Hi, claireb:
Nancyann is correct.
To my knowledge, there is no precise or definite linkage between the size of the acoustic neuroma tumor and post-operative facial paralysis. It's the positioning of the tumor and the surgeon's skill in removing it that have the greatest influence on possible facial paralysis following the AN removal surgery. For your encouragement: my AN was relatively huge (4.5 cm) and I had no facial paralysis, before or after surgery. However, as no ethical surgeon can guarantee the outcome of a surgery that holds real possibilities for post-operative complications, I won't presume to do so either, for the sake of being realistic.
I'm not a physician or a psychoanalyst, but I doubt your mums recent loss of balance is psychosomatic or has manifested itself simply due to the power of suggestion generated by her AN diagnosis. Like most AN patients, my balance before my AN surgery was poor. I could not walk a straight line and absolutely had to grasp the handrail when ascending or descending stairs - or risk stumbling on them. I suffered these symptoms for weeks before I was diagnosed (or had even been examined by a doctor). Following my surgery and subsequent radiation, my balance has slowly but steadily returned as my brain compensates for the hearing loss on my left side. I can walk a straight line and have no trouble walking up or down stairs. Grasping the handrail is now optional for me. Although my initial recovery was fairly rapid, it has taken me a year to feel as if I've recovered completely. FYI: I'm now 64.
Jim