I'm no medical doctor, but in my opinion if you have symptoms of pain in the face when smiling, can't hold smile for very long as muscles get tired, excessive saliva, drooling, eyebrow and lid drooping, eye twitching, biting your lip, tongue or inside of cheek, feelings of sharp shooting pains in face, numbness, etc. and have never had any or all of these symptoms I would think the doctors don't need to "get in there" to know if your facial nerve is being affected or not. The bony canal (space where tumor grows) is sooooo small, room enough for only those three nerves, vestibular, hearing, facial, my guess is when tumor begins growing and pushing on other nerves they will be affected even if on and off symptoms occur over time, even years as in my case. I didn't need my doctor to tell me the facial nerve is or isn't affected by the tumor--I could "feel" it was. I had the above symptoms with the exception of eye twitching before my AN was removed. After my most recent surgery I can now add to this list numbness of the palate and tip of tongue. Hope this passes within the next few months. I am surprised some days when I can "smell" my cup of coffee, but cannot taste it! This isn't the case every day thankfully.
FYI--prolapse where nerve falls out of place in a previous wound opening (dehiscence). Hope this helps? I do have synkenesis of facial/eye movements and some slight drooling that are noticeable to me and doctors, but not my friends (or maybe they are just being nice?) They are slight differences at best. I've been told to NOT have anymore surgeries to that ear, so as long as the tumor never returns I am good to go. Depending on the skill of the surgeon, size of tumor, most facial nerves come out unscathed and I hope this is the case for you.
Below is an article on facial nerves and their intricacies. Very technical but perhaps informative to those interested in which part of the face the nerves control.