What are the implications and necessary interventions for a 15-month-old child with an open fontanelle (soft spot on the skull)?

Management of an Open Fontanel in a 15-Month-Old Child

An open anterior fontanel in a 15-month-old child warrants neuroimaging evaluation, preferably with MRI, to rule out increased intracranial pressure and other pathological conditions.

Normal Fontanel Development and Closure Timeline

• The anterior fontanel typically reaches its maximum size at 1 month of age (approximately 2.2 cm) and then gradually decreases in size 1
• Normal closure timeline:
  • 3% closed by 6 months
  • 26.5% closed by 12 months
  • 93% closed by 24 months 1
• By 15 months, many children's anterior fontanels have begun closing, though complete closure varies

Evaluation of an Open Fontanel at 15 Months

Initial Assessment

1. Measure fontanel size using the Popich and Smith method
2. Assess for bulging or depression of the fontanel
3. Evaluate head circumference and plot on growth chart
4. Check for signs of increased intracranial pressure:
   • Irritability
   • Vomiting
   • Lethargy
   • Altered mental status
   • Sunset eyes
   • Papilledema (if cooperative)

Neuroimaging Recommendations

Brain MRI is the preferred initial imaging modality for evaluating persistent open fontanels at 15 months due to:

1. No radiation exposure (unlike CT)
2. Superior visualization of brain parenchyma
3. Ability to detect subtle abnormalities that may cause increased intracranial pressure 2

While ultrasound can be performed through an open fontanel, it has significant limitations:

• Limited sensitivity for small subdural hematomas
• Poor visualization of posterior fossa
• Inadequate for detecting small extra-axial hemorrhages 2

Potential Causes and Management

Benign Delayed Closure

Some children may have normal delayed closure of the anterior fontanel without pathology 3. This can be managed with:

• Regular monitoring of head circumference
• Periodic fontanel measurements
• Follow-up neurological examinations

Increased Intracranial Pressure

If the fontanel is bulging, this may indicate increased intracranial pressure from:

• Hydrocephalus
• Intracranial mass
• Venous sinus thrombosis
• Meningitis

Management depends on the underlying cause but may include:

• Neurosurgical consultation
• CSF diversion procedures if hydrocephalus is present
• Anticoagulation if venous sinus thrombosis is diagnosed 4

Metabolic/Endocrine Disorders

Several conditions can delay fontanel closure:

• Hypothyroidism
• Rickets
• Osteogenesis imperfecta

Appropriate laboratory testing should be performed:

• Thyroid function tests
• Calcium, phosphorus, alkaline phosphatase
• Vitamin D levels

Avoiding Common Pitfalls

1. Don't assume normality without investigation: While some children may have normal delayed closure, persistent open fontanel at 15 months requires evaluation

2. Avoid unnecessary radiation: Use MRI rather than CT when possible to reduce radiation exposure, especially important in pediatric populations 5

3. Don't rely solely on ultrasound: Despite the convenience of ultrasound through an open fontanel, its limitations make it inadequate as the sole imaging modality 2

4. Consider COVID-19 in differential: Recent case reports have documented bulging fontanels in infants with COVID-19, though this would be unusual at 15 months 6

5. Avoid assuming pathology without comprehensive evaluation: Some children may have normal variant delayed closure requiring only monitoring 3

By following these recommendations, clinicians can appropriately evaluate and manage a 15-month-old with an open fontanel, ensuring that potentially serious conditions are identified and treated promptly while avoiding unnecessary interventions for benign variants.