Closing of anterior and posterior fontanelles

Fontanelle Closures | Children's Hospital Colorado

Your baby has two places where their skull bones don’t fully fuse together in the first several months of life. These “soft spots” are fontanelles, a normal part of your baby’s development.

Issues with fontanelles, such as bulging or sinking, can be signs of other health concerns. Additionally, babies in the Neonatal Intensive Care Unit (NICU) or those with ongoing health conditions will have additional considerations related to their fontanelles.

Children’s Hospital Colorado neonatal experts explain how your baby’s fontanelles should feel and develop and when to seek care.

What are fontanelles?

Fontanelles are the soft spaces on your baby’s head where their skull bones have not yet fused together. These spaces allow for the skull bones to shift as needed during birth and for your baby’s brain to grow. They will close as your baby grows. You should keep your eye on two fontanelles:

• Anterior fontanelle is located near the front, top of your baby’s head. This is the larger of the fontanelles.
• Posterior fontanelle is located near the back of the head.

It’s OK to lightly touch your baby’s fontanelles. A healthy fontanelle should feel soft and flat. A bulging or sunken fontanelle may be a sign of a health issue.

When do fontanelles close?

Typically, fontanelles close by the time your baby is 18 months old. The posterior fontanelle usually closes first — within 2 months of birth. The anterior fontanelle closes between 7 and 18 months. If you feel your baby’s fontanelles are closing too soon or haven’t closed in 18 months, consult your pediatrician.

Fontanelle closure for babies with medical conditions

Premature babies or babies with ongoing medical conditions might have fontanelles close on a different schedule. Conditions like hydrocephalus and brain bleeds commonly affect when fontanelles close, although other conditions can have the same effect.

Your baby’s care team can tell you when to expect your baby’s fontanelles to close based on their condition.

Premature closure of the anterior fontanelle

Sometimes, the anterior fontanelle closes too early. This is known as craniosynostosis and can limit brain growth or create an abnormal head shape. If your baby’s doctor suspects craniosynostosis, they may recommend seeing pediatric craniofacial specialists or pediatric neurosurgeons. Contact your baby’s pediatrician if you feel their fontanelle has closed too early.

Delayed closure of the anterior fontanelle

Just as fontanelles can close too early, fontanelles that close late can also be a sign of medical issues. The most common causes of fontanelles closing outside the normal time range are:

• Achondroplasia: A genetic disorder that affects cartilage and bone growth
• Hypothyroidism: An issue in the thyroid gland that affects hormone production
• Down syndrome
• Increased pressure in the brain

What does a bulging fontanelle mean?

Sometimes when a baby cries or lies down, their fontanelle will bulge above the skull bone. This is normal, as long as the fontanelle returns to its regular position when the baby sits up or stops crying.

A bulging fontanelle when not crying or lying down, it may indicate a more serious medical issue, such as:

• Hydrocephalus: A buildup of fluid in the brain
• Encephalitis: Swelling of the brain usually caused by infection
• Meningitis: Swelling of the membranes that cover the brain and spinal cord
• Bleeding or pressure in the brain

A fontanelle that bulges when your baby is not crying, vomiting or lying down is a medical emergency. Call 911 or go to the nearest emergency room.

What does a sunken fontanelle mean?

A fontanelle that is sunken into the skull can also signal certain medical issues, including:

• Dehydration: When your baby isn’t getting enough fluid; this is the most common cause of sunken fontanelles
• Failure to thrive: Babies who are not gaining enough weight for their age
• Malnutrition: Not getting enough food or having a very imbalanced diet

If your baby has a sunken fontanelle, contact their doctor immediately and seek care as soon as possible.

Fontanelle considerations for babies with medical conditions

Babies born early or with certain medical conditions may have different sized fontanelles than babies born at full term. A larger fontanelle can be a sign of various medical conditions. Your baby’s NICU care team will diagnose such a condition and arrange the right care. If you feel your baby’s fontanelle is larger than typical, talk to your care team.

Babies born prematurely also have a higher rate of bleeding in the brain, which can lead to hydrocephalus. If your baby had bleeding in their brain, pay close attention to their fontanelles and their head circumference. Talk to your baby’s care team if you have any concerns.

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The Abnormal Fontanel | AAFP

JOSEPH KIESLER, M. D., AND RICK RICER, M.D.

