Fontanelle Meaning
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.
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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.
The posterior fontanelle normally fuses 2 to 3 months after birth;
The sphenoidal fontanelle fuses around 6 months after birth;
The mastoid fontanelle fuses next from 6 to 18 months after birth;
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.
FAQs on Fontanelle
1. What is a fontanelle in a newborn's skull?
A fontanelle, commonly known as a soft spot, is a flexible, membrane-covered gap on an infant's skull where the bony plates have not yet fused. These spaces exist at the junctions of the cranial sutures and play a vital role in allowing the skull to change shape during birth and accommodate the rapid growth of the brain during infancy.
2. Why are fontanelles important for a baby's development?
Fontanelles serve two primary and critical functions for a newborn. Firstly, their flexibility allows the baby's cranial bones to overlap slightly, a process called moulding, which helps the head pass through the narrow birth canal. Secondly, they accommodate the brain's extremely rapid growth during the first year of life, which would be restricted by a solid, fused skull.
3. What are the different types of fontanelles in an infant?
An infant skull has six fontanelles, though only two are commonly known. The types are:
- Anterior Fontanelle: The largest, diamond-shaped fontanelle located on the top of the head.
- Posterior Fontanelle: A smaller, triangular-shaped fontanelle on the back of the head.
- Sphenoidal Fontanelles (2): One on each side of the skull at the temple (anterolateral).
- Mastoid Fontanelles (2): One on each side of the skull behind the ears (posterolateral).
4. What is the difference between the anterior and posterior fontanelles?
The primary differences between the two main fontanelles relate to their size, shape, location, and closure time. The anterior fontanelle is large, diamond-shaped, and located at the top-front of the head; it is the last to close. In contrast, the posterior fontanelle is smaller, triangular, located at the back of the head, and typically closes within the first few months of life.
5. At what age do the fontanelles normally close?
The closure timeline varies for each fontanelle. The posterior fontanelle is usually the first to close, typically by 1 to 2 months of age. The much larger anterior fontanelle takes longer, generally closing anytime between 7 and 19 months. The sphenoidal and mastoid fontanelles also close within the first year.
6. How does a fontanelle differ from a cranial suture?
A cranial suture is the fibrous, seam-like joint that connects the bony plates of the skull. A fontanelle, on the other hand, is the wider, membranous gap that exists where two or more sutures meet. Essentially, fontanelles are the soft intersections in the network of sutures, and as a child grows, these gaps ossify (turn to bone) and close, leaving only the suture lines.
7. What are some examples of conditions that can cause delayed fontanelle closure?
Delayed closure of the anterior fontanelle beyond the typical 19-month timeframe can sometimes be a sign of an underlying medical condition. Some common causes include:
- Congenital Hypothyroidism: Insufficient thyroid hormone production from birth.
- Down Syndrome: A genetic chromosomal disorder.
- Achondroplasia: A form of dwarfism.
- Rickets: A deficiency in Vitamin D, calcium, or phosphate.
- Increased Intracranial Pressure: Excess pressure inside the skull.
8. What might a bulging or sunken fontanelle indicate about a baby's health?
Changes in a fontanelle's appearance can be important clinical signs. A bulging fontanelle that feels tense when the baby is calm and upright can indicate increased pressure inside the skull, potentially due to conditions like meningitis or hydrocephalus. Conversely, a sunken or depressed fontanelle is a classic sign of dehydration, indicating the baby has lost a significant amount of fluid.
