Here is a very active forum- have you tried your post on there as well?
http://www.medhelp.org/forums/Chiari-Malformation/show/257
They also have info on Chiari's here on medhelp- which you may already have seen at this link:
http://www.medhelp.org/health_pages/Neurological-Disorders/What-is-Chiari-Malformation/show/125?cid=186
I was tested for Chiari's after someone on a forum suggested it to me and a doctor agreed to order an MRI but it came back I didn't have that malformation.
I recommend you show your neurologist your radiologist reports, where it says possible Chiari's, 4 mm Chiari's- and if your MRI was not done on the latest 3T MRI machine, which has a stronger magnet (3 Tesla) and is supposed to show more detail, and since your Chiari's malformation is so small, you might ask if he would be willing to order another MRI if you could get it on one of these latest machines which could be important with your malformation possibility.
In addition, I would ask the doctor to explain why your CSF flow study demonstrated diminished cerebrospinal flow. I'd ask what is the reason for it, if not Chiari's and is there anything that can be done about it. It might just be your doctor was in a hurry the second time and didn't remember all the details of your case- it sounds like he might be worth another chance, based on your first visit.
Your nystagmus- did it just develop in recent months? If so, this would be a very important thing to bring up to your neurologist (see PM for more info).
Also, if you are experiencing any endocrine pituitary related symptoms not related to your thyroid, which you said you had tested, a pituitary tumor can cause a lot of problems, including headache and is often not seen on a general MRI of the brain, but has to be looked at separately. I also learned after a radiologist saying there may be a small pineal cyst in my own head, that if you have one of those over 5 mm, that can cause headaches. The pineal gland is even smaller than the pituitary!
But when I look at Chiari symptoms on that link I gave you from medhelp, it sounds like a lot of your symptoms are listed there and I'd encourage you to share on medhelp's forum, because there are people there dealing with that and some of them would know a lot more than I do and they might be of help.