Brain Material Properties and Integration of Arachnoid Complex for Biofidelic Impact Response for Human Head Finite Element Model.

Finite element head models offer great potential to study brain-related injuries; however, at present may be limited by geometric and material property simplifications required for continuum-level human body models. Specifically, the mechanical properties of the brain tissues are often represented with simplified linear viscoelastic models, or the material properties have been optimized to specific impact cases. In addition, anatomical structures such as the arachnoid complex have been omitted or implemented in a simple lumped manner. Recent material test data for four brain regions at three strain rates in three modes of loading (tension, compression, and shear) was used to fit material parameters for a hyper-viscoelastic constitutive model. The material model was implemented in a contemporary detailed head finite element model. A detailed representation of the arachnoid trabeculae was implemented with mechanical properties based on experimental data. The enhanced head model was assessed by re-creating 11 ex vivo head impact scenarios and comparing the simulation results with experimental data. The hyper-viscoelastic model faithfully captured mechanical properties of the brain tissue in three modes of loading and multiple strain rates. The enhanced head model showed a high level of biofidelity in all re-created impacts in part due to the improved brain-skull interface associated with implementation of the arachnoid trabeculae. The enhanced head model provides an improved predictive capability with material properties based on tissue level data and is positioned to investigate head injury and tissue damage in the future.

Influence of pia-arachnoid complex on the indentation response of porcine brain at different length scales.

Brain tissues are surrounded by two tightly adhering thin membranes known as the pia-arachnoid complex (PAC), which is pivotal in regulating brain mechanical response upon mechanical impact. Despite the crucial role of PAC as a structural damper protecting the brain, its mechanical contribution has received minimal attention. In this work, the mechanical contribution of PAC on brain tissues against mechanical loading is characterized by using a custom-built indentation apparatus. The indentation responses of the isolated and PAC-overlaid brains are quantitatively compared at different length scales and strain rates. Results show that PAC substantially affects the indentation response of brain tissues at micro- and macro-scales and provides better protection against mechanical impact at a relatively small (µm) length scale. The modulus of the PAC-overlaid brain shows a threefold stiffening at the microscale compared with that of the isolated brain (with instantaneous shear modulus distribution means of 0.85 ± 0.14 kPa versus 2.64 ± 0.43 kPa at the strain rate of 0.64 s-1 and 1.40 ± 0.31 kPa versus 4.02 ± 0.51 at 1.27 s-1). These findings indicate that PAC seriously affects the mechanical response of brain tissues, especially at the microscale, and may have important implications for the studies of brain injury.

Cerebrospinal fluid outflow: a review of the historical and contemporary evidence for arachnoid villi, perineural routes, and dural lymphatics.

Cerebrospinal fluid (CSF) is produced by the choroid plexuses within the ventricles of the brain and circulates through the subarachnoid space of the skull and spinal column to provide buoyancy to and maintain fluid homeostasis of the brain and spinal cord. The question of how CSF drains from the subarachnoid space has long puzzled scientists and clinicians. For many decades, it was believed that arachnoid villi or granulations, outcroppings of arachnoid tissue that project into the dural venous sinuses, served as the major outflow route. However, this concept has been increasingly challenged in recent years, as physiological and imaging evidence from several species has accumulated showing that tracers injected into the CSF can instead be found within lymphatic vessels draining from the cranium and spine. With the recent high-profile rediscovery of meningeal lymphatic vessels located in the dura mater, another debate has emerged regarding the exact anatomical pathway(s) for CSF to reach the lymphatic system, with one side favoring direct efflux to the dural lymphatic vessels within the skull and spinal column and another side advocating for pathways along exiting cranial and spinal nerves. In this review, a summary of the historical and contemporary evidence for the different outflow pathways will be presented, allowing the reader to gain further perspective on the recent advances in the field. An improved understanding of this fundamental physiological process may lead to novel therapeutic approaches for a wide range of neurological conditions, including hydrocephalus, neurodegeneration and multiple sclerosis.

