What is the appropriate evaluation and treatment for a 2-year-1-month-old child with an open fontanelle?

Evaluation of an Open Fontanelle in a 2-Year-1-Month-Old Child

A child with an open anterior fontanelle at 2 years and 1 month of age requires prompt neuroimaging evaluation, preferably with MRI, as this finding is abnormal and warrants investigation for underlying pathology. The anterior fontanelle typically closes between 9-18 months of age, with a mean closure time of 13.8 months 1.

Normal Fontanelle Development and Closure Timeline

• The anterior fontanelle is the largest of the six fontanelles present at birth
• Average size at birth: 2.1 cm 1
• Maximum size: Typically at 1 month (2.2 cm) 2
• Normal closure timeline:
  • 26.5% closed by 12 months 2
  • 93% closed by 24 months 2
  • Mean closure time: 9.7 ± 5.0 months (slightly later in girls than boys) 3

Diagnostic Approach

Initial Assessment

• Measure fontanelle size using oblique measurements (as accurate as traditional methods) 3
• Assess for signs of increased intracranial pressure:
  • Bulging fontanelle
  • Irritability
  • Vomiting
  • Lethargy
  • Headache (if child can communicate this)

Imaging Studies

1. Brain MRI (preferred first-line imaging):

   • Superior for detecting brain parenchymal abnormalities
   • Can identify structural causes of delayed fontanelle closure
   • No radiation exposure

2. Head CT without contrast (alternative if MRI unavailable):

   • Faster acquisition (may not require sedation)
   • Can detect hydrocephalus, mass lesions, and craniosynostosis
   • Caution: Involves radiation exposure 4

3. Skull radiographs:

   • Limited utility but may help evaluate for craniosynostosis
   • Cannot adequately assess intracranial structures

4. Ultrasound (limited role):

   • Not recommended as primary imaging modality despite open fontanelle
   • Lacks sensitivity for small subdural hematomas and posterior fossa lesions 4
   • Guidelines specifically state: "even in infants with open fontanelles, in which US imaging of the brain is possible, US lacks sensitivity for small subdural hematomas, particularly in the posterior fossa, as well as other small extra-axial hemorrhages" 4

Common Causes to Consider

Pathological Causes

• Increased intracranial pressure
  • Hydrocephalus
  • Mass lesions
  • Chronic subdural collections
• Endocrine disorders
  • Hypothyroidism
  • Rickets
• Genetic conditions
  • Down syndrome
  • Achondroplasia
  • Other skeletal dysplasias
• Metabolic disorders

Benign Variants

• Familial pattern of delayed fontanelle closure
• Constitutional delay (rare beyond 24 months)

Management Recommendations

1. Neuroimaging: MRI brain as first-line imaging to evaluate for structural abnormalities

2. Laboratory evaluation:

   • Thyroid function tests (TSH, free T4)
   • Calcium, phosphorus, alkaline phosphatase (for rickets)
   • Consider genetic testing if dysmorphic features present

3. Specialist consultation:

   • Pediatric neurology or neurosurgery evaluation
   • Endocrinology if laboratory abnormalities detected

Important Caveats

• An open fontanelle at 2 years and 1 month is outside normal limits, as 93% of fontanelles close by 24 months 2
• Early fontanelle closure does not necessarily indicate craniosynostosis, but a persistently open fontanelle beyond normal age limits requires evaluation 5
• Avoid the pitfall of assuming this is a normal variant without proper investigation
• While rare cases of persistent open fontanelles beyond 3-4 years have been reported without pathology 6, these are extremely uncommon and should not prevent thorough evaluation

Follow-up Recommendations

• If initial evaluation is negative but fontanelle remains open:
  • Monitor head circumference regularly
  • Follow developmental milestones
  • Consider repeat imaging in 3-6 months if fontanelle remains open
  • Continue endocrine monitoring if indicated

Remember that while some children may have constitutional delay in fontanelle closure, the finding of an open fontanelle at 25 months of age is abnormal until proven otherwise and requires comprehensive evaluation.