Anatomy and Imaging of the Normal Meninges

Functional analysis and transcriptome profile of meninges and skin fibroblasts from human-aged donors

The central nervous system (CNS) is surrounded by three membranes called meninges. Specialised fibroblasts, originating from the mesoderm and neural crest, primarily populate the meninges and serve as a binding agent. Our goal was to compare fibroblasts from meninges and skin obtained from the same human-aged donors, exploring their molecular and cellular characteristics related to CNS functions. We isolated meningeal fibroblasts (MFs) from brain donors and skin fibroblasts (SFs) from the same subjects. A functional analysis was performed measuring cell appearance, metabolic activity, and cellular orientation. We examined fibronectin, serpin H1, β-III-tubulin, and nestin through qPCR and immunofluorescence. A whole transcriptome analysis was also performed to characterise the gene expression of MFs and SFs. MFs appeared more rapidly in the post-tissue processing, while SFs showed an elevated cellular metabolism and a well-defined cellular orientation. The four markers were mostly similar between the MFs and SFs, except for nestin, more expressed in MFs. Transcriptome analysis reveals significant differences, particularly in cyclic adenosine monophosphate (cAMP) metabolism and response to forskolin, both of which are upregulated in MFs. This study highlights MFs' unique characteristics, including the timing of appearance, metabolic activity, and gene expression patterns, particularly in cAMP metabolism and response to forskolin. These findings contribute to a deeper understanding of non-neuronal cells' involvement in CNS activities and potentially open avenues for therapeutic exploration.

Anatomical correlates for the newly discovered meningeal layer in the existing literature: A systematic review

The existence of a previously unrecognized subarachnoid lymphatic-like membrane (SLYM) was reported in a recent study. SLYM is described as an intermediate leptomeningeal layer between the arachnoid and pia mater in mouse and human brains, which divides the subarachnoid space (SAS) into two functional compartments. Being a macroscopic structure, having missed detection in previous studies is surprising. We systematically reviewed the published reports in animals and humans to explore whether prior descriptions of this meningeal layer were reported in some way. A comprehensive search was conducted in PubMed/Medline, EMBASE, Google Scholar, Science Direct, and Web of Science databases using combinations of MeSH terms and keywords with Boolean operators from inception until 31 December 2023. We found at least eight studies that provided structural evidence of an intermediate leptomeningeal layer in the brain or spinal cord. However, unequivocal descriptions for this layer all along the central nervous system were scarce. Obscure names like the epipial, intermediate meningeal, outer pial layers, or intermediate lamella were used to describe it. Its microscopic/ultrastructural details closely resemble the recently reported SLYM. We further examined the counterarguments in current literature that are skeptical of the existence of this layer. The potential physiological and clinical implications of this new meningeal layer are significant, underscoring the urgent need for further exploration of its structural and functional details.

A novel perspective of calvarial development: the cranial morphogenesis and differentiation regulated by dura mater

There are lasting concerns on calvarial development because cranium not only accommodates the growing brain, but also safeguards it from exogenous strikes. In the past decades, most studies attributed the dynamic expansion and remodeling of cranium to the proliferation of osteoprecursors in cranial primordium, and the proliferation of osteoprogenitors at the osteogenic front of cranial suture mesenchyme. Further investigations identified series genes expressed in suture mesenchymal cells as the markers of the progenitors, precursors and postnatal stem cells in cranium. However, similar to many other organs, it is suggested that the reciprocal interactions among different tissues also play essential roles in calvarial development. Actually, there are increasing evidence indicating that dura mater (DM) is indispensable for the calvarial morphogenesis and osteogenesis by secreting multiple growth factors, cytokines and extracellular matrix (ECM). Thus, in this review, we first briefly introduce the development of cranium, suture and DM, and then, comprehensively summarize the latest studies exploring the involvement of ECM in DM and cranium development. Eventually, we discussed the reciprocal interactions between calvarium and DM in calvarial development. Actually, our review provides a novel perspective for cranium development by integrating previous classical researches with a spotlight on the mutual interplay between the developing DM and cranium.

Proteomic interrogation of the meninges reveals the molecular identities of structural components and regional distinctions along the CNS axis

The meninges surround the brain and spinal cord, affording physical protection while also serving as a niche of neuroimmune activity. Though possessing stromal qualities, its complex cellular and extracellular makeup has yet to be elaborated, and it remains unclear whether the meninges vary along the neuroaxis. Hence, studies were carried-out to elucidate the protein composition and structural organization of brain and spinal cord meninges in normal, adult Biozzi ABH mice. First, shotgun, bottom-up proteomics was carried-out. Prominent proteins at both brain and spinal levels included Type II collagen and Type II keratins, representing extracellular matrix (ECM) and cytoskeletal categories, respectively. While the vast majority of total proteins detected was shared between both meningeal locales, more were uniquely detected in brain than in spine. This pattern was also seen when total proteins were subdivided by cellular compartment, except in the case of the ECM category where brain and spinal meninges each had near equal number of unique proteins, and Type V and type III collagen registered exclusively in the spine. Quantitative analysis revealed differential expression of several collagens and cytoskeletal proteins between brain and spinal meninges. High-resolution immunofluorescence and immunogold-scanning electronmicroscopy on sections from whole brain and spinal cord - still encased within bone -identified major proteins detected by proteomics, and highlighted their association with cellular and extracellular elements of variously shaped arachnoid trabeculae. Western blotting aligned with the proteomic and immunohistological analyses, reinforcing differential appearance of proteins in brain vs spinal meninges. Results could reflect regional distinctions in meninges that govern protective and/or neuroimmune functions.

