Syrinx's don't typically just go away (though there is an artifact on MRI which can easily be mistaken for a syrinx...hard to imagine that happening if the MRI was read at Hopkins ).
It is difficult piecing together what your original diagnosis was, what surgery was done, and what sypmtoms you're having so I might be able to make some half way intelligent comment.
"a brain surgery and have had work done on your spinal cord"
Did you have a chiari II and surgery was in childhood? or chiari I and then what was the surgery on the spinal cord?
Hopkins is pretty high power so I assume it is safe you've been checked for e.g. lyme, CSF for MS, etc?
--I can point you to the nerve regrowth post, but I don't have time to go through it as its long and list all the supps.
--Assuming you've had a good conventional work up and nothing can be found (and no response to supps):
A. I don't know the time course i.e. how long has all this been going on, but is there some whopping stress in your life e.g. very toxic job, person living with you, etc?
B. In cases where conventional medicine fails, and particularly when they can't even figure out what is going on diagnostically a number of people find some help with acupuncture. You'd want someone very experienced. Ideal would be like some little old chinese man/woman who's been doing this for decades.