Hello and thank you for your question.
In 9 month olds, the anterior fontanelle (opening between the skull bones on top of the head) stays open until about 18 months to 2 years old. I should be soft and slightly depressed between the bones.
The best way to know if there is a concern about his head or fontanelle size is for him to see his doctor and take a measurement of his head, called a head circumference. This is typically measured at birth and every well check up during the first year of life. If there is a change in head or fontanelle size, this can be detected by taking a measurement and comparing it to prior ones.
There is one aspect about a fontanelle that would be very concerning: if it seems to be bulging above the level of the skull bones. This would be a sign of increased fluid and pressure around the brain and warrants immediate medical attention. If your son's fontanelle looks like what I just described, please take him to his doctor today.
If the fontanelle is not bulging and his head circumference is progressing along his usual curve on his growth chart, there should be no cause for concern.
If you have further questions when you return online, feel free to ask.
Hello. I see that you are back online. Do you have further questions?