What if the anterior fontanelle (soft spot) cannot be palpated in a 4-month-old infant?

Unable to Palpate Anterior Fontanelle at 4 Months

If the anterior fontanelle cannot be palpated in a 4-month-old infant, immediately measure head circumference and plot it on a growth chart to assess for microcephaly or abnormal head growth, and perform a complete neurological examination to assess for signs of increased intracranial pressure. 1

Initial Assessment

The inability to palpate the anterior fontanelle at 4 months raises concern for premature closure (craniosynostosis) or replacement by a fontanellar bone, both of which require systematic evaluation:

Key Clinical Evaluations

• Head circumference measurement: Plot on standardized growth charts to identify microcephaly or abnormal growth patterns that suggest premature suture fusion 1
• Neurological examination: Assess for signs of increased intracranial pressure including altered mental status, vomiting, lethargy, scalp bruising or bogginess, and large or rapidly enlarging head circumference 2, 1
• Developmental assessment: Implement developmental surveillance and screening to identify any delays that may accompany craniosynostosis 1

Diagnostic Approach

Clinical Diagnosis Priority

The diagnosis of craniosynostosis and skull malformations is strictly clinical and does not require routine radiographic imaging. 3 Direct X-ray imaging is not indicated as a routine examination, since ultrasound imaging can provide the same information for suspected cranial suture and anterior fontanelle anomalies 3

Imaging Recommendations

• Ultrasound examination: Often sufficient for suspected anomalies of the cranial sutures and anterior fontanelle 3
• CT imaging: Indicated only for treatment planning in selected cases, not as a routine diagnostic tool 3
• MRI consideration: Consider if there are concerns about brain development or other neurological symptoms 1

Differential Considerations

Premature Closure (Craniosynostosis)

Premature closure of the anterior fontanelle may be associated with craniosynostosis, which can involve sagittal, metopic, or coronal sutures 4. This requires:

• Close monitoring of head growth and neurological development over time 1
• Early intervention services if developmental delays are identified 1
• Surgical consultation if craniosynostosis is confirmed and causing functional impairment 4

Fontanellar Bone

Replacement of the anterior fontanelle with a single fontanellar bone is an uncommon finding that may occur as an isolated anomaly or in association with craniosynostosis 4. When this occurs as an isolated finding without craniosynostosis, conservative management with observation is appropriate, as these children develop normally 4

Management Algorithm

For isolated premature fontanelle closure without other abnormalities:

• Serial head circumference measurements at regular intervals 1
• Ongoing developmental surveillance 1
• Observation without intervention if growth and development remain normal 4

For premature closure with abnormal head growth or neurological signs:

• Ultrasound imaging to assess suture status 3
• CT imaging for surgical planning if intervention is needed 3
• Neurosurgical consultation 4

Important Clinical Caveats

The normal range for anterior fontanelle closure extends from 4 to 26 months, with 26.5% of normal children having closure by 12 months and 93% by 24 months 5, 6. Therefore, closure at 4 months, while early, falls within the possible normal range if all other parameters are normal 5. However, the inability to palpate the fontanelle requires confirmation that this represents true closure versus replacement by a fontanellar bone, which has different implications 4.