This is the third tutorial on the skull and this is on the sutures, so it’s quite a short, little tutorial. Hopefully, you know all the bones by now. I’m just going to go over the sutures of the skull, which you will have seen, but we don’t know the names of yet.
There are four main sutures you need to know. And then there are some other sutures which I’ll go over. Sutures are just the joints of the skull. They’re these lines here. They’re fibrous joints between the bones of the skull.
In the newborn infant, you’ve got some areas of the skull which are unossified. You’ve got soft spots in the skull, which close during the first few years of life. These are known as fontanels. You’ve got a posterior fontanel, which is here. It’s an unossified little soft spot where the bone is still waiting to close up. And then you’ve got an anterior fontanel over here.
The first suture I’m going to say is the coronal suture. It’s this suture running here. It’s called the coronal suture because it lies in the coronal plane. The second suture you can see is this one here, connecting the parietal bones. This runs right down the median sagittal plane, so it’s called the sagittal suture. The sagittal suture meets the suture here, which separates the parietal bones from the occipital bones and this suture is called the lambdoid suture and that’s because if you know the Greek symbol, lambda, it’s vaguely shaped like this. And then you’ve got the suture here, which separates the parietal bone from the temporal bone, so this is the squamous suture. If you remember back that tutorial, this part of the temporal bone is the squamous part, so this is the squamous suture.
Those are the four big sutures – the coronal suture, the sagittal suture, the lambdoid suture and the squamous suture.
Then you’ve got the other little sutures. This one here, this tiny, little suture separating the parietal bone from the sphenoid bone is called the sphenoparietal suture. And then you’ve got the squamous part of the temporal bone separated from the sphenoid bone. This is called the sphenosquamous suture. And then this area of suture is called the parietomastoid suture because it separates the parietal bone from the mastoid area of the temporal bone. And then you’ve got this suture here, which separates the occipital bone from the mastoid process. That’s the occipitomastoid suture.
That’s eight sutures I went over. The main ones you need to know – the coronal, sagittal, lambdoid and squamous suture. And then you’ve got the sphenoparietal suture, the sphenosquamous suture, the parietomastoid suture and the occipitomastoid suture.
Just a few more things to point out and you’ll hear these names going around. Where the sagittal suture intersects the coronal suture, you’ve got this point here, which is known as bregma. And then spinning around to the back where the sagittal suture intersects the lambdoid suture, you’ve got this point here, which is called lambda – again, because of the lambda shape.
And then you’ve got another point where all these sutures intersect, this is called asterion. You’ve got that on the other side. And then where the frontal bone meets the nasal bone here (so these nasal bones meeting the frontal bone, the big frontal bone), you’ve got a point called nasion.
That’s the sutures of the skull. Hopefully, they’re pretty simple, straightforward.
Okay, so the last important point to mention is this point here where all these sutures intersect. This is the weakest part of the skull and it’s called pterion. This point is important because just underneath runs the middle meningeal artery. You can imagine if the skull is broken at this point, that artery is at risk of being damaged. And if that artery is damaged, you can get an extradural hematoma.
If I just bring in the arteries, you can have a look at that. I’m just going to make the skull more see-through. If you focus on that point, you can see this is where pterion is and this, underneath it lies the middle meningeal artery, the anterior division of the middle meningeal artery.
If that artery is ruptured, you can see it lies outside the brain, so you’ll get an extradural hematoma because blood from that will press against the outside membrane of the brain, which is the dura mater. Blood will accumulate between the skull and the brain, so it’s outside the dura, so it’s extradural. You’re at risk of getting an extradural hematoma if you get a structure through the pterion. That’s here, this weak point where the middle meningeal artery runs beneath.