Should I Be Worried About A Lump At The Occipital Bone Of A Child Which Sometimes Itches But Does Not Hurt?

My 6 year old son has a lump which I recall him having since a small child that it s from his occipital bone up his scalp maybe the size of a powerball? Or an avecado seed? It seems to have over the years grown with him. I asked him if it ever hurt and he said no but it always itches should I be worried?