Cerebrospinal fluid secretion by the choroid plexus?

Cerebrospinal fluid analysis of metabolites is not correlated to microdialysis measurements in acute brain injured patients

BACKGROUND

Cerebral microdialysis (CMD) has become an established bedside monitoring modality but its implementation remains complex and costly and is therefore performed only in a few well-trained academic centers. This study investigated the relationship between cerebrospinal fluid (CSF) and CMD glucose and lactate concentrations.

METHODS

Two centers retrospective study of prospectively collected data. Consecutive adult (>18 years) acutely brain injured patients admitted to the Intensive Care Unit between 2010 and 2021 were eligible if CSF and CMD glucose and lactate concentrations were concomitantly measured at least once.

RESULTS

Of 113 patients being monitored with an external ventricular drainage and CMD, 49 patients (25 from Innsbruck and 24 from Brussels) were eligible for the final analysis, including a total of 96 measurements. Median CMD glucose and lactate concentrations were 1.15 (0.51-1.57) mmol/L and 3.44 (2.24-5.37) mmol/L, respectively; median CSF glucose and lactate concentrations were 4.67 (4.03-5.34) mmol/L and 3.40 (2.85-4.10) mmol/L, respectively. For the first measurements, no correlation between CSF and CMD glucose concentrations (R2 <0.01; p = 0.95) and CSF and CMD lactate concentrations (R2 =0.16; p = 0.09) was found. Considering all measurements, the repeated measure correlation analysis also showed no correlation for glucose (rrm = -0.01; 95% Confidence Intervals -0.306 to 0.281; p = 0.93) and lactate (rrm = -0.11; 95% Confidence Intervals -0.424 to 0.236; p = 0.55).

CONCLUSIONS

In this study including acute brain injured patients, no correlation between CSF and brain tissue measurements of glucose and lactate was observed. As such, CSF measurements of such metabolites cannot replace CMD findings.

Cerebrospinal Fluid-Basic Concepts Review

Cerebrospinal fluid plays a crucial role in protecting the central nervous system (CNS) by providing mechanical support, acting as a shock absorber, and transporting nutrients and waste products. It is produced in the ventricles of the brain and circulates through the brain and spinal cord in a continuous flow. In the current review, we presented basic concepts related to cerebrospinal fluid history, cerebrospinal fluid production, circulation, and its main components, the role of the blood-brain barrier and the blood-cerebrospinal fluid barrier in the maintenance of cerebrospinal fluid homeostasis, and the utility of Albumin Quotient (Q_Alb) evaluation in the diagnosis of CNS diseases. We also discussed the collection of cerebrospinal fluid (type, number of tubes, and volume), time of transport to the laboratory, and storage conditions. Finally, we briefly presented the role of cerebrospinal fluid examination in CNS disease diagnosis of various etiologies and highlighted that research on identifying cerebrospinal fluid biomarkers indicating disease presence or severity, evaluating treatment effectiveness, and enabling understanding of pathogenesis and disease mechanisms is of great importance. Thus, in our opinion, research on cerebrospinal fluid is still necessary for both the improvement of CNS disease management and the discovery of new treatment options.

Evaluation of the Preventive Effects of Neostigmine Plus Atropine on Post-Dural Puncture Headache

Background

Post-dural puncture headache (PDPH) is one of the most common side effects of spinal anesthesia. Several strategies and drugs have been suggested for the treatment and/or prevention of this headache. The aim of this study is evaluating the effects of intravenous prescription of neostigmine plus atropine 15 minutes after dural puncture on incidence and severity of PDPH during 5 days of follow-up in the setting of lower limb orthopedic surgeries.

Materials and Methods

In a randomized, controlled, double-blind clinical trial, 99 patients of lower limb orthopedic surgeries were randomized into study (49 patients) and control groups (50 patients). Fifteen minutes after dural puncture, participants in the two groups intravenously took neostigmine (40 μg/kg) plus atropine (20 μg/kg) and placebo (normal saline), respectively. Side effects of the studied drugs and incidence, severity, and duration of PDPH were evaluated 5 days after surgery.

Results

A total of 20 patients in the study group and 31 in the control group showed a headache-with-PDPH profile during 5 days of follow-up (P-value = 0.035). The mean duration of PDPH was 1.15 ± 0.48 and 1.32 ± 0.54 days in the study and control groups, respectively (P-value = 0.254).

