How often with arachnoid cysts does it require surgery?

Rarely: Uless enlarging and causing neurological symptoms specific to that cyst, nothing is surgically done usually.Monitoring is important.

Very rare: Usually they are just followed unless it is causing a problem like seizures.

Rarely: Arachnoid cysts are not rare as an incidental finding on MRI or ct scan. Most cause no symptoms and require no treatment. Occasionally they may cause epileptic seizures or neurological impairment; if that is the case surgery may be required.