Am Fam Physician. 2003;67(12):2547-2552

The diagnosis of an abnormal fontanel requires an understanding of the wide variation of normal. At birth, an infant has six fontanels. The anterior fontanel is the largest and most important for clinical evaluation. The average size of the anterior fontanel is 2.1 cm, and the median time of closure is 13.8 months. The most common causes of a large anterior fontanel or delayed fontanel closure are achondroplasia, hypothyroidism, Down syndrome, increased intracranial pressure, and rickets. A bulging anterior fontanel can be a result of increased intracranial pressure or intracranial and extracranial tumors, and a sunken fontanel usually is a sign of dehydration. A physical examination helps the physician determine which imaging modality, such as plain films, ultrasonography, computed tomographic scan, or magnetic resonance imaging, to use for diagnosis.

Examination of a newborn's fontanels offers the physician a window into the infant's developing brain and general state of health. The word “fontanel” is derived from the Latin fonticulus and the Old French fontaine, meaning a little fountain or spring.^1–3 The normal fontanel varies widely in shape and time of closure. The incidence of abnormal fontanel differs, depending on the abnormality and cause.

Anatomy of the Fontanels

Fontanels are the fibrous, membrane-covered gaps created when more than two cranial bones are juxtaposed, as opposed to sutures, which are narrow seams of fibrous connective tissue that separate the flat bones of the skull.

A newborn has six fontanels (Figure 1): the anterior and posterior, two mastoid, and two sphenoid.⁴ The rhomboid-shaped anterior fontanel, located at the juncture of the two parietal and two frontal bones, is the most prominent. The superior sagittal dural venous sinus is partially situated beneath the anterior fontanel. The triangular posterior fontanel is located at the junction of the occipital and two parietal bones.^1,5

Growth and Development of the Skull

The flat bones of the skull develop as part of the membranous neurocranium. Needle-like spicules radiate from a primary ossification center toward the periphery. These irregular bone islands are remodeled into flattened sheets of bone by osteoblast and osteoclast activity. During fetal and postnatal life, the membranous bones enlarge by resorption centrally and by apposition of new layers at the edges of the sutures.⁵

Growth of the cranium is triggered by brain growth, two thirds of which occurs by two years of age. Except for the metopic suture between the frontal bones, which closes at two years of age, the sutures remain open until brain growth ceases in the second decade of life.⁶ Once a suture is fused, growth perpendicular to that suture is restricted. Therefore, fontanel size is influenced by brain growth, dural attachments, suture development, and osteogenesis. ⁷

Examination of the Fontanels

PHYSICAL EXAMINATION

The newborn's skull is molded during birth. The frontal bone flattens, the occipital bone is pulled outward, and the parietal bones override. These changes aid delivery through the birth canal and usually resolve after three to five days.⁸ The newborn's skull should be evaluated for shape, circumference, suture ridges, and size of anterior and posterior fontanels. Size is calculated by the average of the anteroposterior and transverse dimensions⁹(Figure 2).

The fontanels should be examined while the infant is calm and held in both supine and upright positions. In select cases, such as newborns with multiple hemangiomas or heart failure, the anterior fontanel is auscultated to detect a bruit, which can indicate an arteriovenous malformation.¹⁰ Palpation of the fontanel in the upright position may reveal a normal, slight pulsation. If the fontanels are closed and intracranial pressure has increased, percussion produces a “cracked-pot” sound (dull, lacking resonance), known as Macewen's sign.

Any associated dysmorphic facial features should be noted. Asymmetry of the head is detected by looking at the infant's head from above. Head circumference is an important indicator of brain development and should be monitored over time, especially if a fontanel closes early.^6,11

IMAGING

Plain radiographs of the skull are the least expensive way to evaluate the sutures and cranial bones, but they are limited by the lack of mineralization of the neonatal cranium. Bridging of bone over a suture, an indistinct suture, or sclerosis along the suture margins indicates fusion. Cortical thinning, widened sutures, and a beaten-metal appearance known as “thumbprinting” are associated with increased intracranial pressure.¹²