Conclusion

Preventive administration of 40 μg/kg neostigmine plus 20 μg/kg of atropine may be effective in reducing the incidence and severity of PDPH after spinal anesthesia in lower limb orthopedic surgeries.

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.

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.

Coupling between cerebrovascular oscillations and CSF flow fluctuations during wakefulness: An fMRI study

It is commonly believed that cerebrospinal fluid (CSF) movement is facilitated by blood vessel wall movements (i.e., hemodynamic oscillations) in the brain. A coherent pattern of low frequency hemodynamic oscillations and CSF movement was recently found during non-rapid eye movement (NREM) sleep via functional MRI. This finding raises other fundamental questions: 1) the explanation of coupling between hemodynamic oscillations and CSF movement from fMRI signals; 2) the existence of the coupling during wakefulness; 3) the direction of CSF movement. In this resting state fMRI study, we proposed a mechanical model to explain the coupling between hemodynamics and CSF movement through the lens of fMRI. Time delays between CSF movement and global hemodynamics were calculated. The observed delays between hemodynamics and CSF movement match those predicted by the model. Moreover, by conducting separate fMRI scans of the brain and neck, we confirmed the low frequency CSF movement at the fourth ventricle is bidirectional. Our finding also demonstrates that CSF movement is facilitated by changes in cerebral blood volume mainly in the low frequency range, even when the individual is awake.

Fluid transport in the brain

The brain harbors a unique ability to, figuratively speaking, shift its gears. During wakefulness, the brain is geared fully toward processing information and behaving, while homeostatic functions predominate during sleep. The blood-brain barrier establishes a stable environment that is optimal for neuronal function, yet the barrier imposes a physiological problem; transcapillary filtration that forms extracellular fluid in other organs is reduced to a minimum in brain. Consequently, the brain depends on a special fluid [the cerebrospinal fluid (CSF)] that is flushed into brain along the unique perivascular spaces created by astrocytic vascular endfeet. We describe this pathway, coined the term glymphatic system, based on its dependency on astrocytic vascular endfeet and their adluminal expression of aquaporin-4 water channels facing toward CSF-filled perivascular spaces. Glymphatic clearance of potentially harmful metabolic or protein waste products, such as amyloid-β, is primarily active during sleep, when its physiological drivers, the cardiac cycle, respiration, and slow vasomotion, together efficiently propel CSF inflow along periarterial spaces. The brain's extracellular space contains an abundance of proteoglycans and hyaluronan, which provide a low-resistance hydraulic conduit that rapidly can expand and shrink during the sleep-wake cycle. We describe this unique fluid system of the brain, which meets the brain's requisites to maintain homeostasis similar to peripheral organs, considering the blood-brain-barrier and the paths for formation and egress of the CSF.

No Arachnoid Granulations-No Problems: Number, Size, and Distribution of Arachnoid Granulations From Birth to 80 Years of Age

Introduction: The study aims to quantify changes in the number, size, and distribution of arachnoid granulations during the human lifespan to elucidate their role in cerebrospinal fluid physiology.

Material and Methods: 3T magnetic resonance imaging of the brain was performed in 120 subjects of different ages (neonate, 2 years, 10 years, 20 years, 40 years, 60 years, and 80 years) all with the normal findings of the cerebrospinal fluid system (CSF). At each age, 10 male and 10 female subjects were analyzed. Group scanned at neonatal age was re-scanned at the age of two, while all other groups were scanned once. Arachnoid granulations were analyzed on T2 coronal and axial sections. Each arachnoid granulation was described concerning size and position relative to the superior sagittal, transverse, and sigmoid sinuses and surrounding cranial bones.

Results: Our study shows that 85% of neonates and 2-year-old children do not have visible arachnoid granulations in the dural sinuses and cranial bones on magnetic resonance imaging. With age, the percentage of patients with arachnoid granulations in the superior sagittal sinus increases significantly, but there is no increase in the sigmoid and transverse sinuses. However, numerous individuals in different age groups do not have arachnoid granulations in dural sinuses. Arachnoid granulations in the cranial bones are found only around the superior sagittal sinus, for the first time at the age of 10, and over time their number increases significantly. From the age of 60 onwards, arachnoid granulations were more numerous in the cranial bones than in the dural sinuses.

