Hi Polly and welcome to our exclusive group .....
Actually, we are not exclusive because we have a wide variety of medical issues that bind us together in this forum. Therefore, even if it turns out you do not have an AN, you will be welcome here at any time. You will find this a very caring, supportive group of new friends, who are very willing to share their personal experiences.
You are correct that nausea can definitely accompany the balance issues.
If your instrumentation is made of titanium, there should be no problem with the MRI. An AN shows up much higher in the head than your neck so it should be able to be seen easily. My AN came after I had had previous brain surgery, in which teflon pads were left at the brain stem (on purpose). The first MRI I had following that surgery was a zoo. At first they were refusing to do it at all. Then, they agreed to do it if they had an operative report assuring them of the make-up of the pads. Had to have the hospital fax a report, etc. Finally all settled and on with the MRI. All this is to say, if you have documentation of the make-up of your instrumentation, you might avoid any hassle. Better yet, if you have any imaging films/CDs or reports of your neck, take it all with you to avoid any issues.
Best thoughts and ask away ...... that's what we're here for. Be sure to let us know what you find out next week.
Clarice