My son has hyper pigmentary mosaicsism. We got to childrens hospital yearly to keep a look out. He has large bone like knot on the front left side of his head. It is painless and has been checked my his pediatrician a well his dermatologist specialist at ACH. Both assure me it is fine. No one has told me what it is or what we can do if it continues to get larger. Children are often cruel and he starts school next year.