Review

Authors: John M Leonard

Central nervous system tuberculosis (CNS-TB) takes three clinical forms: meningitis (TBM), intracranial tuberculoma, and spinal arachnoiditis. TBM predominates in the western world and presents as a subacute to chronic meningitis syndrome with a prodrome of malaise, fever, and headache progressing to altered mentation and focal neurologic signs, followed by stupor, coma, and death within five to eight weeks of onset. The CSF formula typically shows a lymphocytic pleocytosis, and low glucose and high protein concentrations. Diagnosis rests on serial samples of CSF for smear and culture, combined with CSF PCR. Brain CT and MRI aid in diagnosis, assessment for complications, and monitoring of the clinical course. In a patient with compatible clinical features, the combination of meningeal enhancement and any degree of hydrocephalus is strongly suggestive of TBM. Vasculitis leading to infarcts in the basal ganglia occurs commonly and is a major determinant of morbidity and mortality. Treatment is most effective when started in the early stages of disease, and should be initiated promptly on the basis of strong clinical suspicion without waiting for laboratory confirmation. The initial 4 drug regimen (isoniazid, rifampin, pyrazinamide, ethambutol) covers the possibility of infection with a resistant strain, maximizes antimicrobial impact, and reduces the likelihood of emerging resistance on therapy. Adjunctive corticosteroid therapy has been shown to reduce morbidity and mortality in all but late stage disease.

Topics: Anti-Inflammatory Agents; Antitubercular Agents; Arachnoiditis; Brain; Cerebrospinal Fluid; Humans; Magnetic Resonance Imaging; Mycobacterium; Polymerase Chain Reaction; Tomography, X-Ray Computed; Tuberculoma, Intracranial; Tuberculosis, Meningeal

PubMed: 28281443
DOI: 10.1128/microbiolspec.TNMI7-0044-2017

Authors: Riikka Pietilä, Francesca Del Gaudio, Liqun He...

Leptomeninges, consisting of the pia mater and arachnoid, form a connective tissue investment and barrier enclosure of the brain. The exact nature of leptomeningeal cells has long been debated. In this study, we identify five molecularly distinct fibroblast-like transcriptomes in cerebral leptomeninges; link them to anatomically distinct cell types of the pia, inner arachnoid, outer arachnoid barrier, and dural border layer; and contrast them to a sixth fibroblast-like transcriptome present in the choroid plexus and median eminence. Newly identified transcriptional markers enabled molecular characterization of cell types responsible for adherence of arachnoid layers to one another and for the arachnoid barrier. These markers also proved useful in identifying the molecular features of leptomeningeal development, injury, and repair that were preserved or changed after traumatic brain injury. Together, the findings highlight the value of identifying fibroblast transcriptional subsets and their cellular locations toward advancing the understanding of leptomeningeal physiology and pathology.

Topics: Mice; Animals; Meninges; Arachnoid; Pia Mater; Choroid Plexus; Brain

PubMed: 37776854
DOI: 10.1016/j.neuron.2023.09.002

Review

Authors: Krishnakali Dasgupta, Juhee Jeong

The meninges are membranous layers surrounding the central nervous system. In the head, the meninges lie between the brain and the skull, and interact closely with both during development. The cranial meninges originate from a mesenchymal sheath on the surface of the developing brain, called primary meninx, and undergo differentiation into three layers with distinct histological characteristics: the dura mater, the arachnoid mater, and the pia mater. While genetic regulation of meningeal development is still poorly understood, mouse mutants and other models with meningeal defects have demonstrated the importance of the meninges to normal development of the calvaria and the brain. For the calvaria, the interactions with the meninges are necessary for the progression of calvarial osteogenesis during early development. In later stages, the meninges control the patterning of the skull and the fate of the sutures. For the brain, the meninges regulate diverse processes including cell survival, cell migration, generation of neurons from progenitors, and vascularization. Also, the meninges serve as a stem cell niche for the brain in the postnatal life. Given these important roles of the meninges, further investigation into the molecular mechanisms underlying meningeal development can provide novel insights into the coordinated development of the head.

Topics: Animals; Arachnoid; Brain; Cell Differentiation; Developmental Biology; Dura Mater; Humans; Meninges; Pia Mater; Skull

PubMed: 30801905
DOI: 10.1002/dvg.23288

Authors: Leon C D Smyth, Di Xu, Serhat V Okar...

The arachnoid barrier delineates the border between the central nervous system and dura mater. Although the arachnoid barrier creates a partition, communication between the central nervous system and the dura mater is crucial for waste clearance and immune surveillance. How the arachnoid barrier balances separation and communication is poorly understood. Here, using transcriptomic data, we developed transgenic mice to examine specific anatomical structures that function as routes across the arachnoid barrier. Bridging veins create discontinuities where they cross the arachnoid barrier, forming structures that we termed arachnoid cuff exit (ACE) points. The openings that ACE points create allow the exchange of fluids and molecules between the subarachnoid space and the dura, enabling the drainage of cerebrospinal fluid and limited entry of molecules from the dura to the subarachnoid space. In healthy human volunteers, magnetic resonance imaging tracers transit along bridging veins in a similar manner to access the subarachnoid space. Notably, in neuroinflammatory conditions such as experimental autoimmune encephalomyelitis, ACE points also enable cellular trafficking, representing a route for immune cells to directly enter the subarachnoid space from the dura mater. Collectively, our results indicate that ACE points are a critical part of the anatomy of neuroimmune communication in both mice and humans that link the central nervous system with the dura and its immunological diversity and waste clearance systems.

