Bronco,
I am not sure what precisely the odds are but they are very small, in single digits. However, many bilateral ANs grow at different speeds and because yours is so small, it is possible (I would like to emphasize that the chances of it are slim) that another one willl show up on the other side. I was watched by Neurofibromatosis clinic since 1988 (that's when I had my first AN surgery) and was told that overwhelming majority of ANs on the other side show up within the next few years, usually not more that 7. Unfortunately, we have posters that had another AN show up 20+ years later but that is exceedingly rare. So, keep having those MRIs!
My understanding of the situation is that all ANs, even sporadic, involve chromosome 22. In sporadic AN the genetic defect is confined to the tumor cells. In NF2 the same genetic defect is present in ALL cells in the body and you have 50% of passing it to your children. In NF2 somatic mosaic, the defect is in some cells but not the others, making it more difficult to pass the condition to the children but also making it more difficult to estimate the chances of your passing it to your children. Having said that, even NF2 is a very variable conditon and nobody can predict with any certainty if, when and where a person with NF2 will develop the tumors. The medical knowledge is not there yet.
One of the biggest problems with bilateral ANs is complete deafness eventually rendering people in their prime years unable to work and have a social life. Single sided deafness is bad enough but in my experience it stops me from very few things that requre bilateral hearing. I really advise all newbies with small tumors to save their hearing on that side because you simply don't know what is going to happen to you in the future, be it another AN, age-related hearing loss or something else that might make you completely deaf. It is possible now ( but not guaranteed) for small tumors and serviceable hearing. Make sure you doctor knows it is your priority #1 and shop around for the best doctor to save your hearing. It is absolutely worth a try.
Another thing to realise is that medicine goes at a very fast pace. There is now a genetic test for NF2 (not 100% accurate, unfortunately), MRIs with contrast which means more tumors are found when they are small and surgical innovations which means smaller incisions, less bleeding, very possible facial nerve preservation, possible hearing nerve preservation if the tumor is small, etc. Every five years the medicine makes a big leap forward. So, if you wait and watch for those five years and your hearing is still serviceable, chances are that doctors will be able to save it. On the other hand, if you choose to do something soon, it is still possible to save it.
Best of luck to you and please keep us posted!
Eve
