What should be told to the parents of a 6-week-old infant with an open posterior fontanelle (fontanelle is a soft spot on the skull)?

Management of Open Posterior Fontanelle in a Six-Week-Old Infant

The posterior fontanelle normally closes by 2-3 months of age, so parents should be informed that their 6-week-old infant's open posterior fontanelle is normal and expected to close within the next few weeks.

Normal Fontanelle Development

• The posterior fontanelle is typically smaller than the anterior fontanelle and closes much earlier, usually by 2-3 months of age 1
• The anterior fontanelle is larger and remains open longer, with a median closure time of 13.8 months 1
• Normal fontanelle closure timing has significant variation among healthy infants 2

Assessment of Fontanelles in Infants

• Fontanelle examination is an important part of infant assessment as abnormal fontanelles can indicate underlying conditions 1
• When examining fontanelles, clinicians should consider:
  • Size of the fontanelle (compared to age-appropriate norms)
  • Tension (normal, bulging, or sunken)
  • Premature or delayed closure 3

Clinical Significance of Posterior Fontanelle

• An open posterior fontanelle at 6 weeks of age is within normal developmental parameters 1, 2
• The posterior fontanelle serves as an acoustic window for cranial ultrasonography in neonates, particularly useful for visualizing occipital structures 4
• Posterior fontanelle ultrasound can help detect intraventricular hemorrhage that might be missed when imaging only through the anterior fontanelle 4

When to Consider Further Evaluation

• Further evaluation would be warranted if:
  • The posterior fontanelle remains open beyond 3 months of age 1
  • There are abnormal neurological findings or signs of increased intracranial pressure 3
  • The head circumference is not following expected growth curves 3
  • There are other concerning physical examination findings suggesting a syndromic condition 1

Follow-up Recommendations

• Routine well-child visits should include:
  • Measurement and plotting of head circumference 3
  • Assessment of fontanelle size and tension 1
  • Monitoring of developmental milestones 3
• If the posterior fontanelle has not closed by the 3-month well-child visit, closer follow-up may be indicated 1, 2

Common Pitfalls to Avoid

• Misinterpreting a normal open posterior fontanelle at 6 weeks as pathological 1
• Failing to distinguish between the posterior fontanelle and other normal skull sutures 1
• Unnecessary referrals or imaging studies for a developmentally normal finding 3
• Not recognizing truly abnormal fontanelles that may indicate underlying conditions such as increased intracranial pressure, hypothyroidism, or skeletal dysplasias 1