In the research I did leading up to my treatment, I stumbled upon a couple well-documented (by doctors/respected medical facilities) cases in which "spontaneous disappearance" of an AN occurred. However, the impression I had was that these dramatic cases were extremely isolated, probably on the order of less than one in every ten thousand. The doctors were totally mystified as to the cause of the tumor disappearing. Sorry to say, I wouldn't count on it happening for you. It seems to be as random of an event as getting an AN in the first place.
On the other hand, a few people have reported their tumor shrinking by a very small amount, often only to grow back in size later on, or possibly fluctuate back and forth in size. I suspect some of these reports are simply the result of the margin of error (2 mm) inherent in MRIs, while others are simply the result of different radiologists interpreting subsequent MRIs differently.
Usually, ANs either stay the same size or grow very slowly (1 to 2 mm per year on average). Some go through unexplained growth spurts. The best you can rationally hope for, without treatment, is that it stays the same size for many years to come.
Best wishes,
TW