hendi51:
Hi, and welcome to the forum.
Dana is totally correct in that the size of the AN tumor and loss of balance (disequilibrium) are not necessarily related. It's the location of the tumor that causes most of the problems. My AN was relatively huge but I didn't develop symptoms, aside from the typical one-sided hearing loss, until 6 months prior to my diagnosis. Until then, I was fine (I thought). In fact, the 4.5 cm tumor had pushed my brain to one side and was beginning to compress my brainstem. My primary care doctor was alarmed when he looked at my MRI (he called from his home, in the evening, which is very rare) and the neurosurgeon who I chose to perform the surgery was equally concerned. So, in my experience, having severe symptoms does not automatically equate to having a large tumor.
Your husband may well be a candidate for non-invasive radiation treatment. You will both need to learn as much as you can - this website is a fount of AN information - and make an informed treatment choices. Don't rush into anything but don't waste time, either. These AN tumors can grow very slowly or very quickly, in 'spurts' - and bigger is definitely not better!
We're here to support and help you and your husband in any way possible. Please stay connected.
Jim