Hi,
the same ENT that you saw recommended to me to have the balance (VNG) test. His reasoning is that it would give an indication about whether I would have balance problems post-treatment. If the balance nerve is already compromised, then it is most likely that balance will not be an issue post surgery, since the other side has already compensated. I suppose similar reasoning goes for radiation (i.e. if your nerve is still functioning, then you might end up with mixed signals to the brain, and more balance problems, so this might factor in your choice of treatment).
The test itself is quite long (at least two hours if I recall well). They make you wear some special goggles and you follow some lights. They pour warm and cold water in your ears and from this test they can tell how each side responds separately. It was interesting to find out that even though I had never experienced any balance problems I had 90% weakness on my AN side. For me this translated to no problems post op. If I knew that my nerve was still functioning, then I might have expected and planned more for vestibular problems.
I don't think this test is absolutely necessary, and it is not standard procedure - my understanding is that most people don't do it. You should be able to do it closer to home if you don't want to travel all the way to Toronto. I had it done locally.
Marianna