Fontanelle of newborns: closing time and causes of bone anomalies

Fontanelle of newborns: closing time and causes of bone anomalies

24.05.2022 0 By admin

fontanel in newborns

The skull of a newborn child contains several small openings – fontanelles. The timeliness of their closure is one of the indicators of the health of the baby. Fontanelles in newborns are connective tissue soft areas on the baby’s head, where there is no bone tissue. They are easily palpable with hands, therefore, special care is required for the child until the moment when ossification occurs and the physiological openings close. Fontanelles are necessary so that the head of the child can, having changed its configuration safely for health, pass through the birth canal of the mother.

What are fontanelles and where are they located

fontanel in newborns

In order to facilitate the passage of a rather large fetal head through the birth canal of a woman, an adjustment in the size of the skull is required at the time the baby is born. This is what fontanelles are designed for, which change the shape of the skull to fit the individual characteristics of the female body. For full adaptation to the birth canal, one fontanel is not enough, since there are various options for introducing the fetal head into the woman’s small pelvis. Based on the physiological need, four holes with a connective tissue movable sheath were formed.

Anatomically, the following fontanelles are distinguished in a newborn:

  • front (large);
  • rear (small);
  • lateral wedge-shaped;
  • lateral mastoid.

Each of the physiological openings has a different location and unequal periods of ossification. The largest is the anterior fontanel. Its characteristics are as follows:

  • closes last;
  • has the largest dimensions – about 2.8 cm after the birth of a child;
  • the place where the fontanel is located is located in the area of fusion of the frontal and parietal bones;
  • has a diamond shape with a maximum anterior-posterior dimension;
  • with a number of diseases it may not close at all.

The anterior fontanel most of all changes the baby’s skull at the time of passage through the birth canal, so its intrauterine formation is crucial for the successful physiological appearance of the baby.

The place where the small fontanel is located is located in the area of fusion of the parietal and occipital bones. Its shape is closer to triangular, and the maximum size does not exceed 1.1 cm. mastoid – slightly behind, where the temporal bone connects to the occipital. Their dimensions do not exceed 1.3 cm, and the shape varies – more often polygonal, less often triangular or diamond-shaped.

Time of ossification of fontanels

baby's fontanel

The time of overgrowth of the physiological opening in the skull varies greatly depending on the size and shape of the fontanel. The ossification process can be delayed under various pathological conditions, as well as due to the genetic characteristics of the child’s skeleton. Below is the rate of closing the holes in the skull, depending on the size of the fontanel:

  • Anterior (large) fontanel. Grows last. The minimum period when the physiological hole heals is 275 days from the moment the child is born. Normally, it should completely close no later than the two-year-old age of the baby.
  • Posterior (small) fontanel. It closes first. Already 35 days after birth, the bone tissue completely covers it. The maximum period of time for closing a small fontanel is 65 days from the moment of birth.
  • Lateral wedge-shaped fontanel. Normally, the closure of this hole occurs in the second turn. The time intervals when the wedge-shaped fontanelle closes vary quite a lot within the first year of a child’s life. Most scientists consider normal ossification of this area in the period of seven months from the moment of birth.
  • Lateral mastoid fontanel. The periods of its ossification vary quite seriously depending on the features of the shape of the baby’s skull. Often it closes with a wedge-shaped fontanelle. However, normally it can remain open up to a year and a half. If after 18 months it is still determined, then the ossification process is already considered pathological.

The normal closure of the fontanelles is not the same process for different babies, so you should not sound the alarm if the physiological opening has not been overgrown during the first 18 months. However, even a large fontanel must close by 2.5 years. If the process is delayed, then various pathological conditions should be excluded.

Painful conditions that interfere with the closure of the fontanelles

Normal ossification of the skull often indicates a healthy development of the child. However, there are pathological processes, the progression of which is easy to notice by the state of the fontanelles. External bulging of an open foramen indicates high intracranial pressure. This is observed in the following diseases:

  • congenital hyperproduction of cerebrospinal fluid;
  • hydrocephalus;
  • inflammation of the meningeal membranes;
  • encephalitis;
  • intracranial hemorrhage.

All pathological conditions leading to bulging of the fontanel seriously slow down its closure. A large fontanel overgrows especially for a long time, and with the progression of brain diseases, it can remain unclosed for many years. And even a small fontanel may not overgrow by the age of six months, which clearly indicates problems inside the baby’s skull.

A sunken fontanel accelerates the closure of the hole, but this situation is also not normal. This condition often signals dehydration – a lack of fluid in the baby’s body.

The problem can lead to electrolyte imbalance and dysfunction of the heart and kidneys, which is extremely negative for the health of the child. That is why the retraction of the fontanel and its early closure is an occasion for an early appeal to a pediatrician or a pediatric neurologist.

One of the frequent causes of late closure of fontanelles is not congenital anomalies, but an acquired condition. Vitamin D deficiency affects the condition of the bone tissue, which leads to a rather serious disease – rickets. However, with this disease in a child, not only late ossification of the skull is observed, often the disease is accompanied by other skeletal lesions and developmental delays.



Thus, the fontanel in newborns is a kind of indicator of the normal health of the baby.

The time of overgrowth of natural holes in the cranial cavity can vary quite seriously, however, the externally connective tissue zone should be on the same level with the bone tissue. But you don’t have to worry about brain injury. The shell covering the physiological openings is quite strong. In the neonatal age, it is she who helps to monitor the state of the central nervous system using a safe ultrasound method. After completion of ossification, such an examination will no longer be available. In the presence of pathological pulsation or excessive bulging of the fontanel, which significantly slows down its closure, immediate medical attention is required. Often, a timely visit to a specialist prevents serious illnesses in early childhood.

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