Bulging Fontanelle

Case by Christopher Sarkis MD 

Patient Presentation

A 5-month-old, fully vaccinated female infant presented to the Emergency Department (ED) with a 3-day history of fever and increased fussiness. The initial assessment revealed the following vital signs: a temperature of 39.3°C, heart rate of 140 beats per minute, respiratory rate of 30 breaths per minute, blood pressure of 92/60 mmHg, and oxygen saturation of 99% on room air.

A physical examination was noteworthy for a bulging fontanelle and irritability—she was inconsolable per her parents.

Diagnostic Findings

A head CT scan was performed to investigate further, which showed no acute intracranial abnormalities. A lumbar puncture was performed that demonstrated clear cerebrospinal fluid with pleocytosis, consistent with a diagnosis of viral meningitis. Pleocytosis, an increased number of white blood cells in the CSF, is a hallmark of meningitis, indicating an inflammatory response.

Educational Pearls

• Assessing a Fontanelle: To accurately assess the status of a fontanelle, ensure the infant is in an upright position and calm. Gently palpate the fontanelles, feeling for any abnormalities such as bulging or sunken areas. Keep in mind that some variation is normal depending on hydration status. A sunken fontanelle can be a sign of dehydration.

• Bulging Fontanelle: A bulging fontanelle in infants is a critical sign that should raise concerns for intracranial pathology. It necessitates immediate further investigation, often including head imaging and/or a lumbar puncture, to rule out conditions such as meningitis, intracranial hemorrhage, or a space-occupying lesion.

• True Irritability with Fever: Infants presenting with fever and true irritability—characterized by being inconsolable—are at high risk for serious infections, including meningitis. Determining whether an infant is truly irritable can be challenging, as young babies express discomfort in various ways. Look for subtle signs such as difficulty in soothing despite meeting all basic needs, inconsolability even without the direct presence of a provider, and persistent crying that is different from usual patterns. Monitor for physical cues like tensed body, clenched fists, arching the back, and turning away.