Mechanical Properties of the Cranial Meninges: A Systematic Review.

The meninges are membranous tissues that are pivotal in maintaining homeostasis of the central nervous system. Despite the importance of the cranial meninges in nervous system physiology and in head injury mechanics, our knowledge of the tissues' mechanical behavior and structural composition is limited. This systematic review analyzes the existing literature on the mechanical properties of the meningeal tissues. Publications were identified from a search of Scopus, Academic Search Complete, and Web of Science and screened for eligibility according to Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. The review details the wide range of testing techniques employed to date and the significant variability in the observed experimental findings. Our findings identify many gaps in the current literature that can serve as a guide for future work for meningeal mechanics investigators. The review identifies no peer-reviewed mechanical data on the falx and tentorium tissues, both of which have been identified as key structures in influencing brain injury mechanics. A dearth of mechanical data for the pia-arachnoid complex also was identified (no experimental mechanics studies on the human pia-arachnoid complex were identified), which is desirable for biofidelic modeling of human head injuries. Finally, this review provides recommendations on how experiments can be conducted to allow for standardization of test methodologies, enabling simplified comparisons and conclusions on meningeal mechanics.

Ex-vivo quantification of ovine pia arachnoid complex biomechanical properties under uniaxial tension.

BACKGROUND: The pia arachnoid complex (PAC) is a cerebrospinal fluid-filled tissue conglomerate that surrounds the brain and spinal cord. Pia mater adheres directly to the surface of the brain while the arachnoid mater adheres to the deep surface of the dura mater. Collagen fibers, known as subarachnoid trabeculae (SAT) fibers, and microvascular structure lie intermediately to the pia and arachnoid meninges. Due to its structural role, alterations to the biomechanical properties of the PAC may change surface stress loading in traumatic brain injury (TBI) caused by sub-concussive hits. The aim of this study was to quantify the mechanical and morphological properties of ovine PAC. METHODS: Ovine brain samples (n = 10) were removed from the skull and tissue was harvested within 30 min post-mortem. To access the PAC, ovine skulls were split medially from the occipital region down the nasal bone on the superior and inferior aspects of the skull. A template was used to remove arachnoid samples from the left and right sides of the frontal and occipital regions of the brain. 10 ex-vivo samples were tested with uniaxial tension at 2 mm s-1, average strain rate of 0.59 s-1, until failure at < 5 h post extraction. The force and displacement data were acquired at 100 Hz. PAC tissue collagen fiber microstructure was characterized using second-harmonic generation (SHG) imaging on a subset of n = 4 stained tissue samples. To differentiate transverse blood vessels from SAT by visualization of cell nuclei and endothelial cells, samples were stained with DAPI and anti-von Willebrand Factor, respectively. The Mooney-Rivlin model for average stress-strain curve fit was used to model PAC material properties. RESULTS: The elastic modulus, ultimate stress, and ultimate strain were found to be 7.7 ± 3.0, 2.7 ± 0.76 MPa, and 0.60 ± 0.13, respectively. No statistical significance was found across brain dissection locations in terms of biomechanical properties. SHG images were post-processed to obtain average SAT fiber intersection density, concentration, porosity, tortuosity, segment length, orientation, radial counts, and diameter as 0.23, 26.14, 73.86%, 1.07 ± 0.28, 17.33 ± 15.25 µm, 84.66 ± 49.18°, 8.15%, 3.46 ± 1.62 µm, respectively. CONCLUSION: For the sizes, strain, and strain rates tested, our results suggest that ovine PAC mechanical behavior is isotropic, and that the Mooney-Rivlin model is an appropriate curve-fitting constitutive equation for obtaining material parameters of PAC tissues.

Investigation of wave propagation through head layers with focus on understanding blast wave transmission.

