What does AFOF (Anterior Fontanelle Openness Factor) mean for a 9-month-old child?

AFOF (Anterior Fontanelle Open Factor) in a 9-Month-Old Child

An open anterior fontanelle at 9 months of age is completely normal and does not require intervention, as only 26.5% of healthy children have a closed fontanelle by 12 months, with the majority (93%) closing by 24 months. 1

Normal Developmental Timeline

The anterior fontanelle follows a predictable growth pattern in healthy children:

• Peak size occurs at 1 month of age (mean 2.2 cm), after which it progressively decreases 1
• At 6 months: Only 3% of healthy children have a closed fontanelle 1
• At 9 months: The fontanelle remains open in the vast majority of children
• At 12 months: Mean size is 1.0 cm (range 0.3-2.0 cm), with 73.5% still open 1
• At 24 months: Mean size is 0.5 cm (range 0.3-0.7 cm), with 93% closed 1

Key Clinical Considerations

The size and closure timing of the anterior fontanelle shows no correlation with:

• Gender 1
• Weight, length, or head circumference development 1
• Risk of craniosynostosis when open 2

Important clinical pitfall: Early fontanelle closure does NOT predict craniosynostosis, with sensitivity of only 36.1% and specificity of 72% for this diagnosis 2. Conversely, a widely open fontanelle can exist even in the presence of craniosynostosis, leading to potential misdiagnosis 2.

When to Be Concerned

An open fontanelle at 9 months warrants further evaluation only if accompanied by:

• Signs of increased intracranial pressure (bulging fontanelle, altered consciousness, vomiting) 3
• Abnormal head growth patterns (accelerated or decelerated head circumference) 1
• Developmental delays or neurological deficits 3
• Dysmorphic features suggesting genetic syndromes 2

Racial Variations

There are significant racial differences in fontanelle size and closure patterns 4:

• Nigerian infants show larger mean fontanelle size at birth (3.4 cm) compared to Caucasian and Chinese populations 4
• By 12 months, Nigerian infants demonstrate smaller mean sizes than Caucasian and Chinese populations 4
• Local reference standards should be used when assessing whether a fontanelle size is abnormal 4

Reassurance and Follow-Up

For an otherwise healthy 9-month-old with an open fontanelle:

• No intervention is needed 1, 3
• Continue routine well-child visits with head circumference monitoring 1
• Reassess at 12 and 24 months 1
• Persistent patency beyond 24 months in an otherwise normal child may warrant conservative observation without aggressive workup 3