Hello, our 2013 son was diagnosed with Arnold Chiari Brain Malformation Type I, almost 3 years ago. He is & was a multi sport athlete. Playing Football & Baseball were his favorite sports. After a series of a fall, and probable football concussion, even with state of the art & expensive helmets that had been purchased for him to wear while playing, he was sent for a CT scan as a precaution. Nothing found. The following year, 2 more football concussions. He was always on the field, playing offense - QB & defense - MLB. He then went to see a Neurologist, & he ordered an MRI. Which finally discovered his mild, 10 - 14 cm Chiari. We were sent to see a Neuro Surgeon Specialist. He advised no more direct contact sports, particularly football. This absolutely crushed our son, for a long long time. Truthfully, he never got over it. Our son was fortunate to have attended away NFL camps, for the previous 6 years, were he medaled. He even requested that the Dr. take his records to a Neuro Surgeon Convention for a vote, on as to whether or not he could still play football. Well, the Dr. obliged. The vote came back favoring caution & no direct contact sports like football, but that the vote was not unanimous. We went with caution. It devastated him! Eventually our son put everything into Baseball, year around! The Neuro Surgeon had left it that our son did not need surgery, nor to see him again until before he started College, unless he began to have problems & / or symptoms. So, after our son graduated last Spring, we scheduled a follow up with the Dr., & needed his official opinion, etc., before College & in layman's terms in writing for his medical records, because this is such a rare & often unheard of condition. Well, at the appointment, he was given the news...NO RESTRICTIONS! None! Even said that he could have played football now!
The Specialist considers his condition mild, and does not think his Chiari will grow or have complications. And says that He likely never would have known that he ever had it, if not for the MRI. Our son only had an occasional headache over the past 3 years, which may or may not have been from the Chiari. He rarely ever took even an over the counter pain med. He started on the school Soccer Team, against my then wishes. But, with his Dad's Stroke 4/2012, I just didn't have the fight left in me. And the Dr., had originally cleared him for Soccer. We said no then. But he had no problems. And he will be leaving for College in a couple weeks, as he was recruited as a Pitcher, but when they see how he runs...and how fast he runs & masterfully steals bases...they might just change his position(s)! 
JK! Chiari is supposed to effect balance. So, my point is not to brag, but to offer hope. It is not always the dior diagnosis we as parents fear. I empathize with all whom have loved ones, or they themselves suffer from Chiari. I have read & read about it, feared the worst... But, now their is light at the end of the long tunnel! Even his College Coach & staff have been great about it! Praise God! Sometimes, there can be happy endings to things, that we never dreamed possible!