Anteriorfontanelle

The anterior fontanelle, commonly known as the anterior fontanel, is a soft membranous gap in an infant’s skull where the developing bones have not yet fused. It is located at the top of the head, at the junction of the frontal bones and the two parietal bones, forming a roughly diamond-shaped area that is covered by a tough but flexible membrane.

Function and development: Fontanelles allow for growth of the brain after birth and enable some reshaping of the skull during vaginal delivery. The anterior fontanelle is the largest fontanelle and changes in size as the skull bones grow. Over the first months to years, the sutures widen and then gradually ossify, with closure typically occurring by about 18 to 24 months.

Clinical significance: In physical examination, the fontanelle is palpated to assess its size, tension, and contour. A soft, flat fontanelle that is slightly depressed relative to the surrounding bone is normal in infancy. A sunken fontanelle may indicate dehydration or insufficient fluid intake; a tense, bulging fontanelle at rest can signal increased intracranial pressure, meningitis, or other serious conditions and warrants prompt medical evaluation. An abnormally small fontanelle or delayed closure can reflect craniosynostosis or other disorders affecting skull growth.

Related note: The posterior fontanelle, which is smaller, is located at the junction of the lambdoid and sagittal sutures and typically closes earlier, within a few months after birth.