Blast-induced traumatic brain injury (bTBI) is a critical health concern. This issue is being addressed in terms of identifying a cause-effect relationship between the mechanical insult in the form of a blast and resulting injury to the brain. Understanding wave propagation through the head is an important aspect in this regard. The objective of this work was to study the blast wave propagation through the layered architecture of the head with an emphasis on understanding the wave transmission mechanism. Toward this end, one-dimensional (1D) finite element head model is built for a simplified surrogate, human, and rat. Motivated from experimental investigations, four different head layer configurations have been considered. These configurations are: (A) Skull-Brain, (B) Skin-Skull-Brain, (C) Skin-Skull-Dura-Arachnoid-CSF-Pia-Brain, (D) Skin-Skull-Dura-Arachnoid-AT-Pia-Brain. The validated head model is subjected to flattop and Friedlander loading implied in the blast, and the resulting response is evaluated in terms of brain pressures. Our results suggest that wave propagation through head parenchyma plays an important role in blast wave transmission. The thickness, material properties of head layers, and rise time of an input pulse govern the temporal evolution of pressure in the brain. The key findings of this work are: (a) Skin and meninges amplify the applied input pressure, whereas air sinus has an attenuation effect. (b) Model is able to describe experimentally recorded peak pressures and rise times in the brain, including variations within the aforementioned experimental head models of TBI. This reinforces that the wave transmission is an important loading pathway to the brain. (c) Equivalent layer theory for modeling meningeal layers as a single layer has been proposed, and it gives reasonable agreement with each meningeal layer modeled explicitly. This modeling approach has a great utility in 3D head models. The potential applications of 1D head model in evaluation of new helmet materials, brain sensor calibration, and brain pressure estimation for a given explosive strength have also been demonstrated. Overall, these results provide important insights into the understanding of mechanics of blast wave transmission in the head.

Micromechanical heterogeneity of the rat pia-arachnoid complex.

To better understand the onset of damage occurring in the brain upon traumatic events, it is essential to analyze how external mechanical loads propagate through the skull and meninges and down to the brain cortex. However, despite their crucial role as structural dampers protecting the brain, the mechanical properties and dynamic behavior of the meningeal layers are still poorly understood. Here, we characterized the local mechanical heterogeneity of rat pia-arachnoid complex (PAC) at the microscale via atomic force microscopy (AFM) indentation experiments to understand how microstructural variations at the tissue level can differentially affect load propagation. By coupling AFM mechanical testing with fresh tissue immunofluorescent staining, we could directly observe the effect of specific anatomical features on the local mechanical properties of tissue. We observed a two-fold stiffening of vascularized tissue when compared to non-vascularized PAC (with instantaneous Young's modulus distribution means of 1.32  ±â€¯ 0.03 kPa and 2.79  ±â€¯ 0.08 kPa, respectively), and statistically significant differences between regions of low- and high-vimentin density, reflecting trabecular density (with means of 0.67  ±â€¯ 0.05 kPa and 1.29  ±â€¯ 0.06 kPa, respectively). No significant differences were observed between cortical and cerebellar PAC. Additionally, by performing force relaxation experiments at the AFM, we identified the characteristic time constant τ1 of PAC tissue to be in the range of 2.7  ±â€¯ 1.2 s to 3.1  ±â€¯ 0.9 s for the different PAC regions analyzed. Taken together, the results presented point at the complex biomechanical nature of the meningeal tissue, and underscore the need to account for its heterogeneity when modeling its behavior into finite element simulations or other computational methods enabling the prediction of load propagation during injury events. STATEMENT OF SIGNIFICANCE: The meningeal layers are pivotal in shielding the brain during injury events, yet the mechanical properties of this complex biological interface are still under investigation. Here, we present the first anatomically-informed micromechanical characterization of mammalian pia-arachnoid complex (PAC). We developed a protocol for the isolation and fresh immunostaining of rat PAC and subjected the tissue to AFM indentation and relaxation experiments, while visualizing the local anatomy via fluorescence microscopy. We found statistically significant variations in regional PAC stiffness according to the degree of vascularization and trabecular cell density, besides identifying the tissue's characteristic relaxation constant. In essence, this study captures the relationship between anatomy and mechanical heterogeneity in a key component of the brain-skull interface for the first time.

