At least one Chiari neurosurgeon has commented that there is a 40% chance of surgical failure within 2 years of a typical posterior fossa decompression surgery. This same neurosurgeon, Dr. Fraser Henderson, believes that many of these failures can be avoided by checking for cervical instability before surgery. Cervical instability in many cases is caused by EDS (Ehler's Danlos Syndrome) or hypermobility. The instability is fixed by fusion in the areas which need support.
Dr. Henderson is one of the leading Chiari neurosurgeons in the United States. His exams are incredibly thorough, and he uses a variety of measurements to isolate which part of the spine of skull might cause a surgical failure. He asks for tests that few other neurosurgeons ask for, to include a rotational CT scan, and an upright flexion/extension MRI.
If there was only one suggestion I could make to every member of this site, it's to check for EDS or hypermobility. There is an incredibly high number of Chiari patients who have it. A rheumatologist or geneticist can (typically) diagnose EDS (hypermobility is considered the same in many circles, although hypermobility is considered to not have a genetic component to it). EDS is passed down through one parent in almost all cases, so if your Mom or Dad was extremely flexible, could touch their tongues to their noses, bend their thumbs to their forearms, had joint or dislocation problems, velvety soft skin and unusually wide scarring, they probably passed this to you. I'll add a few links at the end of this page, one will have the pictures of EDS skin symptoms.
I would also encourage all of you to watch this video. I know it's long (over an hour), but you are the only person who can decide what the best course of action is for you and your family, and being educated about Chiari complications can only help.
The slideshow Dr. Henderson used is here:
Here is the EDS pictures link, you'll have to scroll down to see all of the pictures:
Great article about EDS:
And finally, here is a MRI picture of my 7-year old daughter. I had to push her doctor for an MRI, and push to get an upright instead of a traditional MRI, and in the end, the radiologist only noted a small pineal cyst (she's been having migraines and visual problems). I have measured, and her clivo-axial angle (angle at the top of the spine) is 105 degrees. Dr. Henderson has noted 165 degrees is normal, anything under 135 degrees is symptomatic. Push for your own health, and that of your loved ones. Learn as much as you can about Chiari, because your radiologist, doctors, and specialists will not know as much as you do. Ask questions, post discussions, send me a message, and I will be happy to send you reading material. I don't always get to the discussions, but I always respond to my messages (mostly sooner, but sometimes later). If you don't understand a term in an article, Google it. If you have a hard time with technology, bribe the neighbor's 17 year old kid by making cookies. Seriously, send me a friend request and a message. And ALWAYS get your MRI disks and look at the pictures yourself.