Fontanelle

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This is about the human anatomical feature. For other meanings, see fontanelle (disambiguation).

The skull at birth, showing the anterior and posterior fontanelles.

The skull at birth, showing the lateral fontanelle.

In human anatomy, a fontanelle (or fontanel) is one of two "soft spots" on a newborn human's skull. There are, however, 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.

There is also a much larger, diamond-shaped anterior fontanelle where the two frontal and two parietal bones abut. This fontanelle remains open until the child is about two years of age. In cleidocranial dysostosis it is often late in closing or never closes.

The anterior fontanelle 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.