The anterior fontanelle is the large diamond-shaped soft spot on top of a baby's head, where the two halves of the frontal bone and the two parietal bones have not yet met. It lies at the future site of bregma, at the junction of the coronal, sagittal and metopic sutures. Covered by a tough membrane, it allows the skull to mould during birth and to expand with the rapidly growing brain.
| Articulations |
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|---|---|
| Landmarks |
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| Ossification | A membrane-covered gap between membrane-ossifying vault bones; it gradually shrinks and usually closes between about 12 and 18 months of age, though normal closure ranges up to about 2 years. |
The anterior fontanelle is checked at every infant examination. A tense or bulging fontanelle in a calm, upright baby suggests raised intracranial pressure from causes such as meningitis, hydrocephalus or bleeding, while a sunken fontanelle is a sign of dehydration. Early closure may point to craniosynostosis, and late closure to conditions such as hypothyroidism, rickets, Down syndrome or raised pressure. In infants it also provides an acoustic window for cranial ultrasound.
A tense, raised anterior fontanelle in an infant, an important warning sign of raised intracranial pressure from meningitis, hydrocephalus or intracranial haemorrhage.
A depressed fontanelle that signals significant dehydration in an infant, often from vomiting, diarrhoea or poor feeding.
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