Fontanelle

Fontanelle or fontanel is a feature of the infant skull. It can also be referred to as a soft spot on the infant skull. In anatomical terms, fontanelles are soft membranous gaps or sutures between the cranial bones. This makes the calvaria of the infant or the fetus. Fontanelle mainly consists of the posterior fontanelle and anterior fontanelle. These membranous sutures expand and stretch and deform the neurocranium as the brain expands faster than the growth of the surrounding bones. In general terms, this is the fontanelle meaning.

A bulging fontanelle can be considered as an outward curving of an infant’s soft spot. This soft spot on baby head is the fontanelle. In this article, we will discuss the structure of the fontanelle along with its various other disorders.

Structure of the Fontanelle

The fontanelle mainly consists of the anterior and posterior fontanelle. In this section, we will look into the various parts of the bony bump on back of skull.

(Image will be uploaded soon)

Posterior Fontanelle

This is triangular. It is located at the junction of the sagittal suture and the lambdoid suture. The posterior fontanelle ossifies (closes) within 6-8 weeks after birth. The mesenchymal tissue turns into bone. This is known as intramembranous ossification. During birth, the posterior fontanelle remains quite small and a tough membrane covers the open area where the two parietal bones join the occipital bone. This happens at the lambda.

Anterior Fontanelle 

The anterior fontanelle is a membrane-filled cavity located between two frontal and two parietal bones of the fetal skull. The shape of anterior fontanelle is like a diamond. It is situated between the coronal and the sagittal suture. The anterior fontanelle persists approximately until 18 months after the birth of the infant.

Sometimes there is a certain delay in the closing of the anterior fontanelle. It may be due to cleidocranial dysostosis. However other causes of delayed anterior fontanelle closure include achondroplasia, hypothyroidism, Down syndrome, increased intracranial pressure, and rickets. Palpating the anterior fontanelle is often used to examine infants. In some cases, the anterior fontanelle is late in closing (8-24 months) or may never close. This is all about the full anterior fontanelle.

Apart from the anterior and posterior fontanelle, two other fontanelles also exist and are quite significant. They are the mastoid fontanelle and sphenoidal fontanelle. The sphenoidal or the anterolateral fontanelle is located between the sphenoid, parietal, temporal, and frontal bones. However, the mastoid or the posterolateral fontanelle is located between the temporal, occipital, and parietal bones.

Fontanelle Fusion or Closing of The Fontanelles 

The fontanelle fusion can be observed very distinctly in the case of humans. Generally, all the fontanelles are closed by five years of age. 38 percent of the fontanelles are fused by the end of the first year and 96 percent of the rest are fused by the end of the second year. Let’s look into fontanelle fusion in detail. 

1. The posterior fontanelle normally fuses 2 to 3 months after birth;

2. The sphenoidal fontanelle fuses around 6 months after birth;

3. The mastoid fontanelle fuses next from 6 to 18 months after birth; 

4. The anterior fontanelle is normally the last to close between 12–18 months.

This is all about fontanelle fusion.

Disorders of the Fontanelles

There are various disorders of the fontanelles like bulging fontanelle or a bony bump on the back of the skull. In normal cases, a bulging fontanelle depicts an increase in cranial pressure. This can happen due to encephalitis, hydrocephalus, meningitis, or Active Head Trauma (AHT). Sunken or depressed fontanelles may happen due to dehydration and malnutrition. The bony bump on the back of the skull is sometimes known as an occipital bun or inion hook. The enlarged fontanelle may happen due to Down syndrome, IUGR, or premature birth. Apart from all of these, one should be careful while handling the soft spots on the baby head as it can be dangerous if not treated with care.

Interesting Facts About Fontanelles

• During birth, fontanelles enable the bony plates of the skull to flex, allowing the child's head to pass through the birth canal.

• The late fusion of Fontanelles and sutures allows the postnatal growth of cerebral volume.

• Often pulsations are felt on a baby’s fontanelles. These pulsating soft spots are actually due to the beating of the baby’s heart.