 What I'd like to show you now are the spaces that surround the brain. The brain that we looked at in our introduction had had its tough outer covering called the duramodder, or tough mother, hard mother, had been removed so that you could see the gyri and the sulci. And in that, I mentioned that the brain had smooth, thin coverings called the leptomaninges, which consist of the Pia and the arachnoid that cover this bare gyris of the cortex, as well as a outer tough covering, which I'm going to introduce you to now. And the duramodder is very, very tough. I cannot pull it apart. And it anchors the brain within the different regions of the cranium or skull. So it keeps the brain from shifting right to left by having a central partition called the falx attached to the base of the skull. And it also has an area called the tentorium, which you see here, which separates the occipital lobe above it, where my fingers are, from the cerebellum, which would be sitting in this region here. So the brainstem is in its own compartment, as well as the hemispheres and theirs, and there is no right-to-left shift. Because the brain is in the skull, which cannot expand, any kind of additional space occupying structures such as cerebral spinal fluid or blood will cause the brain to be distorted because the duramodder cannot accommodate. They are in a fixed and closed box. So let's look at this duramodder. The surface of the duramodder, the lateral surface, has on it an artery. These are branches that you can see here, still with some blood in them, of the middle meningeal artery. The middle meningeal artery, along with the trigeminal nerve, supplied the dura. That means the dura is exquisitely sensitive. I want to show you a model that I have. I'm going to take off the skull. And let's say I'm going to turn it around so it's a little easier for you to see. This is the posterior part of the skull, the anterior or frontal region. And we have areas or fossey, a temporal fossa and a posterior fossa and an anterior fossa. So the frontal lobes sit here, the temporal lobes sit here, and the cerebellum and brainstem sit back here. And that structure I just showed you, the tentorium, is spanning across from this area here to this area here and along the posterior area. And that separates the brainstem from the cortex. And this has some very important consequences. This middle meningeal artery that comes up through an external foramen spreads out over the surface of the skull, even leaves an indentation on it. And when you take out and look at a skull cap, you can see the grooves from that artery. And that is the same artery that you see here. So given that this artery is right underneath the temporal bone here. This is the temporal bone. That means that a trauma to the temporal side of the skull can lacerate, can cut these arteries. And then you have bleeding into what we call the epidural space. And because this is arterial blood, this is very life-threatening. It's the most life-threatening of the hemorrhages into the three cerebral spaces that I'm going to talk about. So the first hemorrhage we can have is an epidural, arterial bleed usually due to trauma. There can be other regions, but this is the most common. Then there is what we call the subdural space. So if I reflect back the dura, I can see that coming over to the surface of the dura are large veins. And they are emptying into a sinus, a fold in the dura, the superior sagittal sinus, where most of the superficial blood from the brain is draining. These veins that come across and have to bridge over to the venous structure, which you can't see right now, but I'll show you in a minute. These bridging veins can easily be sheared or torn, particularly in a brain where there has been some atrophy. And this bleed then is into this space under the dura and is a subdural bleed. So subdural hematoma is an important thing to recognize. And what happens is that hematoma, as it increases in size, pushes and depresses and damages the cerebral cortex if not evacuated and eventually can lead to death. I showed you the tentorium on this loose piece of dura and said that the brainstem went through it. So now what I want to do is let you peer down and see the tentorium in place. So if I lift up the brain and pull back on the cerebellum, you can see the tentorium and there is a notch in it, the tentorial notch. Through that goes the brainstem. So this tentorium separates but is also a barrier to expansion. Anything above the tentorium, which is everything in either hemisphere, gets pushed down through that small notch that I just showed you. So that part of the dura is really important. And both epidural and subdural hemorrhages can push the brain down through this tentorial notch. Enough about the dura at the moment. And I want now to show you the leptomeninges or the smooth covering of the brain. So this brain has the leptomeninges gone here. You can just pull them off very easily. And here you can see them in place inside you. Now there's really two layers here but because the cerebral spinal fluid has drained out when the brain was removed from the body, I cannot easily separate those two layers. But the vessels that supply the cerebral cortex run in the space in between those two layers. The outer layer is called the arachnoid. The inner layer is called the pia. The space between them is called the subarachnoid space. And that is another potential space that can fill with blood. An example would be if you had a small, let me move this here. If you had a small vessel such as, let's take a large vessel such as this carotid artery that you can see here. At places where your vessels like the basilar artery branch, they can have aneurysms or small dilatations or weaknesses. And with time and age and increased blood pressure, these aneurysms, as they are called, these dilatations can rupture. And when they rupture, because the vessels are running in this subarachnoid space, they can rupture into the area between those two layers. And this is a frightful situation because the blood goes through the CSF space and completely covers the brain. It's arterial blood and is very often fatal. So this is, again, a coronal section with your gray and white matter, not quite so easily seen on this specimen, as well as a ventricular space. And it's being held together, you see, by a bit of the corpus callosum right here in the center. So here's our big ventricle. So this section is actually back in the occipital lobe, but that doesn't really matter. What I want you to see are the leptomeninges here. So these are the leptomeninges, they're collapsed, but you can imagine if there was blood, it would surround and go up and down and around all of these in the case of a subarachnoid hemorrhage. Right here in the midline, the meninges have these little projections from the arachnoid. Remember, the outer layer is the arachnoid. These arachnoid projections, or villi as they are called, actually project into the main sinus that runs down the middle of the dura, the superior sagittal sinus. And these arachnoid granulations we'll talk about when we talk about the circulation of cerebral spinal fluid. On this brain, they're even more visible. There is a cluster of them right here and here if you look at them close up. And they are projecting again into that mid-sagittal sinus into this space here. If I pull it apart into this area here, this would have been filled with venous blood, but it's not there now, postmortem, but those little projections are into there and we'll talk about that as a way of removing the cerebral spinal fluid. This brain is also notable for showing you the veins on the surface. These veins at the time of death were quite congested, so they allow you to see the large number of veins that would be draining or bridging into that superior sagittal sinus that was located between the two hemispheres. I'd like to show you a pathological specimen, which unfortunately I don't know the history on this individual, but it does demonstrate that this blood or hematoma, which has been fixed, is on top of the leptomeninges, which you can see here, and the dura has been removed, so it's in the subdural space. So this is a good example of a subdural hematoma. This is an example of an aneurysm that bled into the subarachnoid space. Here we are in the frontal lobe, you can see the basal ganglia and the lateral ventricles on either side. And here is the anterior cerebral artery and if we come closer, we can see that there is actually a clip on what was a small berry aneurysm. I don't know if the surgery was unsuccessful or if this was a previous surgery and this was a secondary event because aneurysms, if there's one there's often another and they often bleed again. So here is a great example of how when the vessels rupture, they rupture into the subarachnoid space. We can look at this more posterior section, coronal section, and you can see that all the sulci are outlined by blood that is moving through where the cerebral spinal fluid should be. So we have blood in the subarachnoid space. Here the blood has ruptured up into the parenchyma of the tissue. In fact, in some cases there's enough pressure in a large anterior cerebral artery aneurysm, for example on this large artery here, that you could blow blood, so to speak, into the lateral ventricle. It's like turning a fire hose on a bowl of custard. It just burrows right through here and fills the ventricles with blood, but that didn't happen here. But the temporal lobe and the frontal lobe are separated by this lateral fissure and there's lots of blood in the lateral fissure as well as over here on this frontal lobe section. You can nicely see if you zoom in close the blood in this subarachnoid space. So this shows you the space unfortunately filled with blood instead of CSF, but this is the typical result of aneurysm that ruptures.