Soft spot on baby's head: When to expect it to close

QUES: When I took my daughter in for her 12-month check-up, my doctor discovered that her soft spot had completely closed, which he said shouldn't happen until closer to two years. Also, her head has not grown since her nine-month check up. She is developing normally as far as I can tell. My doctor has referred her to a pediatrician. Could early closure of the soft spot indicate a problem?

ANS: The "soft spot" is the area on top of the head where the bones of the skull have not quite joined. During pregnancy, the skull develops sort of like a jigsaw puzzle; it's not all one bone, but rather many bones that eventually meet and fuse. Some bones meet and fuse before the baby is born. Others fuse after birth to allow room for the brain's tremendous growth over the first year. More than 50 percent of the total growth of the head occurs in this first year of life. If all the bones fused early, there would be no room for the brain as it grows.

There are often several "soft spots" present at birth, but most are so small and last for so little time, that parents are unaware of them. But by two months, only two of these spots should be present:

The smaller is the posterior fontanel, on the back part of the top of the head. It's usually difficult to find at two months of age and should be completely gone (because the bones have fused) by four months.

The anterior fontanel is the one most parents recognize as the soft spot. It's on top of the head toward the front. Four bones come together at this spot, but, because of their rounded corners, they don't quite meet. This soft spot may close as early as nine months of age or as late as two years. The average is between 12 to 14 months.

So, what does it mean when the soft spot seems to have closed up early? Most of the time, it means that it is still present but is difficult to feel because a tough, fibrous cartilage membrane develops over the soft spot as it is closing. This membrane can make it difficult to determine if the soft spot is still open.

However, if the soft spot does indeed close early, it could be a condition called craniosynostosis, which can cause some problems. Craniosynostosis occurs in about one in 2,500 babies and usually requires surgery. If left untreated, compression of the brain may eventually occur and the other bones of the skull become deformed as they grow. This may cause vision difficulties and significant disfigurement of the face.

The fact that your daughter's soft spot seems closed is not necessarily a problem. It may be that it is, in fact, not closed, just difficult to feel. But even if it is closed at her age, that falls within the normal range of time for closure. However, if her head has not grown over the last three months, that could indicate a problem. Even after the soft spot has closed, the head continues to grow to allow for brain growth. If her skull, indeed, has not expanded over these last three months, I certainly agree with your doctor that she should be evaluated by a pediatrician.

You can expect the pediatrician to do a complete history and physical, including review of all the head-circumference measurements up until this point. It's important that you bring a record of all these with you. If the the pediatrician feels that her head growth is abnormal, x-rays of the skull -- or more likely, a CAT scan -- of the head will be done. This will allow for a thorough look at the bones to assess their condition.

The fact that your daughter seems to be developing appropriately is important and would tend to indicate that her soft spot is also normal. But making sure the rest of her skull is growing normally is just as important. Good luck with your visit to the pediatrician.

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