Nursing care
Why a bulging fontanelle signals rising ICP in infants, and how to assess it fairly
Written and reviewed by Dana Whitfield, RN, MSN · 4 min read · Updated October 2026
Short answer
An infant's skull bones are not yet fused, and the fontanelles are membrane-covered gaps between them. When fluid builds up or the brain swells, pressure pushes outward on these soft spots, so a tense, bulging fontanelle becomes a visible sign of raised intracranial pressure. Crying, lying flat and vomiting can mimic it, so assess the baby calm and upright.
Follow the pressure in an open skull
In older children and adults, the skull is a rigid box, so rising intracranial pressure quickly compresses brain tissue and blood vessels. In infants, the skull bones are separated by sutures and larger membranous gaps called fontanelles. This open structure allows the head to grow and gives some room for expansion when pressure builds inside.
When fluid accumulates, as in hydrocephalus, or when the brain swells with infection or bleeding, pressure pushes outward against the softest point. The normally flat or slightly curved fontanelle becomes tense and bulges above the bone edges. With more sustained pressure the sutures between the skull bones can separate, another sign the nurse may feel or see.
Why infants show raised ICP differently
Because the skull can expand, infants may not show the classic adult pattern early. Headache cannot be reported, and neck stiffness is often absent. Instead, raised ICP may appear as drowsiness, irritability, vomiting, poor feeding, a bulging fontanelle or separated sutures. The open skull buys time, but it also hides the problem behind nonspecific behaviour.
Conditions behind a truly bulging fontanelle include hydrocephalus, meningitis, encephalitis, intracranial bleeding and other causes of raised intracranial pressure. In infants with meningitis, fever and neck stiffness may be absent and a bulging fontanelle may be one of the few clear signs.
Assess without false positives
Crying, coughing, straining, vomiting and lying flat all raise venous and intracranial pressure briefly and can make a healthy fontanelle feel full or bulging. Assess when the infant is calm, ideally held upright or sitting supported, and gently palpate the anterior fontanelle with the fingertips. A normal fontanelle feels firm and very slightly curved inward.
A fontanelle that stays tense and raised when the infant is quiet and upright is the concerning finding. Combine it with other data: level of alertness, feeding, vomiting, temperature, cry, and head circumference plotted over time. A bulging fontanelle with fever or excessive drowsiness needs emergency care. Document the position and behaviour at the time of the assessment.
Turn the mechanism into nursing actions
Report a persistently bulging fontanelle immediately, along with vital signs, temperature, level of consciousness and any vomiting or seizure activity. Measure head circumference with the same technique each time and compare with previous measurements. If infection is suspected, prepare for cultures and isolation as directed, because suspected meningitis is time-critical.
Keep the infant calm and limit unnecessary stimulation, position with the head raised as ordered, and observe closely for decreasing responsiveness, poor feeding or changes in breathing. Teach parents to report a soft spot that stays swollen when the baby is calm, especially with fever, persistent vomiting, unusual sleepiness or irritability that does not settle with comforting.
Work through a hypothetical exam-style scenario
Imagine a hypothetical 4-month-old brought in after two days of poor feeding and vomiting. He is screaming during the assessment and his fontanelle feels full. The options are to document a bulging fontanelle and call the provider, to reassure the parents that crying explains it, or to settle the infant, sit him upright and reassess.
Settling the infant and reassessing upright is the strongest first step, with prompt reporting if the fontanelle stays tense. Documenting during screaming risks a false positive, and dismissing the finding ignores poor feeding and vomiting. The tested reasoning is that crying raises pressure transiently, while true raised ICP keeps the fontanelle bulging when the infant is calm.
Sources and further reading
MedlinePlus: Fontanelles, bulging. Mechanism of bulging, normal feel, false bulging with crying, lying down or vomiting, assessment calm and head-up, causes and emergency care with fever or drowsiness.
MedlinePlus: Increased intracranial pressure. Infant signs of raised ICP: drowsiness, separated sutures, bulging fontanelle and vomiting.
MSD Manual Professional: Acute bacterial meningitis. Fever and neck stiffness may be absent in infants; fontanelles may bulge from increased intracranial pressure.
CDC: Meningococcal disease symptoms. Infant signs including irritability, poor feeding, inactivity and bulging anterior fontanelle.
The next step on this is the same as on everything else here: answer questions and read the rationales. Our pediatrics practice questions are the closest set to what this page covers.
Common questions
Why does raised intracranial pressure make the fontanelle bulge?
The fontanelle is a membrane-covered gap in the infant's unfused skull. When fluid builds up or the brain swells, pressure pushes outward against this soft spot, making it tense and raised.
How should a nurse assess an infant's fontanelle?
Assess with the infant calm and upright, palpating gently with the fingertips. Crying, vomiting and lying flat can make it feel full temporarily, so a bulge that persists when calm is the concerning finding.
What does a bulging fontanelle with fever suggest?
It can suggest meningitis or another serious intracranial problem and needs emergency assessment. Infants with meningitis may not show neck stiffness, so the fontanelle is an important sign.