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Video transcript

so there are two main types of stroke ischemic stroke and hemorrhagic stroke and in this video we'll cover hemorrhagic strokes and hemorrhagic strokes account for approximately 25% of all strokes so let me just orient you to what we're looking at here right now we're looking at an under side view so an under side view of a brain because this view of the brain allows us to see the vessels that are most commonly involved with hemorrhagic strokes vessels of the Circle of Willis here so what's a hemorrhagic stroke well a hemorrhagic stroke is essentially when one of your blood vessels in your brain sort of springs a leak and begins to sort of leak blood out of the vessel and into the skull cavity so that's bad for two reasons I mean one you're losing blood from within your cerebral circulation and I'll show you on our friend here if you start bleeding into your cranium that blood leaking out of your vessels is going to take up room right I mean your cranium is a closed space so your blood has nowhere to go so if you start bleeding into this closed cranium space you're going to increase pressure in there and you're going to start to actually compress your brain and another thing to think about all of that blood leaking out of the vessel is blood obviously not continuing through the vessel to downstream vessels that serve downstream parts of the brain so you'll start to have brain tissue die off in that distribution and it gets even worse so you see all this blood leaking out onto this underside surface of the brain it turns out that blood contacting the outside of blood vessels irritates those blood vessels so when these vessels feel all this blood they start to get irritated and start to clamp down a bit let me show you what I mean here so here's your blood vessel as it normally looks it's at a nice wide diameter and it's letting lots of blood cells through but if blood is sitting around here on the outside of other blood vessels it eventually starts to break down into its components and we'll call those blood breakdown products and these products start to irritate this normal blood vessel so what do normal blood vessels do in response they undergo what's called vasospasm they sort of close up a little so you can probably immediately appreciate that not as much blood is going to get through this artery after it's become irritated and it's spasmed and clamped down a bit so let's say that all of these blood vessels clamp down in response to irritation by blood breakdown products and so they don't deliver enough blood to the brain tissue in their area then our patient would have developed a secondary stroke so you really have to be careful of vasospasm causing secondary strokes after an initial hemorrhagic stroke so those are three ways in which hemorrhagic strokes are really bad but what causes a hemorrhagic stroke let's look at two of the most common causes so what might cause a cerebral blood vessels to just rupture well usually they have to have an underlying weakness first such as an aneurysm an outpouching of the blood vessel walls so what happens in an aneurysm is that an area of this circle of willis the vessels in the Circle of Willis actually balloon out like that and they happen at a few places more commonly than others so they happen here where I've drawn it at the posterior communicating artery they happen out here in the middle cerebral artery they happen in the anterior communicating artery and they can happen here sort of near the junction of the internal carotid and the MCA and the ACA so they could happen in other places as well but these are some of the more common places that aneurysms can pop up so I said that these aneurysms are weakened outpouching zuv the artery wall and they can be caused by long-standing hypertension putting lots of stress on these artery walls or they can sort of happen if you have a problem with your arterial walls just for some genetic reason and so these aneurysms can sort of spontaneously rupture or rupture if you get hit in the head or if you get tackled or checked and hockey or something like that if you sustained some major trauma they can also rupture and so if one of them ruptures then all of a sudden you'll start to leak blood out of your cerebral circulation so that's one of the major causes of hemorrhagic strokes a ruptured aneurysm and by the way these are colloquially called berry aneurysms because they look like little berries that have sort of developed off of your art so the second major cause of hemorrhagic stroke that we'll talk about is a arteriovenous malformation or an AVM so I'll just draw this for you down below in the sort of normal setup of our circulation we have big arteries that then give off smaller arterioles they sort of divide into smaller arterioles that then go on and divide into small or arterioles until you reach the level of the capillary which is super small and also the level where gas exchange between your blood and your body tissues takes place on the flipside on the other side we have the other half of the capillary which drains blood from the the first half of the capillary and then you have a little venule which is a small vein and then you have a vein a proper vein and that might empty into a really really big vein let's say the inferior vena cava or something like that a really big vein okay so the important thing to keep in mind here is that blood in the arterial system is that really high pressure and I'll use p4 pressure high pressure and as it's sort of as blood sort of progresses through the arterial system to get to the capillary it decreases in pressure okay so when it's in the capillary it's that really low pressure and essentially the same pressure as the venule side and the reason for this is because our capillaries are really thin and delicate and if we hit them with some high pressure blood they would sort of just rupture and explode and release blood everywhere and actually it turns out that that's sort of what happens with an arteriovenous malformation this whole system here isn't formed the way that I've drawn it in an arteriovenous malformation what actually happens is that the arteriole end is that this whole capillary system this whole capillary segment is bypassed and you get arterioles that are actually just directly connected to the small veins on the other side and so you just end up getting blood at still really high pressures going straight into the veins and so that's really not good for the vein because they've sort of evolved to deal with lower pressures and now without that dampening down effect of the capillaries that step down a pressure that's sort of afforded by the capillaries you get this high pressure blood going straight from arterial system into venous system and this high pressure puts this sort of arteriovenous malformation at a high high risk for rupturing and so you can imagine if that happened in your brain you'd end up with a hemorrhagic stroke so while a VMs can occur really anywhere in your body they often appear within the brain or within the central nervous system and why do they happen well they're congenital it's due to sort of a defect of blood vessel formation in development so those are a couple of the major causes of hemorrhagic stroke