If the anterior fontanel is open, ultrasonography is useful to evaluate ventricular dilatation.¹³ A computed tomographic (CT) scan can detect a fused suture, dilated ventricles, enlarged subarachnoid space, brain size, or an intracranial or extracranial mass. ¹⁴ Magnetic resonance imaging (MRI) can detect cortical and white-matter abnormalities, such as degenerative diseases, and document the extent of calvarial masses. Disadvantages of CT scans and MRI include cost, the need for sedation, and, in the case of CT, irradiation.^13,15

Normal Fontanel

POSTERIOR FONTANEL

At birth, the average size of the posterior fontanel is 0.5 cm in white infants and 0.7 cm in black infants.¹⁶ The fontanel usually is completely closed by two months of age.¹⁰

ANTERIOR FONTANEL

The key feature of a normal anterior fontanel is variation. On the first day of an infant's life, the normal fontanel ranges from 0.6 cm to 3.6 cm, with a mean of 2.1 cm.¹⁷ Black infants have larger fontanels (1.4 cm to 4.7 cm).¹⁶ The fontanels of full-term and preterm infants are similar in size once preterm infants reach term. The fontanel can enlarge in the first few months of life,¹⁸ and the median age of closure is 13. 8 months. By three months of age, the anterior fontanel is closed in 1 percent of infants; by 12 months, it is closed in 38 percent; and by 24 months, it is closed in 96 percent. Anterior fontanels tend to close earlier in boys than in girls; the initial size of the fontanel is not a predictor of when it will close.¹⁹

Abnormal Anterior Fontanel

LARGE FONTANEL AND DELAYED FONTANEL CLOSURE

A list of the medical conditions associated with a large fontanel or delayed fontanel closure can be found in Table 1.^20,21 Achondroplasia, congenital hypothyroidism, Down syndrome, rickets, and increased intracranial pressure are among the most common conditions.

Achondroplasia is an autosomal-dominant disorder of the epiphyseal plate cartilage that results in dwarfism.²² At birth, the infant has an enlarged head, low nasal bridge, prominent forehead, and shortened extremities, in addition to a large fontanel.⁹

An elevated thyroid-stimulating hormone level on a newborn screening usually detects congenital hypothyroidism, but an abnormally large anterior fontanel in conjunction with an open posterior fontanel can be an early sign of the disorder. Myxedema and growth deficiency are later signs.

A third fontanel between the anterior and posterior fontanels is associated with hypothyroidism and Down syndrome. ²³ Infants with Down syndrome often have a single palmar crease, flat occiput and facies, rounded ears, and slanted palpebral fissures.

Rickets resulting from vitamin D deficiency rarely occurs in the United States but is one of the five most common childhood diseases in developing nations. Risk factors include breastfeeding without vitamin D supplementation, dark skin, and low sunlight exposure. One of the signs of rickets is craniotabes, a softened outer table of the occipital bone that buckles under pressure, producing a reaction similar to a ping-pong ball indenting and popping back out. Craniotabes is not present at birth but develops over the first few months of life. Craniotabes can occur normally in premature infants and in children younger than six months.^18,24,25 Disorders associated with increased intracranial pressure that results in an abnormally large fontanel or delayed fontanel closure are discussed later in this article.

SMALL FONTANEL OR EARLY FONTANEL CLOSURE

Fontanel closure that occurs as early as three months of age can be within normal limits, but careful monitoring of head circumference in such cases is essential to exclude a pathologic condition. The fontanel sometimes can be open but difficult to detect during a physical examination. Craniosynostosis and abnormal brain development are associated with a small fontanel or early fontanel closure.²⁰

Craniosynostosis is the premature closing of one or more cranial sutures, resulting in an abnormal head shape. The condition can be idiopathic or caused by hyperthyroidism, hypophosphatasia, rickets, or hyperparathyroidism.²⁰ It is also associated with more than 50 syndromes, such as Apert's, Crouzon's and Pfeiffer's. The risk of primary isolated craniosynostosis is 0.4 per 1,000 live births, and the sagittal suture is most commonly involved.

Examination at birth of an infant with craniosynostosis might reveal a ridge over a suture or lack of movement along a suture when alternating sides are gently pressed. Overriding of sutures from the normal molding process should resolve within the first few days of life.⁹ Later physical findings in infants with primary craniosynostosis include stunted cranial growth, increased intracranial pressure, proptosis, strabismus, and hearing impairment.²⁶

Plain radiographs of the skull are used for initial evaluation. If craniosynostosis is present, a three-dimensional CT scan is obtained to detect any underlying brain abnormalities and to assist planning for surgery. ²⁷

Abnormal brain development that results in microcephaly also can cause a small anterior fontanel or early fontanel closure. Prenatal trauma to the brain, such as maternal alcohol abuse, and postnatal trauma, such as hypoxia, are potential causes of microcephaly.²⁰Table 2^20,28 lists the differential diagnosis for microcephaly.