Craniovascular variation in four late Holocene human samples from southern South America

Craniovascular traits in the endocranium (traces of middle meningeal vessels and dural venous sinuses, emissary foramina) provide evidence of vascular anatomy in osteological samples. We investigate the craniovascular variation in four South American samples and the effect of artificial cranial modifications (ACM). CT scans of human adult crania from four archeological samples from southern South America (including skulls with ACM) are used for the analyses. The craniovascular features in the four samples are described, skulls with and without ACM are compared, and additionally, South Americans are compared to a previously analyzed sample of Europeans. Of the four South American samples, the Southern Patagonian differs the most, showing the most distinct cranial dimensions, no ACM, and larger diameters of the emissary foramina. Unlike previous studies, we did not find any major differences in craniovascular features between modified and non-modified skulls, except that the skulls with ACM present somewhat smaller foramina. South Americans significantly differed from Europeans, especially in the anteroposterior dominance of the middle meningeal artery, in the pattern of sinus confluence, in the occurrence of enlarged occipito-marginal sinuses, and in foramina frequencies and diameters. Craniovascular morphology is not affected by the cranial size, even in skulls with ACM, indicating a minor or null influence of structural topological factors. Concerning the samples from distinct geographic and climatic environments, it must be evaluated whether the craniovascular morphogenesis might be partially influenced by specific functions possibly associated with thermoregulation, intracranial pressure, and the maintenance of intracranial homeostasis.

Torcular pseudomass in a 14-month-old child: illustrative case

BACKGROUND

"Torcular pseudomass," or redundant soft tissue in the torcular region, is not an infrequent incidental finding on advanced imaging of the brain in infants and young children. It was recently codified among pediatric neuroradiologists; however, its report in the pediatric neurosurgical community has not previously been elucidated.

OBSERVATIONS

The authors present a case of a 14-month-old child who presented with fever and a first-time seizure. Computed tomography of the head suggested an epidural abscess; however, magnetic resonance imaging characteristics of the lesion were consistent with torcular pseudomass, a normal variant. At the 3-month follow-up, the child was continuing to do well and had not had another seizure. There have been no indications for surgical intervention or additional radiographic surveillance.

LESSONS

The differential diagnosis for torcular pseudomass includes dural venous sinus thrombosis, dermoid cysts, occipital encephalocele, eosinophilic granuloma, and primary and metastatic tumors, such as neuroblastoma. The management of each of these disorders in the differential diagnosis may be much more invasive than continued observation in the case of torcular pseudomass. Therefore, it is important for pediatric neurosurgeons to become familiar with this developmental anomaly of the dura and occipital skull.

Neuroimmune signaling at the brain borders

The central nervous system (CNS) has been viewed as an immunologically privileged site, but emerging works are uncovering a large array of neuroimmune interactions primarily occurring at its borders. CNS barriers sites host diverse population of both innate and adaptive immune cells capable of, directly and indirectly, influence the function of the residing cells of the brain parenchyma. These structures are only starting to reveal their role in controlling brain function under normal and pathological conditions and represent an underexplored therapeutic target for the treatment of brain disorders. This review will highlight the development of the CNS barriers to host neuro-immune interactions and emphasize their newly described roles in neurodevelopmental, neurological, and neurodegenerative disorders, particularly for the meninges.

Anatomy of the Ventricles, Subarachnoid Spaces, and Meninges

The ventricular system, subarachnoid spaces, and meninges are structures that lend structure, support, and protection to the brain and spinal cord. This article provides a detailed look at the anatomy of the intracranial portions of these structures with a particular focus on neuroimaging methods.

Addressing Blood–Brain Barrier Impairment in Alzheimer’s Disease

The blood–brain barrier (BBB) plays a vital role in maintaining the specialized microenvironment of the brain tissue. It facilitates communication while separating the peripheral circulation system from the brain parenchyma. However, normal aging and neurodegenerative diseases can alter and damage the physiological properties of the BBB. In this review, we first briefly present the essential pathways maintaining and regulating BBB integrity, and further review the mechanisms of BBB breakdown associated with normal aging and peripheral inflammation-causing neurodegeneration and cognitive impairments. We also discuss how BBB disruption can cause or contribute to Alzheimer’s disease (AD), the most common form of dementia and a devastating neurological disorder. Next, we document overlaps between AD and vascular dementia (VaD) and briefly sum up the techniques for identifying biomarkers linked to BBB deterioration. Finally, we conclude that BBB breakdown could be used as a biomarker to help diagnose cognitive impairment associated with normal aging and neurodegenerative diseases such as AD.

