Lymphatic drainage of the brain and the pathophysiology of neurological disease

A budget for brain metabolic water production by glucose catabolism during rest, rises in activity and sleep

Maintaining brain fluid homeostasis is of critical importance for creating a stable environment conducive to optimal neuronal functioning, nutrient distribution, and waste product removal. In this study, we employed previously published data on brain oxygen and glucose consumption in awake rodents or humans to quantify the metabolic water production associated with distinct pathways of glucose metabolism. It is predicted that neuronal mitochondria are the primary source of metabolic water at rest, resulting in a continuous efflux into the cytosol, interstitial fluid, and cerebrospinal fluid. Net metabolic water production is predicted to be reduced by increases in activity due to a shift in metabolism from glucose oxidation to include glycolysis in neurons and ATP hydrolysis by the major cation pumps, which involves water consumption (ATP + H2O → ADP + Pi). In comparison, glycogenolysis, which occurs concurrently with the activation of astrocytes, potentially represents a major but previously unidentified contributor to metabolic water. Metabolic water production is dependent on the state of the brain, with a reduction of 30-40% occurring during deep sleep. Our estimates indicate that metabolic water functions as a conduit for interstitial fluid production within the brain, enabling flexible and efficient distribution of fluid that flows seamlessly from the parenchyma to the subarachnoid space and lymphatic vessels to facilitate the removal of brain waste, independent of the glymphatic system.

Current Understanding of the Pathophysiology of Idiopathic Intracranial Hypertension

PURPOSE OF REVIEW

Development of safe targeted therapies for idiopathic intracranial hypertension requires a thorough understanding of recent evidence discovering the pathophysiology of the condition. The aim is to provide a review of studies that inform on the underpinning mechanisms that have been associated with idiopathic intracranial hypertension.

RECENT FINDINGS

People living with active idiopathic intracranial hypertension and obesity have been found to have with insulin resistance, hyperleptinaemia, and adverse cardiovascular outcomes. Clinically their adipose tissue is predominantly located in the truncal region and on detailed laboratory analysis the cells are primed for weight gain. There is evidence of androgen excess, altered glucocorticoid regulation and changes in pro-inflammatory cytokines. There are distinct alterations in metabolic pathways found in serum, urine and cerebrospinal fluid, that resolve following disease remission. These findings are associated with raised intracranial pressure and are likely secondary to cerebrospinal fluid hypersecretion. Idiopathic intracranial hypertension has a profile of systemic metabolic changes, endocrine dysfunction and cardiovascular risk profile distinct from that associated with obesity alone. These systemic metabolic changes are likely to contribute to dysregulation of cerebrospinal fluid dynamics, primarily hypersecretion but with a possible additional effect of reduced clearance resulting in the core feature of raised intracranial pressure.

Meningeal lymphatic vessel crosstalk with central nervous system immune cells in aging and neurodegenerative diseases

Meningeal lymphatic vessels form a relationship between the nervous system and periphery, which is relevant in both health and disease. Meningeal lymphatic vessels not only play a key role in the drainage of brain metabolites but also contribute to antigen delivery and immune cell activation. The advent of novel genomic technologies has enabled rapid progress in the characterization of myeloid and lymphoid cells and their interactions with meningeal lymphatic vessels within the central nervous system. In this review, we provide an overview of the multifaceted roles of meningeal lymphatic vessels within the context of the central nervous system immune network, highlighting recent discoveries on the immunological niche provided by meningeal lymphatic vessels. Furthermore, we delve into the mechanisms of crosstalk between meningeal lymphatic vessels and immune cells in the central nervous system under both homeostatic conditions and neurodegenerative diseases, discussing how these interactions shape the pathological outcomes. Regulation of meningeal lymphatic vessel function and structure can influence lymphatic drainage, cerebrospinal fluid-borne immune modulators, and immune cell populations in aging and neurodegenerative disorders, thereby playing a key role in shaping meningeal and brain parenchyma immunity.

Cribriform Brain Unraveling Virchow-Robin Space Dilation

Virchow-Robin spaces (VRS) are perivascular compartments in the brain lined by the pia mater, surrounding penetrating arteries and veins. They play a crucial role in interstitial fluid drainage within the glymphatic system and may contribute to immune responses. Typically small and asymptomatic, these spaces can sometimes enlarge, forming dilated Virchow-Robin spaces, which are often identified incidentally on MRI, especially in elderly individuals. Their clinical significance has been increasingly recognized due to their potential link with neurodegenerative diseases. We present the case of a 60-year-old retired firefighter who experienced recurrent syncopal episodes along with progressive neurological symptoms, including bradykinesia and memory impairment. Brain MRI revealed extensive cystic dilation of periventricular spaces, predominantly in the lenticulostriate region, characteristic of dilated VRS. This case underscores the importance of understanding the mechanisms underlying VRS dilation, distinguishing it from other brain lesions such as lacunar infarcts, neoplasms, and infectious diseases, and highlights the role of MRI in diagnosis. Additionally, we review the literature on dilated VRS and its potential implications in neurodegenerative diseases, including Alzheimer's disease and chronic traumatic encephalopathy (CTE).

Neuropathological features of cerebrovascular diseases

Optimal blood flow through a patent cerebral circulation is critical for supply of oxygen and nutrients for brain function. The integrity of vascular elements within arterial vessels of any calibre can be compromised by various disease processes. Pathological changes in the walls of veins and the venous system may also alter the dynamics of cerebral perfusion. The consequences of both systemic vascular and cerebrovascular diseases range from acute focal changes to irreversible chronic restructuring of the brain parenchyma. Cerebral infarcts of different sizes may instigate a cascade of programmed cell death mechanisms including autophagy and mitophagy and processes that range from necroptosis to ferroptosis. Recent advances also emphasise the role of the vascular inflammasome in the pathology of cerebral infarction. Here, we summarise current knowledge on frequencies, epidemiological features and the neuropathology of common cerebrovascular disorders among which cerebral small vessel diseases have become of particular interest. We also highlight the current spectrum of monogenic and polygenic genetic disorders affecting the intracranial vasculature. With the advent of DNA screening technologies, it is now realised that several cerebrovascular disorders exhibit strong genetic traits. Whilst several gene defects and their aberrant products are identified, the precise role or mechanisms of how they influence angiogenesis, vasculogenesis, vessel integrity or the extracellular matrix remain largely unclear. Despite such genetic advances, histopathological examination remains the gold standard for diagnosis and characterisation of most cerebrovascular disorders.

New perspectives on the glymphatic system and the relationship between glymphatic system and neurodegenerative diseases

Neurodegenerative diseases (ND) are characterized by the accumulation of aggregated proteins. The glymphatic system, through its rapid exchange mechanisms between cerebrospinal fluid (CSF) and interstitial fluid (ISF), facilitates the movement of metabolic substances within the brain, serving functions akin to those of the peripheral lymphatic system. This emerging waste clearance mechanism offers a novel perspective on the removal of pathological substances in ND. This article elucidates recent discoveries regarding the glymphatic system and updates relevant concepts within its model. It discusses the potential roles of the glymphatic system in ND, including Alzheimer's disease (AD), Parkinson's disease (PD), and multiple system atrophy (MSA), and proposes the glymphatic system as a novel therapeutic target for these conditions.

Associations of inferior frontal sulcal hyperintensities on brain MRI with cerebral small vessel disease, cognitive function, and depression symptoms

Inferior frontal sulcal hyperintensities (IFSH) observed on fluid-attenuated inversion recovery (FLAIR) MRI have been proposed as indicators of elevated cerebrospinal fluid waste accumulation in cerebral small vessel disease (CSVD). However, to validate IFSH as a reliable imaging biomarker, further replication studies are required. The objective of this study was to investigate associations between IFSH and CSVD, and their potential repercussions, i.e., cognitive impairment and depression. We prospectively recruited 47 patients with CSVD and 29 cognitively normal controls (NC). IFSH were rated visually based on FLAIR MRI. Using different regression models, we explored the relationship between IFSH, group status (CSVD vs. NC), CSVD severity assessed with MRI, cognitive function, and symptoms of depression. Patients with CSVD were more likely to have higher IFSH scores compared to NC (OR 5.64, 95% CI 1.91-16.60), and greater CSVD severity on MRI predicted more severe IFSH (OR 1.47, 95% CI 1.14-1.88). Higher IFSH scores were associated with lower cognitive function (-0.96, 95% CI -1.81 to -0.10), and higher levels of depression (0.33, 95% CI 0.01-0.65). CSVD and IFSH may be tightly linked to each other, and the accumulation of waste products, indicated by IFSH, could have detrimental effects on cognitive function and symptoms of depression.

