Fontanelles in Babies: All You Need to Know

Fontanelles in babies are often a cause for concern for new parents, but they're completely normal and close with time. This article will tell you everything you need to know about these curious anatomical structures.

Written and verified by the doctor Leonardo Biolatto.

Last update: 07 June, 2022

When birth occurs, the fontanelles in babies–better known as soft spots–often become a topic of conversation in families. Some are concerned about their size, their sponginess, or the time that passes while they remain open.

All concerns are logical and understandable, as we adults don’t have fontanelles like babies. Thus, we’re struck by their presence, the possibility of bumping them, and the fact that they show a heartbeat.

At birth, the bones of the skull are not totally connected and closed to each other. This is precisely what allows the child to come out through the birth canal, decreasing its cephalic diameter. One bone is placed on top of another and the head is refined, changing its shape.

In fact, a birth, we don’t have six bones in the skull as we do when we’re adults. Rather, there are some more. This happens, for example, with the frontal bone, which consists of two parts when we’re babies. Over time, these bones will join together in a process we know as ossification.

The areas where the bones of the skull join together are the sutures. Between the sutures are the baby’s fontanelles, which are still soft and of considerable size. Thanks to them, the child’s head can enlarge easily along with the growth of the body.

There are two main fontanelles in an infant: The anterior and posterior fontanelles. Other soft spaces are also fontanelles, but they’re smaller and usually close earlier. Once they close, the solid bone will become present.

Sutures of the skull and their relationship with fontanelles in babies

Sutures are the areas of union between the bones of the skull. As we explained before, in infants, the sutures contain fontanelles. In other words, soft spots that are not yet bones, but over which ossification will take place.

While the sutures have yet to ossify, they’re mobile. We could say that they’re joints, in a sense. As the baby grows, this soft tissue between the sutures expands and becomes bone. When they finally close completely, cranial growth is complete.

The most important sutures of the head are:

• Metopic: This is the one that separates the frontal bone into two parts at birth. It runs along the forehead and reaches the nose.
• Sagittal: This is the suture that runs through the skull from the back to the front, through the middle part.
• Coronal: This runs through the skull from side to side, transversal to the sagittal.
• Lambdoid: This suture joins the parietal bones to the occipital bone at the back.

Continue reading: What’s a Craniotomy and When’s It Necessary?

When do infant fontanelles close?

The fontanelles have to close, although they don’t close immediately at birth. Rather, they go through a process that accompanies the growth of the child and that, based on these times, causes the ossification.

The expected dates for the baby’s fontanelles to close are approximate. This doesn’t mean that all children coincide with these dates, but they should serve as a reference to make a consultation with a pediatrician:

• The anterior fontanelle should close and ossify completely around 18 months of age.
• On the other hand, the posterior fontanel closes around the fourth month of life, as it’s much smaller than the anterior fontanel.

If the closure time takes longer, a medical consultation is necessary. The pediatrician will evaluate the size of the baby’s fontanelles, their consistency, and the rest of the baby’s overall health. If something indicates that it’s okay to wait a little longer, the doctor will recommend a follow-up visit.

If there are any doubts about a pathological process, the pediatrician may request a cranial ultrasound. This study doesn’t pose any risk for the child and allows the doctor to rule out diseases such as craniosynostosis or hydrocephalus.

Find out more: What Are the Different Lobes of the Brain?

Deformities of the fontanelles

There are signs in the baby’s fontanelles that can warn us of the existence of an abnormality. Parents should be attentive to this to consult a health professional promptly.

First, we must clarify that the heartbeats that appear in this tissue are normal and don’t represent an abnormality. The baby’s fontanelles have many blood vessels and transmit the heartbeat.

However, if there’s a bulge, this may be a problem. If it happens when crying, it’s usually benign, as it’s a response to increased intracranial pressure. However, if the bulging is present when the child is calm, then parents should seek out an evaluation for hydrocephalus.

A sunken fontanel may be a symptom of dehydration. It appears more frequently in infants with severe gastroenteritis that causes continuous vomiting, preventing them from drinking fluids.

The importance of fontanelles in babies

A baby’s fontanelles are very important and it’s normal to be concerned about them if we’re new parents. If you have any worries, it’s best to consult a pediatrician to dispel your doubts. In general, there’ll be no problems with this anatomical area, but it can warn us of other pathological processes.