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I'm sorry, mom. I want to know if he has MS symptoms, you know, neurological symptoms. Have you read the Mayo Clinic website regarding Chiari malformation? Which type does he have? Type 4 is the most serious. Have they diagnosed him with that?
It is very important for the neurologist to look at the MRI and determine if the reason his brain is going down into his spinal cord is because he doesn't have enough room in his skull for his brain. Just because the brain is going down in there doesn't mean that there isn't much room. Everyone's brain does this to a certain extent - it's a matter of how many millimeters it extends, if the reason is because there is not enough room, and if brain fluid moves unimpeded from the brain to the spinal cord or not. They CAN do a dye contrast study to determine that.
Opening up the skull should be your last resort. You do not want to hear that straight off by a neurological surgeon. The thing to remember is that surgeons find "nails everywhere that they want to hammer." You want a conservative approach.
I do not know if the Chiari can cause voices. Just because he has this problem doesn't mean the voices are from it. However, you need to understand all of the specifics on HIS particular Chiari so that this can possibly be determined.
I'm so sorry about the headaches. I hope you get some more specific information soon.