Outflow of cerebrospinal fluid is predominantly through lymphatic vessels and is reduced in aged mice.

Cerebrospinal fluid (CSF) has been commonly accepted to drain through arachnoid projections from the subarachnoid space to the dural venous sinuses. However, a lymphatic component to CSF outflow has long been known. Here, we utilize lymphatic-reporter mice and high-resolution stereomicroscopy to characterize the anatomical routes and dynamics of outflow of CSF. After infusion into a lateral ventricle, tracers spread into the paravascular spaces of the pia mater and cortex of the brain. Tracers also rapidly reach lymph nodes using perineural routes through foramina in the skull. Using noninvasive imaging techniques that can quantify the transport of tracers to the blood and lymph nodes, we find that lymphatic vessels are the major outflow pathway for both large and small molecular tracers in mice. A significant decline in CSF lymphatic outflow is found in aged compared to young mice, suggesting that the lymphatic system may represent a target for age-associated neurological conditions.

The influence of fibroblast on the arachnoid leptomeningeal cells in vitro.

OBJECTIVE: Fibroblast is pervasive in the setting of injury. Its invasion into the arachnoid tissue causes scarring, cortical adhesion of the brain, and obstruction of cerebrospinal fluid outflow. The purpose of this study is to determine the phenotypic and physiologic effects of fibroblasts on arachnoid in culture. METHODS: We studied the effects of fibroblast on the arachnoid cell growth, motility, phenotypic changes, and transport properties. Immortalized rat (Rattus norvegicus, Sprague Dawley breed) arachnoid cells were grown with fibroblast on opposite sides of polyethylene membranes or co-cultured in plastic wells. Arachnoid cell growth rate and DNA content, morphology, transport physiology, and extracellular matriceal content were determined in the presence of normal and irradiated fibroblast cells. RESULTS: When arachnoid cells were grown in the presence of fibroblasts, mannitol permeability increased and transepithelial electrical resistance (TEER) decreased. Arachnoid cell growth rate also significantly decreased. When arachnoid cells were grown in close proximity (i.e. on the same monolayer) with fibroblasts, the arachnoid cells were overrun by day 2, yet when physically separated, no significant change was seen in growth. Apoptosis increased markedly in arachnoid cultures in the presence of fibroblast. Fibroblast caused arachnoid cell to exhibit avoidance behavior, and irradiated fibroblast induced arachnoidal cells to move faster and exhibited greater directional changes. Subcellular glycosaminoglycan (GAG) content was significantly altered by fibroblast. INTERPRETATION: Fibroblasts influence arachnoid cell's mannitol transport likely via soluble factors. While the arachnoid cells did not change morphologically, cell growth was influenced. Over time, the cells had profound changes in transport and motility. The immortalized arachnoid cell/fibroblast culture system provides a unique model mimicking the pathologic event of leptomeningeal scarring.

Pathways of cerebrospinal fluid outflow: a deeper understanding of resorption.

INTRODUCTION: Cerebrospinal fluid (CSF) absorption has long been held to predominantly entail drainage into the venous outflow system via the intracranial arachnoid granulations. Newer data suggest pathways involving spinal arachnoid granulations and lymphatic channels may also make substantial contributions to CSF outflow. METHODS: The putative major CSF outflow pathways and their proportionate contribution to CSF absorption were reviewed in this article. RESULTS: CSF is absorbed and drained in bulk not just through cerebral arachnoid granulations (CAG) but also through spinal arachnoid granulations (SAG) and a lymphatic pathway involving egress through cranial and spinal nerve sheaths. The proportions of CSF that efflux through each of these major pathways have yet to be determined with any certainty in humans, though existing evidence (the majority of which is derived from animal studies) suggests that lymphatic pathways may account for up to 50% of CSF outflow-presumably leaving the CAG and SAG to process the balance. CONCLUSION: Knowledge of the CSF pathways holds implications for our ability to understand, prognose, and even treat diseases related to CSF circulation and so is a matter of considerable relevance to neuroradiology and neurology.

