Hi, Catherine:
There is no reason why you should lose all hearing in your ear on the side with the AN (and certainly not in the other ear). With such a small tumor (barely the size that an MRI can detect) and still-perfect hearing, you can probably save most or all of your hearing by getting radiotherapy such as CyberKnife (CK) to treat the tumor before it degrades the hearing nerve.
However, it's not as straight-forward as that. CK (as well as microsurgery and other forms of radiotherapy) can also damage the hearing nerve. So, you have to weigh the risk of hearing loss from the AN vs from the treatment for the AN. With your tumor being so very small and your hearing perfectly preserved so far, watchful waiting is a very reasonable course to take at this time. Should you begin to notice hearing loss or tinnitus (a ringing sound in the ear), however, you should consult with doctors who do microsurgery, CK, GammaKnife and other forms of radiotherapy (standard FSR, or fractionated stereotactic radiotherapy) to figure out which treatment protocol is most likely to preserve your remaining hearing.
My opinion is informed from a conversation I had with Dr. Steven Chang, esteemed doctor of CK and microsurgery at Stanford University Medical Center in California and one of the world's leading authority's and practitioners on treating ANs. He told me when I was in watch-and-wait that the sooner I had CK, the better the chance of preserving my remaining hearing. Please keep in mind that my AN was way bigger than yours and growing much faster than the norm. So watch-and-wait was not a good option for me; I needed treatment and soon. And, too, I had already lost a significant amount of hearing on my AN side, so treatment to stop the ravages of my tumor was more pressing.
Your situation is different. You should be in no rush to seek treatment, although researching your future treatment options now while you can bide your time will be way less stressful than waiting until it becomes a more pressing matter (if that time ever arrives; some ANs don't grow for 20 years, so you may never need treatment). The point I'm trying to make is that you should not assume it is a done deal that you will lose your hearing over time on the AN side. Do not fear; this is not a foregone conclusion. It is the opinion of only one doctor. There are certainly others who will give you a rosier prognosis.
Best wishes,
TW