I have an arachnoid cyst of 2cmx1.8cm in the middle fossa. This is not present in my previous two MRI scans, taken before 3 years. What could be the reason for this to come up? Had no trauma. I have double vision. Scan shows flattening of temporal lobe. Can this be the reason for double vision. Is there a probability for misdiagnosing this as arachnoid cyst instead of something else?