Rostral cranial fossa and sinonasal neoplasms with cribriform plate involvement in 32 dogs and 17 cats

The rostral cranial fossa (RCF) consists of the sphenoid and ethmoid bones, which accommodate the olfactory bulbs and nerves along the recesses of the cribriform plate. Neoplasms located in the vicinities of the RCF can compress and/or invade the cribriform plate. Here we describe the clinical and pathologic findings of neoplasms involving the cribriform plate in 32 dogs and 17 cats autopsied over a 13-y period. The average ages of affected dogs and cats were 9.2 y and 9.7 y, respectively. No sex or breed predisposition was evident in dogs, but 13 of 18 cats were spayed females and 14 of 18 were domestic shorthair cats. The main clinical signs were seizures (10 cases) and epistaxis (5 cases) in dogs, and red-to-brown nasal discharge (5 cases) and seizures (4 cases) in cats. In dogs, the 22 sinonasal neoplasms included adenocarcinoma (14 cases), transitional carcinoma (4), squamous cell carcinoma (2), lymphoma (1), and histiocytic sarcoma (1); the 10 intracranial neoplasms consisted of high-grade gliomas (3 cases), psammomatous meningiomas (2), histiocytic sarcomas (2), olfactory neuroblastomas (2), and a meningeal granular cell tumor (1). In cats, the 14 sinonasal neoplasms included lymphoma (8 cases), adenocarcinoma (4), adenosquamous carcinoma (1), and squamous cell carcinoma (1); the 3 intracranial neoplasms consisted of oligodendroglioma (1), transitional meningioma (1), and olfactory neuroblastoma (1).

Cerebral artery and brain pathology correlates of antemortem cerebral artery 4D flow MRI

Large-scale clinical research studies often incorporate neuroimaging biomarkers to understand underlying pathologic changes that occur in aging and neurodegenerative disease and are associated with cognitive decline and clinical impairment. Of particular interest are neuroimaging methods designed to understand various aspects of cerebrovascular disease that can lead to dementia and also co-occur with neurodegenerative diseases such as Alzheimer's disease. Neurovascular 4D flow magnetic resonance imaging is one such method that measures hemodynamic characteristics of medium-large cerebral vessels, but it remains unclear how measures derived from 4D flow imaging including pulsatility index, cerebral blood flow, and cross-sectional area relate to underlying pathologic changes in cerebral arteries and downstream cerebrovascular pathology. For example, pulsatility index is thought to be a marker of vessel compliance, which may be due to fibrotic and/or atherosclerotic changes. This observational study investigates imaging-pathologic correlates of cerebral artery 4D flow MRI in 20 initial brain donors (mean (SD) age at death 78.2 (10.3) years; 3.2 (1.4) years from MRI to autopsy) from the Wisconsin Alzheimer's Disease Research Center that underwent antemortem imaging and postmortem assessment of cerebral artery and brain pathology to identify possible pathologic correlates of 4D flow MRI. Our results suggest that 4D flow MRI measures recapitulate expected hemodynamic and structural relationships across cerebral arteries, but also that measures like MRI cross-sectional area may reflect arterial fibrosis whereas mean blood flow may indicate downstream cerebrovascular disease including white matter rarefaction and arteriolosclerosis. In contrast, associations were minimal with pulsatility index and cerebral artery or brain pathology across participants but were moderate across arterial segments. To our knowledge, this is the first study to investigate pathologic correlates of antemortem 4D flow MRI in cerebral arteries. These results provide preliminary insights regarding the pathologic processes contributing to cerebral artery hemodynamics measured with 4D flow MRI that will help inform interpretation of large-scale clinical aging and dementia studies utilizing this method. Future work with larger samples is needed to confirm these findings.

Evidence for direct CO2 -mediated alterations in cerebral oxidative metabolism in humans

AIM

How the cerebral metabolic rates of oxygen and glucose utilization (CMRO2 and CMRGlc, respectively) are affected by alterations in arterial PCO2 (PaCO2) is equivocal and therefore was the primary question of this study.

METHODS

This retrospective analysis involved pooled data from four separate studies, involving 41 healthy adults (35 males/6 females). Participants completed stepwise steady-state alterations in PaCO2 ranging between 30 and 60 mmHg. The CMRO2 and CMRGlc were assessed via the Fick approach (CBF × arterial-internal jugular venous difference of oxygen or glucose content, respectively) utilizing duplex ultrasound of the internal carotid artery and vertebral artery to calculate cerebral blood flow (CBF).

RESULTS

The CMRO2 was altered by 0.5 mL × min-1 (95% CI: -0.6 to -0.3) per mmHg change in PaCO2 (p < 0.001) which corresponded to a 9.8% (95% CI: -13.2 to -6.5) change in CMRO2 with a 9 mmHg change in PaCO2 (inclusive of hypo- and hypercapnia). The CMRGlc was reduced by 7.7% (95% CI: -15.4 to -0.08, p = 0.045; i.e., reduction in net glucose uptake) and the oxidative glucose index (ratio of oxygen to glucose uptake) was reduced by 5.6% (95% CI: -11.2 to 0.06, p = 0.049) with a + 9 mmHg increase in PaCO2.

CONCLUSION

Collectively, the CMRO2 is altered by approximately 1% per mmHg change in PaCO2. Further, glucose is incompletely oxidized during hypercapnia, indicating reductions in CMRO2 are either met by compensatory increases in nonoxidative glucose metabolism or explained by a reduction in total energy production.

Navigating Central Oxytocin Transport: Known Realms and Uncharted Territories

Complex mechanisms govern the transport and action of oxytocin (Oxt), a neuropeptide and hormone that mediates diverse physiologic processes. While Oxt exerts site-specific and rapid effects in the brain via axonal and somatodendritic release, volume transmission via CSF and the neurovascular interface can act as an additional mechanism to distribute Oxt signals across distant brain regions on a slower timescale. This review focuses on modes of Oxt transport and action in the CNS, with particular emphasis on the roles of perivascular spaces, the blood-brain barrier (BBB), and circumventricular organs in coordinating the triadic interaction among circulating blood, CSF, and parenchyma. Perivascular spaces, critical conduits for CSF flow, play a pivotal role in Oxt diffusion and distribution within the CNS and reciprocally undergo Oxt-mediated structural and functional reconstruction. While the BBB modulates the movement of Oxt between systemic and cerebral circulation in a majority of brain regions, circumventricular organs without a functional BBB can allow for diffusion, monitoring, and feedback regulation of bloodborne peripheral signals such as Oxt. Recognition of these additional transport mechanisms provides enhanced insight into the systemic propagation and regulation of Oxt activity.

Neuroinflammation in Alzheimer's disease: insights from peripheral immune cells

Alzheimer's disease (AD) is a serious brain disorder characterized by the presence of beta-amyloid plaques, tau pathology, inflammation, neurodegeneration, and cerebrovascular dysfunction. The presence of chronic neuroinflammation, breaches in the blood-brain barrier (BBB), and increased levels of inflammatory mediators are central to the pathogenesis of AD. These factors promote the penetration of immune cells into the brain, potentially exacerbating clinical symptoms and neuronal death in AD patients. While microglia, the resident immune cells of the central nervous system (CNS), play a crucial role in AD, recent evidence suggests the infiltration of cerebral vessels and parenchyma by peripheral immune cells, including neutrophils, T lymphocytes, B lymphocytes, NK cells, and monocytes in AD. These cells participate in the regulation of immunity and inflammation, which is expected to play a huge role in future immunotherapy. Given the crucial role of peripheral immune cells in AD, this article seeks to offer a comprehensive overview of their contributions to neuroinflammation in the disease. Understanding the role of these cells in the neuroinflammatory response is vital for developing new diagnostic markers and therapeutic targets to enhance the diagnosis and treatment of AD patients.

