Spinal subarachnoid space

The spinal subarachnoid space is the space between the arachnoid mater and pia mater in the spine and is continuous with the intracranial subarachnoid space.

It communicates with the intracranial subarachnoid space via the foramen magnum and ends at the level of the S2 vertebra.  It is a relatively large space, containing approximately half of the total volume of cerebrospinal fluid (75mLs out of 150mLs) .

As the spinal cord ends at the level of L2, the subarachnoid space distal to this forms the lumbar cistern and is an ideal space to access the CSF via a lumbar puncture .  With this procedure, the CSF can be analyzed and measured, a spinal anaethetic given or contrast be injected for myelography.