CSF pathways: a review

An in vitro experimental investigation of oscillatory flow in the cerebral aqueduct

This in vitro study aims at clarifying the relation between the oscillatory flow of cerebrospinal fluid (CSF) in the cerebral aqueduct, a narrow conduit connecting the third and fourth ventricles, and the corresponding interventricular pressure difference. Dimensional analysis is used in designing an anatomically correct scaled model of the aqueduct flow, with physical similarity maintained by adjusting the flow frequency and the properties of the working fluid. The time-varying pressure difference across the aqueduct corresponding to a given oscillatory flow rate is measured in parametric ranges covering the range of flow conditions commonly encountered in healthy subjects. Parametric dependences are delineated for the time-averaged pressure fluctuations and for the phase lag between the transaqueductal pressure difference and the flow rate, both having clinical relevance. The results are validated through comparisons with predictions obtained with a previously derived computational model. The parametric quantification in this study enables the derivation of a simple formula for the relation between the transaqueductal pressure and the stroke volume. This relationship can be useful in the quantification of transmantle pressure differences based on non-invasive magnetic-resonance-velocimetry measurements of aqueduct flow for investigation of CSF-related disorders.

The presence of a foramen of Luschka in the American alligator (Alligator mississippiensis) and the continuity of the intraventricular and subdural spaces

In humans and most mammals, there is a notch-like portal, the foramen of Luschka (or lateral foramen), which connects the lumen of the fourth ventricle with the subdural space. Gross dissection, light and scanning electron microscopy, and μCT analysis revealed the presence of a foramen of Luschka in the American alligator (Alligator mississippiensis). In this species, the foramen of Luschka is a notch in the dorsolateral wall of the pons immediately caudal to the peduncular base of the cerebellum, near the rostral end of the telovelar membrane over the fourth ventricle. At the foramen of Luschka there was a transition from a superficial pia mater lining to a deep ependymal lining. There was continuity between the lumen of the fourth ventricle and the subdural space, via the foramen of Luschka. This anatomical continuity was further demonstrated by injecting Evans blue into the lateral ventricle which led to extravasation through the foramen of Luschka and pooling of the dye on the lateral surface of the brain. Simultaneous subdural and intraventricular recordings of cerebrospinal fluid (CSF) pressures revealed a stable agreement between the two pressures at rest. Perturbation of the system allowed for static and dynamic differences to develop, which could indicate varying flow patterns of CSF through the foramen of Luschka.

Predictive value of spinal CSF volume in the preoperative assessment of patients with idiopathic normal-pressure hydrocephalus

Introduction

The pathophysiology, diagnosis, and management of idiopathic normal pressure hydrocephalus (iNPH) remain unclear. Although some prognostic tests recommended in iNPH guidelines should have high sensitivity and high predictive value, there is often no positive clinical response to surgical treatment.

Materials and methods

In our study, 19 patients with clinical and neuroradiological signs of iNPH were selected for preoperative evaluation and possible further surgical treatment according to the guidelines. MR volumetry of the intracranial and spinal space was performed. Patients were exposed to prolonged external lumbar drainage in excess of 10 ml per hour during 3 days. Clinical response to lumbar drainage was assessed by a walk test and a mini-mental test.

Results

Twelve of 19 patients showed a positive clinical response and underwent a shunting procedure. Volumetric values of intracranial space content in responders and non-responders showed no statistically significant difference. Total CSF volume (sum of cranial and spinal CSF volumes) was higher than previously published. No correlation was found between spinal canal length, CSF pressure, and CSF spinal volume. The results show that there is a significantly higher CSF volume in the spinal space in the responder group (n = 12) (120.5 ± 14.9 ml) compared with the non-responder group (103.1 ± 27.4 ml; n = 7).

Discussion

This study demonstrates for the first time that CSF volume in the spinal space may have predictive value in the preoperative assessment of iNPH patients. The results suggest that patients with increased spinal CSF volume have decreased compliance. Additional prospective randomized clinical trials are needed to confirm our results.

Cerebrospinal fluid and blood profiles of transfer RNA fragments show age, sex, and Parkinson's disease-related changes

Transfer RNA fragments (tRFs) have recently been shown to be an important family of small regulatory RNAs with diverse functions. Recent reports have revealed modified tRF blood levels in a number of nervous system conditions including epilepsy, ischemic stroke, and neurodegenerative diseases, but little is known about tRF levels in the cerebrospinal fluid (CSF). To address this issue, we studied age, sex, and Parkinson's disease (PD) effects on the distributions of tRFs in the CSF and blood data of healthy controls and PD patients from the NIH and the Parkinson's Progression Markers Initiative (PPMI) small RNA-seq datasets. We discovered that long tRFs are expressed in higher levels in the CSF than in the blood. Furthermore, the CSF showed a pronounced age-associated decline in the level of tRFs cleaved from the 3'-end and anti-codon loop of the parental tRNA (3'-tRFs, i-tRFs), and more pronounced profile differences than the blood profiles between the sexes. In comparison, we observed moderate age-related elevation of blood 3'-tRF levels. In addition, distinct sets of tRFs in the CSF and in the blood segregated PD patients from controls. Finally, we found enrichment of tRFs predicted to target cholinergic mRNAs (Cholino-tRFs) among mitochondrial-originated tRFs, raising the possibility that the neurodegeneration-related mitochondrial impairment in PD patients may lead to deregulation of their cholinergic tone. Our findings demonstrate that the CSF and blood tRF profiles are distinct and that the CSF tRF profiles are modified in a sex-, age-, and disease-related manner, suggesting that they reflect the inter-individual cerebral differences and calling for incorporating this important subset of small RNA regulators into future studies.

Mechanisms of reduced cerebral blood flow in cerebral edema and elevated intracranial pressure

A mechanism of elevated intracranial pressure (ICP) in cerebral edema and its effects on cerebral blood flow (CBF) are presented in this paper. To study and demonstrate these effects, a mathematical model of intracranial hydrodynamics was developed. The model simulates the intracranial hydrodynamics and the changes that occur when cerebral edema predominates. To account for an edema pathology, the model includes resistances to cerebrospinal fluid (CSF) and interstitial fluid (ISF) flows within the parenchyma. The resistances change as the intercellular space becomes smaller due to swelling of brain cells. The model demonstrates the effect of changes in these resistances on ICP and venous resistance to blood flow by accounting for the key interactions between pressure, volume, and flow in the intracranial compartments in pathophysiological conditions. The model represents normal intracranial physiology as well as pathological conditions. Simulating cerebral edema with increased resistance to cerebral ISF flow resulted in elevated ICP, increased brain volume, markedly reduced ventricular volume, and decreased CBF as observed in the neurointensive care patients. The model indicates that in high ICP values, alternation of the arterial-arteriolar resistance to flow minimally affects CBF, whereas at low ICP they have a much greater effect on CBF. The model demonstrates and elucidates intracranial mechanisms related to elevated ICP.NEW & NOTEWORTHY Study goal was to elucidate the role of "bulk flow" of ISF through brain parenchyma. A model was developed to simulate fluid shifts in brain edema, ICP elevation, and their effect on CBF. Bulk flow resistance affected by edema elevates ICP and reduces CBF. Bulk flow affects transmural pressure and volume distribution in brain compartments. Changes in bulk flow resistance result in increase of venous resistance to flow and decrease in CBF.