Craniovascular traits and braincase morphology in craniosynostotic human skulls

Middle meningeal vessels, dural venous sinuses, and emissary veins leave imprints and canals in the endocranium, and thus provide evidence of vascular patterns in osteological samples. This paper investigates whether craniovascular morphology undergoes changes in craniosynostotic human skulls, and if specific alterations may reflect structural and functional relationships in the cranium. The analyzed osteological sample consists of adult individuals with craniosynostoses generally associated with dolichocephalic or brachycephalic proportions, and a control sample of anatomically normal adult skulls. The pattern and dominance of the middle meningeal artery, the morphology of the confluence of the sinuses, and the size and number of the emissary foramina were evaluated. Craniovascular morphology was more diverse in craniosynostotic skulls than in anatomically normal skulls. The craniosynostotic skulls often displayed enlarged occipito-marginal sinuses and more numerous emissary foramina. The craniosynostotic skulls associated with more brachycephalic morphology often presented enlarged emissary foramina, while the craniosynostotic skulls associated with dolichocephalic effects frequently displayed more developed posterior branches of the middle meningeal artery. The course and morphology of the middle meningeal vessels, dural venous sinuses, and emissary veins in craniosynostotic skulls can be related to the redistribution of growth forces, higher intracranial pressure, venous hypertension, or thermal constraints. These functional and structural changes are of interest in both anthropology and medicine, involving epigenetic traits that concern the functional and ontogenetic balance between soft and hard tissues.

Central Nervous System Fibroblast-Like Cells in Stroke and Other Neurological Disorders

Fibroblasts are the most common cell type of connective tissues. In the central nervous system (CNS), fibroblast-like cells are mainly located in the meninges and perivascular Virchow-Robin space. The origins of these fibroblast-like cells and their functions in both CNS development and pathological conditions remain largely unknown. In this review, we first introduce the anatomic location and molecular markers of CNS fibroblast-like cells. Next, the functions of fibroblast-like cells in CNS development and neurological disorders, including stroke, CNS traumatic injuries, and other neurological diseases, are discussed. Third, current challenges and future directions in the field are summarized. We hope to provide a synthetic review that stimulates future research on CNS fibroblast-like cells.

Arachnoid and dural reflections

The dura mater is the major gateway for accessing most extra-axial lesions and all intra-axial lesions of the central nervous system. It provides a protective barrier against external trauma, infections, and the spread of malignant cells. Knowledge of the anatomical details of dural reflections around various corners of the skull bases provides the neurosurgeon with confidence during transdural approaches. Such knowledge is indispensable for protection of neurovascular structures in the vicinity of these dural reflections. The same concept is applicable to arachnoid folds and reflections during intradural excursions to expose intra- and extra-axial lesions of the brain. Without a detailed understanding of arachnoid membranes and cisterns, the neurosurgeon cannot confidently navigate the deep corridors of the skull base while safely protecting neurovascular structures. This chapter covers the surgical anatomy of dural and arachnoid reflections applicable to microneurosurgical approaches to various regions of the skull base.

Asymmetric pathological pachymeningeal enhancement: A new imaging feature for cerebral venous thrombosis

PURPOSE

Cerebral venous thrombosis (CVT) has various clinical presentations and has a median onset delay of 7 days. So it is important to find more identifiable early imaging manifestations for CVT.

METHOD

This was a retrospective study. Patients with CVT (CVT group, n = 26) diagnosed by conventional imaging techniques (magnetic resonance imaging and/or digital subtraction angiogram) and patients with symptomatic intracranial atherosclerosis (control group, n = 30) were included. Magnetic resonance black-blood thrombus imaging (MRBTI) technique had been performed in both groups. The CVT group was divided into 3 groups based on the duration of clinical onset: ≤7 days (group 1), between 7 and 30 days (group 2), and >30 days (group 3). Pathological pachymeningeal enhancement and its characteristics were analyzed between the CVT group and the control group.

RESULTS

Pathological pachymeningeal enhancement was found in 14 CVT patients (54 %) and none in control group (P value = 0.000). The bilateral pathological pachymeningeal enhancement was involved in 10 CVT patients, 6 patients were asymmetric, and 4 patients had ipsilateral enhancement. Asymmetric pathological pachymeningeal enhancement was 71 % and predominantly located on the thrombosed sinus side. Strong enhancement was found in the venous sinus wall beside the thrombus. Pathological pachymeningeal enhancement percentages of three subgroups were 75 % in group 1, 55 % in group 2, and 29 % in group 3 and had no statistical differences (p value = 0.198).

CONCLUSIONS

Current findings suggest asymmetrical pathological pachymeningeal enhancement was associated was CVT and may be a new imaging feature for CVT.