Future of neurocritical care: Integrating neurophysics, multimodal monitoring, and machine learning

Multimodal monitoring (MMM) in the intensive care unit (ICU) has become increasingly sophisticated with the integration of neurophysical principles. However, the challenge remains to select and interpret the most appropriate combination of neuromonitoring modalities to optimize patient outcomes. This manuscript reviewed current neuromonitoring tools, focusing on intracranial pressure, cerebral electrical activity, metabolism, and invasive and noninvasive autoregulation monitoring. In addition, the integration of advanced machine learning and data science tools within the ICU were discussed. Invasive monitoring includes analysis of intracranial pressure waveforms, jugular venous oximetry, monitoring of brain tissue oxygenation, thermal diffusion flowmetry, electrocorticography, depth electroencephalography, and cerebral microdialysis. Noninvasive measures include transcranial Doppler, tympanic membrane displacement, near-infrared spectroscopy, optic nerve sheath diameter, positron emission tomography, and systemic hemodynamic monitoring including heart rate variability analysis. The neurophysical basis and clinical relevance of each method within the ICU setting were examined. Machine learning algorithms have shown promise by helping to analyze and interpret data in real time from continuous MMM tools, helping clinicians make more accurate and timely decisions. These algorithms can integrate diverse data streams to generate predictive models for patient outcomes and optimize treatment strategies. MMM, grounded in neurophysics, offers a more nuanced understanding of cerebral physiology and disease in the ICU. Although each modality has its strengths and limitations, its integrated use, especially in combination with machine learning algorithms, can offer invaluable information for individualized patient care.

Atypical Presentation of Idiopathic Intracranial Hypertension: A Case Series and Literature Review

Idiopathic intracranial hypertension (IIH) is a condition in which intracranial pressure (ICP) increases without an apparent cause. Typically, patients present with headaches, dizziness, pulsatile tinnitus, visual disturbances, blurred vision, diplopia, photophobia, visual field defects, and papilledema on fundoscopy. The association between IIH, spontaneous cerebrospinal fluid (CSF) rhinorrhea, and arachnoid cysts has been discussed in the literature; however, there is no clear explanation for this association. We aimed to present a series of four patients with a confirmed diagnosis of IIH with atypical presentations, discuss the management of each case, and provide an explanation for this association to alert clinicians to the atypical presentation of IIH and facilitate early diagnosis and proper treatment of this condition by CSF diversion. This was a retrospective case series of all patients who were diagnosed with IIH and showed improvement after ventriculoperitoneal shunt insertion after failure of at least one operative intervention resulting from primary radiological and clinical findings in 2001 to 2022. Data on demographics, clinical presentation, radiological findings, surgical management, and diagnostic criteria for IIH were recorded. We identified four patients with a confirmed diagnosis of IIH who presented with atypical presentations as follows: intracranial arachnoid cyst, cervical spine arachnoid cyst, giant Virchow perivascular space, and spontaneous CSF (CSF) rhinorrhea. All patients responded to CSF diversion after failure of surgical treatment targeting the primary pathology. IIH should be suspected after the failure of primary surgical treatment in cases of spontaneous CSF rhinorrhea, spinal and cranial arachnoid cysts, and symptomatic ventriculoperitoneal shunt. Treatment in such situations should be directed toward IIH with CSF diversion.

Lymphatic network drainage resolves cerebral edema and facilitates recovery from experimental cerebral malaria

While brain swelling, associated with fluid accumulation, is a known feature of pediatric cerebral malaria (CM), how fluid and macromolecules are drained from the brain during recovery from CM is unknown. Using the experimental CM (ECM) model, we show that fluid accumulation in the brain during CM is driven by vasogenic edema and not by perivascular cerebrospinal fluid (CSF) influx. We identify that fluid and molecules are removed from the brain extremely quickly in mice with ECM to the deep cervical lymph nodes (dcLNs), predominantly through basal routes and across the cribriform plate and the nasal lymphatics. In agreement, we demonstrate that ligation of the afferent lymphatic vessels draining to the dcLNs significantly impairs fluid drainage from the brain and lowers anti-malarial drug recovery from the ECM syndrome. Collectively, our results provide insight into the pathways that coordinate recovery from CM.

Inferior Frontal Sulcal Hyperintensities on Brain MRI Are Associated with Amyloid Positivity beyond Age-Results from the Multicentre Observational DELCODE Study

Inferior frontal sulcal hyperintensities (IFSHs) on fluid-attenuated inversion recovery (FLAIR) sequences have been proposed to be indicative of glymphatic dysfunction. Replication studies in large and diverse samples are nonetheless needed to confirm them as an imaging biomarker. We investigated whether IFSHs were tied to Alzheimer's disease (AD) pathology and cognitive performance. We used data from 361 participants along the AD continuum, who were enrolled in the multicentre DELCODE study. The IFSHs were rated visually based on FLAIR magnetic resonance imaging. We performed ordinal regression to examine the relationship between the IFSHs and cerebrospinal fluid-derived amyloid positivity and tau positivity (Aβ42/40 ratio ≤ 0.08; pTau181 ≥ 73.65 pg/mL) and linear regression to examine the relationship between cognitive performance (i.e., Mini-Mental State Examination and global cognitive and domain-specific performance) and the IFSHs. We controlled the models for age, sex, years of education, and history of hypertension. The IFSH scores were higher in those participants with amyloid positivity (OR: 1.95, 95% CI: 1.05-3.59) but not tau positivity (OR: 1.12, 95% CI: 0.57-2.18). The IFSH scores were higher in older participants (OR: 1.05, 95% CI: 1.00-1.10) and lower in males compared to females (OR: 0.44, 95% CI: 0.26-0.76). We did not find sufficient evidence linking the IFSH scores with cognitive performance after correcting for demographics and AD biomarker positivity. IFSHs may reflect the aberrant accumulation of amyloid β beyond age.

Extracranial transport of brain lymphatics via cranial nerve in human

Extracranial waste transport from the brain interstitial fluid to the deep cervical lymph node (dCLN) is not extensively understood. The present study aims to show the cranial nerves that have a role in the transport of brain lymphatics vessels (LVs), their localization, diameter, and number using podoplanin (PDPN) and CD31 immunohistochemistry (IHC) and Western blotting. Cranial nerve samples from 6 human cases (3 cadavers, and 3 autopsies) were evaluated for IHC and 3 autopsies for Western blotting. The IHC staining showed LVs along the optic, olfactory, oculomotor, trigeminal, facial, glossopharyngeal, accessory, and vagus nerves. However, no LVs present along the trochlear, abducens, vestibulocochlear, and hypoglossal nerves. The LVs were predominantly localized at the endoneurium of the cranial nerve that has motor components, and LVs in the cranial nerves that had sensory components were present in all 3 layers. The number of LVs accompanying the olfactory, optic, and trigeminal nerves was classified as numerous; oculomotor, glossopharyngeal, vagus, and accessory was moderate; and facial nerves was few. The largest diameter of LVs was in the epineurium and the smallest one was in the endoneurium. The majority of Western blotting results correlated with the IHC. The present findings suggest that specific cranial nerves with variable quantities provide a pathway for the transport of wastes from the brain to dCLN. Thus, the knowledge of the transport of brain lymphatics along cranial nerves may help understand the pathophysiology of various neurological diseases.

