Definition and research guide
This page combines a MeSH definition, publication statistics and selected research abstracts. It is a starting point for reading the literature, not a medical textbook or a systematic evidence review.
Content available: 4 complete abstracts (715 words), 10 references. Full article text is not stored or reproduced here; follow the PMID, DOI or PMC links to read the original sources and their access terms.
Definition
A delicate membrane enveloping the brain and spinal cord. It lies between the pia mater and the dura mater. It is separated from the pia mater by the subarachnoid cavity which is filled with cerebrospinal fluid.
Definition: NLM Medical Subject Headings (MeSH) scope note (Public domain (U.S. National Library of Medicine); attribution requested). View the MeSH record.
Also known as: Arachnoids; Arachnoid Mater; Arachnoid Maters.
Where it fits in the MeSH classification
- Broader topics
- Meninges
- Narrower topics
- Subarachnoid Space
Related concepts
- Pia Mater
- Dura Mater
- Cerebrospinal Fluid
Research landscape
PubMed indexes 9,390 records tagged with the MeSH heading “Arachnoid” (counts retrieved 2026-10-29). 603 of them (6.4%) were published from 2020 onward, and the busiest period so far is through 1999 with 6,192 records.
Reviews account for 498 records (5.3%) and meta-analyses for 12. Randomized controlled trials number 168 (1.8%) as a share of all records on the topic. Randomized trials make up only a small share of this literature, so much of what is known comes from laboratory, observational or descriptive work.
Show the data
| Period | Records |
|---|---|
| through 1999 | 6,192 |
| 2000-2009 | 1,346 |
| 2010-2019 | 1,249 |
| 2020 onward | 603 |
Publication-type chart data
| Type | Records | Share |
|---|---|---|
| Reviews | 498 | 5.3% |
| Meta-analyses | 12 | 0.1% |
| Randomized controlled trials | 168 | 1.8% |
Method: PubMed query "Arachnoid"[MeSH Terms] with publication-type and date filters, retrieved 2026-10-29.
Reading the evidence in neuroscience
Neuroscience draws on tools with different strengths: cellular and animal work can manipulate circuits directly, while human imaging and electrophysiology observe the living brain at lower resolution. Small imaging studies are prone to false positives, and findings in animals do not always carry over to people. Clinical neurology and psychiatry rely on trials and cohort studies whose outcomes are often symptom scales. Check the species, the sample size, how the outcome was measured and whether results were replicated.
Evidence from open-access studies
These open-access studies come from PubMed’s best-match results for this heading (papers whose main topic it is), ranked here by citation count, with one recent addition. Each abstract is reproduced in full under its recorded open licence so that you can read the authors’ own words. They illustrate the literature; they are not a systematic summary of it. Citation counts measure attention, not reliability or clinical benefit.
| Study / authors | Year | Source label / design | Europe PMC citations | Licence / source |
|---|---|---|---|---|
| Flow of cerebrospinal fluid is driven by arterial pulsations and is reduced in hypertension | 2018 | Research article Design not recorded in structured metadata | 956 | cc by PMID 30451853 · DOI · PMC6242982 |
| Cerebrospinal fluid outflow: a review of the historical and contemporary evidence for arachnoid villi, perineural routes, and dural lymphatics | 2021 | Review article Design not recorded in structured metadata | 333 | cc by PMID 33427948 · DOI · PMC8004496 |
| Test of the 'glymphatic' hypothesis demonstrates diffusive and aquaporin-4-independent solute transport in rodent brain parenchyma | 2017 | Research article Design not recorded in structured metadata | 308 | cc by PMID 28826498 · DOI · PMC5578736 |
| Non-invasive characterization of perivascular subarachnoid spaces | 2026 | Research article Design not recorded in structured metadata | 1 | cc by PMID 42693113 · DOI · PMC13542271 |
Flow of cerebrospinal fluid is driven by arterial pulsations and is reduced in hypertension [1]
Abstract reading summary — source excerpts
- Opening excerpt
- Flow of cerebrospinal fluid (CSF) through perivascular spaces (PVSs) in the brain is important for clearance of metabolic waste.
- Closing excerpt
- We conclude that particle tracking velocimetry enables the study of CSF flow in unprecedented detail and that studying the PVS in vivo avoids fixation artifacts.
- Interpretation limits
- Verbatim excerpts from the authors’ abstract; the closing excerpt may describe a finding, limitation or recommendation. Design, population, effect size and uncertainty have not been independently extracted or appraised. Read the complete abstract and linked paper before interpreting the findings.
