with high-density lipoprotein levels.

CONCLUSION

Cerebral glymphatic system dysfunction may mainly occur in the T2DM stage. Various clinical variables were found to affect the DTI-ALPS index in different glucose metabolism states. This study enhances our understanding of the pathophysiology of diabetic brain damage and provides some potential biological evidence for its early diagnosis.

Diffusion Tensor Image Analysis ALong the Perivascular Space (DTI-ALPS): Revisiting the Meaning and Significance of the Method

More than 5 years have passed since the Diffusion Tensor Image Analysis ALong the Perivascular Space (DTI-ALPS) method was proposed with the intention of evaluating the glymphatic system. This method is handy due to its noninvasiveness, provision of a simple index in a straightforward formula, and the possibility of retrospective analysis. Therefore, the ALPS method was adopted to evaluate the glymphatic system for many disorders in many studies. The purpose of this review is to look back and discuss the ALPS method at this moment.The ALPS-index was found to be an indicator of a number of conditions related to the glymphatic system. Thus, although this was expected in the original report, the results of the ALPS method are often interpreted as uniquely corresponding to the function of the glymphatic system. However, a number of subsequent studies have pointed out the problems on the data interpretation. As they rightly point out, a higher ALPS-index indicates predominant Brownian motion of water molecules in the radial direction at the lateral ventricular body level, no more and no less. Fortunately, the term "ALPS-index" has become common and is now known as a common term by many researchers. Therefore, the ALPS-index should simply be expressed as high or low, and whether it reflects a glymphatic system is better to be discussed carefully. In other words, when a decreased ALPS-index is observed, it should be expressed as "decreased ALPS-index" and not directly as "glymphatic dysfunction". Recently, various methods have been proposed to evaluate the glymphatic system. It has become clear that these methods also do not seem to reflect the entirety of the extremely complex glymphatic system. This means that it would be desirable to use various methods in combination to evaluate the glymphatic system in a comprehensive manner.

Bilateral glymphatic dysfunction and its association with disease duration in unilateral temporal lobe epilepsy patients with hippocampal sclerosis

OBJECTIVE

In this study, the diffusion tensor imaging along perivascular space analysis (DTI-ALPS) technique was utilized to evaluate the functional changes in the glymphatic system of the bilateral hemispheres in patients with unilateral temporal lobe epilepsy (TLE) accompanied by hippocampal sclerosis (HS). The aim was to gain insights into the alterations in the glymphatic system function in TLE patients.

METHODS

A total of 61 unilateral TLE patients with HS and 53 healthy controls (HCs) from the Department of Neurosurgery at Xiangya Hospital were included in the study. All subjects underwent DTI using the same 3 T MR Scanner, and the DTI-ALPS index was calculated. Differences in the DTI-ALPS index between TLE patients and HCs were evaluated, along with the correlation between the DTI-ALPS index of TLE and clinical features of epilepsy. These features included age, age of onset, seizure duration, and neuropsychological scores.

RESULTS

Compared to the bilateral means of the HCs, both the ipsilateral and contralateral DTI-ALPS index of the TLE patients were significantly decreased (TLE ipsilateral 1.41 ± 0.172 vs. HC bilateral mean: 1.49 ± 0.116, p = 0.006; TLE contralateral: 1.42 ± 0.158 vs. HC bilateral mean: 1.49 ± 0.116, p = 0.015). The ipsilateral DTI-ALPS index in TLE patients showed a significant negative correlation with disease duration (r = -0.352, p = 0.005).

CONCLUSIONS

The present study suggests the presence of bilateral dysfunctions in the glymphatic system and also highlight a laterality feature in these dysfunctions. Additionally, the study found a significant negative correlation between the ipsilateral DTI-ALPS index and disease duration, underscoring the significance of early effective interventions and indicating potential for the development of innovative treatments targeting the glymphatic system.

The relationship between inflammation, impaired glymphatic system, and neurodegenerative disorders: A vicious cycle

The term "glymphatic" emerged roughly a decade ago, marking a pivotal point in neuroscience research. The glymphatic system, a glial-dependent perivascular network distributed throughout the brain, has since become a focal point of investigation. There is increasing evidence suggesting that impairment of the glymphatic system appears to be a common feature of neurodegenerative disorders, and this impairment exacerbates as disease progression. Nevertheless, the common factors contributing to glymphatic system dysfunction across most neurodegenerative disorders remain unclear. Inflammation, however, is suspected to play a pivotal role. Dysfunction of the glymphatic system can lead to a significant accumulation of protein and waste products, which can trigger inflammation. The interaction between the glymphatic system and inflammation appears to be cyclical and potentially synergistic. Yet, current research is limited, and there is a lack of comprehensive models explaining this association. In this perspective review, we propose a novel model suggesting that inflammation, impaired glymphatic function, and neurodegenerative disorders interconnected in a vicious cycle. By presenting experimental evidence from the existing literature, we aim to demonstrate that: (1) inflammation aggravates glymphatic system dysfunction, (2) the impaired glymphatic system exacerbated neurodegenerative disorders progression, (3) neurodegenerative disorders progression promotes inflammation. Finally, the implication of proposed model is discussed.

The cerebral lymphatic drainage system and its implications in epilepsy

The central nervous system has long been thought to lack a clearance system similar to the peripheral lymphatic system. Therefore, the clearance of metabolic waste in the central nervous system has been a subject of great interest in neuroscience. Recently, the cerebral lymphatic drainage system, including the parenchymal clearance system and the meningeal lymphatic network, has attracted considerable attention. It has been extensively studied in various neurological disorders. Solute accumulation and neuroinflammation after epilepsy impair the blood-brain barrier, affecting the exchange and clearance between cerebrospinal fluid and interstitial fluid. Restoring their normal function may improve the prognosis of epilepsy. However, few studies have focused on providing a comprehensive overview of the brain clearance system and its significance in epilepsy. Therefore, this review addressed the structural composition, functions, and methods used to assess the cerebral lymphatic system, as well as the neglected association with epilepsy, and provided a theoretical basis for therapeutic approaches in epilepsy.