2 year old son - large head mis-shapen forehead

Last week I noticed my 23 month old sons forehead was bulging a bit starting above is right eyebrow to the top of his forehead. I was extremely alarmed since I had not noticed this before. Since birth his head has been in the 98%, so we have been closely monitering his head since. I took him to his ped. to investigate this bulge and our ped. said his head seemed to be forming correctly and had no explanation for the mis-shapen forehard. Although after measureing the head circum. the ped. found that my sons head had grown rapidly since his 18 month check-up and was concerned this was above the normal growth rate. He suggested we get a CT scan but did not require it, it was more for peace of mind. It seems to me that an asymmetrical forehead that seemed to occur overnight coupled with rapid head growth would be cause for alarm, but I don't want to get a CT if not neccesary. Does anyone know about spontaneous lumps bumps and rapid head growth.