This could be a lymph
node that became swollen in the past and has remained enlarged or it could be a benign bony lump on the skull bone called a osteoma
. I would encourage you to have a physician look at it who may arrange an XR or CT scan
depending on his assessment to further elucidate a diagnosis. Its unlikely after this period of time to be anything sinister and if it doesn't bother you its unlikely that you will need to have it removed.