Management of Persistently Open Anterior Fontanelle at 24 Months
A persistently open anterior fontanelle at 24 months in an otherwise healthy child warrants systematic evaluation to exclude underlying pathology, but can represent a normal variant if all investigations are reassuring. 1
Initial Assessment
The evaluation should focus on identifying conditions associated with delayed fontanelle closure:
- Measure and plot head circumference on a growth chart to assess for microcephaly, macrocephaly, or abnormal growth trajectory 2
- Perform complete neurological examination looking specifically for signs of increased intracranial pressure (altered mental status, vomiting, lethargy, bulging fontanelle) 2
- Conduct developmental assessment to identify any delays that may accompany underlying conditions 2
- Obtain targeted history including growth patterns, feeding difficulties, constipation (hypothyroidism), bone pain, or fractures (metabolic bone disease) 1
Diagnostic Workup
Laboratory evaluation should be performed before assuming a benign variant:
- Thyroid function tests (TSH, free T4) to exclude hypothyroidism, a common cause of delayed closure 1
- Serum calcium, phosphate, and alkaline phosphatase to evaluate for metabolic bone disease including rickets and hypophosphatasia 1, 3
- 25-hydroxyvitamin D level if nutritional rickets is suspected 3
- Consider genetic evaluation if dysmorphic features or developmental delays are present, as delayed closure occurs in Down syndrome and achondroplasia 1
Imaging Approach
Imaging is not routinely required for isolated delayed fontanelle closure:
- Ultrasound examination is often sufficient for assessing cranial sutures and fontanelle status 2
- CT imaging should be reserved only for surgical planning in selected cases, not as routine diagnostic tool 2
- MRI consideration if concerns exist about brain development or neurological symptoms 2
- Skull radiographs may show associated findings but are not necessary for diagnosis 4, 5
Management Strategy
If Evaluation is Normal
Serial monitoring is appropriate when all investigations are reassuring:
- Continue regular head circumference measurements at routine well-child visits 2
- Ongoing developmental surveillance to ensure normal neurodevelopmental progression 2
- Reassure parents that delayed closure beyond 24 months can be a normal outlier when pathology is excluded 4
- Document fontanelle size at each visit; mean closure time is 9.7 months but normal range extends to 26 months, with some healthy children having persistent opening beyond this 4, 6
If Abnormalities are Identified
Specific treatment depends on underlying etiology:
- Hypothyroidism: Initiate thyroid hormone replacement 1
- Nutritional rickets: Provide appropriate vitamin D and calcium supplementation with careful monitoring 3
- Hypophosphatasia: Avoid high-dose calcium and vitamin D, which can cause severe complications including hypercalcemia and nephrocalcinosis 3
- Increased intracranial pressure: Urgent neurosurgical consultation 1
Critical Pitfalls to Avoid
Do not initiate calcium and vitamin D supplementation without laboratory confirmation of nutritional rickets. In rare bone-mineralizing disorders like hypophosphatasia (characterized by LOW alkaline phosphatase), this therapy can induce severe complications including hypercalcemia, hypercalciuria, and nephrocalcinosis 3
Do not assume benign variant without excluding treatable conditions. While persistent open fontanelle can be normal, hypothyroidism and metabolic bone disease require specific treatment 1, 4
Early fontanelle closure is not associated with microcephaly and represents a different clinical concern requiring evaluation for craniosynostosis 6