BULGING OR SUNKEN FONTANELS

Disorders associated with increased intracranial pressure can cause a bulging anterior fontanel. The most common disorders are meningitis, encephalitis, hydrocephalus, hypoxic-ischemic injury, trauma, and intracranial hemorrhage.²⁰Table 3²⁰ lists the differential diagnoses for a bulging fontanel. Palpation may reveal a tense fontanel that feels similar to bone.²³

Meningitis and encephalitis also cause temperature instability, poor feeding, and irritability. If meningitis is suspected, a lumbar puncture should be performed to evaluate the cerebrospinal fluid for Gram stain, protein, glucose, cell count, and culture. A CT scan of a child with meningitis shows the subarachnoid space expanding into the anterior fontanel.²¹

Hydrocephalus can result from an imbalance between the production and the absorption of cerebral spinal fluid. This condition affects 3 per 1,000 live births. Most cases occur before two years of age, while the anterior fontanel is still open. Physical signs include an abnormal rate of head growth, frontal bossing of the forehead, widened sutures, and dilated scalp veins. Imaging with ultrasonography, CT, or MRI shows enlarged ventricles in the absence of brain atrophy. Because ultrasonic waves will not penetrate bone, the anterior fontanel must be open if ultrasonography is used for diagnosis.^13,15

Hypoxic-ischemic injury results in cytotoxic edema and diffuse brain swelling. Associated findings include poor feeding, decreased muscle tone, respiratory difficulties, and alterations in consciousness. Intracranial hemorrhage can be intraventricular, parenchymal, subarachnoid, or subdural. Associated findings include decreased muscle tone, seizures, decreased hematocrit, vomiting, and alterations in consciousness.²⁰

Tumors also should be considered in the differential diagnosis of a bulging fontanel. Dermoid tumors of the scalp are the most frequent lesions presenting over the anterior fontanel and also may be found over the posterior fontanel.^29,30 They usually are slow-growing and nontender, and they are twice as common among girls. A CT scan is necessary to exclude intracranial involvement.³⁰ Brain tumors, which can present with signs of increased intracranial pressure and focal neurologic findings, are best diagnosed with MRI.³¹

The primary cause of a sunken fontanel is dehydration. Other signs include reduced peripheral perfusion, poor skin turgor, and sunken eyes.³²

Final Comment

An abnormal fontanel in an infant can indicate a serious medical condition. Therefore, it is important to understand the wide variation of normal, how to examine the fontanels, and which diagnoses to consider when an abnormality is found. Consultation with a pediatric neurosurgeon should be considered if the diagnosis or presence of an abnormality is unclear.

Fontanelle in a newborn

Fontanelles are non-ossified areas between the bones of the skull. By the time of birth, the baby has 6 fontanelles:

• front (large) - has a diamond shape, its size is from 0.6 to 3.6 cm (average 2.1)
• back (small) - its dimensions are about 0.5 cm
• paired lateral: wedge and mastoid

The size of the fontanelles is determined by a large number of factors: gestational age, hereditary predisposition, metabolic state, the presence of diseases, and other components.

What are fontanelles for?

They allow the movement of the bones of the skull and the reshaping of the head for safe passage through the birth canal.

Mothers who have given birth naturally remember what a strange head shape the baby had after birth, and how it became normal after 3-5 days.

Nature designed it so that the bones of the skull during childbirth would not damage the brain, and the baby would not get stuck in the birth canal at birth.

What about skull growth?

It may be surprising, but the brain does not grow behind the bones of the skull, but the cranium increases due to the active growth of the brain. This process is especially active in the first two years of a child's life.

At the same time, the growth of the skull does not occur due to an increase in fontanelles, but due to the growth of each individual bone and the elongation of the sutures (the boundaries of the connection of the bones). If the suture between the frontal bones closes at an average of 2 years, then the remaining sutures remain open until the age of 18-20, until the end of brain growth.