Read complete abstract (150 words)
Flow of cerebrospinal fluid (CSF) through perivascular spaces (PVSs) in the brain is important for clearance of metabolic waste. Arterial pulsations are thought to drive flow, but this has never been quantitatively shown. We used particle tracking to quantify CSF flow velocities in PVSs of live mice. CSF flow is pulsatile and driven primarily by the cardiac cycle. The speed of the arterial wall matches that of the CSF, suggesting arterial wall motion is the principal driving mechanism, via a process known as perivascular pumping. Increasing blood pressure leaves the artery diameter unchanged but changes the pulsations of the arterial wall, increasing backflow and thereby reducing net flow in the PVS. Perfusion-fixation alters the normal flow direction and causes a 10-fold reduction in PVS size. We conclude that particle tracking velocimetry enables the study of CSF flow in unprecedented detail and that studying the PVS in vivo avoids fixation artifacts.
Abstract reproduced from the open-access article under the recorded cc by licence; © the authors. PMID 30451853 · DOI · PMC6242982
Cerebrospinal fluid outflow: a review of the historical and contemporary evidence for arachnoid villi, perineural routes, and dural lymphatics [2]
Abstract reading summary — source excerpts
- Opening excerpt
- 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.
- Closing excerpt
- 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.
- Interpretation limits
- Verbatim excerpts from the authors’ abstract; the closing excerpt may describe a finding, limitation or recommendation. Design, population, effect size and uncertainty have not been independently extracted or appraised. Read the complete abstract and linked paper before interpreting the findings.
Read complete abstract (244 words)
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.
Abstract reproduced from the open-access article under the recorded cc by licence; © the authors. PMID 33427948 · DOI · PMC8004496
Test of the 'glymphatic' hypothesis demonstrates diffusive and aquaporin-4-independent solute transport in rodent brain parenchyma [3]
Abstract reading summary — source excerpts
- Opening excerpt
- Transport of solutes through brain involves diffusion and convection.
- Closing excerpt
- Our results do not support the proposed glymphatic mechanism of convective solute transport in brain parenchyma.
- Interpretation limits
- Verbatim excerpts from the authors’ abstract; the closing excerpt may describe a finding, limitation or recommendation. Design, population, effect size and uncertainty have not been independently extracted or appraised. Read the complete abstract and linked paper before interpreting the findings.
Read complete abstract (153 words)
Transport of solutes through brain involves diffusion and convection. The importance of convective flow in the subarachnoid and paravascular spaces has long been recognized; a recently proposed 'glymphatic' clearance mechanism additionally suggests that aquaporin-4 (AQP4) water channels facilitate convective transport through brain parenchyma. Here, the major experimental underpinnings of the glymphatic mechanism were re-examined by measurements of solute movement in mouse brain following intracisternal or intraparenchymal solute injection. We found that: (i) transport of fluorescent dextrans in brain parenchyma depended on dextran size in a manner consistent with diffusive rather than convective transport; (ii) transport of dextrans in the parenchymal extracellular space, measured by 2-photon fluorescence recovery after photobleaching, was not affected just after cardiorespiratory arrest; and (iii) Aqp4 gene deletion did not impair transport of fluorescent solutes from sub-arachnoid space to brain in mice or rats. Our results do not support the proposed glymphatic mechanism of convective solute transport in brain parenchyma.
Abstract reproduced from the open-access article under the recorded cc by licence; © the authors. PMID 28826498 · DOI · PMC5578736
Non-invasive characterization of perivascular subarachnoid spaces [4]
Abstract reading summary — source excerpts
- Opening excerpt
- Cerebrospinal fluid (CSF) is thought to facilitate brain waste clearance and immune surveillance, yet its compartmentalization remains unclear.
- Closing excerpt
- We find that CSF dynamics may be more spatially distinct than previously thought, providing a possible foundation for understanding brain CSF patterns in health and disease.
- Interpretation limits
- Verbatim excerpts from the authors’ abstract; the closing excerpt may describe a finding, limitation or recommendation. Design, population, effect size and uncertainty have not been independently extracted or appraised. Read the complete abstract and linked paper before interpreting the findings.
