ripple in my skull

i have this weird long bump on the back of my skull (not just my head/skin, it's fuckin rock hard) which could be described as a "ripple" because it isn't just a small round bump like most i sometimes get from accidentally hitting my head on concrete or something. it's kinda painful to put my head against a hard surface on that spot too. I only noticed it a little while ago. is this something i should be concerned about? and what the fuck do you think it is?

call of cthulhu