A new surgical method for treating syringomyelia secondary to arachnoiditis following cervical spine surgery: the syringo-cisterna magna shunt

PURPOSE

The 5-year postoperative failure rate of conventional shunt treatment for syringomyelia is 50%, with arachnoditis, shunt obstruction, and shunt malfunction being the most common causes. We report a new syringo-cisterna magna (SCM) shunt that allows syrinx cerebrospinal fluid (CSF) drainage normally into the cerebellomedullary cisterns through the subarachnoid space.

METHODS

Between November 2012 and February 2017, six patients (mean age: 57.25 years; sex: four male and two female) received the SCM shunt. They had spinal cord injury, abscess formation after a spine operation, and cerebral meningitis-related syringomyelia (syrinx between C0 and T9), and presented sensory changes and motor weakness. Preoperatively and at 1 year postoperatively, the syrinx length and diameter were assessed using magnetic resonance imaging (MRI). Clinical outcomes were evaluated using the visual analog scale (VAS) and Japanese Orthopedic Association (JOA) scores.

RESULTS

Motor weakness improved, pain subsided, and sensory disturbance resolved in all patients who returned to work within 6 weeks postoperatively. In all cases, the syrinx collapsed (length: 3.3 levels decreased; diameter: decreased from 7.90 to 4.64 mm, p = 0.046) on postoperative MRI. No patient experienced syrinx recurrence and shunt malfunction on MRI or showed spinal instability signs on plain radiography. The VAS (pre- vs post-shunt: 6.50 vs 3.83, p = 0.027) and JOA scores (pre- vs post-shunt: 10.00 vs 11.17, p = 0.167) were improved postoperatively.

CONCLUSION

We developed a new shunting system allowing syrinx CSF drainage to the posterior fossa, with symptomatic improvement, minimal complications, and syrinx decrease on follow-up MRI. The SCM shunt is effective for treating syringomyelia.

Cerebrospinal fluid dynamics along the optic nerve

The cerebrospinal fluid (CSF) plays an important role in delivering nutrients and eliminating the metabolic wastes of the central nervous system. An interrupted CSF flow could cause disorders of the brain and eyes such as Alzheimer's disease and glaucoma. This review provides an overview of the anatomy and flow pathways of the CSF system with an emphasis on the optic nerve. Imaging technologies used for visualizing the CSF dynamics and the anatomic structures associated with CSF circulation have been highlighted. Recent advances in the use of computational models to predict CSF flow patterns have been introduced. Open questions and potential mechanisms underlying CSF circulation at the optic nerves have also been discussed.

Chronic CSF leak from lumbar-peritoneal shunt tract: A case report

Background

We describe a case of long-standing intracranial hypotension caused by an iatrogenic arachnoid diverticulum. This case illustrates two learning points. First, excessive CSF absorption may occur through an acquired arachnoid-epidural venous plexus at a dural defect. Second, a long-standing CSF leak may benefit from definitive surgical repair in the first instance.

Case Description

A 55-year-old female, with known idiopathic intracranial hypertension, presented with disabling chronic low-pressure symptoms after having a lumboperitoneal shunt removed 5 years previously. MRI scan revealed a Chiari I malformation (CMI) and a small dural interruption at the L3/4 space. CT myelography confirmed the abnormality. Intraoperatively, a dural defect and arachnoid bleb with an overlying attachment of adipose tissue and a vessel were found. Postoperatively, the patient has marked resolution of her headaches and dizziness and is mobilizing independently.

Conclusion

Excessive CSF absorption appears to have occurred through an acquired arachnoid-epidural venous plexus. A high index of suspicion for intracranial hypotension is required in patients with low pressure symptoms and a CMI.

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.

Hydrogel Check-Valves for the Treatment of Hydrocephalic Fluid Retention with Wireless Fully-Passive Sensor for the Intracranial Pressure Measurement

Hydrocephalus (HCP) is a neurological disease resulting from the disruption of the cerebrospinal fluid (CSF) drainage mechanism in the brain. Reliable draining of CSF is necessary to treat hydrocephalus. The current standard of care is an implantable shunt system. However, shunts have a high failure rate caused by mechanical malfunctions, obstructions, infection, blockage, breakage, and over or under drainage. Such shunt failures can be difficult to diagnose due to nonspecific systems and the lack of long-term implantable pressure sensors. Herein, we present the evaluation of a fully realized and passive implantable valve made of hydrogel to restore CSF draining operations within the cranium. The valves are designed to achieve a non-zero cracking pressure and no reverse flow leakage by using hydrogel swelling. The valves were evaluated in a realistic fluidic environment with ex vivo CSF and brain tissue. They display a successful operation across a range of conditions, with negligible reverse flow leakage. Additionally, a novel wireless pressure sensor was incorporated alongside the valve for in situ intracranial pressure measurement. The wireless pressure sensor successfully replicated standard measurements. Those evaluations show the reproducibility of the valve and sensor functions and support the system’s potential as a chronic implant to replace standard shunt systems.

The Sheep as a Comprehensive Animal Model to Investigate Interdependent Physiological Pressure Propagation and Multiparameter Influence on Cerebrospinal Fluid Dynamics

The present study aims to develop a suitable animal model for evaluating the physiological interactions between cerebrospinal fluid (CSF) dynamics, hemodynamics, and abdominal compartment pressures. We seek to contribute to the enhanced recognition of the pathophysiology of CSF-dependent neurological disorders like hydrocephalus and the improvement of available treatment options. To date, no comprehensive animal model of CSF dynamics exists, and establishing an accurate model will advance our understanding of complex CSF physiology. Persisting knowledge gaps surrounding the communication and pressure propagation between the cerebrospinal space and adjacent anatomical compartments exacerbate the development of novel therapies for neurological diseases. Hence, the need for further investigation of the interactions of vascular, craniospinal, and abdominal pressures remains beyond dispute. Moreover, the results of this animal study support the optimization of in vitro test benches for medical device development, e.g., ventriculoperitoneal shunts. Six female white alpine sheep were surgically equipped with pressure sensors to investigate the physiological values of intracranial, intrathecal, arterial, central venous, jugular venous, vesical pressure, and four differently located abdominal pressures. These values were measured simultaneously during the acute animal trial with sheep under general anesthesia. Both carotid and femoral arterial blood pressure indicate a reliable and comparable representation of the systematic blood pressure. However, the jugular venous pressure and the central venous pressure in sheep in dorsal recumbency do not correlate well under general anesthesia. Furthermore, there is a trend for possible comparability of lateral intraventricular and lumbar intrathecal pressure. Nevertheless, animal body position during measurements must be considered since different body constitutions can alter the horizontal line between the cerebral ventricles and the lumbar subarachnoid space. While intra-abdominal pressure measurement in the four different abdominal quadrants yielded greater inter-individual variability, intra-vesical pressure measurements in our setting delivered comparable values for all sheep. We established a novel and comprehensive ovine animal model to investigate interdependent physiologic pressure propagation and multiparameter influences on CSF dynamics. The results of this study will contribute to further in vitro bench testing, the derivation of novel quantitative models, and the development of a pathologic ovine hydrocephalus model.

Morphometrics of the Spinal Cord and Surrounding Structures in Alligator mississippiensis

Simple Summary

Morphometric analysis of the spinal cord and surrounding tissue of the American alligator (Alligator mississippiensis) reveals that there are four significantly discrete regions; cervical, thoracic, lumbar, and caudal. Crocodylians, unlike mammals, have a caudal spinal cord that extends throughout the length of their tail (which accounts for roughly 50% of their total body length). Alligator mississippiensis has one of the largest ranges of body sizes among terrestrial vertebrates, this study documents how the different spinal structures change with increasing body size. Though most of the structures exhibit slightly positive allometry, a few exhibit slightly negative allometry; these differences mean that there are significant relational changes as hatchlings grow into large adults. This study provides the first documentation that A. mississippiensis has an expansive subdural space, a lumbar cistern, at the pelvis.

