Hi and welcome to the Chiari forum.
Since we are not medical professionals...we can only guess and give some ideas from our own experiences.
I do not have hydrocephalus, so I can not comment on that aspect...but it looks like your odontoid bone may be partially retroflexed.
Here is a link with a few names of Chiari Drs in Australia....none in Melbourne....as here in the States you may have to travel....as you will want a Dr that has experience with this and ALL related conditions.
Mine was 5mm and I had surgery because I had a cine mri which showed a lot fluid blockage.
That was 8 years ago.
thanks. im working on finding someone in melbourne australia who can give me second opinion
Sorry but I'd ask for a second opinion because it sounds like you got blown off and that's not ok!
If you having symptoms of hydrocephalus they could do a lumbar puncture. Which usually after they do test...a person feels better for a while.