Hi Ann,
Sounds like good news, if have to have an AN. I will try to answer some of your questions.
I doubt it is microscopic, an MRI is only good down to 1-2 mm (the spacing of the slices). So I'm sure it is 8mm x 5mm.
Many people refer to the size of their AN by its largest dimension, but the radiologists who read the MRIs will always do all three measurements.
With mild symptoms and a small size, watch and wait for six months makes good sense as your first step.
The onset or increase of symptoms may or may not indicate growth, but they at least suggest activity of the AN and changes in the area. I think they are a good basis for deciding to take action earlier rather than later. For any treatment, smaller is better in terms of good outcomes. Once they are out of the canal, other nerves and the brainstem itself come into play.
If malignancy is your only concern about radiation, I think you should consider doing Cyberknife or Gammaknife. On small tumors especially, it is a good way to go, with better hearing preservation and lower facial nerve risk than surgery. There are so few cases of malignant AN after radiation that a rate can only be estimated, and no one is sure if it is really any different from the background rate. Sandra posted an article two months ago that gives a good overview of radiation treatment:
http://www.emedicine.com/ent/TOPIC668.HTM#GammaKnife. "Eight case reports of malignant transformation of acoustic neuroma can be found: 2 followed external beam radiotherapy, 2 followed stereotactic radiotherapy, and only 4 were spontaneous."
Since you will have six months, I would also suggest taking a look at the Cyberknife forum, and posting a question or two about the chances of getting a malignant AN. There are two very experienced radiation oncologists who answer questions there, and will set the record straight for you. They can provide lots of information about other issues as well, such as possible swelling during the year following radiation.
There are a number of balance tests and measurements of balance nerve function, ranging from walking heel to toe for the doctor, to wearing video goggles and having your eye movements monitored in various positions, or with water in your ears. I found them pleasant enough, and they can help identify what the AN is up to and how well your AN side balance nerve is working.
Take care,
Steve