Causes & Risk Factors
Arachnoid cyst
An arachnoid cyst is a fluid-filled sac related to the arachnoid membrane that can sometimes obstruct CSF flow and cause hydrocephalus.
In short: Arachnoid cyst
- It is a benign fluid collection related to the arachnoid membrane.
- Many arachnoid cysts cause no problems.
- Some can obstruct CSF flow and cause hydrocephalus.
- Treatment may involve fenestration (creating an opening) when needed.
What it is
An arachnoid cyst is a benign, fluid-filled sac that forms in association with the arachnoid membrane around the brain. Many are found incidentally and cause no symptoms.
Understanding Arachnoid cyst
While many arachnoid cysts are harmless and stable, some — depending on their size and location — can press on or obstruct the CSF pathways, causing hydrocephalus or other symptoms. When an arachnoid cyst is causing problems, treatment may involve creating an opening in the cyst (fenestration), sometimes endoscopically, to allow fluid to drain into the normal CSF spaces; a shunt is occasionally used. The decision to treat depends on whether the cyst is causing symptoms or obstruction, since many require only monitoring.
Why it matters
Understanding arachnoid cysts helps families see that these common fluid collections are often harmless, but that some can obstruct CSF flow and cause hydrocephalus, in which case treatment can relieve the problem.
Common questions
What is an arachnoid cyst?
A benign fluid-filled sac related to the arachnoid membrane.
Do they always cause problems?
No — many cause no symptoms.
How is a problematic one treated?
Often by creating an opening (fenestration), sometimes endoscopically.
Bottom line
An arachnoid cyst is a benign fluid sac that is often harmless but can sometimes obstruct CSF flow and cause hydrocephalus.
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