At 9.5 son's head is 56.5cm, 3 standard deviations above the mean. was 55.5cm at almost 9. was in 90 and 89 percentile before this. normal or concern?

Why at age 9 years: are you still measuring head circumference? It can grow very little and very slowly at this age not as it was during infancy, because the fontanelles were still open, if you're suspecting something wrong with your child 's head talk to your pediatrician first, he or she after examining your child might request an imaging study, a simple CT scan would suffice, but that would be the MD's judgement