I have an arachnoid cyst and a chiari 1 malformation. i know it depends on the person but how likely is it that i will need surgery?

Only eval will tell: The only way to know if you'll need surgery is your exam by a neurosurgeon who does chiari decompressions. He will thoroughly evaluate your clinical symptoms, physical symptoms, MRI findings and base his opinion on those findings. Most arachnoid cysts do not require surgery as they are present from the beginning of your brain development. See a neurosurgeon and good luck!

See below: Again the answer will vary depending on the patient, but here goes. If the arachnoid cyst is not growing or causing any pressure problems, it can probably just be watched. If the chiari malformation is not causing problems it too can just be watched. If the headaches, or other symptoms, get worse then consult your neurosurgeon. Good luck.