Understanding the pathophysiology of idiopathic intracranial hypertension (IIH): a review of recent developments

Idiopathic intracranial hypertension (IIH) is a condition of significant morbidity and rising prevalence. It typically affects young people living with obesity, mostly women of reproductive age, and can present with headaches, visual abnormalities, tinnitus and cognitive dysfunction. Raised intracranial pressure without a secondary identified cause remains a key diagnostic feature of this condition, however, the underlying pathophysiological mechanisms that drive this increase are poorly understood. Previous theories have focused on cerebrospinal fluid (CSF) hypersecretion or impaired reabsorption, however, the recent characterisation of the glymphatic system in many other neurological conditions necessitates a re-evaluation of these hypotheses. Further, the impact of metabolic dysfunction and hormonal dysregulation in this population group must also be considered. Given the emerging evidence, it is likely that IIH is triggered by the interaction of multiple aetiological factors that ultimately results in the disruption of CSF dynamics. This review aims to provide a comprehensive update on the current theories regarding the pathogenesis of IIH.

Connecting the Dots: The Cerebral Lymphatic System as a Bridge Between the Central Nervous System and Peripheral System in Health and Disease

As a recently discovered waste removal system in the brain, cerebral lymphatic system is thought to play an important role in regulating the homeostasis of the central nervous system. Currently, more and more attention is being focused on the cerebral lymphatic system. Further understanding of the structural and functional characteristics of cerebral lymphatic system is essential to better understand the pathogenesis of diseases and to explore therapeutic approaches. In this review, we summarize the structural components and functional characteristics of cerebral lymphatic system. More importantly, it is closely associated with peripheral system diseases in the gastrointestinal tract, liver, and kidney. However, there is still a gap in the study of the cerebral lymphatic system. However, we believe that it is a critical mediator of the interactions between the central nervous system and the peripheral system.

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.

Approaches for Increasing Cerebral Efflux of Amyloid-β in Experimental Systems

Amyloid protein-β (Aβ) concentrations are increased in the brain in both early onset and late onset Alzheimer's disease (AD). In early onset AD, cerebral Aβ production is increased and its clearance is decreased, while increased Aβ burden in late onset AD is due to impaired clearance. Aβ has been the focus of AD therapeutics since development of the amyloid hypothesis, but efforts to slow AD progression by lowering brain Aβ failed until phase 3 trials with the monoclonal antibodies lecanemab and donanemab. In addition to promoting phagocytic clearance of Aβ, antibodies lower cerebral Aβ by efflux of Aβ-antibody complexes across the capillary endothelia, dissolving Aβ aggregates, and a "peripheral sink" mechanism. Although the blood-brain barrier is the main route by which soluble Aβ leaves the brain (facilitated by low-density lipoprotein receptor-related protein-1 and ATP-binding cassette sub-family B member 1), Aβ can also be removed via the blood-cerebrospinal fluid barrier, glymphatic drainage, and intramural periarterial drainage. This review discusses experimental approaches to increase cerebral Aβ efflux via these mechanisms, clinical applications of these approaches, and findings in clinical trials with these approaches in patients with AD or mild cognitive impairment. Based on negative findings in clinical trials with previous approaches targeting monomeric Aβ, increasing the cerebral efflux of soluble Aβ is unlikely to slow AD progression if used as monotherapy. But if used as an adjunct to treatment with lecanemab or donanemab, this approach might allow greater slowing of AD progression than treatment with either antibody alone.

Effect of Cerebral Small Vessel Disease Burden on Infarct Growth Rate and Stroke Outcomes in Large Vessel Occlusion Stroke Receiving Endovascular Treatment

This study aimed to investigate the association between cerebral small vessel disease (CSVD) burden and infarct growth rate (IGR) in patients with large vessel occlusion (LVO) stroke who underwent endovascular treatment (EVT). A retrospective analysis was conducted on a cohort of 495 patients with anterior circulation stroke who received EVT. CSVD burden was assessed using a CSVD score based on neuroimaging features. IGR was calculated from diffusion-weighted imaging (DWI) lesion volumes divided by the time from stroke onset to imaging. Clinical outcomes included stroke progression and functional outcomes at 3 months. Multivariate analyses were performed to assess the relationship between CSVD burden, IGR, and clinical outcomes. The fast IGR group had a higher proportion of high CSVD scores than the slow IGR group (24.4% vs. 0.8%, p < 0.001). High CSVD burden was significantly associated with a faster IGR (odds ratio [95% confidence interval], 26.26 [6.26-110.14], p < 0.001) after adjusting for confounding factors. High CSVD burden also independently predicted stroke progression and poor functional outcomes. This study highlights a significant relationship between CSVD burden and IGR in LVO stroke patients undergoing EVT. High CSVD burden was associated with faster infarct growth and worse clinical outcomes.

Patients of idiopathic normal-pressure hydrocephalus have small dural sac in cervical and upper thoracic levels: A supposed causal association

Background

Idiopathic normal pressure hydrocephalus (iNPH) is a neurological disorder presenting a triad including dementia and ventricular enlargement. The mechanism causing excessive cerebrospinal fluid (CSF) accumulation in the ventricles in iNPH is poorly understood. We hypothesized that the age-related degradation of the spinal shock-absorbing system composed of a spinal dural sac (SDS) and surrounding soft tissue, preventing ventricular enlargement caused by wide CSF pulsation driven by heartbeats, may be involved in the ventricular enlargement observed in iNPH.

Methods

Sixty-four patients with iNPH in their seventies who underwent a lumboperitoneal shunt and a control group of 79 people in the same age group who underwent brain check-ups were included in the study. We compared the sizes of the cervical and upper parts of the thoracic SDS using magnetic resonance imaging between the two groups.

Results

The anterior-posterior distances of the dural sac at C5 were shorter in patients with iNPH of both sexes than those in the control group (P = 0.0008 in men and P = 0.0047 in women). The number of disc levels with disappeared CSF space surrounding the cervical cord was more in iNPH (P = 0.0176 and P = 0.0003). The midsagittal area of the upper part of the spinal sac, C2-Th4, was smaller in iNPH (P = 0.0057 and P = 0.0290).

Conclusion

Narrowing of the cervical dural sac and midsagittal area in the upper part of the SDS in patients with iNPH may reflect the degradation of the shock-absorbing mechanism for CSF pressure pulsations, which may cause iNPH or at least aggravate iNPH by other unknown causes.

Peritumoral Edema in Gliomas: A Review of Mechanisms and Management

Treating malignant glioma is challenging owing to its highly invasive potential in healthy brain tissue and the formation of intense surrounding edema. Peritumoral edema in gliomas can lead to severe symptoms including neurological dysfunction and brain herniation. For the past 50 years, the standard treatment for peritumoral edema has been steroid therapy. However, the discovery of cerebral lymphatic vessels a decade ago prompted a re-evaluation of the mechanisms involved in brain fluid regulation and the formation of cerebral edema. This review aimed to describe the clinical features of peritumoral edema in gliomas. The mechanisms currently known to cause glioma-related edema are summarized, the limitations in current cerebral edema therapies are discussed, and the prospects for future cerebral edema therapies are presented. Further research concerning edema surrounding gliomas is needed to enhance patient prognosis and improve treatment efficacy.

Sensory gamma entrainment: Impact on amyloid protein and therapeutic mechanism

The deposition of amyloid β peptide (Aβ) is one of the main pathological features of AD. The much-talked sensory gamma entrainment may be a new treatment for Aβ load. Here we reviewed the generation and clearance pathways of Aβ, aberrant gamma oscillation in AD, and the therapeutic effect of sensory gamma entrainment on AD. In addition, we discuss these results based on stimulus parameters and possible potential mechanisms. This provides the support for sensory gamma entrainment targeting Aβ to improve AD.

Intracranial pressure for clinicians: it is not just a number

BACKGROUND

Invasive intracranial pressure (ICP) monitoring is a standard practice in severe brain injury cases, where it allows to derive cerebral perfusion pressure (CPP); ICP-tracing can also provide additional information about intracranial dynamics, forecast episodes of intracranial hypertension and set targets for a tailored therapy to prevent secondary brain injury. Nevertheless, controversies about the advantages of an ICP clinical management are still debated.

