Fontanelle Closure Timeline
The anterior fontanelle typically closes between 9 to 14 months of age, with most children achieving complete closure by 24 months. 1, 2
Normal Anterior Fontanelle Development
Size Progression by Age
- At birth: The average anterior fontanelle measures approximately 2.0-2.1 cm in width 1, 3
- 1 month: Fontanelle reaches maximum size at approximately 2.2 cm 4
- 6 months: Size decreases to approximately 1.5-2.0 cm 2, 4
- 12 months: Reduces to approximately 0.6-1.0 cm 3, 4
- 24 months: Measures approximately 0.5 cm if still open 4
Closure Timeline
- Mean closure time: 9.7 months (range varies by study from 9-14 months) 2
- 6 months: Only 3% of children have closed fontanelles 4
- 12 months: Approximately 26.5% have achieved closure 4
- 18 months: Median closure occurs at 13.8 months 1
- 24 months: 93% of children have complete closure 4
Clinical Considerations
Gender Differences
There are no clinically significant gender differences in fontanelle size or closure timing, though boys may show slightly earlier closure (9.2 months) compared to girls (10.3 months) 2, 3, 4
Measurement Technique
Both traditional anterior-posterior and transverse measurements, as well as oblique diagonal measurements, are equally accurate for clinical assessment 2, 4
Racial Variations
Important racial differences exist in fontanelle size and closure patterns. Nigerian infants demonstrate larger fontanelles at birth (3.4 cm) compared to Caucasian populations, but achieve earlier closure by 12 months 5. Local population references should be used when classifying fontanelle size as normal or abnormal 5
Abnormal Fontanelle Patterns
Delayed Closure (Beyond 24 Months)
The most common causes of delayed fontanelle closure include 1:
- Achondroplasia
- Hypothyroidism
- Down syndrome
- Increased intracranial pressure
- Rickets
Large Fontanelles
Children with fontanelles measuring above the 95th percentile require close monitoring and investigation for potentially associated diseases 2
Early Closure
Early fontanelle closure is not associated with microcephaly and does not necessarily indicate pathology 2
Imaging Considerations
Ultrasound Window
The anterior fontanelle serves as an acoustic window for brain ultrasonography in infants 6. Following fontanelle closure, CT and MRI become the primary imaging modalities for intracranial assessment 6
Growth Hormone Therapy Monitoring
In children receiving growth hormone therapy (such as those with Prader-Willi syndrome), head circumference should be monitored at each visit, as GH treatment can cause abnormal head growth, especially if fontanelles are open when therapy is initiated 6