In a healthy infant, the anterior fontanel (“soft spot”) lies at the junction of the sagittal, coronal, and frontal sutures. It is flat, soft yet firm, well-demarcated against surrounding skull bones, and normally measures about 2.5 × 4–5 cm at birth, usually closing by 18–20 months. The posterior fontanel is located at the junction of the sagittal and lambdoidal sutures, measuring 1–2 cm, and typically closes by 3 months of age. Subtle pulsations may be visible, reflecting arterial pulsation.

A bulging fontanel—widened, tense, and markedly pulsatile—is a cardinal sign of increased intracranial pressure (ICP) and represents a medical emergency. Causes include meningitis, encephalitis, hydrocephalus, intracranial hemorrhage, or fluid overload. Physiologic bulging may occur transiently during crying, coughing, or lying down; therefore, assessment should be performed with the infant upright and relaxed.

Pathophysiology

A bulging fontanel arises when intracranial pressure exceeds the compensatory capacity of the infant skull. Key mechanisms include:

• Increased cerebrospinal fluid (CSF) volume: Hydrocephalus, obstruction of CSF flow, or overproduction of CSF can distend the ventricles and exert pressure on the cranial vault.

• Cerebral edema: Infections (meningitis, encephalitis), hypoxic-ischemic injury, or trauma lead to swelling of brain tissue, increasing ICP.

• Intracranial hemorrhage: Bleeding within the ventricles or subarachnoid space increases volume within the rigid skull, causing bulging of the fontanel.

• Mass lesions: Brain tumors or abscesses occupy intracranial space, elevating ICP.

• Cardiac or systemic causes: Congestive heart failure or fluid overload can increase cerebral venous pressure, contributing to bulging.

Physiologic bulging during crying, coughing, or supine positioning is transient and self-limiting, reflecting brief elevations in venous pressure rather than pathological ICP.

Emergency Interventions

Immediate actions for a bulging fontanel:

1. Measure fontanel size and head circumference; note head shape.

2. Assess vital signs and level of consciousness (LOC): spontaneous activity, postural reflexes, sensory responses, and posture (flexed vs. opisthotonos or hypotonia).

3. Observe for early seizure activity: tremors, twitching, abnormal limb movements.

4. Monitor for other signs of increased ICP: abnormal respiratory patterns, high-pitched cry.

5. Ensure airway patency and have size-appropriate emergency equipment ready.

6. Administer oxygen and establish IV access.

7. Manage seizures with anticonvulsants.

8. Administer antibiotics, antipyretics, and osmotic diuretics as indicated.

9. If ICP remains elevated: consider neuromuscular blockade, intubation, mechanical ventilation, barbiturate coma, or therapeutic hypothermia.

History Taking

Once stabilized, gather detailed history from the parent or caregiver:

• Recent infections or trauma, including birth trauma

• Presence of fever, rash, or other systemic symptoms

• Behavioral changes: vomiting, lethargy, poor feeding

• Family history of neurologic or infectious conditions

Physical Examination

• Fontanel: Assess location and size:

  • Anterior fontanel: junction of sagittal, coronal, and frontal sutures; 2.5 × 4–5 cm at birth; closes ~18–20 months

  • Posterior fontanel: junction of sagittal and lambdoidal sutures; 1–2 cm at birth; closes ~3 months

• Evaluate for tense, widened, pulsatile fontanel

• Neurologic: decreased LOC, irritability, drowsiness, eventual coma

• Other: abnormal pupil size or reactivity, seizure activity

• Vital signs: may show instability with severe ICP

Medical Causes of Bulging Fontanel

Special Considerations

• Monitor vital signs, LOC, and urine output (indwelling catheter if necessary)

• Restrict fluids as indicated

• Position infant supine with 30° head elevation to promote venous drainage and reduce ICP

• Diagnostic tests may include:

  • Skull X-ray or cranial ultrasonography

  • Computed tomography (CT) scan or MRI

  • Cerebral angiography

  • Full sepsis workup: blood cultures, urine cultures, CBC, electrolytes

Patient Counseling

• Explain diagnostic procedures and treatments to caregivers in clear, reassuring language

• Encourage caregiver involvement in monitoring and comforting the infant

• Provide guidance on signs requiring immediate medical attention (e.g., worsening LOC, seizures, high-pitched crying, vomiting)

Pediatric Pointers

• Bulging fontanel may be subtle in neonates; careful palpation in a calm, upright infant is critical

• Consider neurologic and infectious etiologies promptly

• Monitor for early signs of seizures and ICP elevation

References

1. American Academy of Pediatrics. (2011). Urinary tract infection: Clinical practice guideline for the diagnosis and management of the initial UTI in febrile infants and children 2 to 24 months. Pediatrics, 128(3), 595–610.

2. Ardell, S., Offringa, M., & Soll, R. (2010). Prophylactic vitamin K for the prevention of vitamin K deficiency bleeding in preterm neonates. Cochrane Database of Systematic Reviews, 2010(1), CD008342.

3. Volpe, J. J. (2018). Neurology of the Newborn, 6th Edition. Elsevier.

4. Rennie, J. M., & Roberton, N. R. C. (2012). Textbook of Neonatology, 5th Edition. Churchill Livingstone.

5. McIntosh, N., & Helms, P. J. (2014). Forfar and Arneil’s Textbook of Pediatrics, 8th Edition. Elsevier.

6. Tunkel, A. R., & Scheld, W. M. (2010). Meningitis: Pathogenesis, Diagnosis, and Management. Springer.

7. Barone, C., et al. (2016). Hydrocephalus in neonates: Clinical evaluation and management strategies. Journal of Pediatrics, 169, 43–50.