Hi, katherine:
Like all the previous posters, I'm sorry to learn that you have a AN re-growth. This is something many AN surgical patients fear.
Unfortunately, tumor re-growth does occur. It is quite problematic for surgeons to totally remove every cell of the tumor, as it resides in a place that is both hard to see and reach and of course, some sensitive, important nerves are often very involved with the sticky tumor substance making 100% removal almost impossible. Sometimes, just a few cells left intact can regrow into another acoustic neuroma, although this is relatively rare, but obviously, not unknown.
I would assume (and hope) that you'll be a candidate for (non-invasive) radiation treatment of your 'new' AN but your doctor will have to make that determination. Meanwhile, try not to become too anxious over this unpleasant development because there is a very good chance that you'll not need surgery, again.
Jim