Dural Arteriovenous Fistulas: Operative Strategies

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- Colleagues and friends, thank you for joining us for another session of the Virtual Operating Room. My name is Aaron Cohen. Our guest today's Dr. Michael Lawton from the Barrow Neurological Institute. Michael, thank you for joining us. You've been truly one of the amazing speakers in this series and we sincerely appreciate all your incredible contributions to Microsurgery.

- Thanks for having me.

- Thank you. I know you're gonna talk to us about surgical treatment of Dural Arteriovenous Malformations, really an incredible topic, a great interest in that. So we're all ears and look forward to learning from you. Please go ahead.

- Okay, Aaron, thank you so much for once again, hosting me on your show. It's a privilege to be here. So I'm gonna talk to you about Dural Arteriovenous Fistulas or DAVFs, Operative Strategies. This is a slide that just summarizes an important distinction between DAVFs and brain AVMs. And I'll just walk you through, because I think it's important from the get go that we differentiate these two. They're very different. The Fistulas are located in the Dura, AVMs in the brain. The arterial supply for a DAVFs is meningeal, whereas for AVMs it's the cerebral or cerebellar circulation. Native arteries of the brain. The pathology for DAVFs is a Fistula, a simple artery to vein connection. Whereas an AVM has a Nidus. Venous drainage for DAVFs when it's dangerous is Retrograde. It's different from AVM where the venous drainage is in the normal antegrade direction in the veins. Interestingly, we think of DAVFs is a little bit more benign, but in fact, the high risk ones have a bleed rate that's dramatically higher than what we see in AVMs. Difference of almost tenfold. 15 to 20% is the range of the high risk 2 to 4% is the range for AVM. Treatments of dural fistulas are primarily an endovascular disorder in this day and age, whereas ABMS are not endovascular. They're primarily surgical in my view anyway, or in some radius surgical. The surgical treatment is also different for official it's of venous interruption, whereas with AVMs it's the Resection. And lastly, Pathogenesis. The Dural AV Fistula pathogenesis is much better understood and thought to be acquired. Whereas with AVMs, these are thought to be congenital. So as you can see, almost on every category here, these are quite different. All right. So next is Natural History. I think, well, there've been many classifications for Dural AV Fistulas and I have gravitated to the Board of Classification because it's simplest, it's hard to remember the cognac and the various other classifications for DAVFs. And so this one I think it's key. It boils down to just three types and even within this key type is the type three. Type one is drainage anterograde into the sinus. So the sinuses open, the flow is in the normal direction, and these are relatively benign. This is what you will often see with the transfer of sigmoid Dural AV Fistula low-risk that can cause pulsatile tinnitus or other nagging symptoms. But these don't bleed. The type twos are a combination of both antegrade drainage into the sinus and also retrograde drainage innovate cortical veins. And these are also low risk. The type three is the one to be on the lookout for, and that's one that drains exclusively into the cortical veins in a retrograde manner. And these are those high risk dural fistulas that I was referencing in the previous slide. You can see now going through all three types of the type two is really a blend of the one to three. So if you just know one in three, you kind of get this classification system. So indications for surgery are really those that are a high bleeding risk or Borden Type III. Those that have progressive neurologic deficits. And you'll often see these both based on the patient's history, but also if you look at MRI, you can see a lot of white matter signal change due to the venous hypertension and venous congestion. You can have lesions that are treated endovascularly, unsuccessfully or incompletely and that's an indication. And lastly, those that are already ruptured and have intracerebral hematoma. Oftentimes you can't avoid an operation because the clot Borden is so hot. Now I want to digress for just a minute and talk about the pathogenesis because it's a topic that's near and dear, I spent them, I researched as a resident at studying this disease. And the beauty of it was that there was a wonderful surgical model for it where you could create a carotid to juggler fistula. This was a rat model. And by doing so you would create venous hypertension. You would essentially materialize the venous system, create venous hypertension dramatically by raising the precious tenfold. And in addition, you would occlude the draining veins in the contralateral side and also put some thrombus in the sagittal sinus. So it was a three step model system. And if you just let that sit for a while, what you see here, and this is you can induce these dural fistulas to form the Control angiogram is that a lateral view of the rat skull. And you can see the normal cerebral circulation up on the top here and on the bottom here, you can see the dural fistula forming down there. So here is the fistula. You can see here the draining of venous outflow, and that is a classic finding for these induced dural fistulas. Now here's another example. You can see the normal control over here with the sagittal sinus here at the circle of Willis. If you look with a careful is set down in here. Our vascular trunk is down in here. So you can see the normal anatomy very nicely there. And when you look at this specimen here, our fistulas site is here with a draining venous outflow coming off to the side. So that is the model system. Those are the findings. And if you then correlate the animals that produced fistula with the amount of angiogenesis activity in their dura by harvesting a dura sample adjacent to the sinus. What I was able to show is that there's increased angiogenesis activity. This is a rat cornea as to say a very crude in today's era, but it was able to demonstrate really for the first time how angiogenesis activity is a big part of this pathogenesis. And based on that I proposed this pathophysiology where it all begins with the venous outflow obstruction and venous hypertension as a result that results