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

Ashutosh Kumar, Department of Anatomy, All India Institute of Medical Sciences (AIIMS), Patna, India.
Rajesh Kumar, Department of Anatomy, All India Institute of Medical Sciences (AIIMS), Patna, India.
Ravi K. Narayan, Department of Anatomy, All India Institute of Medical Sciences (AIIMS), Patna, India.
Banshi Nath, Department of Anatomy, All India Institute of Medical Sciences (AIIMS), Patna, India.
Ashok K. Datusalia, Department of Pharmacology and Toxicology, National Institute of Pharmaceutical Education and Research-Raebareli, Lucknow, India.
Ashok K. Rastogi, Department of Forensic Medicine and Toxicology, All India Institute of Medical Sciences (AIIMS), Patna, India.
Rakesh K. Jha, Department of Anatomy, All India Institute of Medical Sciences (AIIMS), Patna, India.
Pankaj Kumar, Regional Institute of Ophthalmology, Indira Gandhi Institute of Medical Sciences, Patna, India.
Vikas Pareek, Haskins Laboratories, Yale Child Study Centre, Yale School of Medicine, University of Connecticut, New Haven, Connecticut, USA.
Pranav Prasoon, Department of Anatomy and Cell Biology, George Washington University, Washington, DC, USA.
Muneeb A. Faiq, New York University (NYU) Langone Health Center, NYU Robert I Grossman School of Medicine, New York, New York, USA.
Prabhat Agrawal, Spine Surgery Clinic, Department of Orthopedics, All India Institute of Medical Sciences (AIIMS), Patna, India.
Surya Nandan Prasad, Department of Radiodiagnosis, All India Institute of Medical Sciences (AIIMS), Patna, India.
Chiman Kumari, Department of Anatomy, Postgraduate Institute of Medical Education and Research (PGIMER), Chandigarh, India.
Adil Asghar, Department of Anatomy, All India Institute of Medical Sciences (AIIMS), Patna, India.

Document Type

Journal Article

Publication Date

1-1-2025

Journal

Anatomical record (Hoboken, N.J. : 2007)

Volume

308

Issue

1

DOI

10.1002/ar.25524

Keywords

CSF; brain; glymphatic system; magnetic resonance imaging; meninges; scanning electron microscopy

Abstract

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.

Department

Anatomy and Regenerative Biology

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