Cranial arachnoid protrusions and contiguous diploic veins in CSF drainage.

BACKGROUND AND PURPOSE: Studies have suggested that arachnoid villi or granulations found in the walls of the cranial dural sinuses, olfactory mucosa, and cranial nerve sheaths function as outlets for intracranial CSF. However, their role as CSF outlets has not yet been verified. Here we show that arachnoid protrusions and contiguous diploic veins provide an alternative drainage route for intracranial CSF. MATERIALS AND METHODS: Four hundred patients with intact skull, dura mater, and dural sinuses underwent MR imaging to explore arachnoids protruding into the skull and diploic veins. Patients with symptoms of increased intracranial pressure or intracranial hypotension were excluded. For 15 patients undergoing craniotomy, both peripheral and diploic venous blood was collected. Albumin and the CSF-specific biomarkers were measured by enzyme-linked immunosorbent assay. RESULTS: With MR imaging, arachnoid protrusions into the skull and contiguous diploic veins were consistently identified throughout the cranium with their characteristic appearance depending on the cranial region. In addition, elevated amounts of prostaglandin D synthase and cystatin C were confirmed in diploic veins compared with peripheral venous blood. CONCLUSIONS: Diploic veins are distributed ubiquitously throughout the cranium. A portion of the intracranial CSF may be drained through arachnoid protrusions and contiguous diploic veins.

Constitutive modeling of pia-arachnoid complex.

The pia-arachnoid complex (PAC) covering the brain plays an important role in the mechanical response of the brain during impact or inertial loading. Recent studies have revealed the complicated material behavior of the PAC. In this study, the nonlinear viscoelastic, transversely isotropic material properties of the PAC were modeled as Mooney-Rivlin ground substance with collagen fibers strengthening within the meningeal plane through an exponential model. The material constants needed were determined using experimental data from in-plane tension, normal traction, and shear tests conducted on bovine specimens. Results from this study provide essential information to properly model the PAC membrane, an important component in the skull/brain interface, in a computational brain model. Such an improved representation of the skull/brain interface will enhance the accuracy of finite element models used in brain injury mechanism studies under various loading conditions.

Novel therapeutic use of polysaccharide nanosheets for arachnoid plasty and enhancement of venous tensile strength in rat microneurosurgery.

Subdural effusion sometimes occurs during neurosurgery after opening the Sylvian fissure, due to cerebrospinal fluid (CSF) leakage from the torn arachnoid membrane. Unexpected bleeding from the fragile bridging veins may also result from brain retraction. Neurosurgeons must always watch carefully for these complications during surgery. To prevent such complications, we have attempted the clinical application of a polysaccharide nanosheet that is semi-absorbent and has a potent physical adhesive strength to investigate its therapeutic utility for arachnoid plasty and enhancement of bridging vein tensile strength in Sprague-Dawley rats. The use of overlapping nanosheets completely prevented CSF leakage from injured arachnoid membranes in the cerebral cortex. No inflammatory infiltration was observed on the cerebral surface after 6 months of follow up. In addition, the use of nanosheet bandages significantly reinforced venous tensile strength. This reinforcement increased with the number of overlaid nanosheets. We report that polysaccharide nanosheets can be used for arachnoid plasty without chemical bonding agents and for reinforcement of venous tensile strength in rat vessels. Nanosheets may be an effective neurosurgical tool.

Immortalization and functional characterization of rat arachnoid cell lines.