Nate cerebral congestion, which produces a venous ischemia. It triggers an angiogenesis cascade that angiogenesis leads in theory to collateral venous drainage. And that's sort of the corrective mechanism here, but if it goes awry, you can go down the left side of this flow chart. And that leads to, from this propagation, Malignant clinical course, with this vicious cycle here of worsening outflow obstruction, increased venous hypertension and so forth. So that was how I thought about these Dural AV fistulas way back when and subsequent research here showed how there was in fact, this venous hypertension process going on that you could track that down to a production of hypoxia inducible factor one or F1 in these perivenural spaces. And so a venous hypertensive mechanism here that induces this angiogenesis cascade. So with that in mind, what we have here is acquired lesion with the pathogenesis that I just discussed all triggered by some underlying sinus thrombosis or occlusion. That leads to these probably benign lesions, at least initially but they begin and then as they mature and progress, they can become more malignant forming these type two and type three lesions and then prompting treatment. So most of them are treated endovascularly either with a transvenous or transarterial approach with the intent of interrupting that draining vein and blocking the fistula. There is no nidus. So you don't need the traditional receptive strategies that we use for brain AVMs. These are simple venous interruptions, which make them a very elegant and simple operation. So here's a table. This table is meant to show you how I think about these things. I'd divide them into supratentorial, tentorial and infratentorial and the rest of this talk is really just walking you through these different locations. And I'll start with the supratentorial fistulas. The supratentorial compartment you know, you don't see these everywhere. You see them in very specific spots and the key ones are Ethmoidal, Super Sagittal Sinus, Sphenoparietal Sinus and the Cavernous Sinus. So here's an example of your classic ethmoidal dural fistula. Here, what you see is the classic venous barracks here, riding above the cribriform plate. And when we look on these axial views, you see it here just on the inner aspect of the thermo sinus you can see the barracks over here, coming up again from the cribriform plate. You see it here and here. So this is your classic findings on CT angiography for these ethmoidal fistulas. You almost don't need an angiogram at this point because it's so half and mnemonic for this diagnosis. So the surgery for this is a Bifocal Craniotomy. You really only need a little opening here in the midline to get down to the cribriform plate, but what I'll sometimes do is a wider craniotomy so that these cuts in the frontal bone are well hidden at the superior temporal line. So here now is the video and you're looking down on the cribriform plate and these are very easy lesions. All you need to do is to find the arterialized vein on the frontal surface. You follow it down to the cribriform plate. What we see here is the vein coming out of the cribriform plate here and up in an arterialized way. And so that's our pathology. We simply apply a clip at that point to interrupt the fistulas flow. I'm applying a mini clips just below that because you want that distance here to be as small as possible or as close to the fistula as you can get it. And that you can see interrupts the flow. So now this arterialized vein here, and this varix here are essentially quiet now. You don't see any filling here of the vein, which indicates that we've succeeded. We've interrupted the fistula and we have cured the problem. They're also very gratifying because you'll often see the color of the vein change from that arterialized reddish color to make purple. And once the fistula is interrupted, we can go ahead and cauterize and divide the vein just for good measure. Here's a nice view now of the olfactory bulb, right in here, sitting in the cribriform plate, you can see the vein coming out and our problem is solved. The rest of this is just cauterizing the vein, making sure that it's completely dead and you can see a nice example of the viruses that are often associated with these. Even though they're small ethmoidal theaters, you can see fairly dramatic lodgement of a vein to form these large viruses that really are the points of rupture. And as we think of the pathophysiology, sometimes you'll have rupture from the Venus varix that's remote from the actual fistula site. And so it can be a little bit misleading as to where the actual pathology is. Here now is another case. This is again another ethmoidal neural tube especially you can see feeding vessels here, coming over to this fistula over here, both from the left and also from the right. These ethmoidals get supply often from both sides. Same Bifrontal Craniotomy as before. And in this case, we felt there were two distinct ethmoidal fistulas, one on each side. And so we're gonna go to both sides of the fox. So again, this is our exposure, it's bicoronal incision larger than necessarily flaps just for cosmesis and away we go. All right, so here now is the view again, down the cribriform plate, here's our pathology coming out of the cribriform region. And as we isolate the pathology, we can see exactly where we need to get that clip. But so this is all just very seal dilation here, downstream. The vein is coming up. But we just need to apply that clip low. We need to interrupt that artery to venous connection. And with those clips in place, we now have interrupted the flow. This is another clip for good measure. And now we can cauterize and cut these connections to the vein. Once you have the clips on and the veins interrupted, it's important just to look around and make sure that the fistula hasn't connected to other veins that might be present. So here you can see some stagnation in the veins, no active flow in the veins and the fistulas were nicely interrupted. So very straightforward, here the postoperative angiogram shows the elimination of fistula from both sides and this patient did well. All right, so that covers the Ethmoidal fistulas. And now we'll turn our attention to a different type of fistula. This one here is an example of a sphenoparietal sinus dural fistula. You can see the CT scan, large hemorrhage here. This is an example