Lump on head

I have a healthy 11 month old son. He has never fallen and hit his head. I noticed months ago that he had a lump on the left side of his head near his temple under the skin. There is no sort of open cut or pus or nothing. His skin is just bulged up.  It has grown a little bigger. It does not seem to bother him unless you are touching it. It is hard and does not move at all. I take him to the pediatrition next week. My question is is it something I need to have looked at immediatley? What could it possibly be?

[margypops]

It sounds like a cyst , but it is always best to get it checked out, then you will feel better and the Doctor will know how to treat it.good luck