Brain, Meninges & CSF Anatomy
Arachnoid mater
The arachnoid mater is the thin, web-like middle membrane covering the brain, between the dura and pia.
In short: Arachnoid mater
- It is one of the three meninges.
- Cerebrospinal fluid circulates beneath it.
- It is part of every encephalocele sac's membranes.
- It lies between the tough dura and the delicate pia.
What it is
It is the middle, web-like brain membrane, sitting between the tough outer dura and the delicate inner pia. Cerebrospinal fluid circulates in the space beneath it.
Understanding Arachnoid mater
Together with the dura and pia, the arachnoid makes up the meninges that protrude in an encephalocele and surround the brain and CSF. Because CSF flows beneath the arachnoid, this layer is part of the fluid environment that surgeons must manage when closing a defect.
Why it matters
Understanding the arachnoid as one of the three meninges helps families see what makes up the sac's membranes and why all three layers are part of the brain's protective covering.
Common questions
Where is the arachnoid?
Between the dura and pia.
What flows beneath it?
Cerebrospinal fluid.
Is it part of the sac?
Yes — it is one of the meninges.
Bottom line
The arachnoid mater is the middle, web-like meningeal membrane around the brain.
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