What size should a large fontanel be in a newborn

What size should a large fontanel be in a newborn

25.05.2022 0 By admin

A large fontanel in a newborn is an anatomical formation that performs several important functions. It has the shape of a rhombus and closes individually for each child, on average, by 18 months of age. There are generally accepted standards for the size of a large fontanel. Changes in the formation itself or the timing of its closure indicate the presence of pathology. Finding out the causes of violations is necessary for carrying out adequate therapeutic measures. Timely therapy will avoid negative consequences.

What are the sizes of the fontanel in the norm

The size of a large fontanel depends on age, immediately after birth it ranges from 2.5 to 3.2 cm.

large fontanel in a newborn

A large fontanel in a newborn is located between the frontal and parietal bones

With age up to a year, the size of the anatomical formation decreases:

  • 3-6 months – 1.8-2.1 cm;
  • 6-9 months – 1-1.2 cm.

Starting from the age of 9 months, there is a process of gradual closure of the large fontanel, which is completed up to 1.5 years. It is allowed to delay closing up to the age of two years of the child, which is determined by the individual characteristics of the organism. According to statistics, in about 5% of people, the large fontanel never closes completely, leaving a trace of 2-3 mm, this is considered a variant of the norm.

In addition to size, the assessment of the normal state of a large fontanel in a newborn includes several more criteria:

  • the shape should be in the form of a diamond;
  • localization between the frontal and parietal bones;
  • smooth bone edges;
  • the surface of the fontanel has practically no depressions, and there is also no protrusion;
  • slight pulsation is allowed.

Changes in size, shape and condition are the result of various factors that require diagnosis.

The determination of the norm is carried out by a pediatrician or neurologist during routine examinations of a child up to a year old. Parents can independently assess the condition of the large fontanel by gently probing with their fingers.

Why do you need a large fontanel in a newborn

During fetal development, the bones of the skull are formed. They are interconnected by connective tissue sutures and can slightly shift relative to each other. The place of convergence of several seams is a “membrane”, which is called the fontanel.

There are several formations:

  • anterior or large fontanel;
  • posterior or small fontanel;
  • paired wedge-shaped and mastoid fontanelles, which are small in size.

The presence of fontanelles and connective tissue sutures is necessary to prevent injuries to the fetal head during passage through the birth canal. This is possible due to a slight change in the shape of the skull due to a slight “displacement” of the bones of the vault. During the passage of the child’s head through the birth canal, the edges of the bones of the crown in the area of u200bu200bthe connection between them, which is called the sagittal suture, “layer” on top of each other. This leads to a decrease in the diameter of the head and facilitates the course of childbirth.

large fontanel size

The size of the large fontanel is determined by palpation

In a newly born baby and in the first year of his life, a large fontanel performs several functions:

  • prevention of tissue damage due to stretching during brain growth;
  • participation in the regulation of intracranial pressure;
  • ensuring sufficient cooling of the brain;
  • prevention of damage to brain tissue due to “depreciation”.

Education continues to perform biological functions until the moment of its infection.

Interosseous sutures, small, wedge-shaped and mastoid fontanelles overgrow faster and have less functional value.

What are the changes in the fontanel

Possible pathological conditions are indicated by changes in the large fontanel, which you should pay attention to:

  • increase or decrease in size;
  • change in the edges of the fontanel, they become soft, uneven;
  • swelling or pitting;
  • excessively early or late closing.

Individual or complex changes are the basis for an unscheduled examination by a doctor, as they can be the result of various pathological processes.

Causes of changes in the large fontanel

Changing the size, shape, earlier or later closing of the fontanelles is a manifestation of various pathological processes. They can be caused by such diseases:

  • Rickets is a violation of the metabolism of calcium and phosphorus salts, due to an insufficient amount of the active form of vitamin D. Pathology leads to a violation of the formation of bone tissue. At the same time, the fontanel closes later, it increases in size, and the edges become soft. At the same time, other signs of rickets appear, which include bone thickening along the edges of the sternum, emotional changes. Harrison’s groove is formed, which is a deformation in the form of a transverse depression, localized in the lower part of the chest.
  • Congenital hypothyroidism is a decrease in the functional activity of the thyroid gland. It manifests itself as a late fusion of a large fontanel without changing its shape and size. Also, the child is worried about lethargy, drowsiness, and constipation develops.
  • A rare genetic pathology , accompanied by a violation of the growth of bone and cartilage tissue. It is characterized by the large size of the fontanel, its late closure. The growth of the limbs slows down, the legs and arms become relatively short, and the head is wide with a protruding forehead.
  • Down syndrome is a chromosomal pathology characterized by the presence of an extra chromosome in 21 pairs. A large fontanel in a newborn is enlarged and closes late. The disease has a characteristic clinical picture, the diagnosis is confirmed on the basis of the results of karyotyping.
  • Craniosynostosis is a rare disorder in which the bones of the skull fuse together quickly, resulting in a lack of space for the brain to grow.
  • Brain defectsaccompanied by a decrease in structures in volume, which include microcephaly – a decrease in the volume of structures of the central nervous system leads to a noticeable decrease in the large fontanel in volume.
  • Dehydration or dehydration of the child against the background of indomitable vomiting, severe diarrhea is a condition accompanied by a decrease in the amount of fluid in the body with the retraction of a large fontanel.
  • Hydrocephalus – an increase in the volume of cerebrospinal fluid in the ventricles and between the membranes of the brain, which leads to an increase in the fontanel, it becomes convex, tense, pulsating.
  • Hypervitaminosis D – an increase in the level of vitamin D in the body of a child, leading to a rapid decrease in size and subsequent closure of the large fontanel. The condition is possible against the background of artificial feeding of a child using unadapted milk formulas or the use of an incorrect dosage of vitamin D prescribed for the treatment of rickets.
  • Postponed craniocerebral trauma , tumor formations in the structures of the central nervous system, leading to disruption of the production or resorption of cerebrospinal fluid.

A large number of causes of changes in the large fontanel in a child requires a reliable diagnosis, the results of which depend on subsequent therapeutic and preventive measures.

What to do to avoid unwanted consequences

Changes in the large fontanel require an appointment with a pediatrician. Based on the data of the clinical examination, he will prescribe additional objective diagnostics, which includes the appointment of various methods of laboratory, instrumental or functional research. These include ultrasound of the brain, blood tests, cerebrospinal fluid, determination of the level of mineral salts, active forms of vitamin D, karyotyping.

Based on the diagnostic examination, further therapeutic and preventive tactics are determined. Depending on the pathology, conservative therapy is prescribed using drugs of various pharmacological groups. In some cases, surgery may be required to normalize intracranial pressure.

Regardless of the alleged reason for the increase or decrease in the large fontanel, as well as other changes, a consultation with a doctor is required. Only a specialist will help to reliably determine the nature of violations and their possible consequences, as well as prescribe appropriate therapeutic or preventive measures.


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