My pediatrician had us go for a CAT scan when at 9 months, my son's head circumfrence went from routinely 50% to off the charts. We went and had the CAT scan done and everything was fine. I was worried, but my doctor told me it was probably genetic. My husband has a big head circumfrence so it made sense to me. But, I was glad we had it checked and now don't have to worry. Our son was developing fine, so I wasn't too worried. But, you are always worried when you hear that something "may" be wrong with their head/brain area. I am glad that everything turned out ok. My son is now 22 months old and still has off the charts head circumfrence, but is developing normally. He wears the same size hat as my 5 year old, so that has been tough trying to find hats for him.