Abstract

Understanding the fluid dynamics of the cerebrospinal fluid requires a quantitative description of the spaces in which it flows, including the spinal cord and surrounding meninges. The morphometrics of the spinal cord and surrounding tissues were studied in specimens of the American alligator (Alligator mississippiensis) ranging from hatchlings through adults. Within any size class of alligators (i.e., hatchlings), along the axial length there are significant differences in the size of the spinal cord, meninges, and vertebral canal; these differences can be used to define discrete cervical, thoracic, lumbar and caudal regions. When compared across the range of body sizes in Alligator, every structure in each spinal region had a distinctive growth rate; thus, the physical arrangements between the structures changed as the alligator grew. The combination of regional differentiation and differential growth rates was particularly apparent in the lumbar meninges where a unique form of lumbar cistern could be identified and shown to decrease in relative size as the alligator ages. This analysis of the spinal cord and surrounding tissues was undertaken to develop a data set that could be used for computational flow dynamics of the crocodilian cerebrospinal fluid, and also to assist in the analysis of fossil archosaurs.

Cerebrospinal fluid-tissue exchange revealed by phase alternate labeling with null recovery MRI

PURPOSE

To develop phase alternate labeling with null recovery (PALAN) MRI methods for the quantification of the water exchange between cerebrospinal fluid (CSF) and other surrounding tissues in the brain.

METHOD

In both T₁ -PALAN and apparent diffusion coefficient (ADC)-PALAN MRI methods, the cerebrospinal fluid signal was nulled, whereas the partial recovery of other tissues with shorter T₁ (T₁ -PALAN) or lower ADC values (ADC-PALAN) was labeled by alternating the phase of pulses. The water exchange was extracted from the difference between the recovery curves of CSF with and without labeling.

RESULTS

Both T₁ -PALAN and ADC-PALAN observed a rapid occurrence of CSF water exchange with the surrounding tissues at 67 ± 56 ms and 13 ± 2 ms transit times, respectively. The T₁ and ADC-PALAN signal peaked at 1.5 s. The CSF water exchange was 1153 ± 270 mL/100 mL/min with T₁ -PALAN in the third and lateral ventricles, which was higher than 891 ± 60 mL/100 mL/min obtained by ADC-PALAN. T₁ -PALAN ∆S values for the rostral and caudal ventricles are 0.015 ± 0.013 and 0.034 ± 0.01 (p = 0.022, n = 5), whereas similar ΔS values in both rostral and caudal lateral ventricles were observed by ADC-PALAN (3.9 ± 1.9 × 10^-3 vs 4.4 ± 1.4 × 10^-3 ; p = 0.66 and n = 5).

CONCLUSION

The PALAN methods are suitable tools to study CSF water exchange across different compartments in the brain.

Transvascular in vivo microscopy of the subarachnoid space

BACKGROUND

The micro-architectonics of the subarachnoid space (SAS) remain partially understood and largely ignored, likely the result of the inability to image these structures in vivo. We explored transvascular imaging with high-frequency optical coherence tomography (HF-OCT) to interrogate the SAS.

METHODS

In vivo HF-OCT was performed in 10 dogs in both the posterior and anterior cerebral circulations. The conduit vessels used were the basilar, anterior spinal, and middle and anterior cerebral arteries through which the perivascular SAS was imaged. The HF-OCT imaging probe was introduced via a microcatheter and images were acquired using a contrast injection (3.5 mL/s) for blood clearance. Segmentation and three-dimensional rendering of HF-OCT images were performed to study the different configurations and porosity of the subarachnoid trabeculae (SAT) as a function of location.

RESULTS

Of 13 acquisitions, three were excluded due to suboptimal image quality. Analysis of 15 locations from seven animals was performed showing six distinct configurations of arachnoid structures in the posterior circulation and middle cerebral artery, ranging from minimal presence of SAT to dense networks and membranes. Different locations showed predilection for specific arachnoid morphologies. At the basilar bifurcation, a thick, fenestrated membrane had a unique morphology. SAT average thickness was 100 µm and did not vary significantly based on location. Similarly, the porosity of the SAT averaged 91% and showed low variability.

CONCLUSION

We have demonstrated the feasibility to image the structures of the SAS with transvascular HF-OCT. Future studies are planned to further map the SAT to increase our understanding of their function and possible impact on neurovascular pathologies.

Arachnoid Membranes: Crawling Back into Radiologic Consciousness

The arachnoid membranes are projections of connective tissue in the subarachnoid space that connect the arachnoid mater to the pia mater. These are underappreciated and largely unrecognized by most neuroradiologists despite being found to be increasingly important in the pathogenesis, imaging, and treatment of communicating hydrocephalus. This review aims to provide neuroradiologists with an overview of the history, embryology, histology, anatomy, and normal imaging appearance of these membranes, as well as some examples of their clinical importance.

Turning the Curve Into Straight: Phenogenetics of the Spine Morphology and Coordinate Maintenance in the Zebrafish

The vertebral column, or spine, provides mechanical support and determines body axis posture and motion. The most common malformation altering spine morphology and function is adolescent idiopathic scoliosis (AIS), a three-dimensional spinal deformity that affects approximately 4% of the population worldwide. Due to AIS genetic heterogenicity and the lack of suitable animal models for its study, the etiology of this condition remains unclear, thus limiting treatment options. We here review current advances in zebrafish phenogenetics concerning AIS-like models and highlight the recently discovered biological processes leading to spine malformations. First, we focus on gene functions and phenotypes controlling critical aspects of postembryonic aspects that prime in spine architecture development and straightening. Second, we summarize how primary cilia assembly and biomechanical stimulus transduction, cerebrospinal fluid components and flow driven by motile cilia have been implicated in the pathogenesis of AIS-like phenotypes. Third, we highlight the inflammatory responses associated with scoliosis. We finally discuss recent innovations and methodologies for morphometrically characterize and analyze the zebrafish spine. Ongoing phenotyping projects are expected to identify novel and unprecedented postembryonic gene functions controlling spine morphology and mutant models of AIS. Importantly, imaging and gene editing technologies are allowing deep phenotyping studies in the zebrafish, opening new experimental paradigms in the morphometric and three-dimensional assessment of spinal malformations. In the future, fully elucidating the phenogenetic underpinnings of AIS etiology in zebrafish and humans will undoubtedly lead to innovative pharmacological treatments against spinal deformities.

Investigation of the Presence of Arachnoid Granulation in Fetuses and Early Infancy

The aim of our study is to investigate the importance of arachnoid granulation in cerebrospinal fluid physiology in fetuses and early infancy. Using the random sampling method, postmortem fetuses more than 26 weeks of gestation age and the children under the age of 1 year were chosen from the autopsy materials. Two male and two female intrauterine dead fetus; three male and three female, totally six children under the age of 1 year and one 3-year-old male were included in this study. In cases of intrauterine fetuses more than 26 weeks of gestation and children under the age of 1 year, complete invagination of arachnoid villi into the superior sagittal sinus was examined histologically. In the intrauterine period and in the first 6 months of life, arachnoid villi structures were not found in histologic preparations although in preparations taken after the 6 months of life samples showed similarities to arachnoid granulations. These structures were considered as arachnoid villi drafts after immunohistochemical analysis. In the control case who were 3 years old, maturation of arachnoid villi was complete and the arachnoid villi were invaginated into the superior sagittal sinus as fingerlike extensions. In our study, we think that the failure after E3V intervention in the treatment of hydrocephalus in cases under the age of 1 years may be related to the completion of arachnoid granulation development after the 18th month of life and the immature resorption capacity in this period.

