I have always had more luck explaining all this stuff through pictures. Trying to tell someone I have a kinky brain stem doesn't always go over well :) But I do...and it explains a lot.
The image below is that of a normal brain with a fabulously perfect brain stem. See the arrows? They are pointing to two things.
The first arrow on your left points to a lovely C-2 vertebrae that is exactly as it should be....straight.
The second is pointing to this persons cerebellum. See the arrow on the right sitting in the dark grey line? This is cerebral fluid nicely cushioning this persons cerebellum....my neuro calls this a lake...dunno why? I think it looks like a stream...or river. Lakes are round.
This is your brain....(well not yours but a brain anyway).
The image below is that of a kinky brain...this is me without skin. Ew!
The arrow on your left points to a very bent C-2 that is causing a "kink" in my brain stem. It is as painful as it looks...really :) THIS is Basilar Invagination
The arrow on your right points to my cerebellum with very little cerebral fluid cushioning my brain. My neruo says I have no "lake" and my brain stem and cerebellum are very squished...THIS is Chiari Malformation
This is my brain on Basilar Invagination...
Every time I look at this image I get a sinking feeling. It's not like they could be wrong ya know? It's very clear something is not right here....second opinions would tell me the same thing...third opinions did too.