Fontanelles

Introduction

Examination of the fontanelles provides evidence of altered intracranial pressure and, less commonly, is an index of the rate of development and ossification of the calvaria, which may be altered in a wide variety of disorders. In order to utilize fontanelle size and patency as a clue to altered morphogenesis, it is necessary to have normal age-related standards.

Figs. 7.22 and 7.23 outline the constant and accessory fontanelles present at birth. The most common accessory fontanelle is the parietal (sagittal) fontanelle, otherwise known as a third fontanelle, which is found in 6.3 percent of infants and may be more common in infants with Down syndrome. The "metopic" fontanelle represents the extremely long anterior arm of the anterior fontanelle which, in the process of closure, becomes separated from the anterior fontanelle. A metopic fontanelle has been reported in association with craniofacial dysostosis, cleidocranial dysostosis, spina bifida occulta, and meningomyelocoele. It can also occur as an isolated finding. An increased incidence of open metopic fontanelles is found in infants with congenital rubella syndrome, Down syndrome, cleft lip with or without cleft palate, and widened sutures. The metopic fontanelle is easy to palpate, and the discovery of its presence during the examination of the newborn infant may be important clinically.

Figure 7.22 Cranium at birth. From Caffey (1978), by permission.

Anterior fontanelle

Anterior

Superior median fissure

Posterior

Figure 7.22 Cranium at birth. From Caffey (1978), by permission.

Anterior fontanelle

Anterior

Third Fontanelle Down

Posterior lateral fontanelle

Superior median fissure

Posterior

Fetal Head Fontanelles

Metopic suture

Anterior fontanelle

Metopic suture

Posterior lateral fontanelle

Anterior fontanelle

Lateral Fontanelle

Cerebellar fontanelle

Figure 7.23 Fontanelles at birth (constant and accessory). From Caffey (1978), by permission.

I Posterior fontanelle

. Posterior lateral

—fontanelle Occipital bone N

Glabellar fontanelle

Metopic fontanelle

Anterior fontanelle v Anterior lateral fontanelle

Parietal (sagittal, or third) fontanelle

Cerebellar fontanelle

Figure 7.23 Fontanelles at birth (constant and accessory). From Caffey (1978), by permission.

With increasing age, the fontanelles and sutures become smaller and narrower due to the ingrowth of bone into these remnants of the fetal membranous and cartilaginous skull. There is considerable variation in the velocity of this process in different individuals, and on the two sides of the same skull (Fig. 7.23). The anterior fontanelle usually is reduced to fingertip size by the first half of the second year. The posterior fontanelle may close during the last two months before birth or the first two months following birth. The anterolateral fontanelles disappear during the first three months of life, and the posterolateral fontanelles during the second year of life. The frontal (metopic) suture between the two halves of the frontal squamosa begins to close in the second year and is usually completely obliterated during the third year. It persists throughout life in about 10 percent of individuals. The great sutures of the vault (coronal, lambdoidal, sagittal) persist normally throughout infancy and childhood and do not completely close before the 30th year.

By comparing measurements with age-related fontanelle dimensions in normal persons, the clinician should be able to identify those individuals having either an abnormally large or small fontanelle for age. The presence of an unusually large fontanelle, without increased intracranial pressure, can be a valuable clue in the recognition of a variety of pathological disorders. An usually small anterior fontanelle for age may be a secondary feature in disorders that affect brain growth, such as primary microcephaly; it may be due to craniosynostosis, or it may be caused by accelerated osseous maturation secondary to maternal hyperthyroidism or hyperthyroidism in early life. Males have a slightly larger anterior fontanelle than females during the first six months of life.

Occasionally, numerous large and small accessory ossification centers may be seen within the sutures. These intrasutural or wormian bones can be mistaken for multiple fracture fragments but are present in the normal healthy individual. However, wormian bones can be associated with inherited disorders such as osteogenesis imperfecta.

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Responses

  • bodo
    How many fontanelles are present at birth?
    6 years ago
  • indro
    How many major fontanels are present at birth?
    5 years ago
  • mirren
    How many fontanelle are present at birth?
    5 years ago
  • tiia
    What is small anterior fontanelle related to?
    5 years ago

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