Spontaneous Intracranial Hypotension Without CSF Leakage-Concept of a Pathological Cranial to Spinal Fluid Shift

Objective: Spontaneous intracranial hypotension (SIH) is typically caused by CSF leakage from a spinal dural tear, a meningeal diverticulum, or a CSF venous fistula. However, some patients present with classic orthostatic symptoms and typical intracranial imaging findings without evidence of CSF leakage despite repeated diagnostic work-up. This article aims to elaborate a hypothesis that would explain a pathologically increased orthostatic shift of CSF from the cranial to the spinal compartment in the absence of a CSF leak.

Medical Hypothesis: The symptoms of SIH are caused by a decrease in intracranial CSF volume, intracranial hypotension, and downward displacement of intracranial structures. A combination of pathologically increased spinal compliance, decreased intracranial CSF volume, low CSF outflow resistance, and decreased venous pressure might result in a pathological orthostatic cranial-to-spinal CSF shift. Thus, in rare cases, intracranial hypotension may occur in the absence of CSF leakage from the dural sac.

Conclusion: We propose a pathophysiological concept for the subgroup of SIH patients with typical cranial imaging findings and no evidence of CSF leakage. In these patients, reducing the compliance or the volume of the spinal compartment seems to be the appropriate therapeutic strategy.

Lamina terminalis fenestration: An important neurosurgical corridor

Cerebrospinal fluid (CSF) disorders are challenging conditions in neurosurgical practice. The majority of CSF is contained in the basal cisterns of the brain, which are subarachnoid compartments that communicate with each other, and contribute to the circulation of CSF. Yaşargil et al. (1976) was the first to provide the systematic classification and naming of the basal cisterns. The lamina terminalis (LT) starts from the gyrus rectus and descends to the lateral aspect of the optic chiasm. It is a thick arachnoidal membrane delineating the anterior wall of the third ventricle that borders the LT cistern. With the introduction of the operating microscope and the progressive development of modern neurosurgery, the arachnoid and basal cisterns have been used as surgical corridors in order to reach deep areas of the brain and to release CSF for brain relaxation. In this way, the LT is used as a surgical corridor for the treatment of several conditions such as obstructive hydrocephalus and diencephalic tumors. In this chapter, we will describe the anatomy of the LT, possible conditions treated by opening the LT, the different surgical approaches to opening the LT, along with their advantages and disadvantages.

Cerebrospinal fluid drainage kinetics across the cribriform plate are reduced with aging

Background

Continuous circulation and drainage of cerebrospinal fluid (CSF) are essential for the elimination of CSF-borne metabolic products and neuronal function. While multiple CSF drainage pathways have been identified, the significance of each to normal drainage and whether there are differential changes at CSF outflow regions in the aging brain are unclear.

Methods

Dynamic in vivo imaging of near infrared fluorescently-labeled albumin was used to simultaneously visualize the flow of CSF at outflow regions on the dorsal side (transcranial and -spinal) of the central nervous system. This was followed by kinetic analysis, which included the elimination rate constants for these regions. In addition, tracer distribution in ex vivo tissues were assessed, including the nasal/cribriform region, dorsal and ventral surfaces of the brain, spinal cord, cranial dura, skull base, optic and trigeminal nerves and cervical lymph nodes.

Results

Based on the in vivo data, there was evidence of CSF elimination, as determined by the rate of clearance, from the nasal route across the cribriform plate and spinal subarachnoid space, but not from the dorsal dural regions. Using ex vivo tissue samples, the presence of tracer was confirmed in the cribriform area and olfactory regions, around pial blood vessels, spinal subarachnoid space, spinal cord and cervical lymph nodes but not for the dorsal dura, skull base or the other cranial nerves. Also, ex vivo tissues showed retention of tracer along brain fissures and regions associated with cisterns on the brain surfaces, but not in the brain parenchyma. Aging reduced CSF elimination across the cribriform plate but not that from the spinal SAS nor retention on the brain surfaces.

Conclusions

Collectively, these data show that the main CSF outflow sites were the nasal region across the cribriform plate and from the spinal regions in mice. In young adult mice, the contribution of the nasal and cribriform route to outflow was much higher than from the spinal regions. In older mice, the contribution of the nasal route to CSF outflow was reduced significantly but not for the spinal routes. This kinetic approach may have significance in determining early changes in CSF drainage in neurological disorder, age-related cognitive decline and brain diseases.

Subarachnoid space trabeculae architecture

INTRODUCTION

The motion of the brain relative to the skull is influenced by the architecture of the subarachnoid space (SAS), and in particular, by the arachnoid trabeculae. In previous studies of these structures, specific shapes were identified. However, the work presented here shows much finer detail of the SAS geometries using SEM and TEM.

MATERIALS AND METHODS

These images were acquired by maintaining the SAS structure of a rat using glutaraldehyde formaldehyde to strengthen the tissues via crosslinking with the biological proteins.

RESULTS

The results showed the detailed shape of five dominant arachnoid trabeculae structures: single strands, branched strands, tree like shapes, sheets, and trabecular networks. Each of these architectures would provide a different response when exposed to a tensile load and would provide different levels of resistance to the flow of the cerebrospinal fluid (CSF) within the SAS.

CONCLUSION

This very detailed level of geometric information will therefore allow more accurate finite element models of the SAS to be developed.

Insights into the natural history of spontaneous intracranial hypotension from infusion testing

Objective

To assess the pathophysiologic changes in patients with spontaneous intracranial hypotension (SIH) based on measures of CSF dynamics, and on the duration of symptoms, in a retrospective case-controlled study.

Methods

We included consecutive patients investigated for SIH at our department from January 2012 to February 2018. CSF leak was considered confirmed if extrathecal contrast spillage was seen on imaging (CT or MRI) after intrathecal contrast application, or dural breach was detected by direct intraoperative visualization. We divided patients with a confirmed CSF leak into 3 groups depending on the symptom duration, as follows: ≤10, 11–52, and >52 weeks. Clinical characteristics and measures of CSF fluid dynamics obtained by computerized lumbar infusion testing were analyzed over time and compared with a reference population.

Results

Among the 137 patients included, 69 had a confirmed CSF leak. Whereas 93.1% with <10 weeks of symptoms displayed typical orthostatic headache, only 62.5% with >10 weeks of symptoms did (p = 0.004). Analysis of infusion tests revealed differences between groups with different symptom duration for CSF outflow resistance (p < 0.001), lumbar baseline pressure (p = 0.013), lumbar plateau pressure (p < 0.001), baseline pressure amplitude (p = 0.021), plateau pressure amplitude (p = 0.001), pressure–volume index (p = 0.001), elastance (p < 0.001), and CSF production rate (p = 0.001). Compared to the reference population, only patients with acute symptoms showed a significantly altered CSF dynamics profile.

Conclusion

A CSF leak dramatically alters CSF dynamics acutely, but the pattern changes over time. There is an association between the clinical presentation and changes in CSF dynamics.

