Dr Dyanne Ifeoma Imo-Ivoke, Dr Aisha Abdullahi, Dr Helen Yates

Did you know there are six fontanelles in the newborn skull?! As paediatricians we feel for the anterior fontanelle as an automatic part of our examination (some call it the ‘paediatrician’s handshake’!) but have you thought about all the important information we can get from this teeny part of our routine check?

A normal anterior fontanelle is open, soft, and flat (not dipped or bulging) at birth. There’s quite a wide range of ‘normal’ anterior fontanelle size – generally 0.6 – 3.6 cm, but it can be bigger (up to 4.7cm in dark-skinned babies). The best way to measure a fontanelle is by taking the average length and width.

If a fontanelle is very small or closed, bulging, sunken, or very large, this could be something to worry about – we’ll get on to that later in the article.

In most babies, the anterior fontanelle closes by 13-14 months – but again, there is quite a wide range of ‘normal’. About 1% close by three months of age, and 98 – 100% are closed at 24 months.

The posterior fontanelle is usually closed by 6 – 12 weeks. If it’s open beyond 3 months of age, this should prompt further review.

In babies with conditions like Down’s syndrome, neonatal hypothyroidism, and congenital infections such as Rubella, you might find a third fontanelle (between the anterior and posterior fontanelle). The third fontanelle is not really a true fontanelle but a gap in the bone along the sagittal suture.

The small fontanelle

When a fontanelle is too small to feel on examination it is said to be closed – and they often close earlier in boys than girls! Small fontanelles are completely normal and interestingly their initial size does not predict closure time.

Some of the causes of a small fontanelle are:

  • Primary microcephaly
  • Hyperthyroidism
  • Underlying brain abnormalities, such as holoprosencephaly (which may be picked up on an antenatal screening scan)
  • Secondary microcephaly
  • Craniosynostosis

When reviewing a baby with small anterior fontanelle, think about the following:

  1. History of feeding and handling (as you would for any baby!)
  2. Measurement and plotting of the head circumference
  3. Examination of the skull – pay attention to shape and sutures and examine in both supine and upright positions
  4. Check ear position! Asymmetry is often spotted this way
  5. General clinical examination

If all the above are normal, the child can be safely followed up in the community.

The large fontanelle

There are lots of causes of a large fontanelle, some benign and some less so. As with all fontanelle examinations, the infant should be examined both supine, upright and while calm – tricky though this is!

Some of those causes are:

  • Hypothyroidism – this may present with other clinical features, such as reduced tone and large tongue
  • Rickets and Vitamin D deficiency
  • Skeletal disorders such as achondroplasia, osteogenesis imperfecta
  • Hypophosphatemia
  • Chromosomal abnormalities such as Down syndrome
  • Congenital infections like Rubella and Syphilis
  • Maternal drugs such as ACE inhibitor
  • Genetic syndromes such as Beckwith–Wiedemann syndrome.
  • Benign macrocephaly – There is a large fontanelle and a larger than expected head circumference
  • Prematurity
  • Intrauterine growth restriction (IUGR) and malnutrition

If you’re examining a baby who you suspect might have a large fontanelle – here are some things to guide you, as it is a daunting list of differentials!

As before, measure and plot the head circumference. Do a thorough physical examination – focus on the skeletal system, dysmorphism and growth issues, as well as a neuro exam, and don’t forget a developmental assessment.

Referral to a paediatric team should be made if large fontanelle is confirmed.

The full/bulging fontanelle

This is the part of fontanelle examination we have probably all heard of – and fear! A bulging fontanelle in a settled baby may be due to infection or raised intracranial pressure and therefore something not to miss. However, it is important to remember that the most common cause for this is crying or straining – but a bulging fontanelle at rest should be seen and discussed with a senior. Causes can include:

  • Non-pathological like vomiting, straining, crying or coughing
  • Increased or impaired CSF absorption leading to hydrocephalus
  • Increased pressure in the brain due to intracranial tumour or other space-occupying lesion
  • Infections such as meningitis and encephalitis
  • Cerebral oedema
  • Hypervitaminosis A
  • Hypoparathyroidism

Ensure baby is settled (if you are able to!) and examine in supine and upright positions and measure and plot the head circumference (do you see a pattern here?!) If the child is unwell or irritable do not spend time trying to settle and have a low threshold to escalate. Consider further treatment/imaging based on your findings.

The sunken fontanelle

A truly sunken fontanelle is often really difficult to detect – but never fear! In the context of dehydration/hypovolemia it’s unlikely to be the only clinical sign you will find on your examination. A thorough history is your friend. The baby should be managed based on clinical condition – what do they look like from the end of the bed? Examine with your ABCDE in mind – do you need to put out a resus call?

Assess the hydration status!

  • Consciousness level (AVPU)
  • Cap refill time
  • Skin turgor
  • Mucous membranes
  • Urine output

Further investigations

The vast majority of babies will need no further investigations, but here is a quick rundown of the options. If you have found something abnormal, consider if there are any tests that will help you get the diagnosis.

  • ‘Basic’ laboratory investigations – including thyroid function, bone profile, U&Es
  • Is genetic testing indicated? This will always need consultant discussion.
  • Skull X-ray is readily available – but its use is limited and it doesn’t give any information about the underlying brain structure – is it worth the radiation?
  • Cranial ultrasound – available at the bedside (although it’s a while since I did one!) and can provide information about things like intraventricular bleeds
  • CT provides good information about both the brain and the bones (and 3D CT is even better!) – however it comes with the risks of radiation
  • MRI is really useful for babies with other dysmorphic features or neurological abnormalities but will usually need to be done with sedation, which has its own set of risks.

Worried about any of these – get a review!

  • History of vomiting
  • Ridging of sutures beyond the 1st week of life
  • Abnormal skull shape
  • Abnormal head circumference (too big or too large!)  Check if the it follows the centile on the growth chart
  • Abnormal systemic examination – particularly neuro examination
  • Bulging fontanelle
  • Unwell baby

Hopefully after that whistle stop tour of the fontanelles you feel more confident in your approach to this particularly clinical conundrum. If in doubt – examine, measure, and plot!

Authors: Dr Dyanne Ifeoma Imo-Ivoke (OOPE -Future Leaders Fellow. NHSE, Yorkshire and Humber), Dr Aisha Abdullahi (ST2, Hull Royal Infirmary) and Dr Helen Yates (Consultant Neonatologist, Hull Royal Infirmary)

Edited for PaediatricFOAM by subeditors Dr Sarah Walker and Dr Ailsa McIlwane

2 thoughts on “The Paediatrician’s Handshake – Say Hello to The Fontanelles”

  1. A really good summary of what’s important about fontanelle. Most importantly made easy to remember and apply clinically.

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