A neurosurgeon specializes in the skull - take you son to one just to be on the safe side. That type of dr. would be able to reassure you that its nothing he won't outgrow or tell you if something needs to be done.
My son has seen Dr. John Myseros with Children's National Hospital. He has an office in Fairfax that is very convenient (I also live in Centreville). I can't speak highly enough of Dr. Myseros, he led us through some very trying times and now my son is a beauitful 2.5 yr old with absolutely no issues. :) Good luck. If you want his contact info, you can either google it or email me (____@____.com) and I will forward you his address and phone number.