What Does A Small Lump On Base Of Head Indicate?

my 14 yr old son has had a small lump on the lower rear portion of his head for a while; the precise date it 1st appeared is unknown. No trauma is involved. No pain is involved, but he has been experiencing minor headaches intermittently for a week or two, usually when he s inactive, something that he didn t previously experience as far as he knows. There are no other symptoms as far as he knows or we can tell. He seems fine mentally and is sleeping and functioning well (or normal). He takes no medications, but he has used OTC Advil now and then for the headaches He is worried that the lump may be a sign of a brain tumor. Is this likely a tumor or at least something we should get checked out? Or is it more likely nothing to worry about?