What are the concerns and recommendations for an 11-day-old infant's anterior fontanelle?

Evaluation of Anterior Fontanelle in an 11-Day-Old Infant

The anterior fontanelle in an 11-day-old infant should be assessed for size, tension, and pulsation, with particular attention to bulging or sunken appearance as these may indicate serious underlying conditions requiring urgent evaluation.

Normal Anterior Fontanelle Characteristics

• Size: Average size at birth is approximately 2.1 cm 1
• Shape: Diamond-shaped
• Tension: Soft but not sunken
• Closure timing: Median time of closure is 13.8 months 1
• Palpation: Should feel flat to slightly concave when infant is upright and calm

Concerning Findings and Associated Conditions

Bulging Fontanelle

• Urgent concern: May indicate increased intracranial pressure 2
• Potential causes:
  • Intracranial hemorrhage (including abusive head trauma)
  • Meningitis/encephalitis
  • Hydrocephalus
  • Intracranial or extracranial tumors 1
  • Idiopathic intracranial hypertension (rare in infants) 3

Sunken Fontanelle

• Primary concern: Usually indicates dehydration 1
• Clinical correlation: Should be assessed alongside other signs of dehydration (dry mucous membranes, decreased urine output, skin turgor)

Full/Tense Fontanelle

• Warning sign: May be an early indicator of child abuse, particularly abusive head trauma 2
• Associated findings: Look for other concerning physical findings such as:
  • Subconjunctival hemorrhage
  • Bruising (especially on trunk, face, or ears)
  • Bleeding from nose or mouth
  • Rapid head enlargement 2

Evaluation Algorithm

1. Initial assessment:

   • Measure fontanelle size
   • Assess tension (normal, bulging, or sunken)
   • Note pulsations (normal or abnormal)
   • Measure head circumference and plot on growth chart

2. If fontanelle appears normal:

   • Routine follow-up at well-child visits

3. If fontanelle is bulging:

   • Urgent evaluation required
   • Consider cranial ultrasound as initial imaging modality 2, 4
   • Assess for signs of increased intracranial pressure
   • Evaluate for signs of possible abuse 2

4. If fontanelle is sunken:

   • Assess hydration status
   • Consider need for fluid resuscitation

Imaging Considerations

• Cranial ultrasound:

  • First-line imaging for neonates with open fontanelle 2
  • Can detect intraventricular hemorrhage, germinal matrix hemorrhage, and ventricular size 2
  • Limitations: poor visualization of posterior fossa, limited sensitivity for small subdural hematomas 5

• MRI:

  • Preferred for persistent fontanelle abnormalities
  • Superior visualization of brain parenchyma 5
  • No radiation exposure

• CT scan:

  • Generally avoided in infants due to radiation concerns
  • May be necessary in emergency situations when MRI is not available

Important Caveats

• A normal physical examination does not completely rule out the possibility of abusive head trauma 2
• Irritability and anorexia, especially if associated with vomiting, may represent early signs of increased intracranial pressure before fontanelle bulging becomes apparent 3
• The anterior fontanelle serves as an important anatomical diagnostic tool in the assessment of impairments of the skull and brain 6

When to Refer

• Neurosurgical consultation is indicated for:
  • Bulging fontanelle with signs of increased intracranial pressure
  • Abnormal imaging findings
  • Rapidly increasing head circumference

Remember that the anterior fontanelle is a valuable "window" for both clinical assessment and ultrasound imaging of the infant brain 4, making its proper evaluation essential in neonatal care.