FINDINGS

This article reviews recent research on ICP to improve the understanding of the topic and uncover the hidden information in this signal that may be useful in clinical practice. Parameters derived from time-domain as well as frequency domain analysis include compensatory reserve, autoregulation estimation, pulse waveform analysis, and behavior of ICP in time. The possibility to predict the outcome and apply a tailored therapy using a personalised perfusion pressure target is also described.

CONCLUSIONS

ICP is a crucial signal to monitor in severely brain injured patients; a bedside computer can empower standard monitoring giving new metrics that may aid in clinical management, establish a personalized therapy, and help to predict the outcome. Continuous collaboration between engineers and clinicians and application of new technologies to healthcare, is vital to improve the accuracy of current metrics and progress towards better care with individualized dynamic targets.

New trends in brain tumor immunity with the opportunities of lymph nodes targeted drug delivery

Lymph nodes targeted drug delivery is an attractive approach to improve cancer immunotherapy outcomes. Currently, the depth of understanding of afferent and efferent arms in brain immunity reveals the potential clinical applications of lymph node targeted drug delivery in brain tumors, e.g., glioblastoma. In this work, we systematically reviewed the microenvironment of glioblastoma and its structure as a basis for potential immunotherapy, including the glial-lymphatic pathway for substance exchange, the lymphatic drainage pathway from meningeal lymphatic vessels to deep cervical lymph nodes that communicate intra- and extracranial immunity, and the interaction between the blood-brain barrier and effector T cells. Furthermore, the carriers designed for lymph nodes targeted drug delivery were comprehensively summarized. The challenges and opportunities in developing a lymph nodes targeted delivery strategy for glioblastoma using nanotechnology are included at the end.

Mass Spectrometry Imaging in Alzheimer's Disease

Introduction: Amyloid-beta (Aβ) pathology is the precipitating histopathological characteristic of Alzheimer's disease (AD). Although the formation of amyloid plaques in human brains is suggested to be a key factor in initiating AD pathogenesis, it is still not fully understood the upstream events that lead to Aβ plaque formation and its metabolism inside the brains. Methods: Matrix-assisted laser desorption ionization mass spectrometry imaging (MALDI-MSI) has been successfully introduced to study AD pathology in brain tissue both in AD mouse models and human samples. By using MALDI-MSI, a highly selective deposition of Aβ peptides in AD brains with a variety of cerebral amyloid angiopathy (CAA) involvement was observed. Results: MALDI-MSI visualized depositions of shorter peptides in AD brains; Aβ1-36 to Aβ1-39 were quite similarly distributed with Aβ1-40 as a vascular pattern, and deposition of Aβ1-42 and Aβ1-43 was visualized with a distinct senile plaque pattern distributed in parenchyma. Moreover, how MALDI-MSI covered in situ lipidomics of plaque pathology has been reviewed, which is of interest as aberrations in neuronal lipid biochemistry have been implicated in AD pathogenesis. Discussion: In this study, we introduce the methodological concepts and challenges of MALDI-MSI for the studies of AD pathogenesis. Diverse Aβ isoforms including various C- and N-terminal truncations in AD and CAA brain tissues will be visualized. Despite the close relationship between vascular and plaque Aβ deposition, the current strategy will define cross talk between neurodegenerative and cerebrovascular processes at the level of Aβ metabolism.

Pathophysiology and probable etiology of cerebral small vessel disease in vascular dementia and Alzheimer's disease

Vascular cognitive impairment and dementia (VCID) is commonly caused by vascular injuries in cerebral large and small vessels and is a key driver of age-related cognitive decline. Severe VCID includes post-stroke dementia, subcortical ischemic vascular dementia, multi-infarct dementia, and mixed dementia. While VCID is acknowledged as the second most common form of dementia after Alzheimer's disease (AD) accounting for 20% of dementia cases, VCID and AD frequently coexist. In VCID, cerebral small vessel disease (cSVD) often affects arterioles, capillaries, and venules, where arteriolosclerosis and cerebral amyloid angiopathy (CAA) are major pathologies. White matter hyperintensities, recent small subcortical infarcts, lacunes of presumed vascular origin, enlarged perivascular space, microbleeds, and brain atrophy are neuroimaging hallmarks of cSVD. The current primary approach to cSVD treatment is to control vascular risk factors such as hypertension, dyslipidemia, diabetes, and smoking. However, causal therapeutic strategies have not been established partly due to the heterogeneous pathogenesis of cSVD. In this review, we summarize the pathophysiology of cSVD and discuss the probable etiological pathways by focusing on hypoperfusion/hypoxia, blood-brain barriers (BBB) dysregulation, brain fluid drainage disturbances, and vascular inflammation to define potential diagnostic and therapeutic targets for cSVD.

Immunotherapy in glioblastoma treatment: Current state and future prospects

Glioblastoma remains as the most common and aggressive malignant brain tumor, standing with a poor prognosis and treatment prospective. Despite the aggressive standard care, such as surgical resection and chemoradiation, median survival rates are low. In this regard, immunotherapeutic strategies aim to become more attractive for glioblastoma, considering its recent advances and approaches. In this review, we provide an overview of the current status and progress in immunotherapy for glioblastoma, going through the fundamental knowledge on immune targeting to promising strategies, such as Chimeric antigen receptor T-Cell therapy, immune checkpoint inhibitors, cytokine-based treatment, oncolytic virus and vaccine-based techniques. At last, it is discussed innovative methods to overcome diverse challenges, and future perspectives in this area.

Enlarged perivascular space burden associations with arterial stiffness and cognition

Enlarged perivascular spaces (ePVS) are difficult to quantify, and their etiologies and consequences are poorly understood. Vanderbilt Memory and Aging Project participants (n = 327, 73 ± 7 years) completed 3T brain MRI to quantify ePVS volume and count, longitudinal neuropsychological assessment, and cardiac MRI to quantify aortic stiffness. Linear regressions related (1) PWV to ePVS burden and (2) ePVS burden to cross-sectional and longitudinal neuropsychological performance adjusting for key demographic and medical factors. Higher aortic stiffness related to greater basal ganglia ePVS volume (β = 7.0×10-5, p = 0.04). Higher baseline ePVS volume was associated with worse baseline information processing (β = -974, p = 0.003), executive function (β = -81.9, p < 0.001), and visuospatial performances (β = -192, p = 0.02) and worse longitudinal language (β = -54.9, p = 0.05), information processing (β = -147, p = 0.03), executive function (β = -10.9, p = 0.03), and episodic memory performances (β = -10.6, p = 0.02). Results were similar for ePVS count. Greater arterial stiffness relates to worse basal ganglia ePVS burden, suggesting cardiovascular aging as an etiology. ePVS burden is associated with adverse cognitive trajectory, emphasizing the clinical relevance of ePVS.

Cerebrospinal Fluid Protein Concentrations in Hydrocephalus

CSF protein levels are altered in neurological disorders, such as hydrocephalus of different etiologies. In this retrospective observational study, we analyzed cerebrospinal fluid (CSF) samples in hydrocephalic diseases such as aqueductal stenosis (AQS, n = 27), normal pressure hydrocephalus (NPH, n = 24), hydrocephalus communicans (commHC, n = 25) and idiopathic intracranial hypertension (IIH)/pseudotumor cerebri (PC, n = 7) in comparison with neurological patients without hydrocephalic configuration (control, n = 95). CSF was obtained through CSF diversion procedures and lumbar punction and analyzed for protein concentrations according to the institution’s laboratory standards. We found significantly decreased CSF protein levels in patients suffering from AQS (0.13 mg/dL [0.1–0.16 mg/dL] p = 2.28 × 10−8) and from PC (0.18 mg/dL [0.12–0.24 mg/dL] p = 0.01) compared with controls (0.34 mg/dL [0.33–0.35 mg/dL]). Protein levels were not altered in patients suffering from commHC and NPH compared with neurologically healthy individuals. We propose that a decrease in CSF protein levels is part of an active counterregulatory mechanism to lower CSF volume and, subsequently, intracranial pressure in specific diseases. Research regarding said mechanism and more specific proteomic research on a cellular level must still be performed to prove this hypothesis. Differences in protein levels between different diseases point to different etiologies and mechanisms in different hydrocephalic pathologies.

