Hi and welcome to the Chiari forum.
As Mel mentioned above, it is not the length of herniation, but the width and they do not give u that measurement...really if u have a CSF obstruction is what is more concerning then how long it is as it can be 13mm long, but be thin and allow the CSF to flow, or u could have a 2mm herniation that is like a cork and does not allow flow....
Also as Mel mentioned NO Chiro's as they can compress the herniation into ur brainstem causing further issues....do not allow manual manipulation of ur neck and shoulders.
We do have a list of Drs that the members have compiled, not all on the list may be true specialists but it is a means to help u get started with ur research......
Please note- u may have to travel may of us do and our list is not a referral...what works for one may not work for another so u have to visit a few Drs of comparable experience and educate urself so u will know when u find the right dr for u.
Use the Health Pages for more info and to locate the Drs List-
http://www.medhelp.org/health_pages/list?cid=186
Please keep asking questions, and know u r not alone : )