Paul,
Glad you found our forum - it's a good place to ask questions and alleviate concerns. That said, I can only give you my experience and "guess" as to your answer, which is -- yes, I think symptoms can come and go. I KNOW the vertigo/balance issues can come and go because our bodies can compensate. About the hearing and tinnitus symptoms, I know that my PERCEPTION of their severity changes alot, so I'd say, yes, they can waver also. For instance, when I went for followup 6 months after GammaKnife treatment, I said my hearing was worse, but hearing tests (done at same facility) showed no change from previously.
About the claustrophobia - I hear you. I am only a little claustrophobic, so I was able to grit my teeth and get through it. My second MRI was the morning of the GammaKnife treatment and they had me pleasantly "looped" on intravenous who-knows-what drugs that I didn't even notice having an MRI, although I was awake. The third time I got a prescription for Valium. So...if I were you, I'd really emphasize your extreme claustrophobia (don't be afraid to exaggerate a little) and hopefully they could give you some strong medicine.
If your ENT is correct, it is probably best to get the MRI. Have you read much on this site? Acoustic neuromas (vestibula schwannomas) are almost always very slow growing, so there's usually no big rush. And then there are several options on what to do, including "wait and watch," if you do have an AN.
You might want to wander around this site to see if you think your symptoms sound to YOU like an AN. And perhaps get a second opinion from another doctor.
Keep asking us questions. This is a wonderful group of smart, investigative and supportive folks.
Take care,
Dana