I have to agree with Marci that size does matter, but location matters also.. Where your tumor is located has much more of an impact as far as symptoms go, but from what I've learned ANs are easier to treat when they are smaller, this is true for surgery and radiation. My guess is that many larger tumors go undetected for a long time because of their location. My guess is that sometimes these boogers produce no symtoms or such vague ones they are easily dismissed as being of no consequence, age related or are misdiagnosed -- by the time they start causing problems that can't be ignored or call for an MRI, they can become very large. It is my understanding that size, location and how sticky (I believe how sticky the tumor is only a factor for surgical patients -- I can't see how this would affect someone having radiosurgey)) the tumor is are the determining factors in each person's outcome. Unfortunately, there is no way to determine how sticky a tumor is until they get to it during surgery. Also, sometimes a tumor will be wrapped around a nerve or a part of a nerve, for example nervus intermedius or the eye moisturizing nerve, nerve will be caught up in it and have to be sacrificed, which also obviously accounts for the problems some people have.
Wendy