Three-Dimensionally Printed Microelectromechanical-System Hydrogel Valve for Communicating Hydrocephalus

Hydrocephalus (HCP) is a chronic neurological brain disorder caused by a malfunction of the cerebrospinal fluid (CSF) drainage mechanism in the brain. The current standard method to treat HCP is a shunt system. Unfortunately, the shunt system suffers from complications including mechanical malfunctions, obstructions, infections, blockage, breakage, overdrainage, and/or underdrainage. Some of these complications may be attributed to the shunts' physically large and lengthy course making them susceptible to external forces, siphoning effects, and risks of infection. Additionally, intracranial catheters artificially traverse the brain and drain the ventricle rather than the subarachnoid space. We report a 3D-printed microelectromechanical system-based implantable valve to improve HCP treatment. This device provides an alternative approach targeting restoration of near-natural CSF dynamics by artificial arachnoid granulations (AGs), natural components for CSF drainage in the brain. The valve, made of hydrogel, aims to regulate the CSF flow between the subarachnoid space and the superior sagittal sinus, in essence, substituting for the obstructed arachnoid granulations. The valve, operating in a fully passive manner, utilizes the hydrogel swelling feature to create nonzero cracking pressure, P_T ≈ 47.4 ± 6.8 mmH₂O, as well as minimize reverse flow leakage, Q_O ≈ 0.7 μL/min on benchtop experiments. The additional measurements performed in realistic experimental setups using a fixed sheep brain also deliver comparable results, P_T ≈ 113.0 ± 9.8 mmH₂O and Q_O ≈ 3.7 μL/min. In automated loop functional tests, the valve maintains functionality for a maximum of 1536 cycles with the P_T variance of 44.5 mmH₂O < P_T < 61.1 mmH₂O and negligible average reverse flow leakage rates of ∼0.3 μL/min.

In vitro and numerical simulation of blood removal from cerebrospinal fluid: comparison of lumbar drain to Neurapheresis therapy

BACKGROUND

Blood removal from cerebrospinal fluid (CSF) in post-subarachnoid hemorrhage patients may reduce the risk of related secondary brain injury. We formulated a computational fluid dynamics (CFD) model to investigate the impact of a dual-lumen catheter-based CSF filtration system, called Neurapheresis™ therapy, on blood removal from CSF compared to lumbar drain.

METHODS

A subject-specific multiphase CFD model of CSF system-wide solute transport was constructed based on MRI measurements. The Neurapheresis catheter geometry was added to the model within the spinal subarachnoid space (SAS). Neurapheresis flow aspiration and return rate was 2.0 and 1.8 mL/min, versus 0.2 mL/min drainage for lumbar drain. Blood was modeled as a bulk fluid phase within CSF with a 10% initial tracer concentration and identical viscosity and density as CSF. Subject-specific oscillatory CSF flow was applied at the model inlet. The dura and spinal cord geometry were considered to be stationary. Spatial-temporal tracer concentration was quantified based on time-average steady-streaming velocities throughout the domain under Neurapheresis therapy and lumbar drain. To help verify CFD results, an optically clear in vitro CSF model was constructed with fluorescein used as a blood surrogate. Quantitative comparison of numerical and in vitro results was performed by linear regression of spatial-temporal tracer concentration over 24-h.

RESULTS

After 24-h, tracer concentration was reduced to 4.9% under Neurapheresis therapy compared to 6.5% under lumbar drain. Tracer clearance was most rapid between the catheter aspiration and return ports. Neurapheresis therapy was found to have a greater impact on steady-streaming compared to lumbar drain. Steady-streaming in the cranial SAS was ~ 50× smaller than in the spinal SAS for both cases. CFD results were strongly correlated with the in vitro spatial-temporal tracer concentration under Neurapheresis therapy (R² = 0.89 with + 2.13% and - 1.93% tracer concentration confidence interval).

CONCLUSION

A subject-specific CFD model of CSF system-wide solute transport was used to investigate the impact of Neurapheresis therapy on tracer removal from CSF compared to lumbar drain over a 24-h period. Neurapheresis therapy was found to substantially increase tracer clearance compared to lumbar drain. The multiphase CFD results were verified by in vitro fluorescein tracer experiments.

Enhanced in vitro model of the CSF dynamics

BACKGROUND

Fluid dynamics of the craniospinal system are complex and still not completely understood. In vivo flow and pressure measurements of the cerebrospinal fluid (CSF) are limited. Whereas in silico modeling can be an adequate pathway for parameter studies, in vitro modeling of the craniospinal system is essential for testing and evaluation of therapeutic measures associated with innovative implants relating to, for example, normal pressure hydrocephalus and other fluid disorders. Previously-reported in vitro models focused on the investigation of only one hypothesis of the fluid dynamics rather than developing a modular set-up to allow changes in focus of the investigation. The aim of this study is to present an enhanced and validated in vitro model of the CSF system which enables the future embedding of implants, the validation of in silico models or phase-contrast magnetic resonance imaging (PC-MRI) measurements and a variety of sensitivity analyses regarding pathological behavior, such as reduced CSF compliances, higher resistances or altered blood dynamics.

METHODS

The in vitro model consists of a ventricular system which is connected via the aqueduct to the cranial and spinal subarachnoid spaces. Two compliance chambers are integrated to cushion the arteriovenous blood flow generated by a cam plate unit enabling the modeling of patient specific flow dynamics. The CSF dynamics are monitored using three cranial pressure sensors and a spinal ultrasound flow meter. Measurements of the in vitro spinal flow were compared to cervical flow data recorded with PC-MRI from nine healthy young volunteers, and pressure measurements were compared to the literature values reported for intracranial pressure (ICP) to validate the newly developed in vitro model.

RESULTS

The maximum spinal CSF flow recorded in the in vitro simulation was 133.60 ml/min in the caudal direction and 68.01 ml/min in the cranial direction, whereas the PC-MRI flow data of the subjects showed 122.82 ml/min in the caudal and 77.86 ml/min in the cranial direction. In addition, the mean ICP (in vitro) was 12.68 mmHg and the pressure wave amplitude, 4.86 mmHg, which is in the physiological range.

CONCLUSIONS

The in vitro pressure values were in the physiological range. The amplitudes of the flow results were in good agreement with PC-MRI data of young and healthy volunteers. However, the maximum cranial flow in the in vitro model occurred earlier than in the PC-MRI data, which might be due to a lack of an in vitro dynamic compliance. Implementing dynamic compliances and related sensitivity analyses are major aspects of our ongoing research.

Effect of extradural constriction on CSF flow in rat spinal cord

Background

Fluid homeostasis in the central nervous system (CNS) is essential for normal neurological function. Cerebrospinal fluid (CSF) in the subarachnoid space and interstitial fluid circulation in the CNS parenchyma clears metabolites and neurotransmitters and removes pathogens and excess proteins. A thorough understanding of the normal physiology is required in order to understand CNS fluid disorders, including post-traumatic syringomyelia. The aim of this project was to compare fluid transport, using quantitative imaging of tracers, in the spinal cord from animals with normal and obstructed spinal subarachnoid spaces.

Methods

A modified extradural constriction model was used to obstruct CSF flow in the subarachnoid space at the cervicothoracic junction (C7–T1) in Sprague–Dawley rats. Alexa-Fluor 647 Ovalbumin conjugate was injected into the cisterna magna at either 1 or 6 weeks post–surgery. Macroscopic and microscopic fluorescent imaging were performed in animals sacrificed at 10 or 20 min post–injection. Tracer fluorescence intensity was compared at cervical and thoracic spinal cord levels between control and constriction animals at each post-surgery and post-injection time point. The distribution of tracer around arterioles, venules and capillaries was also compared.

