I have always had this hump on the back of my neck, always was assumed it was genetic, grandmother and cousins have same thing. Reading more into this, only thing I came across is buffalo hump / cushing syndrome. I do have very poor back posture, this could be some source to this. the hump has gottan bigger over the years. Usually doenst cause much pain but once rubbed feels kinda like a bruise.. some fatty like tissue there, seems like bone is humped out too.. not sure if the curve of the bone is the natural curve or is worse than normal.
If anyone has heard of this or has the same type thing people respond with any information you might have.. thanks.