Is a Flat Fontanelle Normal in a Healthy Infant?
Yes, a flat fontanelle is the normal finding in a healthy infant. A flat anterior fontanelle that is soft and pulsatile indicates normal intracranial pressure and is the expected physical examination finding in well infants 1.
Normal Fontanelle Characteristics
A normal anterior fontanelle should be:
- Flat or slightly depressed when the infant is upright and calm 1
- Soft and pulsatile to palpation 2
- Average size of 2.1 cm at birth, with normal closure occurring at a median of 13.8 months (range up to 24 months) 1, 3
The anterior fontanelle serves as a critical clinical window for assessing intracranial status in infants 4.
Abnormal Fontanelle Findings Requiring Further Evaluation
Bulging Fontanelle (Pathologic)
A full or bulging fontanelle is abnormal and suggests increased intracranial pressure 2. Key considerations include:
- Associated with increased ICP from conditions such as hydrocephalus, meningitis, intracranial hemorrhage, or tumors 1, 5
- Requires urgent evaluation including neuroimaging and possible lumbar puncture depending on clinical context 2, 1
- In preterm infants with posthemorrhagic hydrocephalus, fontanel fullness combined with progressive splaying of sagittal sutures is a reliable sign of symptomatic increased pressure when assessed by experienced practitioners 2
Clinical pitfall: A bulging fontanelle has low specificity and can occasionally be seen even in mild viral illnesses like COVID-19 without serious pathology 5. However, bacterial meningitis must always be excluded in febrile infants with this finding 2.
Sunken Fontanelle (Pathologic)
A sunken or depressed fontanelle typically indicates dehydration and volume depletion 1.
Delayed Closure (Pathologic)
Delayed fontanelle closure beyond 24 months warrants investigation for 6, 1:
- Hypothyroidism
- Down syndrome
- Achondroplasia
- Rickets
- Increased intracranial pressure
Clinical Assessment Approach
When examining the fontanelle, specifically assess for 2, 1:
- Palpation: Should be soft, not tense or bulging
- Position: Examine with infant upright and calm (crying can cause transient fullness)
- Size: Measure if concerns exist about abnormal growth
- Associated findings: Head circumference trends, suture splaying, scalp bruising or bogginess, neurologic status 2
In summary: A flat, soft fontanelle is the normal and reassuring finding in healthy infants, while bulging or sunken fontanelles require prompt clinical evaluation for underlying pathology.