My Son Is 14 And Had A Dermoid Cyst Removed

My son is 14 and had a dermoid cyst removed from his right temple at age 6 months. At age 4 he had a brain decompression surgery due to a chair malformation. He recovered fully. Today, he came home from school and the area that he had the dermoid cyst removed was indented. It looked as though someone pressed a thumb into his skull. He has no other symptoms-no fever, no headache, no dizziness, no balance deficits, no vision issues, no vomiting. What could this indicate?