Modeling the behavior of mammalian arachnoid cells is critical to understand hydrocephalus and other brain disorders involving abnormal flow of cerebrospinal fluid, yet relatively little is known about the physiology of arachnoid cells due to lack of a robust three-dimensional model system. Explanted primary cultures have been the only option to study transport across arachnoid cell membranes, but practical limitations of primary culture include slow growth, early senescence, and poor reproducibility. The purpose of this study was to create immortalized rat arachnoid cell lines to permit in vitro study of arachnoid granulations and properties of cerebrospinal fluid (CSF) flow. We established and partially characterized two immortalized cell lines generated from primary rat arachnoid cells, using retroviral gene transfer of SV40 large T antigen (SV40 LTAg) either with or without human telomerase (hTERT). The established cell lines stably express either SV40 LTAg alone, or SV40 LTAg and hTERT, and demonstrate high proliferative rate, contact inhibition at confluence, and stable expression of protein markers characteristic of native arachnoid cells over more than 160 passages.

Microsurgical anatomy of Liliequist's membrane demonstrating three-dimensional configuration.

OBJECT: Liliequist's membrane (LM) is an important arachnoid structure in the basal cisterns. The relevant anatomic descriptions of this membrane and how many leaves it has are still controversial. The existing anatomical theories do not satisfy the needs of minimally invasive neurosurgery. We aimed to establish the three-dimensional configuration of LM. METHODS: Fifteen adult formalin-fixed cadaver heads were dissected under a surgical microscope to carefully observe the arachnoid mater in the suprasellar and post-sellar areas and to investigate the arachnoid structure and its surrounding attachments. RESULTS: It was found that the LM actually consists of three types of membranes. The diencephalic membrane (DM) was usually attached by the mesencephalic membrane (MM) from underneath, and above DM it was usually a pair of hypothalamic membranes (HMs) extending superomedially. The pair of HMs was stretched between the DM (or MM) and the hypothalamus and were seldom attached to the carotid-chiasmatic walls between the carotid cistern and the chiasmatic cistern. These three types of membranes (DM, MM, and HM) comprised the main arachnoid structure in the anterior incisural space and often presented as four connected leaves. However, only two thirds of the specimens had all three types of membranes, and there was considerable variation in the characteristics and shapes of the membranes among the specimens. CONCLUSION: All three types of membranes comprising LM serve as important anatomical landmarks and interfaces for surgical procedures in this area.

Mechanical properties of bovine pia-arachnoid complex in shear.

Traumatic brain injury (TBI) has become a major public health and socioeconomic problem that affects 1.5 million Americans annually. Finite element methods have been widely used to investigate TBI mechanisms. The pia-arachnoid complex (PAC) covering the brain plays an important role in the mechanical response of the brain during impact or inertial loading. Existing finite element brain models have tended to oversimplify the response of the PAC due to a lack of accurately defined material properties of this structure, possibly resulting in a loss of accuracy in the model predictions. The objectives of this study were to experimentally determine the material properties of the PAC under shear loading. Bovine PAC was selected in the current study in view of its availability and comparability with previous studies. Tangential shear tests were conducted at 0.8, 7.3, and 72 s(-1). The mean shear moduli were 11.73, 20.04, and 22.37 kPa at the three strain rates tested. The ultimate stress, at the three strain rates, was 9.21, 17.01, and 22.26 kPa, while the ultimate strain was 1.52, 1.58, and 1.81. Results from the current study provide essential information to properly model the PAC membrane, an important component in the skull/brain interface, in a computational model of the human/animal head. Such an improved representation of the in vivo skull/brain interface will enhance future studies investigating brain injury mechanisms under various loading conditions.

Cerebrospinal fluid dynamics in the human cranial subarachnoid space: an overlooked mediator of cerebral disease. II. In vitro arachnoid outflow model.

