Definitions

sphenoidal fontanelle

Fontanelle

[fon-tn-el]
A fontanelle (or fontanel) is an anatomical feature on an infant's skull. Fontanelles are soft spots on a baby's head which, during birth, enable the bony plates of the skull to flex, allowing the child's head to pass through the birth canal. The ossification of the bones of the skull cause the fontanelles to close over by a child's second birthday. The closures eventually form the sutures of the neurocranium. Although there are the two anterior and posterior fontanelles, there are two more fontanelles of interest, the mastoid fontanelle, and the sphenoidal fontanelle.

The skull of a newborn consists of five main bones: two frontal bones, two parietal bones, and one occipital bone. These are joined by fibrous sutures, which allow movement that facilitates childbirth and brain growth. At birth, the skull features a small posterior fontanelle, an open area covered by a tough membrane, where the two parietal bones adjoin the occipital bone (at the lambda). This fontanelle usually closes during the first several months of an infant's life.

The much larger, diamond-shaped anterior fontanelle where the two frontal and two parietal bones join generally remains open until the child is about two years of age, however, in cleidocranial dysostosis it is often late in closing or may never close. The anterior fontanelle's is useful clinically. Examination of an infant includes palpating the anterior fontanelle. A sunken fontanelle indicates dehydration, whereas a very tense or bulging anterior fontanelle indicates raised intracranial pressure.

Parents may worry that their infant may be more prone to injury at the fontanelles. In fact, although they may colloquially be called "soft-spots", the membrane covering the fontanelles is extremely tough and difficult to penetrate. However, the fontanelles allow the infant brain to be imaged using ultrasonography. Once they are closed, most of the brain is inaccessible to ultrasound imaging, as the bony skull presents an acoustic barrier.

In the congenital abnormality called cleidocranial dysostosis the anterior fontanelle may close late or stay open through life.

References in Pop Culture:

  • The dragon in John Gardner's 1971 novel Grendel makes reference to the fontanele as a mark of the universe's progress.
  • A band called The Fontanelles were featured in the 1988 film Hobgoblins (best known as an episode of Mystery Science Theater 3000) playing the song "Kiss Kicker".
  • Fontanel is the name of Barbara Mandrell's former home, the world's largest log cabin at the time of its construction circa 1990.
  • Fontanelle is the title of a 1992 album by Babes in Toyland.
  • An alternative band called Fontanelle, was active in New Zealand in the mid 1990s.
  • The Barenaked Ladies use the term in the lyrics of their 1998 song "When You Dream": "His fontanelle pulses with lives that he's lived."
  • The Decemberists use the term in the lyrics of their 2006 song "The Crane Wife 1&2": "soft as a fontanelle".
  • There is an active post-rock band called Fontanelle.

References

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