Results

Macroscopically, the fluorescence intensity of CSF tracer was significantly greater in spinal cords from animals with a constricted subarachnoid space compared to controls, except at 1 week post-surgery and 10 min post-injection. CSF tracer fluorescence intensity from microscopic images was significantly higher in the white matter of constriction animals 1 week post surgery and 10 min post-injection. At 6 weeks post–constriction surgery, fluorescence intensity in both gray and white matter was significantly increased in animals sacrificed 10 min post-injection. At 20 min post-injection this difference was significant only in the white matter and was less prominent. CSF tracer was found predominantly in the perivascular spaces of arterioles and venules, as well as the basement membrane of capillaries, highlighting the importance of perivascular pathways in the transport of fluid and solutes in the spinal cord.

Conclusions

The presence of a subarachnoid space obstruction may lead to an increase in fluid flow within the spinal cord tissue, presenting as increased flow in the perivascular spaces of arterioles and venules, and the basement membranes of capillaries. Increased fluid retention in the spinal cord in the presence of an obstructed subarachnoid space may be a critical step in the development of post-traumatic syringomyelia.

Electronic supplementary material

The online version of this article (10.1186/s12987-019-0127-8) contains supplementary material, which is available to authorized users.

Micro-CT myelography using contrast-enhanced digital subtraction: feasibility and initial results in healthy rats

PURPOSE

The spinal subarachnoid space (SSAS) is vital for neural performance. Although models of spinal diseases and trauma are used frequently, no methods exist to obtain high-resolution myelograms in rodents. Thereby, our aim was to explore the feasibility of obtaining high-resolution micro-CT myelograms of rats by contrast-enhanced dual-energy (DE) and single-energy (SE) digital subtraction.

METHODS

Micro-CT contrast-enhanced DE and SE imaging protocols were implemented with live adult rats (total of 18 animals). For each protocol, contrast agents based on iodine (Iomeron® 400 and Fenestra® VC) and gold nanoparticles (AuroVist™ 15 nm) were tested. For DE, images at low- and high-energy settings were acquired after contrast injection; for SE, one image was acquired before and the other after contrast injection. Post-processing consisted of region of interest selection, image registration, weighted subtraction, and longitudinal alignment.

RESULTS

High-resolution myelograms were obtained with contrast-enhanced digital subtraction protocols. After qualitative and quantitative (contrast-to-noise ratio) analyses, we found that the SE acquisition protocol with Iomeron® 400 provides the best images. 3D contour renderings allowed visualization of SSAS and identification of some anatomical structures within it.

CONCLUSION

This in vivo study shows the potential of SE contrast-enhanced myelography for imaging SSAS in rat. This approach yields high-resolution 3D images without interference from adjacent anatomical structures, providing an innovative tool for further assessment of studies involving rat SSAS.

Progress in brain targeting drug delivery system by nasal route

The blood-brain barrier (BBB) restricts the transport of potential therapeutic moieties to the brain. Direct targeting the brain via olfactory and trigeminal neural pathways by passing the BBB has gained an important consideration for delivery of wide range of therapeutics to brain. Intranasal route of transportation directly delivers the drugs to brain without systemic absorption, thus avoiding the side effects and enhancing the efficacy of neurotherapeutics. Over the last several decades, different drug delivery systems (DDSs) have been studied for targeting the brain by the nasal route. Novel DDSs such as nanoparticles (NPs), liposomes and polymeric micelles have gained potential as useful tools for targeting the brain without toxicity in nasal mucosa and central nervous system (CNS). Complex geometry of the nasal cavity presented a big challenge to effective delivery of drugs beyond the nasal valve. Recently, pharmaceutical firms utilized latest and emerging nasal drug delivery technologies to overcome these barriers. This review aims to describe the latest development of brain targeted DDSs via nasal administration.

CHEMICAL COMPOUNDS STUDIED IN THIS ARTICLE

Carbopol 934p (PubChem CID: 6581) Carboxy methylcellulose (PubChem CID: 24748) Penetratin (PubChem CID: 101111470) Poly lactic-co-glycolic acid (PubChem CID: 23111554) Tween 80 (PubChem CID: 5284448).

A historical approach to the ventricular system of the brain

Introducción. El sistema ventricular encefálico se conoció, con parcialidad, en el siglo III a.C., fecha desde la que diversos investigadores contribuyeron a una mejor comprensión de dicho sistema, desentrañando sus ubicaciones en el sistema nervioso central y relacionándolos con ciertos aspectos funcionales que surgieron de conceptos filosóficos. Esto permitió un acercamiento más objetivo hacia las cavitaciones relacionadas con la formación de líquido cerebroespinal.Objetivo. Referenciar, de forma cronológica, los conceptos más trascendentes de la historia del sistema ventricular encefálico.Materiales y métodos. Se consultaron diversas fuentes bibliográficas relacionadas con el sistema ventricular, para después ordenarlas según su cronología, de modo que se concluyera con una aproximación más concreta de la morfología funcional del sistema ventricular.Conclusión. Aristóteles fue el primero en abordar el sistema ventricular encefálico, de modo que, conforme el paso de los años, su conocimiento se fue depurando en cuanto a organización, función y número de cavidades, hasta llegar a proponer la existencia de ocho ventrículos. En la actualidad se reconocen cinco ventrículos, de los cuales cuatro son componentes encefálicos: dos en cerebro, uno en diencéfalo, otro en tronco encefálico y un quinto en la parte terminal de la médula espinal.

Transependymal Cerebrospinal Fluid Flow: Opportunity for Drug Delivery?

Drug delivery to the central nervous system (CNS) is complicated by the blood-brain barrier. As a result, many agents that are found to be potentially effective at their site of action cannot be sufficiently or effectively delivered to the CNS and therefore have been discarded and not developed further for clinical use, leaving many CNS diseases untreated. One way to overcome this obstacle is intracerebroventricular (ICV) delivery of the therapeutics directly to cerebrospinal fluid (CSF). Recent experimental and clinical findings reveal that CSF flows from the ventricles throughout the parenchyma towards the subarachnoid space also named minor CSF pathway, while earlier, it was suggested that only in pathological conditions such as hydrocephalus this form of CSF flow occurs. This transependymal flow of CSF provides a route to distribute ICV-infused drugs throughout the brain. More insight on transependymal CSF flow will direct more rational to ICV drug delivery and broaden its clinical indications in managing CNS diseases.

Research into the Physiology of Cerebrospinal Fluid Reaches a New Horizon: Intimate Exchange between Cerebrospinal Fluid and Interstitial Fluid May Contribute to Maintenance of Homeostasis in the Central Nervous System

Cerebrospinal fluid (CSF) plays an essential role in maintaining the homeostasis of the central nervous system. The functions of CSF include: (1) buoyancy of the brain, spinal cord, and nerves; (2) volume adjustment in the cranial cavity; (3) nutrient transport; (4) protein or peptide transport; (5) brain volume regulation through osmoregulation; (6) buffering effect against external forces; (7) signal transduction; (8) drug transport; (9) immune system control; (10) elimination of metabolites and unnecessary substances; and finally (11) cooling of heat generated by neural activity. For CSF to fully mediate these functions, fluid-like movement in the ventricles and subarachnoid space is necessary. Furthermore, the relationship between the behaviors of CSF and interstitial fluid in the brain and spinal cord is important. In this review, we will present classical studies on CSF circulation from its discovery over 2,000 years ago, and will subsequently introduce functions that were recently discovered such as CSF production and absorption, water molecule movement in the interstitial space, exchange between interstitial fluid and CSF, and drainage of CSF and interstitial fluid into both the venous and the lymphatic systems. Finally, we will summarize future challenges in research. This review includes articles published up to February 2016.