Intrathecal Inflammation in Progressive Multiple Sclerosis

Progressive forms of multiple sclerosis (MS) are associated with chronic demyelination, axonal loss, neurodegeneration, cortical and deep gray matter damage, and atrophy. These changes are strictly associated with compartmentalized sustained inflammation within the brain parenchyma, the leptomeninges, and the cerebrospinal fluid. In progressive MS, molecular mechanisms underlying active demyelination differ from processes that drive neurodegeneration at cortical and subcortical locations. The widespread pattern of neurodegeneration is consistent with mechanisms associated with the inflammatory molecular load of the cerebrospinal fluid. This is at variance with gray matter demyelination that typically occurs at focal subpial sites, in the proximity of ectopic meningeal lymphoid follicles. Accordingly, it is possible that variations in the extent and location of neurodegeneration may be accounted for by individual differences in CSF flow, and by the composition of soluble inflammatory factors and their clearance. In addition, “double hit” damage may occur at sites allowing a bidirectional exchange between interstitial fluid and CSF, such as the Virchow–Robin spaces and the periventricular ependymal barrier. An important aspect of CSF inflammation and deep gray matter damage in MS involves dysfunction of the blood–cerebrospinal fluid barrier and inflammation in the choroid plexus. Here, we provide a comprehensive review on the role of intrathecal inflammation compartmentalized to CNS and non-neural tissues in progressive MS.

A preliminary study on the development of a novel biomatrix by decellularization of bovine spinal meninges for tissue engineering applications

Here, we aim at developing a novel biomatrix from decellularized bovine spinal meninges for tissue engineering and regenerative medicine applications. Within this concept, the bovine spinal meninges were decellularized using 1% Triton X-100 for 48 h, and residual nuclear content was determined with double-strand DNA content analysis and agarose gel electrophoresis. The major matrix components such as sulfated GAGs and collagen before and after the decellularization process were analyzed with DMMB, hydroxyproline assay and SDS-PAGE. Subsequently, the native bovine spinal meninges (nBSM) and decellularized BSM (dBSM) were physiochemically characterized via ATR-FTIR spectroscopy, TGA, DMA and tensile strength test. The dsDNA content in the nBSM was 153.39 ± 53.93 ng/mg dry weight, versus in the dBSM was 39.47 ± 4.93 ng/mg (n = 3) dry weight and DNA fragments of more than 200 bp in length were not detected in the dBSM by agarose gel electrophoresis. The sulfated GAGs contents for nBSM and dBSM were observed to be 10.87 ± 1.2 and 11.42 ± 2.01 μg/mg dry weight, respectively. The maximum strength of dBSM in dry and wet conditions was found to be 19.67 ± 0.21 MPa and 13.97 ± 0.17 MPa, while nBSM (dry) was found to be 26.26 ± 0.28 MPa. MTT, SEM, and histology results exhibited that the cells attached to the surface of dBSM, and proliferated on the dBSM. In conclusion, the in vitro preliminary study has demonstrated that the dBSM might be a proper and new bioscaffold for tissue engineering and regenerative medicine applications.

The Hippo Pathway as a Driver of Select Human Cancers

The Hippo pathway regulates myriad biological processes in diverse species and is a key cancer signaling network in humans. Although Hippo has been linked to multiple aspects of cancer, its role in this disease is incompletely understood. Large-scale pan-cancer analyses of core Hippo pathway genes reveal that the pathway is mutated at a high frequency only in select human cancers, including malignant mesothelioma and meningioma. Hippo pathway deregulation is also enriched in squamous epithelial cancers. We discuss cancer-related functions of the Hippo pathway and potential explanations for the cancer-restricted mutation profile of core Hippo pathway genes. Greater understanding of Hippo pathway deregulation in cancers will be essential to guide the imminent use of Hippo-targeted therapies.

Cerebrospinal fluid leaks secondary to dural tears: a review of etiology, clinical evaluation, and management

OBJECTIVE

Damage to the dura mater often occurs in trauma cases of the head and spine, surgical procedures, lumbar punctures, and meningeal diseases. The resulting damage from dural tears, or durotomy, causes cerebrospinal fluid (CSF) to leak out into the surrounding space. The CSF leak induces intracranial hypotension, which can clinically present with a range of symptoms not limited to positional headaches which can confound accurate diagnosis. Current methods of evaluation and management of dural tears are discussed herewith, as well as the present understanding of its etiology, which may be classified as related to surgery, procedure, trauma, or connective tissue disorder.

METHODS

We piloted a MEDLINE® database search of literature, with emphasis on the previous five years, combining keywords such as "cerebrospinal fluid leak," "surgery," "procedure," and "trauma" to yield original research articles and case reports for building a clinical profile.

