Anatomy: Posterior Fossa, Hindbrain & Craniocervical Junction
Subarachnoid space
The subarachnoid space is the CSF-filled space around the brain and spinal cord, where flow is disrupted at the craniocervical junction in Chiari malformation.
In short: Subarachnoid space
- It is the CSF-filled space surrounding the brain and spinal cord.
- CSF circulates within it.
- At the craniocervical junction, this space is crowded in Chiari.
- Restoring flow in this space is a goal of surgery.
What it is
The subarachnoid space is the fluid-filled space between two of the membranes covering the brain and spinal cord (the arachnoid and pia maters), through which cerebrospinal fluid circulates. At the craniocervical junction, this space is crowded and CSF flow is disrupted in Chiari malformation.
Understanding Subarachnoid space
CSF circulates through the subarachnoid space around the brain and down around the spinal cord. At the foramen magnum, the descending tonsils in Chiari malformation crowd this space, narrowing the channels through which CSF normally flows between the head and the spine. This obstruction of CSF flow in the subarachnoid space at the craniocervical junction is central to the pathophysiology of Chiari and its association with syringomyelia. Posterior fossa decompression aims to reopen this space and restore freer CSF flow. Understanding the subarachnoid space helps clarify where CSF circulates and why its crowding at the craniocervical junction is the key problem in Chiari.
Why it matters
Understanding the subarachnoid space helps families see where CSF circulates and why its crowding at the craniocervical junction — the core problem in Chiari — disrupts flow and contributes to syrinx formation.
Common questions
What is the subarachnoid space?
The CSF-filled space around the brain and spinal cord.
How is it affected in Chiari?
It is crowded at the craniocervical junction, disrupting CSF flow.
What does surgery aim to do?
Reopen this space to restore freer CSF flow.
Bottom line
The subarachnoid space is the CSF-filled space around the brain and cord, crowded at the craniocervical junction in Chiari, which surgery aims to reopen.
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