The arachnoid membrane (AM) and granulations (AGs) are important in cerebrospinal fluid (CSF) homeostasis, regulating intracranial pressure in health and disease. We offer a functional perspective of the human AM's transport mechanism to clarify the role of AM in the movement of CSF and metabolites. Using cultures of human AG cells and a specialized perfusion system, we have shown that this in vitro model mimics the in vivo characteristics of unidirectional fluid transport and we present the first report of serum-free permeability values (92.5 microl min(-1) mm Hg(-1) cm(-2)), which in turn are in agreement with the CSF outflow rates derived from a dynamic, in vivo magnetic resonance imaging-based computational model of the subarachnoid cranial space (130.9 microl min(-1) mm Hg(-1) cm(-2)). Lucifer yellow permeability experiments have verified the maintenance of tight junctions by the arachnoidal cells with a peak occurring around 21 days post-seeding, which is when all perfusion experiments were conducted. Addition of ruthenium red to the perfusate, and subsequent analysis of its distribution post-perfusion, has verified the passage of perfusate via both paracellular and transcellular mechanisms with intracellular vacuoles of approximately 1 microm in diameter being the predominant transport mechanism. The comparison of the computational and in vitro models is the first report to measure human CSF dynamics functionally and structurally, enabling the development of innovative approaches to modify CSF outflow and will change concepts and management of neurodegenerative diseases resulting from CSF stagnation.

Microsurgical and endoscopic anatomy of the supratentorial arachnoidal membranes and cisterns.

OBJECTIVE: A limitation of previous studies of the arachnoid cisterns and membranes is that the act of opening the sylvian and interhemispheric fissures and basal arachnoid often led to destruction of the cisternal compartments and their membranous walls. The goal of this study was to overcome this limitation by combining the surgical microscope and endoscope for the examination of the cisternal compartments and their membranous walls. METHODS: The supratentorial cisterns were examined in 22 cadaveric brains using both the operating microscope and the endoscope. RESULTS: There are 2 types of arachnoid membranes: outer and inner. The outer arachnoidal membrane surrounds the whole brain, and the inner membranes divide the subarachnoid space into cisterns. Twelve inner arachnoid membranes were identified in the supratentorial area: diencephalic, mesencephalic, medial carotid, intracarotid, intracrural, olfactory, medial and lateral lamina terminalis, and proximal, medial, intermediate, and lateral sylvian membranes. These membranes partially or completely separate the subarachnoid space into 9 supratentorial cisterns: sylvian, carotid, chiasmatic, lamina terminalis, pericallosal, crural, ambient, oculomotor, and interpeduncular. There is a confluent area between the carotid, interpeduncular, and crural cisterns, which frequently has no membrane separating these cisterns. CONCLUSION: Twelve inner arachnoid membranes and 9 cisterns were identified in this study.

Characterization of arachnoidal cells cultured on three-dimensional nonwoven PET matrix.

PURPOSE: To culture physiologically functional primary arachnoidal cells on a suitable polymer substrate for an in-vitro model of the cerebrospinal fluid outflow pathway. METHODS: Primary cultures of arachnoidal cells were prepared within 24 hours post-mortem from brain tissue obtained from human cadavers at autopsy. Arachnoidal cells were characterized using immunocytochemistry and seeded onto needle punched non-woven poly(ethylene terephthalate)(PET) scaffolds. Metabolic rate, cell growth rate in log phase, morphologic assessment, immunocytochemistry, and protein analysis were used to characterize the cultures in both 2-D and 3-D-culture. Functional outflow assessment was performed using the Lucifer Yellow (LY) permeability assay and hydraulic conductivity (Lp) determination. RESULTS: Cells cultured on PET scaffold grew slightly slower than cells grown in 2-D-culture as measured by metabolic rate and growth rate, however, they often formed sheets that bridged between the adjacent scaffold filaments forming many junctional protein connections. LY permeability coefficients of 2-D cells were compared with cells from scaffolds, and were not significantly different (p > 0.05) for both culture conditions. Average Lp of cells from 2-D-culture and 3-D-scaffolds were compared and shown not to be significantly different. CONCLUSION: Based on the biochemical and functional analysis, it has been shown that cells cultured on 3D-PET scaffolds retained the same properties as cells from 2D-culture plates.