RESULTS

Patients with suspected dural tears should be evaluated based on criteria set by the International Headache Society, radiological findings, and a differential diagnosis to accurately identify the tear and its potential secondary complications. Afflicted patients may be treated promptly with epidural blood patches, epidural infusions, epidural fibrin glue, or surgical repair. At this time, epidural blood patches are the first line of treatment. Dural tears can be prevented to an extent by utilizing minimally invasive techniques and certain positions for lumbar puncture. Surgical, trauma, lumbar puncture, and epidural injection patients should be observed very carefully for dural tears and CSF leaks as the presenting clinical manifestations can be highly individualized and misguiding.

CONCLUSION

Because studies have demonstrated a high frequency of dural tears, particularly in spinal surgery patients, there is a need for prospective studies so that clinicians can develop an elaborate prevention strategy and response to avoid serious, unseen complications.

Histologic Comparison of the Dura Mater among Species

The biocompatibility, biodegradation, feasibility, and efficacy of medical devices like dural sealants and substitutes are often evaluated in various animal models. However, none of these studies explain the rationale for choosing a particular species, and a systematic interspecies comparison of the dura is not available. We hypothesized that histologic characteristics of the dura would differ among species. We systematically investigated basic characteristics of the dura, including thickness, composition, and fibroblast orientation of the dura mater, in 34 samples representing 10 animal species and compared these features with human dura by using hematoxylin and eosin staining and light microscopy. Dura showed many similarities between species in terms of composition. In all species, dura consisted of at least one fibrovascular layer, which contained collagen, fibroblasts, and blood vessels, and a dural border cell layer beneath the fibrovascular layer. Differences between species included the number of fibrovascular layers, fibroblast orientation, and dural thickness. Human dura was the thickest (564 μm) followed by equine (313 μm), bovine (311 μm), and porcine (304 μm) dura. Given the results of this study and factors such as gross anatomy, feasibility, housing, and ethical considerations, we recommend the use of a porcine model for dural research, especially for in vivo studies.

Contrast-enhanced modified 3D T1-weighted TSE black-blood imaging can improve detection of infectious and neoplastic meningitis

OBJECTIVES

To evaluate the diagnostic value of a contrast-enhanced 3D T1-weighted-modified volumetric isotropic turbo spin-echo acquisition sequence (T1-mVISTA) in comparison with a conventional 3D T1-weighted magnetization-prepared rapid gradient-echo (T1-MP-RAGE) sequence for the detection of meningeal enhancement in patients with meningitis.

METHODS

Thirty patients (infectious meningitis, n = 12; neoplastic meningitis, n = 18) and 45 matched controls were enrolled in this retrospective case-control study. Sets of randomly selected T1-mVISTA and T1-MP-RAGE images (both with 0.8-mm isotropic resolution) were read separately 4 weeks apart. Image quality, leptomeningeal and dural enhancement, grading of visual contrast enhancement, and diagnostic confidence were compared using the Kruskal-Wallis rank sum test.

RESULTS

Image quality was rated to be good to excellent in 75 out of 75 cases (100%) for T1-mVISTA and 74 out of 75 cases (98.7%) for T1-MP-RAGE. T1-mVISTA detected significantly more patients with leptomeningeal enhancement (p = 0.006) compared with T1-MP-RAGE (86.7 vs. 50.0%, p < 0.001), each with specificity of 100%. Similarly, sensitivity of T1-mVISTA for the detection of dural and/or leptomeningeal enhancement was also significantly higher compared with that of T1-MP-RAGE (96.7 vs. 80.0%, p = 0.025) without significant differences regarding specificity (97.8 vs. 95.6%, p = 0.317). No significant differences were found for dural enhancement alone. Diagnostic confidence in T1-mVISTA was significantly higher (p = 0.01). Visual contrast enhancement was tendentially higher in T1-mVISTA.

CONCLUSIONS

T1-mVISTA may be an adequate and probably better alternative to T1-MP-RAGE for detection of leptomeningeal diseases.

KEY POINTS

• Black-blood T1-mVISTA showed a significant higher sensitivity for the detection of leptomeningeal enhancement compared with MP-RAGE without losses regarding specificity. • Diagnostic confidence was assessed significantly higher in T1-mVISTA. • T1-mVISTA should be considered a supplement or an alternative to T1-MP-RAGE in patients with suspected leptomeningeal diseases.

