CSF, Ventricles & Brain Anatomy
Subarachnoid space
The subarachnoid space is the fluid-filled space around the brain and spinal cord where cerebrospinal fluid circulates and is absorbed.
In short: Subarachnoid space
- It surrounds the brain and spinal cord, between two of the meninges.
- CSF circulates here after leaving the ventricles.
- CSF is absorbed from here into the bloodstream.
- Problems with flow or absorption here cause communicating hydrocephalus.
What it is
The subarachnoid space is the space surrounding the brain and spinal cord, located between two of the protective membranes (the arachnoid and pia mater). It is filled with CSF.
Understanding Subarachnoid space
After CSF exits the ventricular system through the outlets of the fourth ventricle, it circulates through the subarachnoid space over and around the brain and spinal cord, and is absorbed back into the bloodstream, mainly through arachnoid granulations. Problems with CSF flow over the brain's surface or with absorption from this space cause communicating hydrocephalus, where the ventricles still connect to the subarachnoid space but fluid is not properly circulated or absorbed. The space also contains the basal cisterns, wider pools of CSF at the base of the brain.
Why it matters
Understanding the subarachnoid space helps families see where CSF circulates and is absorbed, and why problems here — rather than within the ventricles — cause the communicating type of hydrocephalus.
Common questions
Where is the subarachnoid space?
Around the brain and spinal cord, between two meninges.
What happens there?
CSF circulates and is absorbed into the bloodstream.
How is it related to hydrocephalus?
Problems with flow or absorption here cause communicating hydrocephalus.
Bottom line
The subarachnoid space surrounds the brain, where CSF circulates and is absorbed; problems here cause communicating hydrocephalus.
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