I have a question reguarding something odd on the back of my skull. I seem to have a lump there, I don't know how long it's been there. I think since I was 8 that I can remember maybe longer. I'm almost 20 now. It doesn't give me any pain and it doesnt grow. It's hard just like part of the skull except its about the size of a small marble. Is it normal for some people to have this or should I be concerned? Basically I can lay my head perfectly flat because of this thing. Like I said though, it seems to be part of the skull as it rounded and not just a protrusion in the middle of no where. Just thought i'd ask.