The Fontanel: A Guide to the Baby’s Soft Spot
Babies and newborns. They aren’t really like you and me, you know. Sure, they eat and sleep and poop. But anyone who has examined a baby’s nooks and craniums can tell you, some of their parts are just different. Did you ever palpate, and recoil from, the fontanel–that creepy soft spot or two found on newborn and infant heads? Whoa.
Questions abound. What is up with that? What are they for? Do they need special care? Can you touch ‘em? And, what’s with the way you can feel the ba-boom of the pulse sometimes, and sometimes not? When will they go away?
According to tradition in Southeast Asia, God blew the breath of life into the first human via his fontanel after they were molded from clay. Hey, maybe. The fontanel—whose name comes from the Old French for ‘little fountain’–is a marvel of biological problem solving.
The architecture of the newborn skull consists of plates of bone, rather than a rigid brainpan. (Take a moment, find a handy newborn, gently and affectionately massage her head, as we go) Grooves, called sutures, crisscross the skull between the bones of the skull. The most prominent of these, the metopic suture, runs from the forehead up to the crown of the baby’s head. A tougher-than-you-think fibrous membrane spans the wider junctions of the sutures. These membranes are the proverbial soft spots: the fontanels.
Fontanels allow the developing homo sapiens brain to make it to–and be protected in–the outside world. During childbirth, the brain of the emerging infant must be able to a) squeeze out the birth canal in his mother’s pelvis, and b) and not be squished in the process.
It gets better. Any casual stroll through a newborn nursery will reveal that some babies have some temporary ‘molding’ of the head, as their fontanels flex, and skull plates override or bend by design. This conical, or coneheaded appearance of the newborn usually resolves in 2-4 days. Siblings may require some special reassurance here, as their new brother’s dome can look pretty freaky. For many parents, this is their first insight into fontanel function. Cool, but the fontanels’ work isn’t done yet.
From baby to baby, and over time, there is a huge range of “what is normal” for fontanels. Infants arrive with six fontanels, total. However, parents and pediatricians alike will pay attention to the two most evident ones, the anterior and posterior fontanels. One is small, and one is big. They merit our attention because, in their way, they can tell us a lot about a babe.
The triangular posterior fontanel is wee, measuring but 0.5 cm on average. It can be felt just behind the crown of the head, along the midline of the baby’s skull. They aren’t “open” long, and are usually closed (fused shut) by 2 months of age.
The kite-shaped anterior fontanel can be felt just above the infant’s forehead. This is the one everyone talks or sings about. On average, the anterior fontanel runs about an inch across, but can range in size from about 0.5 cm, up to over 4 cm in some ethnicities. In more pronounced instances, no pun intended, the fontanel can be up to several inches across.
In most babies, the anterior fontanel will get a little bigger during the middle part of the first year. Literally, new neurons are laid down and the brain grows gangbusters.
So, I am asked quite often, when will the anterior fontanel close? Again, it varies hugely in healthy kids. On average the anterior fontanel ossifies around 14 months. But, its closure can run the gamut from 4 months to almost two years. For each child, the timing of fontanel closure is a combination of genetics, environment, and nutrition that impact brain growth. What’s more, a clinician examining a fontanel must consider the ‘rest of the baby’ before concluding too much if a fontanel too large, too small, closing too early or open too late.
In most babes, the fontanel will be flush with the scalp, with no difference in skin tone or hair cover. One may frequently see pulsing of the fontanel synchronized to the child’s pulse. And, because it transmits pressures within, the anterior fontanel (especially in younger babies) will bulge a bit when the child is straining or bearing down. You can see this rather eerily demonstrated when an infant is mightily pooping, throwing up, or getting a good cry on. While a bit of that might be a little gross, it is normal.
Concave or convex?
It is when the fontanelles bulge–and rising like a fleshy yarmulke—and stay that way, that prompt consultation is a good idea. Fullness in the fontanel may be nothing, or may be misperceived by parents reading too many blogs on the topic. Whenever there’s a question, it helps greatly if family members can discern if changes occurred suddenly, or gradually (Was it like that this morning? Last week?). And, is anything else going on with the child, such as a medical condition, injury, irritability, or illness? On occasion, a full fontanel may reflect increased pressure or inflammation in the brain. Hence, a question about a bulging or full fontanel—especially in an infant with a fever or seeming sick–merits running it by a clinician by phone or with a visit. Pronto.
‘Sunken’ fontanels may occur when babies who are becoming dehydrated due to vomiting, diarrhea, or poor fluid intake. Time and again, parents cannily pick up when their infants have persistently depressed fontanels, describing often before asked that they have a concave appearance. This can be a reliable measure of how well a baby is doing in terms of keeping up her fluid intake. And so, note bene. If your younger infant has a stomach flu, keep an eye on that soft spot. If it looks depressed, pass it on!
Too wide or too small?
As the pros tell us, time is a critical tool in understanding which fontanels are normal…or not. Looking at a fontanel but once has less meaning than the trends of the fontanel size and rate of closure over weeks and months.
Undersized anterior fontanels, or those that have closed before 4 months need to be followed closely. Fortunately, the well timed well child visits in primary care in the first year build in a way to track this regularly. Like height and weight, the skull growth and circumference of infants and toddlers are followed over time. Again some cases are normal, and that is pretty much it.
However early fusing of the skull sutures may restrict skull growth, impinging on neuron development or an unusual head shape. This condition, called craniosynostosis require close collaboration with a specialist to assure that skull growth proceeds normally. Best a happy, growing brainpan, right?
Other fontanels may be wider than expected, or seem to be taking their time to close may have associations with certain conditions…or may be normal. However, I am often asked as kids pass their birthday and begin to toddle with that soft spot still going on: “Does he need a helmet for that?”
To answer this question, I consulted Diana Liacos, sage pediatric nurse practitioner in child neurology at Boston Medical Center. Her answer covers the subject succinctly:
I have not heard of a protective helmet (for toddlers with with open fontanels) except when there is an underlying bony abnormality. (In these cases) causes such as hypothyroidism, rickets, genetic disorders should be explored.
In regards to a toddler learning to walk with an open fontanel, it probably occurs more than we think as most children are learning to walk at 10-12 months, and we do not ‘helmet’ them but most have a fall or two. Maybe that’s why we have wired in by that age ‘righting and parachute responses’.
Well put, Ms Liacos.
Fortunately toddler noggins and their fontanels do a great job of protecting the fragile cargo within. (for a post about head injuries in little kids, see here) Perhaps the best thing we can do in the care and maintenance of fontanels as parents and pediatricians is to keep an eye on them.
The fontanel, then, really is a window into the workings of the brain. That is even the term radiologists use for them when they use the fontanel as a portal for an ultrasound probe to image the chambers and anatomy of an infant’s brain. Handy, and gloriously non-invasive. Fontanels can tell us about a child’s immediate state (pooping, thanks! Or, more water please!), and they provide a marker for head growth and potential medical conditions. In addition, noting and tracking a large or small fontanel is simply good care, and identifies problems early.
Remember, most fontanels are unremarkable (Unlike in life, in medicine it is almost always good to be described as unremarkable!). Regard them. Admire them. They may be soft spots, but they get those babies through some hard times
Photo1 by Tina065
photo2 by leprchn21
Poem by Andrew Lansdown
Cartoon below by me.
Strange, this seeing
the heart in the head.
Look, a drumming
in the cranium,
against the membrane
where the bones are
yet to meet and knit.
May they never
knit entirely, son.
May head and heart
beat in unison
always, as now
in your fontanelle.
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