Normal craniovascular variation in two modern European adult populations

The vascular networks running into the meningeal layers, between the brain and braincase, leave imprints on the endocranial surface. These traces are visible in osteological specimens and skeletal collections, providing indirect evidence of vascular patterns in those cases in which bone remains are the only source of anatomical information, such as in forensic science, bioarchaeology and paleontology. The main vascular elements are associated with the middle meningeal artery, the venous sinuses of the dura mater, and the emissary veins. Most of these vascular systems have been hypothesized to be involved in endocranial thermal regulation. Although these traits deal with macroanatomical features, much information on their variation is still lacking. In this survey, we analyze a set of craniovascular imprints in two European dry skull samples with different neurocranial proportions: a brachycephalic Czech sample (n = 103) and a mesocephalic Italian sample (n = 152). We analyzed variation and distribution, correlation with cranial metrics, and sex differences in the dominance of the branches of the middle meningeal artery, the patterns of confluence of the sinuses, and the size of the emissary foramina. The descriptive statistics provide a reference to compare specimens and samples from different case studies. When compared with the Italian skulls, the Czech skulls display a greater dominance of the anterior branch of the middle meningeal artery and more asymmetric right-dominance of the confluence of the venous sinuses. There is no sex difference in the middle meningeal vessels, but males show a greater prevalence of the occipito-marginal draining system. Differences in the middle meningeal vessels or venous sinuses are apparently not influenced by cranial dimensions or proportions. The mastoid foramina are larger in larger and more brachycephalic skulls, which increases the emissary potential flow in the Czech sample and males, when compared with the Italian samples and females, respectively. The number of mastoid foramina increases in wider skulls. This anatomic information is necessary to develop further morphological and functional inferences on the relationships between neurocranial bones and vessels at the genetic, ontogenetic, and phylogenetic levels.

Isolation and Immunofluorescent Staining of Fresh Rat Pia-Arachnoid Complex Tissue for Micromechanical Characterization

In this article, we describe a protocol for the isolation and staining of fresh tissue of the inner rat meningeal layers, or pia-arachnoid complex (PAC). The PAC is believed to act as a mechanical damper offering a fundamental layer of protection against brain injury; however, its overall mechanical properties are still rather unexplored. In order to perform micromechanical measurements on the PAC, the tissue must be extracted and characterized while maintaining its native mechanical properties (i.e., avoiding any chemical or physical modification that could alter it). In light of this need, we developed a protocol for the immunofluorescent staining of fresh PAC tissue that does not require any fixation or permeabilization step. This approach will allow researchers to investigate important properties of the anatomy of ex vivo PAC tissue while at the same time offering a platform for the mechanical analysis of this complex material. © 2019 by John Wiley & Sons, Inc. Basic Protocol 1: Isolation of fresh rat pia-arachnoid complex tissue Basic Protocol 2: Fresh immunofluorescent staining of rat pia-arachnoid complex tissue Alternate Protocol: Adhesion of pia-arachnoid complex tissue to glass slides for micromechanical characterization.

Torcular pseudomass: a potential diagnostic pitfall in infants and young children

BACKGROUND

Incidental findings on brain MRI may constitute a diagnostic pitfall. We observed an incidental extra-axial midline rounded pseudomass between the torcular Herophili and the occipital squama, with spontaneous resolution, which we called "torcular pseudomass."

OBJECTIVE

We investigated the frequency, imaging features, natural history and developmental background of this finding in a large group of infants and young children.

MATERIALS AND METHODS

We conducted a single-center retrospective study by reviewing all brain MRIs performed in children younger than 3 years between 2007 and 2013 in a specialized pediatric hospital. We looked for soft tissue (minimum 2 mm thick) interposed between the torcula and the occipital squama on midsagittal T1 and T2 images; we recorded the maximal diameters and outcome.

RESULTS

Of 2,283 the children who had brain MRIs during the study period, 291 (12.7%, 95% confidence interval [CI] 0.11, 0.14) presented with a torcular pseudomass (median age 4 months, range 0 days to 35 months, 56% male). MRI features were the same in all of these children: T1 isointensity and T2 hyperintensity to the cerebral cortex, facilitated diffusion on diffusion-weighted imaging and apparent diffusion coefficient maps, and contrast enhancement. The median diameters were: anteroposterior, 5.8 mm; transverse, 10.5 mm; cranio-caudal, 20.6 mm. Follow-up MRI was available in 34.7% (95% CI: 0.20, 0.40) of the children; median follow-up time was 18 months. Among these children, 35.6% (95% CI: 0.26, 0.45) had total involution, 52.5% (95% CI: 0.26, 0.62) had partial involution and 4.1% (95% CI: 0.05, 0.18) showed stability.

CONCLUSION

Redundant soft tissue in the torcular region, or torcular pseudomass, is not an infrequent finding in infants and young children. It should be considered a physiological tissue, reflecting the postnatal developmental process of the brain and cranial vault, without the need for further investigation or follow-up imaging studies.

Blood-brain barrier, cytotoxic chemotherapies and glioblastoma

INTRODUCTION

Glioblastomas (GBM) are the most common and aggressive primary malignant brain tumors in adults. The blood brain barrier (BBB) is a major limitation reducing efficacy of anti-cancer drugs in the treatment of GBM patients. Areas covered: Virtually all GBM recur after the first-line treatment, at least partly, due to invasive tumor cells protected from chemotherapeutic agents by the intact BBB in the brain adjacent to tumor. The passage through the BBB, taken by antitumor drugs, is poorly and heterogeneously documented in the literature. In this review, we have focused our attention on: (i) the BBB, (ii) the passage of chemotherapeutic agents across the BBB and (iii) the strategies investigated to overcome this barrier. Expert commentary: A better preclinical knowledge of the crossing of the BBB by antitumor drugs will allow optimizing their clinical development, alone or combined with BBB bypassing strategies, towards an increased success rate of clinical trials.