Cord Cystic Cavities: Syringomyelia and Prominent Central Canal

Syringomyelia is the term given to cystic cavities in the spinal cord, most of which are associated with congenital malformations of the craniocervical junction and represent dilation of the central canal of the cord. As such, syrinxes can be considered analogous to hydrocephalus. The exact etiology of syrinx formation remains a subject of debate, but there is ample evidence that they are the result of obstruction of the normal flow of cerebrospinal fluid between the intracranial and spinal compartments. The chances that a syrinx will progress over time are much greater when they are associated with a causative lesion (Chiari malformation, tumor, infection, and trauma), but asymptomatic central canal dilation may be a stable incidental finding. Although spinal cord neoplasms are a recognized etiology for syrinx formation, especially in adults, it is not always necessary to administer contrast when evaluating a syrinx for the first time with magnetic resonance imaging.

Anatomy and physiology of cisternostomy

Cisternostomy is defined as opening the basal cisterns to atmospheric pressure. This technique helps to reduce the intracranial pressure in severe head trauma as well as other conditions when the so-called sudden "brain swelling" troubles the surgeon. We elaborated the surgical anatomy of this procedure as well as the proposed physiology of how cisternostomy works. This novel technique may change the current trends in neurosurgery.

Association of Aortic Stiffness With Cognition and Brain Aging in Young and Middle-Aged Adults: The Framingham Third Generation Cohort Study

Aortic stiffness is associated with cognitive decline and cerebrovascular disease late in life, although these associations have not been examined in young adults. Understanding the effects of aortic stiffness on the brain at a young age is important both from a pathophysiological and public health perspective. The aim of this study was to examine the cross-sectional associations of aortic stiffness with cognitive function and brain aging in the Framingham Heart Study Third Generation cohort (47% men; mean age, 46 years). Participants completed the assessment of aortic stiffness (carotid-femoral pulse wave velocity), a neuropsychological test battery assessing multiple domains of cognitive performance and magnetic resonance imaging to examine subclinical markers of brain injury. In adjusted regression models, higher aortic stiffness was associated with poorer processing speed and executive function (Trail Making B-A; β±SE, -0.08±0.03; P<0.01), larger lateral ventricular volumes (β±SE, 0.09±0.03; P<0.01) and a greater burden of white-matter hyperintensities (β±SE, 0.09±0.03; P<0.001). When stratifying by age, aortic stiffness was associated with lateral ventricular volume in young adults (30-45 years), whereas aortic stiffness was associated with white-matter injury and cognition in midlife (45-65 years). In conclusion, aortic stiffness was associated with cognitive function and markers of subclinical brain injury in young to middle-aged adults. Prospective studies are needed to examine whether aortic stiffening in young adulthood is associated with vascular cognitive impairment later in life.

MR assessment of pediatric hydrocephalus: a road map

PURPOSE

This study was conducted to design a rational approach to the MR diagnosis of hydrocephalus based on a pathophysiologic reevaluation of its possible mechanisms and to apply it to the different etiological contexts.

METHOD

A review of the literature reports describing new physiologic models of production and absorption and of the hydrodynamics of the CSF was made.

RESULTS

Besides the secretion of CSF by the choroid plexuses, and its passive, pressure-dependent transdural absorption (arachnoid villi, dural clefts, cranial, and spinal nerve sheaths), water transporters, aquaporins, allow water (if not ions and organic molecules) to exchange freely between the brain parenchyma and the CSF spaces across the ependymal and the pial interfaces (including the Virchow-Robin spaces). Consequently, the CSF bulk flow is not necessarily global, and situations of balanced absorption-secretion may occur separately in different CSF compartments such as the ventricular, intracranial, or intraspinal CSF spaces. This means that rather than from a hypothetical pressure gradient from the plexuses to the dural sinuses, the dynamics of the CSF depend on the force provided in those different compartments by the arterial systolic pulsation of the pericerebral (mostly), intracerebral, and intraventricular (choroid plexuses) vascular beds.

CONCLUSION

Using MR imaging, diverse varieties of hydrocephalus may tentatively be explained by applying those concepts to the correspondingly diverse causal diseases. Hopefully, this may have an impact on the choice of the treatment strategies also.

Monoamine Neurotransmitter Metabolite Concentration as a Marker of Cerebrospinal Fluid Volume Changes

OBJECTIVE

In our previous papers we demonstrated that changes in blood and cerebrospinal fluid (CSF) osmolarity have a strong influence on CSF pressure and volume, which is in accordance with a new proposed hypothesis of CSF physiology. Thus, acute changes in CSF volume should be reflected in the CSF concentration of different central nervous system (CNS) metabolites.

METHODS

In anesthetized cats (n = 4) we measured the outflow volume of CSF by cisternal free drainage at a negative CSF pressure (-10 cmH2O) before and after the intraperitoneal (i.p.) application of a hypo-osmolar substance (distilled water). In samples of CSF collected at different time intervals (30 min) we measured the concentration of homovanillic acid (HVA).

RESULTS

In spite of fact that constant CSF outflow volume was obtained after a 30-min period in our model, the concentration of HVA gradually increased over time and became stable after 90 min. After the i.p. application of distilled water the outflow CSF volume increased significantly, whereas the concentration of HVA significantly decreased over 30 min.

CONCLUSIONS

The results observed suggest that alterations in serum osmolarity change the CSF volume and concentrations of neurotransmitter metabolites because of the osmotic arrival of water from CNS blood capillaries in all CSF compartments.

Phase-contrast magnetic resonance imaging reveals net retrograde aqueductal flow in idiopathic normal pressure hydrocephalus

OBJECT The objective of this study was to assess the net aqueductal stroke volume (ASV) and CSF aqueductal flow rate derived from phase-contrast MRI (PC-MRI) in patients with probable idiopathic normal pressure hydrocephalus (iNPH) before and after ventriculoperitoneal shunt surgery, and to compare observations with intracranial pressure (ICP) scores. METHODS PC-MRI at the level of the sylvian aqueduct was undertaken in patients undergoing assessment for probable iNPH. Aqueductal flow in the craniocaudal direction was defined as positive, or antegrade flow, and net ASV was calculated by subtracting retrograde from antegrade aqueductal flow. Aqueductal flow rate per minute was calculated by multiplying net ASV by heart rate. During the same hospital admission, clinical examination was performed using NPH score and overnight continuous ICP monitoring. Twelve patients were followed prospectively 12 months after shunt placement with clinical assessment and a second PC-MRI. The study also included 2 healthy controls. RESULTS Among 21 patients examined for iNPH, 17 (81%) received a shunt (shunt group), and 4 were treated conservatively (conservative group). Among the patients with shunts, a clinical improvement was observed in 16 (94%) of the 17. Net ASV was negative in 16 (76%) of 21 patients before shunt placement and in 5 (42%) of 12 patients after shunt placement, and increased from a median of -5 μl (range -175 to 27 μl) to a median of 1 μl (range -61 to 30 μl; p = 0.04). Among the 12 patients with PC-MRI after shunt placement, 11 were shunt responders, and in 9 of these 11 either a reduced magnitude of retrograde aqueductal flow, or a complete reversal from retrograde to antegrade flow, occurred. Net ASV was significantly lower in the shunt group than in the conservative group (p = 0.01). The aqueductal flow rate increased from -0.56 ml/min (range -12.78 to 0.58 ml/min) to 0.06 ml/min (range -4.51 to 1.93 ml/min; p = 0.04) after shunt placement. CONCLUSIONS In this cohort of patients with iNPH, retrograde net aqueductal flow was observed in 16 (76%) of 21 patients. It was reversed toward the antegrade direction after shunt placement either by magnitude or completely in 9 (75%) of 12 patients examined using PC-MRI both before and after shunt placement (p = 0.04); 11 of the 12 were shunt responders. The study results question previously established concepts with respect to both CSF circulation pathways and CSF formation rate.

