At what age does the anterior fontanelle typically close?

Anterior Fontanelle Closure in Infants

The anterior fontanelle typically closes at a median age of 13.8 months, with normal closure occurring between 9-18 months of age. 1, 2

Normal Fontanelle Development and Closure

The anterior fontanelle is the largest of the six fontanelles present at birth and serves as an important clinical assessment point during infant development. Its development follows a predictable pattern:

• Size at birth: Average size is approximately 2.1 cm 1
• Maximum size: Typically reaches maximum size around 1 month of age (2.2 cm) 3
• Closure pattern:
  • Begins to decrease in size after 6 months of age 4
  • Median closure time is 13.8 months 1
  • By 12 months, approximately 26.5% of fontanelles are closed 3
  • By 24 months, approximately 93% of fontanelles are closed 3

Normal Variations in Closure Time

Research studies have identified several normal variations in fontanelle closure:

• Gender differences: Boys tend to have slightly earlier closure (9.2 ± 5.1 months) compared to girls (10.3 ± 4.7 months), though this difference is not statistically significant 5
• Range of normal closure:
  • First noted in about 5% of babies at 6 months 4
  • About 8% of babies may still have open fontanelles at 24 months 4
  • The median age of fontanelle closure is 14.5 months in males and 14.3 months in females 4

Clinical Assessment of the Fontanelle

When assessing the anterior fontanelle, clinicians should:

• Measure fontanelle size (either using traditional or oblique measurements - both are equally accurate) 5
• Assess tension (normal, bulging, or sunken)
• Note pulsations
• Measure and plot head circumference on a growth chart 2

Warning Signs Requiring Further Evaluation

Abnormal fontanelle findings that warrant further investigation include:

• Delayed closure (beyond 18-24 months): May indicate achondroplasia, hypothyroidism, Down syndrome, increased intracranial pressure, or rickets 1
• Bulging fontanelle: May indicate increased intracranial pressure, intracranial hemorrhage, meningitis/encephalitis, hydrocephalus, or intracranial tumors 2
• Sunken fontanelle: Usually indicates dehydration 1
• Abnormally large fontanelle: Children with fontanelles measuring above the 95th percentile should be monitored closely and investigated further 5

Clinical Implications

Early fontanelle closure is not typically associated with microcephaly 5. However, fontanelle size and closure timing can provide important clinical information about an infant's development and potential underlying conditions.

The size of the anterior fontanelle is not significantly correlated with weight, length, or head circumference measurements 3, making it an independent clinical parameter that should be routinely assessed during well-child visits.