Hi lolak.:) I hear the fight for disability is a hard one.
My neurosurgeon said the decompression procedure for the chiari malformation almost always resolves the syrinx on it's own, have your doctors explored other causative agents as a possible sister issue? Just a thought.:) I know my syrinx is considered abnormally low spanning from C3 to C4, perhaps your location of C7 could narrow the cause?
Also, there is a great handbook I found most helpful in understanding the anatomical and physiological aspects of the disorder that might help you as well.:)
http://www.asap.org/index.php/disorders/patient-handbook/