Unfortunately, this is becoming more and more common to hear about bone overgrowth as a result of BMP being used in fusions.
One level anterior spinal fusion in the only FDA approved use of BMP in spinal surgeries, as far as I know and it is not approved for cervical spine and can be dangerous and potentially fatal if used in the cervical spine.
If you google something like adverse problems with BMP use in fusions, you will come up with lots and lots of info about it.
You can also go directly to the FDA website, do a search on BMP and you will find even more info as well.
It sounds like you are suffering from bone overgrowth caused by BMP and I hope that you and your doctor will report this to the FDA.
In the mean time, it is possible to remove the bone overgrowth with a surgeon that is experienced in this problem and very, very skilled.
Whether you are now suffering from some permanent nerve damage from it after a year of time, is something that only time would tell if and when the bone overgrowth is removed.
The lesion also sounds like it could be the bone overgrowth as well, but because you have hardware in you, the pictures may or may not be as clear as one would like.
Some things that are going on can not and will not show up with the films done and the only real way to determine all that is going on is to actually go in for surgery and have the spine surgeon take a look.
I would discuss this with your spine surgeon first and then get several other opinions on what to do.
Google as best you can to find a surgeon that has had experience in removing bone overgrowth from BMP, done research in the problem as well.
That is the kind of spine surgeon I would want to use.
Good luck and keep us posted with what you find out and how you are doing.
Fran