Meningeal Tertiary Lymphoid Tissues and Multiple Sclerosis: A Gathering Place for Diverse Types of Immune Cells during CNS Autoimmunity

Collections of leukocytes in the meningeal space have been documented in Multiple Sclerosis (MS). These meningeal aggregates, which in the context of other autoimmune diseases have often been termed tertiary lymphoid tissues (TLT), have been associated with sub-pial cortical damage and disease progression. However, the key molecular and cellular signals required for their formation and maintenance remain unclear. Herein, we review TLT structures in other disease states in order to provide a framework for understanding these structures in the MS meninges. We then assess the evidence that the meningeal compartment serves as an important nexus for immune cells as well as a location for drainage of antigen into cervical lymph nodes. Extrapolating what is known about the molecular and cellular cues that initiate the formation of leukocyte aggregates in non-lymphoid tissues, we speculate on what signals lead to the formation and maintenance of meningeal TLT structures. Referring to the animal model of MS [experimental autoimmune encephalomyelitis (EAE)], we also explore what is known about these structures in supporting B cell and T cell responses during neuroinflammation. Last, we examine the evidence that connects these structures to ongoing neuropathology. Collectively, our review points to the meningeal compartment as an important player in neuroinflammatory processes. Moreover, we hypothesize that in order to gain insights into pro- and anti-inflammatory properties of lymphocytes in MS, one must understand the cellular scaffolds that support lymphocyte retention within the meninges, thus highlighting the importance of non-immune cells (stromal cells) in the neuroinflammatory process.

Pachymeningeal enhancement-a comprehensive review of literature

Pachymeningeal enhancement, synonymous with dural enhancement, is a radiological feature best appreciated on a contrast-enhanced magnetic resonance imaging (MRI). The vasculature of the dura mater is permeable, facilitating avid uptake of contrast agent and subsequent enhancement. Thin, discontinuous enhancement can be normal, seen in half the normal population. In patients complaining of postural headaches worse on sitting, gadolinium-enhanced MRI findings of diffuse pachymeningeal enhancement is highly suggestive of benign intracranial hypotension. In these cases, the process of pachymeningeal enhancement is explained by the Monro-Kellie doctrine as compensatory volume changes by vasocongestion and interstitial oedema of the dura mater due to decreased cerebrospinal fluid (CSF) pressure. Focal and diffuse pachymeningeal enhancement can also be attributed to infectious or inflammatory, neoplastic and iatrogenic aetiologies. Correction of the underlying pathology often results in spontaneous resolution of the pachymeningeal enhancement. There have also been reports of pachymeningeal enhancement associated with cerebral venous sinus thrombosis, temporal arteritis, baroreceptor reflex failure syndrome and arteriovenous fistulae.

The meninges: new therapeutic targets for multiple sclerosis

The central nervous system (CNS) largely comprises nonregenerating cells, including neurons and myelin-producing oligodendrocytes, which are particularly vulnerable to immune cell-mediated damage. To protect the CNS, mechanisms exist that normally restrict the transit of peripheral immune cells into the brain and spinal cord, conferring an "immune-specialized" status. Thus, there has been a long-standing debate as to how these restrictions are overcome in several inflammatory diseases of the CNS, including multiple sclerosis (MS). In this review, we highlight the role of the meninges, tissues that surround and protect the CNS and enclose the cerebral spinal fluid, in promoting chronic inflammation that leads to neuronal damage. Although the meninges have traditionally been considered structures that provide physical protection for the brain and spinal cord, new data have established these tissues as sites of active immunity. It has been hypothesized that the meninges are important players in normal immunosurveillance of the CNS but also serve as initial sites of anti-myelin immune responses. The resulting robust meningeal inflammation elicits loss of localized blood-brain barrier (BBB) integrity and facilitates a large-scale influx of immune cells into the CNS parenchyma. We propose that targeting the cells and molecules mediating these inflammatory responses within the meninges offers promising therapies for MS that are free from the constraints imposed by the BBB. Importantly, such therapies may avoid the systemic immunosuppression often associated with the existing treatments.

Dynamic changes in meningeal inflammation correspond to clinical exacerbations in a murine model of relapsing-remitting multiple sclerosis

Inflammation in the meninges, tissues surrounding the brain and spinal cord that enclose the cerebrospinal fluid, closely parallels clinical exacerbations in relapsing-remitting experimental autoimmune encephalomyelitis (EAE). In preclinical disease, an influx of innate immune cells precedes loss of blood brain barrier (BBB) integrity and large-scale inflammation in the central nervous system (CNS). T cell infiltration into the meninges is observed in acute disease as well as during relapse, when neither BBB permeability nor significant increases in peripherally-derived immune cell numbers in the CNS are observed. These findings support the idea that the meninges are a gateway for immune cell access into the CNS, a finding that has important therapeutic implications.

