At what age do anterior fontanelles (soft spots) typically close?

Anterior Fontanelle Closure Timing

The anterior fontanelle typically closes at a median age of 13.8 months, with the normal range being between 4 to 26 months. 1

Normal Fontanelle Development and Closure

• At birth, infants have six fontanelles, with the anterior fontanelle being the largest and most clinically significant for evaluation 1
• The average size of the anterior fontanelle at birth is approximately 2.1 cm 1
• For full-term infants, the width (50th percentile) at birth is about 2.0 cm, decreasing to 0.6 cm by 12 months of age 2
• The mean fontanelle closure time is 9.7 ± 5.0 months, with slight gender differences (girls: 10.3 ± 4.7 months, boys: 9.2 ± 5.1 months) 3
• There is considerable normal variation in fontanelle size and closure timing among healthy infants 1, 3

Factors Affecting Fontanelle Size and Closure

• Gender differences exist, with boys tending to have slightly smaller fontanelles and earlier closure despite having larger head circumferences 2
• Preterm infants (appropriate for gestational age) initially have larger anterior fontanelles than full-term infants, but this difference typically resolves by 3 months of age 2
• Early fontanelle closure is not necessarily associated with microcephaly 3
• Persistent open anterior fontanelle beyond the typical closure range can be a normal variant in otherwise healthy children 4

Clinical Significance and Evaluation

• Abnormally large anterior fontanelles or delayed closure may indicate underlying conditions such as:

  • Achondroplasia
  • Hypothyroidism
  • Down syndrome
  • Increased intracranial pressure
  • Rickets 1

• A bulging fontanelle may suggest increased intracranial pressure or intracranial/extracranial tumors 1

• A sunken fontanelle is often a sign of dehydration 1

• Early anterior fontanelle closure does not necessarily imply craniosynostosis - a comparative study showed that early closure had only 36.1% sensitivity and 72% specificity for diagnosing craniosynostosis 5

Imaging Considerations

• Ultrasonography through the fontanelle provides an excellent radiation-free window to examine the infant brain 6
• Ultrasound examination is often sufficient for evaluating anomalies of the cranial sutures and anterior fontanelle before considering more advanced imaging 6
• Transfontanellar ultrasound can be used to evaluate various intracranial conditions in newborns or young infants with open fontanelles 6
• When abnormalities are detected, the physician should determine which advanced imaging modality (CT scan, MRI) is most appropriate based on physical examination findings 1

Clinical Implications

• Knowledge of normal fontanelle variation is essential for distinguishing normal from pathological findings 1, 3
• Children with fontanelles measuring above the 95th percentile should be monitored closely and investigated further for potentially associated diseases 3
• Persistent open anterior fontanelle beyond 26 months in an otherwise healthy child with normal development may be a normal variant 4