arachnoid cyst is something you are born with and will have until the end. The analogy that I make to my patients is if you ever seen the tree growing through the fence - as the tree was growing and something was on it's way it actually grew and accommodated the fence in it - arachnoid cyst is the same - as your brain was developing that cystic area was accommodated by growing brain - therefore nothing should be happening after the brain has developed. additionally, if something is supposed to happen - it would have happened when you where a child and not as the age of 53. you do not drain them because they are likely to be connected with CSF producing ventricles and will "grow back" right after the drainage.
Smells that you are experiencing could come from 2 sources - occasionally after sinus surgery - certain smell receptors become "hypersensitive"
and finally - i had one patient who smelled gasoline everywhere she went - eventually was diagnosed with seizure disorder, so EEG in local neurologist office may prove useful (especially if you have loss of "train of thoughts")
Please remember that if you get a satisfactory answer from your Expert to click the green "Accept" button so the Expert is compensated for a job well done. Positive feedback is also appreciated. :)