Everything is individual, and the speed of closing the fontanelles depends on the characteristics of the baby. The norm is the closure of a large fontanel at 3 months. This fact must be compared with monthly increases in head circumference.

Normal indicators of fontanel closure:

• large - 3 to 24 months (average 13.8)
• small - up to 2 months
• lateral in full-term babies at birth are mostly closed.

Important nuances:

• Vitamin D supplementation and maternal diet have no effect on fontanel closure rate
• the speed of closing the large fontanel is determined by the individual characteristics of the child
• if the fontanelles close early, you need to monitor monthly increases in head circumference
• early closure of fontanelles with a slowdown in the growth of head circumference requires careful examination by a pediatrician to rule out microcephaly

Fontanelles are an important indicator of the rate of brain growth. Therefore, the time of their closure requires supervision by a pediatrician or pediatric neurologist.

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"Myths" about fontanelles in children

What are fontanelles and what do they consist of?

The skull of a newborn baby consists of a large number of individual and rapidly growing bones. The flat bones of the skull grow in the center and along the edges. A suture is formed at the meeting point of the two bones of the skull. Where three or more bones of the skull meet, a gap is formed in the form of a polygon. Such gaps covered with strong connective tissue are commonly called fontanelles.

The basis of the fontanel is an extremely strong connective tissue, which gradually ossifies along the edges, which leads to a gradual decrease in the size of the fontanel and its complete closure.

Newborns have 6 fontanelles: anterior (largest), posterior (second largest), two mastoid and two wedge-shaped.
In most term babies, only the first two fontanelles are visible - the other four either close very quickly after birth, or are so small that they are very small.

The main role of the fontanelles is to ensure the elasticity of the child's skull during childbirth and during the first years of life. Thanks to the fontanelles, the bones of the skull of a newborn child remain very mobile, and the size of the child's skull easily adjusts to the size of the mother's small pelvis during childbirth.

What should be the fontanelles in the norm?

The large anterior fontanel is usually well visible and always arouses great interest. A large number of misconceptions are associated with the “normal size” and “terms for closing” a large fontanel, which often frighten inexperienced parents, and often frighten the doctors themselves or worried relatives, friends (whose children had “not so”).

Here are some of them:

- At birth, the size of the large fontanel is the same for all children.
- In fact, the normal size of a large fontanelle varies greatly. The normal range of a large fontanel in newborns is 0.5 cm to 4 cm.

- After birth, the size of the fontanel should only decrease, and an increase in the fontanel is a sign of illness.
-In fact, due to the rapid development of the brain, the size of the large fontanel increases somewhat during the first months of a child's life.

- There is a certain period when the large fontanel should close
- In fact, the timing of the closure of the large fontanel is as individual as other parameters of a child's development (the beginning of walking, teething, the beginning of coherent speech).
Observations on healthy children showed that in 1% of cases the large fontanel closes at three months, in a year the large fontanel is closed in about 40% of children, and in two years in more than 95% of children.

But I repeat once again, even if the fontanel closed at 3 months or at 3 years, and there is no clinic and according to the study of the brain (NSG, TUS) everything is normal, then you should not worry !

-The smaller the fontanelle at birth, the faster it closes.
- In fact, there is no directly proportional relationship between the initial size of the fontanel and the proximity of the moment of its closure.

- Complete closure of the spring means a complete cessation of the growth of the skull and leads to an increase in intracranial pressure
- The bones of the skull grow mainly due to an increase in their central part and expansion of the edges in the suture area.

- The speed of fontanel closure depends on the intake of calcium and vitamin D in the child's body
this process is laid down at the genetic level, therefore, the recommendations of doctors that with a fast-growing fontanel, calcium-containing foods should be removed from the diet, or vice versa, they should be increased with a non-overgrowing fontanel, they have no basis. It is impossible to influence the speed of fontanel closure in healthy children.

Appearance of a large fontanel in a healthy child

Outwardly, a large fontanel in a healthy child looks like a pulsating or non-pulsating diamond-shaped, slightly sunken or slightly convex area of ​​the scalp.
Most inexperienced parents are afraid to touch the fontanel and watch with bated breath as the doctor boldly probes it with his fingers. In fact, a large fontanel is much stronger than it seems, and its careful probing cannot cause no harm to the child.

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