By Dr. Catherine Gant

The fontanelles are the soft gaps between the bones of the skull. They can easily be felt in a newborn baby. It is these gaps which allow the baby's head to be moulded to the shape of the birth canal during a normal delivery. The bones are only loosely joined together, and they can move relative to each other during delivery, allowing the baby’s head to move more easily through the birth canal; this is called moulding. During delivery it is quite common for the bones to over-ride each other, and for the line where the skull bones join (called the sutures) to feel slightly ridged for up to 48 hours after delivery, until the skull returns to its normal shape. 

THE SOFT SPOT

The largest fontanelle is the anterior fontanelle, also called the soft spot. It is a large diamond shapedng on top of the baby's head (see Skull of a newborn, illustration), and is usually about 2 x 3 cms at birth. It feels quite soft and is usually very slightly sunken, this is completely normal and you should make a mental note of how it looks normally as if your baby ever gets diarrhoea or vomiting, further sinking of the fontanelle can be a sign of dehydration. A soft pulse can also sometimes be seen or felt, and this is also normal. The brain underneath is protected by a thick fibrous membrane, which is fairly tough. You should always be very gentle when washing or touching your baby’s soft spot, and discourage older children from pressing against it.

If your baby gets seborrhoeic dermatitis (thick, yellowish scaly skin on his or her head), it can be removed by rubbing aqueous cream into the dry skin an hour before the bath, and then very gently rubbing the dead skin off with a damp cotton wool ball during bathtime. Be very careful not to press down onto the soft spot when you do this.

ABNORMALITIES OF THE SOFT SPOT.

The soft spot can bulge momentarily during crying, straining or coughing, this is completely normal. If your baby does get dehydrated, due to fever, diarrhoea, vomiting or poor feeding, the fontanelle may appear sunken.  In meningitis it can bulge out, sometimes looking like a small egg on top of the head, due to the underlying meningeal swelling. A baby with meningitis is always obviously unwell.

The anterior fontanelle usually closes by 18 months of age, but in some children it can close as early as 9 months, and, as long as the head is growing normally, and the baby developing well, this is not a problem.  Sometimes the soft spot staysfor longer than expected, and there are several medical causes for this, including congenital hypothyroidism (in which the fontanelles may be unusually wide at birth with wide gaps between the bones), Down's syndrome, rickets, hydrocephalus, poor nutrition and prematurity.

If the fontanelle closes prematurely this may reduce the space available for brain development and alter the shape of the head. When the sutures fuse prematurely it is called craniosynostosis, and babies with this condition may need surgery toup the sutures and allow the brain to develop normally. If only one suture is affected the head may grow in an abnormal shape, long and thin, or with a flat back. Craniosynostosis is diagnosed by MRI scan, and is best treated sooner rather than later for the best cosmetic results. Thankfully it is very rare.

There are other fontanelleson the head at birth. The posterior fontanelle, on the back of the head is the largest after the anterior fontanelle. This may have already closed at birth and, if not, it is usually closed by 2 months of age.

Head growth should be measured regularly at your baby's health checks, and your baby's fontanelles will be checked at the same time so any potential problems should be detected early.