Bulging fontanelle

Background

Neonatal suture anatomy.

• Fontanelles are fibrous, membrane-covered gaps between cranial bones
• A newborn has six fontanelles: anterior, posterior, two mastoid, and two sphenoid
  • Anterior and posterior are the most prominent
  • The posterior fontanelle usually closes by 1-2 months of age
  • The anterior fontanelle usually closes between 7-19 months of age
• A bulging fontanelle represents increased intracranial pressure, which may be transient and either benign or malignant
• Key EM concern: meningitis is the most critical diagnosis to rule out in a febrile infant with a bulging fontanelle
• Meticulous history and physical is essential to guide management

Clinical Features

Normal Fontanelle

• Soft, flat, or slightly concave when infant is upright and calm
• May briefly bulge with crying, coughing, or Valsalva maneuver — this is normal and transient
• Sunken fontanelle suggests dehydration

Abnormal (Bulging) Fontanelle

• Tense, convex, non-pulsatile fontanelle when infant is calm and upright
• May feel firm or "full" to palpation
• Assess with infant calm and in upright position (crying and supine position can cause false bulging)

Associated Findings

• Fever + bulging fontanelle → meningitis until proven otherwise
• Irritability, high-pitched cry, poor feeding, vomiting
• Lethargy, altered mental status, seizures (late signs)
• "Sunset" eyes (downward gaze deviation — hydrocephalus)
• Split sutures, rapidly increasing head circumference (increased ICP, hydrocephalus)
• Bruising, retinal hemorrhages → consider NAT
• Papilledema (though difficult to assess in infants)

Red Flags

• Fever + bulging fontanelle (meningitis — requires LP)
• Altered mental status or seizures
• Rapidly enlarging head circumference
• Signs of non-accidental trauma (bruises, retinal hemorrhages)
• Focal neurologic deficits
• Apnea or bradycardia

Differential Diagnosis

Infectious (Most Urgent)

• Meningitis — must rule out in febrile infant
• Encephalitis / meningoencephalitis
• Brain abscess

Increased ICP

• Hydrocephalus (congenital or acquired)
• Intracranial hemorrhage (traumatic or non-accidental trauma)
• Space-occupying lesions (tumor)
• Dural sinus thrombosis
• Idiopathic intracranial hypertension (pseudotumor cerebri)

Metabolic/Endocrine

• Diabetic ketoacidosis
• Inborn errors of metabolism
• Thyroid disorders (hypothyroidism)
• Parathyroid disorders (hypoparathyroidism)
• Hypervitaminosis A
• Uremia

Other

• Leukemia (bone marrow infiltration)
• Anemia (severe)
• Lead encephalopathy
• Congestive Heart Failure (with cerebral venous congestion)
• Roseola infantum (benign, self-limited — may cause transient bulging fontanelle)
• Post-vaccination (benign, self-limited — rare)
• Shigella (meningismus without meningitis)
• Viral syndromes

Benign/Transient

• Crying, Valsalva, supine positioning (normal variant — resolves when calm and upright)

Evaluation

Assessment

• Examine fontanelle with infant calm and upright
• Head circumference and comparison to prior measurements
• Full neurologic exam (tone, reflexes, mental status)
• Fundoscopic exam if possible (retinal hemorrhages → NAT)
• Assess vital signs including temperature

Standard Approach

• Head CT (non-contrast): evaluate for hemorrhage, hydrocephalus, mass, edema
  • Obtain before LP if concern for mass lesion or elevated ICP
• LP (lumbar puncture): if not contraindicated by CT findings
  • Opening pressure, CSF cell count, glucose, protein, Gram stain, culture
  • Send viral studies if encephalitis suspected
  • Consider HSV PCR in neonates
• CBC, BMP, blood cultures
• Blood glucose
• Consider metabolic workup if no infectious or structural cause identified

When to Obtain Imaging Before LP

• Focal neurologic deficits
• Papilledema
• Signs of severely elevated ICP (altered mental status, bradycardia, hypertension)
• History of shunt (shunt malfunction)
• History of CNS disease or mass

Management

• Treat underlying pathology
• Suspected meningitis: empiric antibiotics should NOT be delayed for imaging or LP
  • <1 month: ampicillin + cefotaxime (or ceftriaxone if >28 days) +/- acyclovir
  • 1-3 months: vancomycin + ceftriaxone (or cefotaxime)
  • >3 months: vancomycin + ceftriaxone
• Elevated ICP: see Management of Elevated Intracranial Pressure
  • Head of bed elevation 30 degrees
  • Neurosurgical consultation for hydrocephalus or mass
• Herpes encephalitis: IV acyclovir — start empirically in neonates with any suspicion
• Intracranial hemorrhage: neurosurgical consultation, correct coagulopathy

Disposition

Admit

• All infants with bulging fontanelle + fever (pending LP results and cultures)
• Suspected meningitis or encephalitis
• Intracranial hemorrhage or mass
• New hydrocephalus
• Non-accidental trauma (also alert child protective services)
• Altered mental status or seizures

Discharge

• Discharge is rare — only if clearly benign and transient cause identified (e.g., post-vaccination in well-appearing infant with normal exam)
• Must have reliable caregivers and immediate return access
• Return precautions: fever, poor feeding, irritability, vomiting, seizure, lethargy

See Also

• Meningitis (peds)
• Management of Elevated Intracranial Pressure
• Hydrocephalus
• Non-accidental trauma
• Infant fever