© 2015 Roy Benaroch, MD
“This chair is too big!” exclaimed Goldilocks. “And this chair is too small!”
“Just sit your rear down, missy!” said her mom, who had it up to here with her picky daughter. I mean, seriously?
Doctors and nurses and moms and dads, we all seem to like numbers. Unlike vague, untrustworthy adjectives (big? small?), they’re pointy and specific (23.5 centimeters!) I’ve even been known to crunch a number now and then. But when it comes to percentiles and measurements of growth, those pesky numbers sometimes cause more harm than good.
Tish wrote in, “I’m curious about head size, and when a parent should be concerned. If a child is measuring well above the 97% line, but has no neurological symptoms and his growth curve mostly mimics that of other kids, is it likely just down to genetics?”
Too-short answer: Yes.
Too-long answer: Mostly, yes. But a head size that is too large—larger than expected for age and parents’ head size, or growing too quickly and shooting up off the chart—can actually be a serious and important thing, and can be an early sign of trouble.
Genetics plays a role, sure. The most common cause, by far, for a child to have a big head is “benign familial macrocephaly”. Mom and/or dad has a big noggin’, so Junior has a big noggin. As Tish says, as long as Junior is growing and thriving and otherwise well, a big headed kid with big headed parents needs to plan on buying big hats. But otherwise, there’s usually nothing to worry about.
How big should adult heads be? The data is pretty sparse. Seriously, if one of you wants to launch a survey site measuring normal adult heads to develop some good tables of normal values by gender/size/ethnicity, that would be really helpful. Maybe make it a Facebook page, “Measure your head!” or something like that. Until that’s done, we’re stuck with just a handful of published studies. The classic one is from 1992, and, yes, it’s still quoted in my pediatric textbook right here. All of the data comes from 354 white adults in Great Britain. We learn here that head circumference varies by height and sex. The 97%ile—a good “upper limit of normal” for an adult male of average height is 23 ½”; for a woman, the 97%ile is about 23”. Go check out your own size—see how it compares!—by wrapping a tape measure around your head.
The problem with that 1992 data is: I don’t actually believe it. I measure adult heads pretty frequently, and they’re often over 23-24 inches. There is some newer data out there—a Canadian study from 2012 recruited 280 all-male volunteers—that seems to show adult head circumferences are larger than they were in the 1992, but no one has done a very good, broad survey. So: even though we know big headed parents have big-headed kids, we don’t actually know how to define a big-headed parent. Maybe we should just ask about hat sizes, or ask Goldilocks what her opinion is (that head is too big!)
I did say this answer was the too-long version, didn’t I?
Big heads that we need to worry about fall into one of a few categories. Any head that’s quickly crossing percentiles upwards—going from, say, average, to Large, to HUGE over just a few months—is of Big Concern. A big head in a child who’s not meeting developmental milestones, or is losing milestones, is also a Big Red Flag. And big heads accompanied by obvious physical exam findings, like a bulging fontanelle, or a baby that’s hard to wake, or a baby that’s often fussy or irritable or vomiting—those need a Big Workup, pronto.
But for most kids with a big head, watchful waiting and a tape measure for mom and dad are all that’s needed.
Just-right answer: Frankly, I’m surprised you made it this far. I don’t really have anything else to say about big heads. Perhaps I didn’t think this Goldilocks motif through. Instead of another big head answer, I’ll send you to this short story I wrote. It has princesses and dragons and only a little bit of gore. Enjoy!
edit: The original title of this post was “Head too big? Too Small? Or just right?”– which was fine, until someone pointed out that I never actually got around to discussing small heads. So I changed the title. I can do that.