Conclusion: The results show that the number, size, and distribution of arachnoid granulations in the superior sagittal sinus and surrounding cranial bones change significantly over a lifetime. However, numerous individuals with a completely normal CSF system do not have arachnoid granulations in the dural sinuses, which calls into question their role in CSF physiology. It can be assumed that arachnoid granulations do not play an essential role in CSF absorption as it is generally accepted. Therefore, the lack of arachnoid granulations does not appear to cause problems in intracranial fluid homeostasis.

Direction and magnitude of cerebrospinal fluid flow vary substantially across central nervous system diseases

Background

Several central nervous system diseases are associated with disturbed cerebrospinal fluid (CSF) flow patterns and have typically been characterized in vivo by phase-contrast magnetic resonance imaging (MRI). This technique is, however, limited by its applicability in space and time. Phase-contrast MRI has yet to be compared directly with CSF tracer enhanced imaging, which can be considered gold standard for assessing long-term CSF flow dynamics within the intracranial compartment.

Methods

Here, we studied patients with various CSF disorders and compared MRI biomarkers of CSF space anatomy and phase-contrast MRI at level of the aqueduct and cranio-cervical junction with dynamic intrathecal contrast-enhanced MRI using the contrast agent gadobutrol as CSF tracer. Tracer enrichment of cerebral ventricles was graded 0–4 by visual assessment. An intracranial pressure (ICP) score was used as surrogate marker of intracranial compliance.

Results

The study included 94 patients and disclosed marked variation of CSF flow measures across disease categories. The grade of supra-aqueductal reflux of tracer varied, with strong reflux (grades 3–4) in half of patients. Ventricular tracer reflux correlated with stroke volume and aqueductal CSF pressure gradient. CSF flow in the cerebral aqueduct was retrograde (from 4th to 3rd ventricle) in one third of patients, with estimated CSF net flow volume about 1.0 L/24 h. In the cranio-cervical junction, net flow was cranially directed in 78% patients, with estimated CSF net flow volume about 4.7 L/24 h.

Conclusions

The present observations provide in vivo quantitative evidence for substantial variation in direction and magnitude of CSF flow, with re-direction of aqueductal flow in communicating hydrocephalus, and significant extra-cranial CSF production. The grading of ventricular reflux of tracer shows promise as a clinical useful method to assess CSF flow pattern disturbances in patients.

Graphic abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s12987-021-00251-6.

The Brain's Glymphatic System: Current Controversies

The glymphatic concept along with the discovery of meningeal lymphatic vessels have, in recent years, highlighted that fluid is directionally transported within the central nervous system (CNS). Imaging studies, as well as manipulations of fluid transport, point to a key role of the glymphatic-lymphatic system in clearance of amyloid-β and other proteins. As such, the glymphatic-lymphatic system represents a new target in combating neurodegenerative diseases. Not unexpectedly, introduction of a new plumbing system in the brain has stirred controversies. This opinion article will highlight what we know about the brain's fluid transport systems, where experimental data are lacking, and what is still debated.

Signal Intensity of the Cerebrospinal Fluid after Intravenous Administration of Gadolinium-based Contrast Agents: Strong Contrast Enhancement around the Vein of Labbe

Purpose:

Since the first report on the deposition of gadolinium in the brain parenchyma after repeated intravenous administrations of gadolinium-based contrast agent GBCA (IV-GBCA), the mechanisms of penetration and retention are still remaining a hot topic of discussion and a target of investigation. We routinely obtain endolymphatic hydrops (EH) images at 4 h after IV administration of a single dose (SD) of GBCA (IV-SD-GBCA) using heavily T₂-weighted three-dimensional fluid-attenuated inversion recovery imaging (hT₂W-3D-FLAIR). Occasionally, we have encountered cases, which indicate high-signal intensity (SI) in the cerebrospinal fluid (CSF) surrounding the vein of Labbe. The purpose of the present study was to investigate the degree of contrast enhancement of the CSF surrounding the vein of Labbe on hT₂W-3D-FLAIR after IV-SD-GBCA in comparison with other CSF spaces.

