I have never heard of it. My son is almost 5, and we took him to a neurologist when he was almost 2 because he was such a late walker (21 mos.) He had a few autistic traits, but not very many. The doctor recommended an MRI. It came back normal. At that time, I am not sure what they were looking for, but they did not find any abnormalities. He now has been diagnosed with PDD_NOS. He is walking fine and is getting stronger every day, but I do not think he would really ever play contact sports because he just does not like the chaos of it.
Personally, I was a wreck because I did not want to have my son sedated for the MRI. It all turned out fine, and I went through with it, because a friend of mine had me so concerned that he might have some sort of brain tumor, so I wanted to rule that out. From what I have heard, and maybe research has changed a bit in the last few years, is that nothing really different ever shows up on the brain of an autistic child. I would ask the doctor if this is something life threatening, and how necessary is this in his opinion.
Good luck with it all!