birth marks and its meaning

my son was born 1/28/2009,and we noticed later that on the back of the head. just where the head and back of the neck join . a reddish burgandy color mark about the size of a quarter.we didn't think nothing of it you now maybe a birth mark we said.we asked our pediatrician about the mark showed it to him and he said the same a birth mark. and now our son is 3 almost 4 months old, and we've noticed that it has grown a bit across the back of his neck near the back of the head.It has a elongaded shape about an inch to inch and a half long.what could this be,is their any concern or precautions to take should it be looked at more just to be safe.  

[Howard Rosenberg, MD]

I would suggest a consultation with a local plastic surgeon.  Your pediatrician should be able to refer you to someone.