Materials and Methods:

In 25 patients with a suspicion of EH, a magnetic resonance cisternography (MRC) and an hT₂W-3D-FLAIR were obtained at 4 h after IV-SD-GBCA. The perivascular space (PVS) in the basal ganglia, CSF spaces in the ambient cistern (CSF-Amb), the CSF surrounding the superficial middle cerebral vein (CSF-SMCV), and the CSF surrounding the vein of Labbe (CSF-VL) were segmented on MRC. The PVS and CSF regions were co-registered onto the hT₂W-3D-FLAIR and the SI of the PVS and CSF spaces were measured. The SI ratio (SIR) of the post-contrast hT₂W-3D-FLAIR to the pre-contrast hT₂W-3D-FLAIR was measured. Significant differences were evaluated using Steel-Dwass’s test for multiple comparisons.

Results:

The SIR of the CSF-VL was significantly higher than that of the PVS (P = 0.008), the CSF-Amb (P = 0.021), and the CSF-SMCV (P = 0.023).

Conclusion:

The strong contrast enhancement of CSF space around the vein of Labbe was confirmed on hT₂W-3D-FLAIR at 4 h after IV-GBCA compared to the PVS and the other CSF spaces.

FSI simulation of CSF hydrodynamic changes in a large population of non-communicating hydrocephalus patients during treatment process with regard to their clinical symptoms

3D fluid-structure interaction modelling was utilized for simulation of 13 normal subjects, 11 non-communicating hydrocephalus (NCH) patients at pre-treatment phase, and 3 patients at five post-treatment phases. Evaluation of ventricles volume and maximum CSF pressure (before shunting) following results validation indicated that these parameters were the most proper hydrodynamic indices and the NCH type doesn't have any significant effect on changes in two indices. The results confirmed an appropriate correlation between these indices although the correlation decreased slightly after the occurrence of disease. NCH raises the intensity of vortex and pulsatility (2.4 times) of CSF flow while the flow remains laminar. On day 18 after shunting, the CSF pressure decreased 81.0% and all clinical symptoms of patients vanished except for headache. Continuing this investigation during the treatment process showed that maximum CSF pressure is the most sensitive parameter to patients' clinical symptoms. Maximum CSF pressure has decreased proportional to the level of decrease in clinical symptoms and has returned close to the pressure range in normal subjects faster than other parameters and simultaneous with disappearance of patients' clinical symptoms (from day 81 after shunting). However, phase lag between flow rate and pressure gradient functions and the degree of CSF pulsatility haven't returned to normal subjects' conditions even 981 days after shunting and NCH has also caused a permanent volume change (of 20.1%) in ventricles. Therefore, patients have experienced a new healthy state in new hydrodynamic conditions after shunting and healing. Increase in patients' intracranial compliance was predicted with a more accurate non-invasive method than previous experimental methods up to more than 981 days after shunting. The changes in hydrodynamic parameters along with clinical reports of patients can help to gain more insight into the pathophysiology of NCH patients.

Appearance of the Organum Vasculosum of the Lamina Terminalis on Contrast-enhanced MR Imaging

Purpose:

Circumventricular organs (CVOs) lack a blood brain barrier and are also called “brain windows”. Among CVOs, the organum vasculosum of the lamina terminalis (OVLT) is an osmotic regulator involved in the release of vasopressin. In a previous study of healthy subjects, it was reported that contrast enhancement in the OVLT can be recognized in only 34% of 3 Tesla thin slice contrast-enhanced T₁-weighted images. The purpose of this study was to evaluate the leakage of gadolinium contrast from the OVLT in healthy subjects using heavily T₂-weighted three dimensional-fluid attenuated inversion recovery (3D-FLAIR) (HF) imaging.

Methods:

Eight healthy male subjects were included in this study. A standard dose (0.1 mmol/kg) of gadoteridol was intravenously administered. Magnetic resonance cisternography (MRC) and HF were obtained before and 0.5, 1.5, 3, 4.5 and 6 h after the injection. Enhancement of the OVLT including the surrounding cerebral spinal fluid (CSF) was measured by manually drawing a rectangular ROI centered on the OVLT. The ROI was copied to the HF image and the signal intensity was measured. The signal intensity ratio (SIR) was obtained by dividing the signal intensity value of the OVLT ROI by that of the midbrain.

Results:

The differences between the mean SIR at pre-contrast and those at 0.5, 1.5, 3, 4.5, and 6 h were significant (P < 0.05). The mean SIR at 0.5 h was higher than those at all other time points (P < 0.05).

Conclusion:

Using HF imaging, enhancement around the OVLT was observed in all subjects at 0.5 h after intravenous administration of single dose gadoteridol.