Hi, I Have A 1 Year Old Baby That Fell

Hi, I have a 1 year old baby that fell and hit his head last Sat, about 10 days ago. He was fine, we monitored him for 48 hours. On sat we noticed a soft spoongy area on the side of his head. We are very concerned. The ER doctor said that we can get a CT scan but he didn't not advice due to the amount of radiation. He said that we need to make the decision whether to get the CT scan. Should we?