Mine is at the base of my brain, I have had years of unexplained weakness and numbness on my left side, over and above accident damage. Between '07 and '13 it grew 'significantly' according to my Neuro. I also have early-onset mental issues like Depressive Personality Disorder/Anxiety issues which some attribute to Arachnoid Cysts where present.

Of course, when you have a large lump pressing on parts of your brain, Neuros are loath to admit it may be doing anything at all.

Dave.