Hi ~
AN removal surgery doesn't usually affect tinnitus, although there are exceptions, of course. If you have tinnitus prior to AN surgery, no matter what surgical approach is used, you will very likely still have it, post-op. Occasionally tinnitus is increased after surgery and in relatively rare cases, it decreases. The reason severing the hearing nerve does not affect tinnitus is based on the fact that tinnitus isn't an actual sound your ear picks up but a result of your brain reacting to nerve damage or related issues. Whatever manifestation of 'sound' you 'hear' with your tinnitus (there is a very broad spectrum of tinnitus 'sounds') it is not actual, audible sound but simply your brain reacting to some sort of damage, either to the ear mechanism and/or the hearing nerve. Thus, severing the hearing nerve does not cause the 'sound' to cease.
I'm not a doctor and only suffer from a very mild form of tinnitus so I may be contradicted by others with a more precise understanding of the affliction but I believe I've helped answer your main query as to why tinnitus doesn't disappear when the hearing nerve is severed in Translab AN surgery.
Jim