What do you recommend if i have a 2.82.1cm subarachnoid cyst near my fascial nerves it cause problems but dr said it wouldnt cause it?

Frequent checkups: It sounds like you have an arachnoid cyst of the posterior fossa. These are usually benign lesions in the brain that are under low pressure and usually do not cause any symptoms. Symptoms in your case might include problems with a facial droop or hearing as these nerves are in this area. You may consider having serial MRI scans (with contrast) to make sure there is no tumor and this doesn't grow.