Topics: Animals; Humans; Mice; Arachnoid; Biological Transport; Brain; Dura Mater; Encephalomyelitis, Autoimmune, Experimental; Gene Expression Profiling; Magnetic Resonance Imaging; Mice, Transgenic; Subarachnoid Space; Cerebrospinal Fluid; Veins

PubMed: 38326613
DOI: 10.1038/s41586-023-06993-7

Review

Authors: Christer Betsholtz, Britta Engelhardt, Gou Young Koh...

The dura, arachnoid and pia mater, as the constituent layers of the meninges, along with cerebrospinal fluid in the subarachnoid space and ventricles, are essential protectors of the brain and spinal cord. Complemented by immune cells, blood vessels, lymphatic vessels and nerves, these connective tissue layers have held many secrets that have only recently begun to be revealed. Each meningeal layer is now known to have molecularly distinct types of fibroblasts. Cerebrospinal fluid clearance through peripheral lymphatics and lymph nodes is well documented, but its routes and flow dynamics are debated. Advances made in meningeal immune functions are also debated. This Review considers the cellular and molecular structure and function of the dura, arachnoid and pia mater in the context of conventional views, recent progress, and what is uncertain or unknown. The hallmarks of meningeal pathophysiology are identified toward developing a more complete understanding of the meninges in health and disease.

Topics: Humans; Meninges; Animals; Dura Mater; Arachnoid; Pia Mater

PubMed: 39333784
DOI: 10.1038/s41593-024-01701-8

Authors: Trishna Shah, Sue E Leurgans, Rashi I Mehta...

Arachnoid granulations (AG) are poorly investigated. Historical reports suggest that they regulate brain volume by passively transporting cerebrospinal fluid (CSF) into dural venous sinuses. Here, we studied the microstructure of cerebral AG in humans with the aim of understanding their roles in physiology. We discovered marked variations in AG size, lobation, location, content, and degree of surface encapsulation. High-resolution microscopy shows that AG consist of outer capsule and inner stromal core regions. The fine and porous framework suggests uncharacterized functions of AG in mechanical CSF filtration. Moreover, internal cytokine and immune cell enrichment imply unexplored neuroimmune properties of these structures that localize to the brain-meningeal lymphatic interface. Dramatic age-associated changes in AG structure are additionally identified. This study depicts for the first time microscopic networks of internal channels that communicate with perisinus spaces, suggesting that AG subserve important functions as transarachnoidal flow passageways. These data raise new theories regarding glymphatic-lymphatic coupling and mechanisms of CSF antigen clearance, homeostasis, and diseases.

Topics: Humans; Bone Marrow; Arachnoid; Dura Mater; Lymphatic System; Lymphatic Vessels

PubMed: 36469302
DOI: 10.1084/jem.20220618

Review

Authors: Steven T Proulx

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.

Topics: Animals; Arachnoid; Cerebrospinal Fluid; Cranial Nerves; Ethmoid Bone; Humans; Lymph Nodes; Lymphatic Vessels; Spine

PubMed: 33427948
DOI: 10.1007/s00018-020-03706-5

Authors: André Eduardo de Almeida Franzoi, Tamiris Maier Silva Ferreira, Emanuele Therezinha Schueda Stonoga...

Topics: Humans; Arachnoiditis; Hydrocephalus

PubMed: 37379872
DOI: 10.1055/s-0043-1768159

Review

Authors: Laura V Sainz, Martin U Schuhmann

PURPOSE

Multiple names within the literature refer to a clinical picture affecting infants and consisting of a large or fast growing head circumference with enlarged cortical subarachnoid spaces (CSAS) while cranial sutures are open. This myriad of terms demonstrates the confusion about the entity, that may even group together different etiological processes. In this review, we aim to shed light on this matter in an effort to restate the defining features of the clinical picture and sum the evidence and current understanding of its pathophysiology and related imaging findings.

METHODS

Extensive and updated review of the literature with special focus on defining features, clinical history with long term evaluation and pathophysiological process.

RESULTS

Functional and molecular CSF studies as well as clinical evidence challenges the common pathophysiological theory based on non-functional arachnoid villi. Conversely, there is increasing evidence supporting cerebro-venous system abnormalities as the main pathophysiological factor. Additionally, long term cohorts studies show that it may have subtle but irreversible neurodevelopmental consequences.

CONCLUSION

Subarachnomegaly is an age-related condition of the infancy with radiological enlargement of CSAS and often self limiting course. However, considering the evidence on pathophysiology as outlined herein and long term outcome reports, further research effort is needed to assess the consequences of venous outflow impairment and enlarged CSAS and how this relates to imaging findings and neurodevelopment test results later in life.

Topics: Humans; Hyperemia; Infant; Subarachnoid Space

PubMed: 34687332
DOI: 10.1007/s00381-021-05328-z

Authors: Liyan Chen, Lili Zhao

Topics: Humans; Arachnoid; Magnetic Resonance Imaging

PubMed: 39216070
DOI: 10.4103/neurol-india.Neurol-India-D-24-00403