It depends upon the type some people are born with their brain tonsils too low and of course they have Chari.
Me, and the worst type to have is post-traumatic. I got blown up, hey that's life.
There are many other ways a person can get a sring, look at Arnold Schwarzenegger, a lot of strenuous and I mean incredibly strenuous activity and a lot of bearing down can cause the beginning of a syring to develop.
In my research I have also learned that a person can have Syringomyelia and it takes a traumatic event for a syring to develop and the cerebral brain fluid entering the spinal cord.