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Fontanelles in the baby: when they close and what warning signs to watch for

One of the things that we pediatricians explore in practically all the visits of the baby and the child up to two years are the fontanelles. Sometimes we do it almost imperceptibly by gently stroking their heads. This simple gesture gives us a lot of information. But why are fontanelles so important? Should we parents watch something?

What are Fontanelles?

The newborn’s skull is a sphere made up of different bones that are assembled together like pieces of a puzzle. The lines that separate these bones are called sutures, and the gaps between the junctions of various sutures are called fontanelles . There are six fontanelles , although the ones we usually feel and the ones that give us the most information are the anterior fontanel and the posterior fontanel.

This configuration of the skull, with the bones separated from each other, is essential for two reasons. First, because the diameter of the newborn is somewhat larger than the birth canal. In order to pass, the bones of the skull are mounted a little on top of each other (riding). For this reason, in some newborn babies we can notice more marked reliefs that disappear with the passage of days.

The second reason is that a newborn’s brain has to grow a lot. The sutures are made of a flexible material that allows the brain to grow , which is protected by the bones of the skull. Over time , the sutures turn into bone and the bones of the skull come together . In this way, the protection of the brain is maximum.

When do fontanelles close?

The closure of the fontanelles is variable. The posterior fontanelle usually closes before the second or third month of life ; sometimes it is not even palpable at birth.

The anterior fontanelle is the largest and the most clinically important. It is shaped like a rhombus or diamond and its size is variable but at birth it is usually around 4 x 2.5cm. Some babies are born with a small anterior fontanelle, but it usually increases during the first few months of life. The anterior fontanel usually closes before 2 years of life (on average at 14 months) , and usually between 12 and 18 months of palpation at the fingertip. The anterior fontanelle tends to close earlier in boys than in girls.

Sutures are palpable as small depressions for about the first 6 months of life. At around 2 years of age the bones of the skull begin to join together as the sutures turn into bone.

If the closure of the sutures and fontanels occurs too soon, the baby may have problems. Similarly, late closure of the same may be indicative of some disease.

Early closure of sutures

When one or more sutures are closed prematurely, we speak of craniosynostosis . This supposes a deformation of the skull , since the brain cannot continue to grow in that direction and it does so perpendicular to that suture. We can feel a relief at the level of that suture and the fontanel can be closed. In some cases, premature closure of a suture is only an aesthetic problem . In others, it can cause brain problems since the brain cannot grow.

  • Scaphocephaly : it is the most common craniosynostosis. It is produced by the early closure of the sagittal suture, which causes the skull to grow forward and backward, that is, in an anteroposterior direction. These children’s heads are said to be shaped like an overturned ship.
  • Brachycephaly : in this case, the coronal suture, which separates the parietals from the occipital bone, is closed prematurely. The result is a flat head in the occipital region and domed in the frontal region.
  • Trigonocephaly : due to premature closure of the frontal or metopic suture. The forehead is narrow, with a prominent wedge-shaped skull. The problem is only aesthetic.
  • Turricephaly : Several sutures are closed early, causing the skull to grow upward in a tower. They associate mental problems.

The treatment and prognosis of craniosynostoses will depend on the sutures affected. In some cases, such as scaphocephaly or trigonocephaly, the prognosis is good since it is only an aesthetic alteration. Treatment, where necessary, will be surgical.

Late closure of sutures

At other times, the sutures are closed later than normal and the fontanelles remain excessively large. This occurs most often in children with Down syndrome , congenital hypothyroidism , premature babies, those with delayed itrauterine growth (CIR), rickets (a vitamin D deficiency disease), and some other syndromes ( such as Apert or Russell-Silver syndrome). In some cases, late closure of the fontanelle may be just a variant of normality .

Does vitamin D influence the closure of the fontanelle?

Vitamin D is essential for the proper development of bones (of all, not exclusively of the bones of the skull). Children who do not have enough vitamin D cannot absorb calcium and phosphorus, and bones do not form normally, are soft, and can break easily. This disease is known as rickets . These children usually have a very wide fontanelle and the sutures are closed later, hence many associate vitamin D with closure of fontanelles.

But remember that vitamin D is involved in the formation of all bones. There is no scientific evidence that vitamin D should be discontinued in infants with a small fontanelle or in those with postural plagiocephaly. The current recommendation is that all infants under one year of age who drink breast milk or less than a liter of formula per day should be supplemented with 400IU of vitamin D.

As a parent, what should I watch out for in my baby’s fontanelles?

In well-child checkups during the first months and years of life, pediatricians pay special attention to fontanelles, sutures, and the shape of the head. Measurement of head circumference is also very important (there are also head circumference growth charts for girls and boys). For this reason, it is important that you carry out an adequate follow-up and go to all the reviews.

If at any time you notice a flattening or prominence of any area of the skull, palpate a bony ridge or a lateralization of the head, it is recommended to consult your pediatrician. In the same way, if you notice the fontanelle very bulging or very depressed , if the baby is very irritable or, on the contrary, very sleepy , if he refuses food or if he vomits forcefully repeatedly.

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