My story is similar, but different than yours. On Nov. 5, I suddenly had some hearing loss and tinnitus in my left ear. I say my primary care physician as soon as I could and she put me on a round of prednisone right away. She also referred me to an ENT doctor. The ENT doctor had an audiologist do an audiogram, and I was informed that while I had some hearing loss, the good news is that a hearing aid would work well for me. The ENT doctor said that because my AN was so small -- about the same size as yours was -- that I should take the watch and wait approach, even though I lost some hearing, had tinnitus, and was having balance issues which made me walk with a cane. I was told I should wait six months, have another MRI and see how much my AN had grown. In the meantime, the ENT doctor put me on another round of prednisone, even stronger than my first round.
When the second round of prednisone finished, and I had another audiogram done, my hearing had become progressively worse to the point where now the audiologist said a hearing aid would not do me any good. I lost what hearing I had while in the watch and wait mode.
If I had to do it over again, knowing what I know now, I would have wanted to do what you did and had GammaKnife done. At least then I would have had a possibility of keeping my hearing at a level where I could have used a hearing aid. But, by waiting and doing nothing, I am nearly completely deaf in my ear. And having two separate rounds of prednisone did not help me keep my hearing, unfortunately.
I have no hope that I will ever regain functional hearing in my bad ear. It was irreparably damaged by my AN during my watch and wait period. No amount of training will bring it back because the acoustic nerve was damaged beyond repair. On the other hand, my balance is getting better with vestibular therapy. I highly recommend that for those of us with equilibrium issues. But I have not found anything that works on improving an ear once it has lost functional hearing. However, if you have success in training yours, please post it so that we know!
Best wishes in your future!