Imaging peripheral lymphatic dysfunction in chronic conditions

The lymphatics play important roles in chronic diseases/conditions that comprise the bulk of healthcare worldwide. Yet the ability to routinely image and diagnose lymphatic dysfunction, using commonly available clinical imaging modalities, has been lacking and as a result, the development of effective treatment strategies suffers. Nearly two decades ago, investigational near-infrared fluorescence lymphatic imaging and ICG lymphography were developed as routine diagnostic for clinically evaluating, quantifying, and treating lymphatic dysfunction in cancer-related and primary lymphedema, chronic venous disease, and more recently, autoimmune and neurodegenerative disorders. In this review, we provide an overview of what these non-invasive technologies have taught us about lymphatic (dys) function and anatomy in human studies and in corollary animal studies of human disease. We summarize by commenting on new impactful clinical frontiers in lymphatic science that remain to be facilitated by imaging.

Inferior Frontal Sulcal Hyperintensity on FLAIR Is Associated with Small Vessel Disease but not Alzheimer's Disease Pathology

BACKGROUND

The inferior frontal sulci are essential sites on the route of cerebrospinal fluid outflow. A recent study suggests that inferior frontal sulcal hyperintensities (IFSH) on FLAIR images might be related to glymphatic dysfunction.

OBJECTIVE

To investigate whether IFSH is associated with Alzheimer's disease (AD) pathology and cerebral small vessel disease (SVD) burden.

METHODS

We retrospectively collected data from 272 non-demented subjects in the ADNI3 database. The IFSH was assessed on 3D fluid-attenuated inversion recovery images. The standardized uptake value ratios of amyloid and tau PET were used to reflect the AD pathology burden. To measure the SVD burden, we assessed white matter hyperintensities (WMH), dilation of perivascular spaces, microbleeds, and lacunes. Finally, we performed ordinal logistic regression analyses to investigate the associations between the IFSH score and AD pathology and SVD burden.

RESULTS

The IFSH score was associated with the deep WMH score (OR, 1.79; 95% CI, 1.24 - 2.59) controlling for age and sex. The association remained significant in the multivariable regression models. There was no association between the IFSH score and AD pathology burden.

CONCLUSION

This study suggests that the IFSH sign is associated with SVD but not AD pathology. Further studies are needed to confirm the findings.

Current Status of Lymphangiogenesis: Molecular Mechanism, Immune Tolerance, and Application Prospect

The lymphatic system is a channel for fluid transport and cell migration, but it has always been controversial in promoting and suppressing cancer. VEGFC/VEGFR3 signaling has long been recognized as a major molecular driver of lymphangiogenesis. However, many studies have shown that the neural network of lymphatic signaling is complex. Lymphatic vessels have been found to play an essential role in the immune regulation of tumor metastasis and cardiac repair. This review describes the effects of lipid metabolism, extracellular vesicles, and flow shear forces on lymphangiogenesis. Moreover, the pro-tumor immune tolerance function of lymphatic vessels is discussed, and the tasks of meningeal lymphatic vessels and cardiac lymphatic vessels in diseases are further discussed. Finally, the value of conversion therapy targeting the lymphatic system is introduced from the perspective of immunotherapy and pro-lymphatic biomaterials for lymphangiogenesis.

Cerebrospinal Fluid Biomarkers and Amyloid-β Elimination from the Brain in Cerebral Amyloid Angiopathy-Related Inflammation

BACKGROUND

Cerebrospinal fluid (CSF) biomarkers in patients with cerebral amyloid angiopathy-related inflammation (CAA-ri) have demonstrated inconsistent results.

OBJECTIVE

We investigated the relationship between CSF amyloid-β protein (Aβ) and vascular pathological findings to elucidate the mechanisms of Aβ elimination from the brain in CAA-ri.

METHODS

We examined Aβ40 and Aβ42 levels in CSF samples in 15 patients with CAA-ri and 15 patients with Alzheimer's disease and cerebral amyloid angiopathy (AD-CAA) using ELISA as a cross-sectional study. Furthermore, we pathologically examined Aβ40 and Aβ42 depositions on the leptomeningeal blood vessels (arteries, arterioles, and veins) using brain biopsy samples from six patients with acute CAA-ri and brain tissues of two autopsied patients with CAA-ri.

RESULTS

The median Aβ40 and Aβ42 levels in the CSF showed no significant difference between pre-treatment CAA-ri (Aβ40, 6837 pg/ml; Aβ42, 324 pg/ml) and AD-CAA (Aβ40, 7669 pg/ml, p = 0.345; Aβ42, 355 pg/ml, p = 0.760). Aβ40 and Aβ42 levels in patients with post-treatment CAA-ri (Aβ40, 1770 pg/ml, p = 0.056; Aβ42, 167 pg/ml, p = 0.006) were lower than those in patients with pre-treatment CAA-ri. Regarding Aβ40 and Aβ42 positive arteries, acute CAA-ri cases showed a higher frequency of partially Aβ-deposited blood vessels than postmortem CAA-ri cases (Aβ40, 20.8% versus 3.9%, p = 0.0714; Aβ42, 27.4% versus 2.0%, p = 0.0714, respectively).

CONCLUSION

Lower levels of CSF Aβ40 and Aβ42 could be biomarkers for the cessation of inflammation in CAA-ri reflecting the recovery of the intramural periarterial drainage pathway and vascular function.

Update on the Epidemiology, Pathogenesis, and Biomarkers of Cerebral Autosomal Dominant Arteriopathy With Subcortical Infarcts and Leukoencephalopathy

Cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL) is the most common monogenic disorder of the cerebral small blood vessels. It is caused by mutations in the NOTCH3 gene on chromosome 19, and more than 280 distinct pathogenic mutations have been reported to date. CADASIL was once considered a very rare disease with an estimated prevalence of 1.3-4.1 per 100,000 adults. However, recent large-scale genomic studies have revealed a high prevalence of pathogenic NOTCH3 variants among the general population, with the highest risk being among Asians. The disease severity and age at onset vary significantly even among individuals who carry the same NOTCH3 mutations. It is still unclear whether a significant genotype-phenotype correlation is present in CADASIL. The accumulation of granular osmiophilic material in the vasculature is a characteristic feature of CADASIL. However, the exact pathogenesis of CADASIL remains largely unclear despite various laboratory and clinical observations being made. Major hypotheses proposed so far have included aberrant NOTCH3 signaling, toxic aggregation, and abnormal matrisomes. Several characteristic features have been observed in the brain magnetic resonance images of patients with CADASIL, including subcortical lacunar lesions and white matter hyperintensities in the anterior temporal lobe or external capsule, which were useful in differentiating CADASIL from sporadic stroke in patients. The number of lacunes and the degree of brain atrophy were useful in predicting the clinical outcomes of patients with CADASIL. Several promising blood biomarkers have also recently been discovered for CADASIL, which require further research for validation.

Overview of the meningeal lymphatic vessels in aging and central nervous system disorders

In the aging process and central nervous system (CNS) diseases, the functions of the meningeal lymphatic vessels (MLVs) are impaired. Alterations in MLVs have been observed in aging-related neurodegenerative diseases, brain tumors, and even cerebrovascular disease. These findings reveal a new perspective on aging and CNS disorders and provide a promising therapeutic target. Additionally, recent neuropathological studies have shown that MLVs exchange soluble components between the cerebrospinal fluid (CSF) and interstitial fluid (ISF) and drain metabolites, cellular debris, misfolded proteins, and immune cells from the CSF into the deep cervical lymph nodes (dCLNs), directly connecting the brain with the peripheral circulation. Impairment and dysfunction of meningeal lymphatics can lead to the accumulation of toxic proteins in the brain, exacerbating the progression of neurological disorders. However, for many CNS diseases, the causal relationship between MLVs and neuropathological changes is not fully clear. Here, after a brief historical retrospection, we review recent discoveries about the hallmarks of MLVs and their roles in the aging and CNS diseases, as well as potential therapeutic targets for the treatment of neurologic diseases.

