Subarachnoid space

Last revised by Bálint Botz on 8 Jan 2023

The subarachnoid space is the interval between the arachnoid membrane and the pia mater. It is occupied by delicate connective tissue trabeculae and intercommunicating channels containing cerebrospinal fluid (CSF) as well as branches of the arteries and veins of the brain.

The cavity is small in the normal brain. Over the gyri, the arachnoid membrane and pia mater are in close contact. However, in the sulci, triangular spaces develop because the pia mater is closely applied to the cerebral cortex and the arachnoid membrane bridges the gap between adjacent gyri without descending into each sulcus.

At certain points, the pia mater and arachnoid membrane are separated by wide intervals which communicate freely with each other known as subarachnoid cisterns, in which the subarachnoid tissue is less abundant.

It has been recently shown that the subarachnoid space is subdivided into two functional compartments by the very thin subarachnoid lymphatic-like membrane, which compartmentalizes the flow of cerebrospinal fluid, and has potential roles in neurinflammatory conditions 1.

The subarachnoid space is also contiguous around the spinal cord.

Related pathology

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Cases and figures

  • Figure 1: diagram - meninges
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  • Figure 2: diagram - spinal cord
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  • Figure 3: diagram - meninges
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