Now, back to endochondral ossification.
We discussed how achondroplasia
which is gonna be a lack of growth at the growth plates of long bones
creates people with shortened stature
but otherwise, not any real difficulties or disabilities.
One thing about achondroplasia that I didn´t draw specific attention to
when we were discussing the limbs
is that people would tend to have shortened, relatively flat faces.
That´s because the same process that allows our bones to elongate in our limbs
leads to shortened faces.
If we can´t grow our limb bones long,
we can´t grow our facial bones down.
And so people with achondroplasia tend to have faces that are a bit more infant-like
than the typical appearance and this is again due to a mutation of FGFR3
and if that gene is mutated, the protein is gonna be operating improperly
and closing off those growth plates far sooner than they should.
Another syndrome or condition that´s related to facial development
is Crouzon Syndrome and it´s caused by a mutation of FGFR2.
So remember, FGFR3 is achondroplasia, FGFR2, Crouzon.
It causes malformations of the first pharyngeal arch structures
and we have a whole lecture devoted to those arches
but the´re gonna form the maxilla and the mandible.
And because those malformed facial bones are not quite where they should be,
people with Crouzon Syndrome have premature
closer of some of the sutures in the skull and relatively flattened faces.
Now, premature closure of these sutures can result in very specific
and very interesting malformation of the skull.
If a suture closes too soon, that side of the skull is no longer able to enlarge
and the rest of the skull and its open sutures have to grow away from it.
So if you can picture pinching part of your skull shut,
the rest of it has to balloon away in three dimensions from that pinch point.
Because the brain and the head continue to grow
even if one of the sutures closes too soon
and that locked suture is holding back growth in that one spot,
but not everywhere, so let´s review what these different positional
and kind of inborn errors can be when it comes to sutural closure.
The first one is premature closure of the sagittal suture.
Now, the difficult thing to imagine here is that if a suture closes,
then, the skull is going to enlarge along the same line as that suture.
Now, if we take a look at my sagittal suture would be right here.
If that´s closed, it means my skull can no longer expand laterally.
It can´t grow that direction because it´s pinched tight right at the top of my skull.
So my skull is then going to enlarge anteriorly and posteriorly.
That is called scaphocephaly.
Similarly, if my coronal suture is affected,
I´m going to have the inability of my skull to grow outward anteriorly
so the skull is gonna grow where it can.
It´s going to push laterally and superiorly.
So brachycephaly kind of elongates the skull laterally and a little bit superiorly.
A very interesting one is trigonocephaly.
Now, our frontal suture or metopic suture typically does close.
But if it closes too soon, it pinches the forehead shut
and the only way the skull can expand is laterally and posteriorly.
And that creates a triangle shaped skull when viewed from above.
Now, if I close both my coronal and lambdoid sutures,
I´ve severely restricted the ability of my skull to expand and the only place it can go is up.
So I´m gonna have an expansion of the skull upward and this is called oxycephaly.
So oxycephaly is that large extended skull growing upward
because none of the sutures on the front and back
can accommodate any more growth.
Now, plagiocephaly occurs when one single side of the coronal suture
or one single side of the lambdoid suture close.
So one side is open, the other is closed,
and because of that, the skull grows away from that pinched area
and it results in what´s called the slanted skull.
Plagiocephaly means slanted skull
and it´s gonna give a very distinctive appearance
based on which particular suture is closed.
I should note that there can be something called positional plagiocephaly.
This is not a problem of synostosis
but it´s because a child who is laying down on one side
consistently will actually have that skull flattened on that side
and growth will proceed outward away from that flattened spot.
So it´s a good idea to make sure that your child has a little bit of variation
in exactly how they´re laid down in their crib during their early infancy.
Now, let´s return to this slide.
If we take a look at the child in the top two pictures,
you´ll notice that the skull is enlarged in a posterior and anterior direction.
Because of that, we can pretty well diagnose that the sagittal suture closed too soon.
The skull cannot expand laterally,
so it´s going to expand anterior posteriorly and that is scaphocephaly.
The bottom two pictures depict a child
whose skull cannot expand posteriorly or anteriorly so we have the opposite problem.
We´ve closed off the coronal and the lambdoid sutures and the skull has grown upward
and I hope you can recall that that is called oxycephaly.
And these sort of skull malformations are seen relatively frequently
and you wanna be able to figure out which suture needs to be dealt with.
It can be fixed surgically.
There are some very sophisticated methods available to open up the skull
so the growth can thereafter be accomplished in a fairly normal way
and children with these problems usually recover A-OK
so long as the surgical intervention happens at an early age.
Thank you very much and I´ll see you guys on the next talk.