You could have atlantoaxial or craniocervicalnonstability happening simultaneously just based on the symptoms you listed bc they r same as me and I have no syrinx but I do have atlantoaxial instability and subluxation. I believe all of this is unfortunately not covered enough in med school or something bc I had several top neurosurgeons and neurologists completely miss this for 4 years until I had to figure it all out myself. There is a Dr. Atul Goel who is rated the #1 top neurosurgeon in India and for a few years, he ranked and was awarded an award for being literally the best neurosurgeon in the world. Anyway, he also tackles the atlantoaxial instability problem and he has published many great works on the topic. I watched a lecture of his just today on atlantoaxial instability where he delved into the associated co-morbidities & related problems of this undertreated & under-recognized condition. One of his beliefs is that syringomyelia and syrinx, as well as chiari- are all not just separate "bad" clinical entities, but they are divine natural protection that our bodies create as a defense mechanism to the primary problem of atlantoaxial instability, Subluxation, or dislocation. he claims, and has the literal perfect record of his own patients' success to back his claims up- that he doesn't look at these particular presentations as malformations at all, rather the body's protective mechanisms in response to the AAI or craniocervical instability, to save us from acute sudden death or further brainstem sagging. He also claims that he has abandoned all decompression surgeries now because of this. He claims that once the spinal instability is fixed, the syrinx will go away naturally on its own without requiring any further surgery to address it.
just wanted to share this precious info in case it serves relevant to you! Don't know all your details of the situation but I can say after 4 years of me living with what I have and being gaslit by soooo many doctors simply because they don't understand enough (if anything) about this particular presentation occurring in brainstem or spinal cord