Is a pulsating fontanelle (soft spot on the skull) normal in a 3-month-old infant?

Pulsating Fontanelle in a 3-Month-Old Infant

A pulsating fontanelle in a 3-month-old infant is typically normal and represents the normal transmission of arterial pulsations through the open fontanelle.

Normal Fontanelle Characteristics

• The anterior fontanelle is the largest of the six fontanelles present at birth and the most important for clinical evaluation 1
• Average size of the anterior fontanelle is 2.1 cm 1
• Median time of closure is 13.8 months 1
• Pulsations are normally visible and palpable in healthy infants due to arterial pulsations transmitted through the open fontanelle

When to Be Concerned

A pulsating fontanelle alone is not concerning, but the following associated findings warrant further evaluation:

Abnormal Fontanelle Appearance:

• Bulging fontanelle (remains elevated even when infant is upright and calm) may indicate:

  • Increased intracranial pressure 2
  • Intracranial or extracranial tumors 1
  • Meningitis 3
  • Hydrocephalus 2
  • Benign intracranial hypertension 4, 5
  • Rarely, COVID-19 or other viral infections 6

• Sunken fontanelle usually indicates:

  • Dehydration 1

Concerning Associated Symptoms:

• Fever with bulging fontanelle (not just pulsating) 4
• Vomiting, especially forceful or bilious 2
• Lethargy or decreased responsiveness 2
• Seizures or abnormal movements 3
• Rapidly increasing head circumference 2
• Progressive splaying of the sagittal suture width 2

Evaluation Algorithm

1. Measure fontanelle size and characteristics:

   • Normal: Soft, flat or slightly depressed, pulsatile
   • Concerning: Bulging (even when upright and not crying), very tense, excessively large

2. Check for associated symptoms:

   • Fever, irritability, vomiting, lethargy
   • Measure head circumference and compare to growth charts

3. If only pulsations present with normal fontanelle size and appearance:

   • Reassure parents this is normal
   • Continue routine monitoring at well-child visits

4. If bulging fontanelle or concerning symptoms present:

   • Urgent medical evaluation
   • Consider imaging: Cranial ultrasound (if <6 months), CT, or MRI depending on clinical presentation 7
   • Lumbar puncture may be indicated if meningitis is suspected 4

Common Pitfalls

• Mistaking normal pulsations for abnormal findings: Pulsations alone are normal and reflect cardiac cycle
• Evaluating fontanelle when infant is crying: Crying can cause temporary bulging of the fontanelle; assess when infant is calm
• Confusing fontanelle closure timing: Anterior fontanelle typically closes between 9-18 months (median 13.8 months) 1
• Overlooking positional effects: Fontanelle may appear more prominent when infant is supine or during Valsalva maneuvers

Key Points for Parents

• Pulsations of the fontanelle are normal and reflect the infant's heartbeat
• The anterior fontanelle normally remains open until 9-18 months of age
• Seek medical attention if the fontanelle is bulging when the infant is calm and upright, or if associated with fever, vomiting, irritability, or lethargy