Anterior Fontanelle: Location and Closure Timing
The statement that the anterior fontanelle is a 'soft spot' on a baby's skull located at bregma and usually fuses by the time the baby is 18 months old is true. The anterior fontanelle is indeed located at the bregma (the junction where the coronal and sagittal sutures meet) and typically closes by 18 months of age.
Anatomy and Normal Development of the Anterior Fontanelle
The anterior fontanelle is the largest of the six fontanelles present at birth and serves as an important clinical landmark for assessment of infant development. It is characterized by:
- Location: At the bregma, where the coronal and sagittal sutures intersect
- Size at birth: Average width of approximately 2.0 cm in full-term infants 1
- Normal closure timing: Median time of closure is 13.8 months 1
- Range of normal closure: Typically between 9-18 months, with considerable individual variation 2
Evidence Supporting Normal Closure by 18 Months
Research confirms that the anterior fontanelle typically closes by 18 months:
- A longitudinal study showed that the width of the anterior fontanelle decreases from 2.0 cm at birth to 0.6 cm by 12 months in full-term infants 3
- The median time of closure is 13.8 months, well within the 18-month timeframe mentioned in the statement 1
- By 18 months, the neocortex undergoes significant developmental changes, coinciding with the timing of fontanelle closure 4
Clinical Significance and Variations
There is significant normal variation in fontanelle size and closure timing:
- No significant differences in fontanelle size or closure timing between term and preterm infants after the initial neonatal period 2
- No significant differences between males and females, though males tend to have slightly earlier closure 3
- Fontanelle size correlates negatively with weight and length in some studies, but these correlations are generally weak 2
Abnormal Fontanelle Closure
Abnormal fontanelle closure timing may indicate underlying conditions:
Delayed closure (beyond 18 months) may suggest:
- Achondroplasia
- Hypothyroidism
- Down syndrome
- Increased intracranial pressure
- Rickets 1
Premature closure may suggest:
- Craniosynostosis, requiring timely referral to a craniofacial specialist 5
Clinical Assessment
For clinical assessment of the anterior fontanelle:
- Physical examination is the primary diagnostic approach
- Ultrasound through the fontanelle provides excellent visualization of the infant brain while the fontanelle remains open 3
- For suspected abnormalities, imaging modalities may include ultrasound, CT, or MRI depending on the clinical scenario 1
In conclusion, the statement is accurate based on current medical evidence. The anterior fontanelle is located at the bregma and typically closes by 18 months of age, though there is considerable normal variation in both size and timing of closure.