Blood Cerebrospinal Fluid Barrier Function Disturbance Can Be Followed by Amyloid-β Accumulation

BACKGROUND

Elucidation of the mechanism of amyloid-β accumulation plays an important role in therapeutic strategies for Alzheimer's disease (AD). The aim of this study is to elucidate the relationship between the function of the blood-cerebrospinal fluid barrier (BCSFB) and the clearance of amyloid-β (Aβ).

METHODS

Twenty-five normal older adult volunteers (60-81 years old) participated in this PET study for clarifying the relationship between interstitial water flow and Aβ accumulation. Water dynamics were analyzed using two indices in [15O]H2O PET, the influx ratio (IR) and drain rate (DR), and Aβ accumulation was assessed qualitatively by [18F]flutemetamol PET.

RESULTS

[15O]H2O PET examinations conducted initially and after 2 years showed no significant changes in both indices over the 2-year period (IR: 1.03 ± 0.21 and 1.02 ± 0.20, DR: 1.74 ± 0.43 and 1.67 ± 0.47, respectively). In [18F]flutemetamol PET, on the other hand, one of the 25 participants showed positive results and two showed positive changes after 2 years. In these three participants, the two indices of water dynamics showed low values at both periods (IR: 0.60 ± 0.15 and 0.60 ± 0.13, DR: 1.24 ± 0.12 and 1.11 ± 0.10).

CONCLUSIONS

Our results indicated that BCSFB function disturbances could be followed by Aβ accumulation, because the reduced interstitial flow preceded amyloid accumulation in the positive-change subjects, and amyloid accumulation was not observed in the older adults with sufficiently high values for the two indices. We believe that further elucidation of interstitial water flow will be the key to developing therapeutic strategies for AD, especially with regard to prevention.

The choroid plexus and its role in the pathogenesis of neurological infections

The choroid plexus is situated at an anatomically and functionally important interface within the ventricles of the brain, forming the blood-cerebrospinal fluid barrier that separates the periphery from the central nervous system. In contrast to the blood-brain barrier, the choroid plexus and its epithelial barrier have received considerably less attention. As the main producer of cerebrospinal fluid, the secretory functions of the epithelial cells aid in the maintenance of CNS homeostasis and are capable of relaying inflammatory signals to the brain. The choroid plexus acts as an immunological niche where several types of peripheral immune cells can be found within the stroma including dendritic cells, macrophages, and T cells. Including the epithelia cells, these cells perform immunosurveillance, detecting pathogens and changes in the cytokine milieu. As such, their activation leads to the release of homing molecules to induce chemotaxis of circulating immune cells, driving an immune response at the choroid plexus. Research into the barrier properties have shown how inflammation can alter the structural junctions and promote increased bidirectional transmigration of cells and pathogens. The goal of this review is to highlight our foundational knowledge of the choroid plexus and discuss how recent research has shifted our understanding towards viewing the choroid plexus as a highly dynamic and important contributor to the pathogenesis of neurological infections. With the emergence of several high-profile diseases, including ZIKA and SARS-CoV-2, this review provides a pertinent update on the cellular response of the choroid plexus to these diseases. Historically, pharmacological interventions of CNS disorders have proven difficult to develop, however, a greater focus on the role of the choroid plexus in driving these disorders would provide for novel targets and routes for therapeutics.

Risk factors for unfavourable outcomes after shunt surgery in patients with idiopathic normal-pressure hydrocephalus

A number of vascular risk factors (VRFs) have been reported to be associated with idiopathic normal-pressure hydrocephalus (iNPH), but it remains unclear whether these VRFs are related to patient outcomes after shunt surgery. Therefore, we investigated the risk factors for unfavourable outcomes after shunt surgery in iNPH patients using two samples from Tohoku University Hospital and from a multicentre prospective trial of lumboperitoneal (LP) shunt surgery for patients with iNPH (SINPHONI-2). We enrolled 158 iNPH patients. We compared the prevalence of VRFs and clinical measures between patients with favourable and unfavourable outcomes and identified predictors of unfavourable outcomes using multivariate logistic regression analyses. The presence of hypertension, longer disease duration, more severe urinary dysfunction, and a lower Evans' index were predictors of unfavourable outcomes after shunt surgery. In addition, hypertension and longer disease duration were also predictors in patients with independent walking, and a lower Evans' index was the only predictor in patients who needed assistance to walk or could not walk. Our findings indicate that hypertension is the only VRF related to unfavourable outcomes after shunt surgery in iNPH patients. Larger-scale studies are needed to elucidate the reason why hypertension can affect the irreversibility of symptoms after shunt placement.

Homocysteine is related to enlarged perivascular spaces in the brainstem in patients with isolated pontine infarction

Background

Homocysteine is correlated with several imaging features of cerebral small vessel disease including white matter hyperintensities, lacunes, and enlarged perivascular spaces (EPVS) in the basal ganglia. However, little is known about EPVS in the brainstem. This study aimed to investigate the correlation between serum total homocysteine (tHcy) and EPVS in the brainstem in patients with acute isolated pontine infarction.

Methods

Consecutive patients with isolated pontine infarction were retrospectively enrolled. Clinical characteristics and laboratory tests including tHcy were recorded. Imaging markers of cerebral small vessel disease including EPVS in the basal ganglia (BG-EPVS), EPVS in the centrum semiovale, and EPVS in the midbrain or pons (brainstem-EPVS) were assessed using conventional magnetic resonance imaging. The relation between tHcy and EPVS of different parts in the brain was analyzed using univariate and multivariate regression model.

Results

A total of 227 patients were included (mean age 67.10 ± 9.38 years, male sex 58.6%). The frequencies of brainstem-EPVS and moderate to severe BG-EPVS accounted for 40.1% (91/227) and 40.5% (92/227) respectively. After controlling for confounding factors, multivariate logistic regression analyses showed that tHcy was an independent risk factor for both moderate to severe BG-EPVS (P = 0.003, P for trend < 0.001) and the presence of brainstem-EPVS (P < 0.001, P for trend < 0.001) in a dose-dependent manner. Furthermore, multivariate linear regression model indicated that the presence of brainstem-EPVS (β = 0.264, 95% confidence interval = 0.143-0.402, P < 0.001) and the severity of BG-EPVS (β = 0.162, 95% confidence interval = 0.024-0.197, P = 0.013) were positively associated with serum tHcy.

Conclusions

Serum tHcy is correlated with brainstem-EPVS and BG-EPVS dose-dependently. This study may support a contributing role for homocysteine in the pathophysiology of EPVS in the brainstem and the basal ganglia.

Drainage of senescent astrocytes from brain via meningeal lymphatic routes

Recent progress on the central lymphatic system has greatly increased our understanding of how the brain maintains its own waste homeostasis. Here, we showed that perivascular spaces and meningeal lymphatic vessels form a functional route for clearance of senescent astrocytes from the aging brain. Blocking meningeal lymphatic drainage by ligation of the deep cervical lymph nodes impaired clearance of senescent astrocytes from brain parenchyma, subsequently increasing neuroinflammation in aged mice. By contrast, enhancing meningeal lymphatic vessel diameter by a recombinant adeno-associated virus encoding mouse vascular endothelial growth factor-C (VEGF-C) improved clearance of senescent astrocytes and mitigated neuroinflammation. Mechanistically, VEGF-C was highly expressed in senescent astrocytes, contributing themselves to migrate across lymphatic vessels along C-C motif chemokine ligand 21 (CCL21) gradient by interacting with VEGF receptor 3. Moreover, intra-cisternal injection of antibody against CCL21 hampered senescent astrocytes into the lymphatic vessels and exacerbated short memory defects of aged mice. Together, these findings reveal a new perspective for the meningeal lymphatics in the removal of senescent astrocytes, thus offering a valuable target for therapeutic intervention.

