The arachnoid mater is the thin, translucent middle layer of the meninges, lying just under the dura. Fine web-like strands (arachnoid trabeculae) cross from it to the pia, giving it its spider-web name. The space beneath it, the subarachnoid space, contains cerebrospinal fluid and the major blood vessels of the brain.
| Location | Beneath the dura mater over the whole brain and spinal cord, bridging over the sulci without dipping into them |
|---|---|
| Parts |
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| Connections |
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| Blood Supply | Largely avascular; nourished by CSF and nearby meningeal vessels |
Encloses the cerebrospinal fluid of the subarachnoid space, forms a barrier between the dura and CSF and returns CSF to the blood through the arachnoid granulations.
Arachnoid cysts are fluid-filled sacs within the arachnoid, most often in the middle cranial fossa, and are usually harmless incidental findings. Arachnoiditis, scarring inflammation of the spinal arachnoid after surgery, infection or injected substances, can cause chronic back and leg pain. Meningiomas arise from arachnoid cap cells.
A congenital CSF-filled cyst within the arachnoid, often in the middle cranial fossa, usually without symptoms.
Chronic scarring inflammation of the spinal arachnoid causing clumped nerve roots and persistent burning back and leg pain.
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