Two cases of subfrontal schwannoma, including a rare case located between the endosteal and meningeal layers of the dura

Subfrontal schwannomas arising from the olfactory groove are rare and their origin remains uncertain because olfactory bulbs do not possess Schwann cells. We present two cases of subfrontal schwannomas treated with surgical resection. In one case, the tumor was located between the endosteal and meningeal layers of the dura mater. This rare case suggests that subfrontal schwannomas may originate from the fila olfactoria.

The pia mater: a comprehensive review of literature

INTRODUCTION

The pia mater has received less attention in the literature compared to the dura and arachnoid maters. However, its presence as a direct covering of the nervous system and direct relation to the blood vessels gives it a special importance in neurosurgery.

METHOD

A comprehensive review of the literature was conducted to study all that we could find relating to the pia mater, including history, macro- and microanatomy, embryology, and a full description of the related structures.

CONCLUSION

The pia mater has an important anatomic position, rich history, complicated histology and embryology, and a significant contribution to a number of other structures that may stabilize and protect the nervous system.

Mast cell activation and neutrophil recruitment promotes early and robust inflammation in the meninges in EAE

The meninges are often considered inert tissues that house the CSF and provide protection for the brain and spinal cord. Yet emerging data demonstrates that they are also active sites of immune responses. Furthermore, the blood-CSF barrier surrounding meningeal blood vessels, together with the blood-brain barrier (BBB), is postulated to serve as a gateway for the pathological infiltration of immune cells into the CNS in multiple sclerosis (MS). Our previous studies using mast cell-deficient (Kit(W/Wv)) mice demonstrated that mast cells resident in the dura mater and pia mater exacerbate experimental autoimmune encephalomyelitis (EAE), a rodent model of MS, by facilitating CNS inflammatory cell influx. Here we examined the underlying mechanisms that mediate these effects. We demonstrate that there are dramatic alterations in immune associated gene expression in the meninges in pre-clinical disease, including those associated with mast cell and neutrophil function. Meningeal mast cells are activated within 24 h of disease induction, but do not directly compromise CNS vascular integrity. Rather, through production of TNF, mast cells elicit an early influx of neutrophils, cells known to alter vascular permeability, into the meninges. These data add to the growing evidence that inflammation in the meninges precedes CNS immune cell infiltration and establish that mast cells are among the earliest participants in these disease-initiating events. We hypothesize that mast cell-dependent neutrophil recruitment and activation in the meninges promotes early breakdown of the local BBB and CSF-blood barrier allowing initial immune cell access to the CNS.

The cranial dura mater: a review of its history, embryology, and anatomy

INTRODUCTION

The dura mater is important to the clinician as a barrier to the internal environment of the brain, and surgically, its anatomy should be well known to the neurosurgeon and clinician who interpret imaging.

METHODS

The medical literature was reviewed in regard to the morphology and embryology of specifically, the intracranial dura mater. A historic review of this meningeal layer is also provided.

CONCLUSIONS

Knowledge of the cranial dura mater has a rich history. The embryology is complex, and the surgical anatomy of this layer and its specializations are important to the neurosurgeon.

Innate immunity in the central nervous system

Immune responses in the CNS are common, despite its perception as a site of immune privilege. These responses can be mediated by resident microglia and astrocytes, which are innate immune cells without direct counterparts in the periphery. Furthermore, CNS immune reactions often take place in virtual isolation from the innate/adaptive immune interplay that characterizes peripheral immunity. However, microglia and astrocytes also engage in significant cross-talk with CNS-infiltrating T cells and other components of the innate immune system. Here we review the cellular and molecular basis of innate immunity in the CNS and discuss what is known about how outcomes of these interactions can lead to resolution of infection, neurodegeneration, or neural repair depending on the context.

Mechanisms of dendritic cell trafficking across the blood-brain barrier

Although the central nervous system (CNS) is considered to be an immunoprivileged site, it is susceptible to a host of autoimmune as well as neuroinflammatory disorders owing to recruitment of immune cells across the blood-brain barrier into perivascular and parenchymal spaces. Dendritic cells (DCs), which are involved in both primary and secondary immune responses, are the most potent immune cells in terms of antigen uptake and processing as well as presentation to T cells. In light of the emerging importance of DC traficking into the CNS, these cells represent good candidates for targeted immunotherapy against various neuroinflammatory diseases. This review focuses on potential physiological events and receptor interactions between DCs and the microvascular endothelial cells of the brain as they transmigrate into the CNS during degeneration and injury. A clear understanding of the underlying mechanisms involved in DC migration may advance the development of new therapies that manipulate these mechanistic properties via pharmacologic intervention. Furthermore, therapeutic validation should be in concurrence with the molecular imaging techniques that can detect migration of these cells in vivo. Since the use of noninvasive methods to image migration of DCs into CNS has barely been explored, we highlighted potential molecular imaging techniques to achieve this goal. Overall, information provided will bring this important leukocyte population to the forefront as key players in the immune cascade in the light of the emerging contribution of DCs to CNS health and disease.