Intrathecal delivery and its applications in leptomeningeal disease

Intrathecal delivery (IT) of opiates into the cerebrospinal fluid (CSF) for anesthesia and pain relief has been used clinically for decades, but this relatively straightforward approach of bypassing the blood-brain barrier has been underutilized for other indications because of its lack of utility in delivering small lipid-soluble drugs. However, emerging evidence suggests that IT drug delivery be an efficacious strategy for the treatment of cancers in which there is leptomeningeal spread of disease. In this review, we discuss CSF flow dynamics and CSF clearance pathways in the context of intrathecal delivery. We discuss human and animal studies of several new classes of therapeutic agents-cellular, protein, nucleic acid, and nanoparticle-based small molecules-that may benefit from IT delivery. The complexity of the CSF compartment presents several key challenges in predicting biodistribution of IT-delivered drugs. New approaches and strategies are needed that can overcome the high rates of turnover in the CSF to reach specific tissues or cellular targets.

Neurofilament light chain plasma levels are associated with area of brain damage in experimental cerebral malaria

Neurofilament light chain (NfL), released during central nervous injury, has evolved as a powerful serum marker of disease severity in many neurological disorders, including infectious diseases. So far NfL has not been assessed in cerebral malaria in human or its rodent model experimental cerebral malaria (ECM), a disease that can lead to fatal brain edema or reversible brain edema. In this study we assessed if NfL serum levels can also grade disease severity in an ECM mouse model with reversible (n = 11) and irreversible edema (n = 10). Blood–brain-barrier disruption and brain volume were determined by magnetic resonance imaging. Neurofilament density volume as well as structural integrity were examined by electron microscopy in regions of most severe brain damage (olfactory bulb (OB), cortex and brainstem). NfL plasma levels in mice with irreversible edema (317.0 ± 45.01 pg/ml) or reversible edema (528.3 ± 125.4 pg/ml) were significantly increased compared to controls (103.4 ± 25.78 pg/ml) by three to five fold, but did not differ significantly in mice with reversible or irreversible edema. In both reversible and irreversible edema, the brain region most affected was the OB with highest level of blood–brain-barrier disruption and most pronounced decrease in neurofilament density volume, which correlated with NfL plasma levels (r = − 0.68, p = 0.045). In cortical and brainstem regions neurofilament density was only decreased in mice with irreversible edema and strongest in the brainstem. In reversible edema NfL plasma levels, MRI findings and neurofilament volume density normalized at 3 months’ follow-up. In conclusion, NfL plasma levels are elevated during ECM confirming brain damage. However, NfL plasma levels fail short on reliably indicating on the final outcomes in the acute disease stage that could be either fatal or reversible. Increased levels of plasma NfL during the acute disease stage are thus likely driven by the anatomical location of brain damage, the olfactory bulb, a region that serves as cerebral draining pathway into the nasal lymphatics.

Glymphatic System: Emerging Therapeutic Target for Neurological Diseases

The newly discovered glymphatic system acts as pseudolymphatic vessels subserving brain waste clearance and is functionally dependent on astrocytic aquaporin-4 channels. The glymphatic system primarily functions during sleep as an interchange between cerebrospinal fluid and interstitial fluid, with cerebrospinal fluid flowing into the parenchyma via the perivascular spaces and then exchanging with interstitial fluid. The discovery of meningeal lymphatics helps refine the conceptual framework of glymphatic pathway, as certain waste products collected alongside perivascular spaces ultimately drain into the cervical lymph nodes via meningeal lymphatics, whose function regulates the functioning of the glymphatic system. The glymphatic and meningeal lymphatic systems are critical for the homeostasis of central nervous system, and their malfunctions complicate cerebral dysfunction and diseases. The present review will shed light on the structure, regulation, functions, and interrelationships of the glymphatic system and meningeal lymphatics. We will also expound on their impairments and corresponding targeted intervention in neurodegenerative diseases, traumatic brain injury, stroke, and infectious/autoimmune diseases, offering valuable references for future research.

The Role of Immunity in Alzheimer's Disease

With the increase in the aging population, age-related conditions such as dementia and Alzheimer's disease will become ever more prevalent in society. As there is no cure for dementia and extremely limited therapeutic options, researchers are examining the mechanisms that contribute to the progression of cognitive decline in hopes of developing better therapies and even an effective, long-lasting treatment for this devastating condition. This review will provide an updated perspective on the role of immunity in triggering the changes that lead to the development of dementia. It will detail the latest findings on Aβ- and tau-induced microglial activation, including the role of the inflammasome. The contribution of the adaptive immune system, specifically T cells, will be discussed. Finally, whether the innate and adaptive immune system can be modulated to protect against dementia will be examined, along with an assessment of the prospective candidates for these that are currently in clinical trials.

Brain Fluid Channels for Metabolite Removal

The adult human brain represents only 2 % of the body's total weight, however it is one of the most metabolically active organs in the mammalian body. Its high metabolic activity necessitates an efficacious waste clearance system. Besides the blood, there are two fluids closely linked to the brain and spinal cord drainage system: interstitial fluid (ISF) and cerebrospinal fluid (CSF). The aim of this review is to summarize the latest research clarifying the channels of metabolite removal by fluids from brain tissue, subarachnoid space (SAS) and brain dura (BD). Special attention is focused on lymphatic vascular structures in the brain dura, their localizations within the meninges, morphological properties and topographic anatomy. The review ends with an account of the consequences of brain lymphatic drainage failure. Knowledge of the physiological state of the clearance system is crucial in order to understand the changes related to impaired brain drainage.

Role of Tissue Hydraulic Permeability in Convection-Enhanced Delivery of Nanoparticle-Encapsulated Chemotherapy Drugs to Brain Tumour

PURPOSE

Tissue hydraulic permeability of brain tumours can vary considerably depending on the tissue microstructure, compositions in interstitium and tumour cells. Its effects on drug transport and accumulation remain poorly understood.

METHODS

Mathematical modelling is applied to predict the drug delivery outcomes in tumours with different tissue permeability upon convection-enhanced delivery. The modelling is based on a 3-D realistic tumour model that is extracted from patient magnetic resonance images.

RESULTS

Modelling results show that infusing drugs into a permeable tumour can facilitate a more favourable hydraulic environment for drug transport. The infused drugs will exhibit a relatively uniform distribution and cover a larger tumour volume for effective cell killing. Cross-comparisons show the delivery outcomes are more sensitive to the changes in tissue hydraulic permeability and blood pressure than the fluid flow from the brain ventricle. Quantitative analyses demonstrate that increasing the fluid gain from both the blood and brain ventricle can further improve the interstitial fluid flow, and thereby enhance the delivery outcomes. Furthermore, similar responses to the changes in tissue hydraulic permeability can be found for different types of drugs.

CONCLUSIONS

Tissue hydraulic permeability as an intrinsic property can influence drug accumulation and distribution. Results from this study can deepen the understanding of the interplays between drug and tissues that are involved in the drug delivery processes in chemotherapy.

The blood-brain barrier and the neurovascular unit in subarachnoid hemorrhage: molecular events and potential treatments

The response of the blood-brain barrier (BBB) following a stroke, including subarachnoid hemorrhage (SAH), has been studied extensively. The main components of this reaction are endothelial cells, pericytes, and astrocytes that affect microglia, neurons, and vascular smooth muscle cells. SAH induces alterations in individual BBB cells, leading to brain homeostasis disruption. Recent experiments have uncovered many pathophysiological cascades affecting the BBB following SAH. Targeting some of these pathways is important for restoring brain function following SAH. BBB injury occurs immediately after SAH and has long-lasting consequences, but most changes in the pathophysiological cascades occur in the first few days following SAH. These changes determine the development of early brain injury as well as delayed cerebral ischemia. SAH-induced neuroprotection also plays an important role and weakens the negative impact of SAH. Supporting some of these beneficial cascades while attenuating the major pathophysiological pathways might be decisive in inhibiting the negative impact of bleeding in the subarachnoid space. In this review, we attempt a comprehensive overview of the current knowledge on the molecular and cellular changes in the BBB following SAH and their possible modulation by various drugs and substances.