arachnoid

arachnoid /arach·noid/ (ah-rak´noid)

1. resembling a spider's web.

2. a delicate membrane interposed between the dura mater and the pia mater, separated from the latter by the subarachnoid space.

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a·rach·noid (-rknoid)

adj.

Resembling a cobweb. Used of the arachnoid membrane covering the brain and spinal cord.

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Arachnoid

One of the membranes that sheathes the spinal cord and brain; the arachnoid is the second-layer membrane.

Mentioned in: Central Nervous System Infections

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arachnoid

[ərak′noid]

Etymology: Gk, arachne, spider, eidos, form

resembling a cobweb or spiderweb, such as the arachnoid membrane. arachnoidal, adj.

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arachnoid

1. resembling a spider's web.

2. the delicate membrane interposed between the dura mater and the pia mater, and with them constituting the meninges. Called also arachnoidea.

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cerebral arachnoid, arachnoidea cerebri

the arachnoid investing the brain.

arachnoid cyst

cysts of the pia and arachnoid containing cerebrospinal fluid; may cause gradually increasing pressure on nervous tissue, especially spinal cord, causing ataxia, paresis.

arachnoid fibroblastoma

see meningioma.

arachnoid granulations

villous enlargements of the arachnoid that protrude into dural sinuses or diploic veins and serve to drain cerebrospinal fluid. They are conspicuous in the dorsal sagittal sinus of the horse.

arachnoid membrane

arachnoid; middle layer of the meninges.

spinal arachnoid

the arachnoid investing the spinal cord.

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arachnoid 

The middle member of the three meninges covering the brain, the spinal cord and the optic nerve. From the optic nerve it becomes continuous with the sclera. See sclera.

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arachnoid

adjective Like a cobweb, covered with or consisting of entangled soft fibers or hair-like material noun A member of the arachnoid family

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Patient discussion about arachnoid.

Q. info on arachnoid cyst in the right posterior fossa

A. Posterior fossa cysts are one of the two most damaging kinds because of the structures underneath such as the cerebellum and brain stem and can cause other diseases. It can cause facial pain from pressure on the trigeminal nerve. Most people do not have any symptoms, but those that do, are prone to headaches.

You might could use this also:
http://www.ninds.nih.gov/disorders/arachnoid_cysts/arachnoid_cysts.htm
Hope this helps.

Q. What is the treatment for an arachnoid cyst? My 15 year old son has just been diagnosed with an arachnoid cyst. What is the treatment? Is an operation necessary?

A. There has been active debate about how to treat arachnoid cysts. The need for treatment depends mostly upon the location and size of the cyst. If the cyst is small, not disturbing surrounding tissue, and not causing symptoms, some doctors will refrain from treatment. In the past, doctors placed shunts in the cyst to drain its fluid. Now with microneurosurgical techniques and endoscopic tools that allow for minimally invasive surgery, more doctors are opting to surgically remove the membranes of the cyst or open the cyst so its fluid can drain into the cerebrospinal fluid and be absorbed.

Q. Is there any problem, if an arachnoid cyst ,2cmx1.5cm size, rostral to cerebellar region left untreated? symptoms: repeated headaches, twitching of muscles, tiredness

A. An arachnoid cyst that leads to symptoms usually needs treatment. Mild symptoms as you suggested are ok to left untreated however gradual onset of new symptoms may arise such as seizures, paralysis and other complications, therefore once symptoms occur one should consider treatment.