Read complete abstract (168 words)
Cerebrospinal fluid (CSF) is thought to facilitate brain waste clearance and immune surveillance, yet its compartmentalization remains unclear. Previous work, using invasive dynamic intrathecal MRI contrast imaging, identified a perivascular subarachnoid space (PVSAS) that enhances along the major cerebral arteries with a 'donut'-like appearance. These findings suggest that the PVSAS may be separated from the surrounding broader subarachnoid space (SAS) by a semipermeable perivascular membrane. To investigate if the PVSAS could be observed non-invasively in healthy controls, we used a magnetic resonance imaging technique, CSF-STREAM (CSF-Selective T2-prepared REadout with Acceleration and Mobility-encoding), that assesses CSF-mobility at a high spatial resolution by isolating CSF from blood and tissue signal. Here, we observe high CSF-mobility next to the vasculature, with a steep drop-off into the surrounding SAS around both the middle and anterior cerebral arteries, suggesting the presence of the PVSAS in healthy controls. We find that CSF dynamics may be more spatially distinct than previously thought, providing a possible foundation for understanding brain CSF patterns in health and disease.
Abstract reproduced from the open-access article under the recorded cc by licence; © the authors. PMID 42693113 · DOI · PMC13542271
Key reviews and meta-analyses
The most cited review-type papers among PubMed’s best-match results for this heading, listed with bibliographic details only. Follow the links for the full text and access terms.
- Research article Recent insights into a new hydrodynamics of the cerebrospinal fluid [5]
- Research article Distribution of local anesthetic solutions within the subarachnoid space [6]
- Research article Cerebrospinal fluid flow imaging by using phase-contrast MR technique [7]
- Research article Leptomeningeal carcinomatosis. How does cancer reach the pia-arachnoid? [8]
- Research article Primary leptomeningeal lymphoma: report of 9 cases, diagnosis with immunocytochemical analysis, and review of the literature [9]
- Research article Subarachnoid basal neurocysticercosis: a focus on the most severe form of the disease [10]
References
- Mestre H, Tithof J, Du T, Song W, Peng W, Sweeney AM, et al.. Flow of cerebrospinal fluid is driven by arterial pulsations and is reduced in hypertension. . 2018. PMID 30451853 · DOI · PMC6242982
- Proulx ST. Cerebrospinal fluid outflow: a review of the historical and contemporary evidence for arachnoid villi, perineural routes, and dural lymphatics. . 2021. PMID 33427948 · DOI · PMC8004496
- Smith AJ, Yao X, Dix JA, Jin BJ, Verkman AS. Test of the 'glymphatic' hypothesis demonstrates diffusive and aquaporin-4-independent solute transport in rodent brain parenchyma. . 2017. PMID 28826498 · DOI · PMC5578736
- Fultz NE, Ringstad G, Debiasi M, Roefs ECA, Svensson SF, Eide PK, et al.. Non-invasive characterization of perivascular subarachnoid spaces. . 2026. PMID 42693113 · DOI · PMC13542271
- Bulat M, Klarica M. Recent insights into a new hydrodynamics of the cerebrospinal fluid. Brain Res Rev. 2011. PMID 20817024 · DOI
- Greene NM. Distribution of local anesthetic solutions within the subarachnoid space. Anesth Analg. 1985. PMID 3893222 · DOI
- Battal B, Kocaoglu M, Bulakbasi N, Husmen G, Tuba Sanal H, Tayfun C. Cerebrospinal fluid flow imaging by using phase-contrast MR technique. Br J Radiol. 2011. PMID 21586507 · DOI · PMC3473435
- Kokkoris CP. Leptomeningeal carcinomatosis. How does cancer reach the pia-arachnoid?. Cancer. 1983. PMID 6336971 · DOI
- Lachance DH, O'Neill BP, Macdonald DR, Jaeckle KA, Witzig TE, Li CY, et al.. Primary leptomeningeal lymphoma: report of 9 cases, diagnosis with immunocytochemical analysis, and review of the literature. Neurology. 1991. PMID 1985302 · DOI
- Fleury A, Carrillo-Mezo R, Flisser A, Sciutto E, Corona T. Subarachnoid basal neurocysticercosis: a focus on the most severe form of the disease. Expert Rev Anti Infect Ther. 2011. PMID 21171883 · DOI
About this article
- Sources
- NLM Medical Subject Headings (definition, synonyms); NCBI PubMed (counts, identifiers); Europe PMC (open-access abstracts and citation counts).
- Verification
- Every reference was resolved against PubMed on 2026-10-31; title, year and DOI matched.
- Review state
- automated source verified; no human expert review has been recorded yet.
- Version
- 1, last updated 2026-10-29.
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Evidence strength
EvidenceHelix's computed view of the study designs behind this topic: how common meta-analyses, randomized trials and reviews are, how recent the literature is, and a plain-language reading. It describes the design mix of the literature. It is not a quality appraisal of any study, and it is not medical advice.