Evaluation of the Production and Absorption of Cerebrospinal Fluid

The traditional hypothesis of cerebrospinal fluid (CSF) hydrodynamics presumes that CSF is primarily produced in the choroid plexus (CP), then flows from the ventricles into the subarachnoid spaces, and mainly reabsorbed in the arachnoid granulations. This hypothesis is necessary to reconsider in view of recent research and clinical observations. This literature review presents numerous evidence for a new hypothesis of CSF hydrodynamics-(1) A significantly strong relationship exists between the CSF and interstitial fluid (IF), (2) CSF and IF are mainly produced and absorbed in the parenchymal capillaries of the brain and spinal cord. A considerable amount of CSF and IF are also absorbed by the lymphatic system, and (3) CSF movement is not unidirectional flow. It is only local mixing and diffusion.

Volumetric analysis of cerebrospinal fluid and brain parenchyma in a patient with hydranencephaly and macrocephaly--case report

The aim of this study was to perform for the first time the intracranial volumetric analysis of cerebrospinal fluid (CSF) and brain parenchyma in the supratentorial and infratentorial space in a 30-year-old female patient with hydranencephaly and macrocephaly. A head scan performed using a 3T magnetic resonance was followed by manual segmentation of the brain parenchyma and CSF on T2 coronal brain sections. The volume of CSF and brain parenchyma was measured separately for the supratentorial and infratentorial space. The total volume of the intracranial space was 3645.5 cm³. In the supratentorial space, the volume of CSF was 3375.2 cm³ and the volume of brain parenchyma was 80.3 cm³. In the infratentorial space, the volume of CSF was 101.3 cm³ and the volume of the brain parenchyma was 88.7 cm³. In the supratentorial space, there was severe malacia of almost all brain parenchyma with no visible remnants of the choroid plexuses. Infratentorial structures of the brainstem and cerebellum were hypoplastic but completely developed. Since our patient had no choroid plexuses in the supratentorial space and no obstruction between dural sinuses and CSF, development of hydrocephalus and macrocephaly cannot be explained by the classic hypothesis of CSF physiology with secretion, unidirectional circulation, and absorption as its basic postulates. However, the origin and turnover of the enormous amount of intracranial CSF volume, at least 10-fold larger than normal, and the mechanisms of macroencephaly development could be elucidated by the new hypothesis of CSF physiology recently published by our research team.

Porohyperelastic anatomical models for hydrocephalus and idiopathic intracranial hypertension

OBJECT

Brain deformation can be seen in hydrocephalus and idiopathic intracranial hypertension (IIH) via medical images. The phenomenology of local effects, brain shift, and raised intracranial pressure and herniation are textbook concepts. However, there are still uncertainties regarding the specific processes that occur when brain tissue is subject to the mechanical stress of different temporal and spatial profiles of the 2 neurological disorders. Moreover, recent studies suggest that IIH and hydrocephalus may be diseases with opposite pathogenesis. Nevertheless, the similarities and differences between the 2 subjects have not been thoroughly investigated.

METHODS

An anatomical porohyperelastic finite element model was used to assess the brain tissue responses associated with hydrocephalus and IIH. The same set of boundary conditions, with the exception of brain loading for development of the transmantle pressure gradient, was applied for the 2 models. The distribution of stress and strain during tissue distortion is described by the mechanical parameters.

RESULTS

The results of both the hydrocephalus and IIH models correlated with pathological characteristics. For the hydrocephalus model, periventricular edema was associated with the presence of positive volumetric strain and void ratio in the lateral ventricle horns. By contrast, the IIH model revealed edema across the cerebral mantle, including the centrum semiovale, with a positive void ratio and volumetric strain.

CONCLUSIONS

The model simulates all the clinical features in correlation with the MR images obtained in patients with hydrocephalus and IIH, thus providing support for the role of the transmantle pressure gradient and capillary CSF absorption in CSF-related brain deformation. The finite element methods can be used for a better understanding of the pathophysiological mechanisms of neurological disorders associated with parenchymal volumetric fluctuation.

Imaging of spontaneous ventriculomegaly and vascular malformations in Wistar rats: implications for preclinical research

Wistar rats are widely used in biomedical research and commonly serve as a model organism in neuroscience studies. In most cases when noninvasive imaging is not used, studies assume a consistent baseline condition in rats that lack visible differences. While performing a series of traumatic brain injury studies, we discovered mild spontaneous ventriculomegaly in 70 (43.2%) of 162 Wistar rats that had been obtained from 2 different vendors. Advanced magnetic resonance (MR) imaging techniques, including MR angiography and diffusion tensor imaging, were used to evaluate the rats. Multiple neuropathologic abnormalities, including presumed arteriovenous malformations, aneurysms, cysts, white matter lesions, and astrogliosis were found in association with ventriculomegaly. Postmortem microcomputed tomography and immunohistochemical staining confirmed the presence of aneurysms and arteriovenous malformations. Diffusion tensor imaging showed significant decreases in fractional anisotropy and increases in mean diffusivity, axial diffusivity, and radial diffusivity in multiple white matter tracts (p < 0.05). These results could impact the interpretation, for example, of a pseudo-increase of axon integrity and a pseudo-decrease of myelin integrity, based on characteristics intrinsic to rats with ventriculomegaly. We suggest the use of baseline imaging to prevent the inadvertent introduction of a high degree of variability in preclinical studies of neurologic disease or injury in Wistar rats.

The Role of Circulating Tight Junction Proteins in Evaluating Blood Brain Barrier Disruption following Intracranial Hemorrhage

Brain injury after intracranial hemorrhage (ICH) results in significant morbidity and mortality. Blood brain barrier (BBB) disruption is a hallmark of ICH-induced brain injury; however, data mirroring BBB disruption in human ICH are scarce. The aim of this study was to assess the significance of circulating biomarkers in evaluating BBB disruption after ICH. Twenty-two patients with ICH were recruited in this study. Concentrations of the tight junction proteins (TJs) Claudin-5 (CLDN5), Occludin (OCLN), and zonula occludens 1 (ZO-1) and vascular endothelial growth factor (VEGF) and matrix metalloproteinase-9 (MMP-9) were measured by using enzyme-linked immunosorbent assay in serum and cerebrospinal fluid (CSF) samples obtained from patients with ICH. The white blood cell (WBC) count in blood and CSF, albumin (ALB) levels in the CSF (ALBCSF), and the BBB ratio were significantly higher in the ICH than in controls (p < 0.05). Significantly higher levels of CLDN5, OCLN, ZO-1, MMP-9, and VEGF in CSF were observed in the ICH group; these biomarkers were also positively associated with BBB ratio (p < 0.05). Our data revealed that circulating TJs could be considered the potential biomarkers reflecting the integrity of the BBB in ICH.