of a remote varix here that has bled away from the fistula. The fistula is actually over here at the Sphenoparietal Sinus where that Sylvian vein exits the Sphenoid vein. So the surgical strategy is outlined here. We devascularize on the dura opening, but we need to go to that Sphenoid wing dura near the meningo-orbital band to find the fistula. And once we find that draining vein, we occlude there venous interruption with the clip and cautery. And then once that's in place, we can go to that remote site. We can deal with the hematoma and decompress this gentleman's brain stem or brain compression. So here now is the video. You can see around the left side. Frontal lobe is to your left, the temporal lobe to your right. Sorry, frontal lobe to your right temporal lobe to your left. And as we come down, the sphenoid wing, this is our fistula's vein that drains out of that Sphenoid private side. We can do into assigning green initially. That confirms the shot flow into that vein. And now the dissection at this point is just to get around this Venus varix. This is that sort of thickened venous wall here. This is the vein coming down from it and then it works its way into the . So the occlusive maneuver is that clip right on the vein, as it exits the sphenoparietal sinus. I'm doing this in a tandem clip manner. So we've got a fenestrated clip around a big portion of the vein and a closing clip around the fenestration that interrupts the venous outflow. And once those clips are in place, you can see there's that dramatic discoloration from red to blue, indicating that there's no longer that shunt flow. So we do our IC green. What was once shutting flow is now nice and quiet, and you can see here, this vein is essentially stagnant. So I'm just cauterizing this to eliminate any chance of recanalization or flow. And then we'll cut that. This is our belts and suspenders approach to these. And now once that's in place, we're gonna go after that hematoma. So small little peel incision, and we get into that hemorrhage cavity and see how much clot there was. And we can nicely evacuate the clot just through a little trans frontal opening there. And that takes care of our ICP issues that might have otherwise been problems. So here is just our final overview shot looking down on the carotid system, and there's the internal carotid artery, the just cleaning up. You can see those dilated veins down in the dents. We can advance to the next slide, and now we can turn our attention to a different territory. So those are nice examples in the super tentorial compartment. They show you the principle of the sinus interruption. They show you some of the pathophysiology that you can expect. Now, when we turn our attention to the infratentorial compartment, these are the major players. There's the transverse-sigmoid sinus, throwaway deficient, which is by far and away the most common. But this typically is a well-suited lesion for endovascular therapy. One that we rarely need to treat surgically. These other two, the inferior petrosal sinus and the marginal sinus are also really quite rare. I'm gonna show you on this next slide, an example of the marginal sinus one. You can see here, a lot of these venous viruses, these veins here above the foramen magnum, cisterna Magna. And these go along with the diagnosis of this marginal sinus fistula. The marginal sinus is a sinus that runs around the foramen magnum. And these marginal sinus fistulas are right in that region. And you can see here on the angiogram, these enormous dilation of the veins, you can see viruses here, you can see viruses here. And this blood flow is just kind of working its way around the brain stem, searching for a way to get out. 'Cause there's been some compromise in that venous circulation. So the strategy here is a far lateral craniotomy with C1 hemilaminectomy. This is the view interoperatively after the far lateral has been done. Our cervical spinal cord is here. Our occiput is over here and our conduit is over here, just , so this is the midline. This is a midline incision here. And the key is to very carefully open the dura because just underneath are those dilated viruses that we don't wanna encounter too early. So as our dural opening is executed, you can see the very nicely. The fistula is gonna be right here in the dura itself. And as that dura elevates, you can see the pathology. This is that nice kind of dilated tissue that you see. It's almost like a vein that's been . It's got that whitish color, you can almost see some on the wall. And as we opened that beautiful arachnoid here in the cisterna Magna, you can begin to see these viruses. And the whole key here is to really isolate the vein as it exit to dura. You wanna not be confused by all of the other tortuosity of the venous system that's coming into view here. You don't wanna be confused by the arteries that are there, but we just wanna focus on the fistula, which is here. And the venous outflow, which is here, and the interruption is gonna be as close to the dura as possible, where those fistula and vein join each other. So now we can see things clearly, this is an IC green, just to show you how the fistula is here. The outflow is here. It continues on, in a secure way. And you can see the heat map here of our IC green, that sort of matches that circuitous course. And this is really just confirmation that we've identified and decoded deciphered, this pathology properly. And now the venous interruption here is just a simple clip, right here, as the vein exits the dura. Now that we've interrupted the vein, you can cauterize the fistula. And I've added an additional clip here just to make sure that I'm all the way across. You see how that first clip was just a little bit shy. So I'm adding this booster clip to reach all the way across the vein and finish it off. So these are good strong clips that nicely polster one another. And now we've definitively sealed that shunt, we can remove one of those clips. And now we've taken care of business. This is just an additional dissection. These veins are so interesting. They're beautiful to look at. You can see just beneath them the back of the Medulla, the fourth ventricle and the normal arterial anatomy, and the vertebral artery is there. And so here I'm just gonna transect the vein just to make sure that there is no connection whatsoever. And now the fistula goes upwards with the dura. You can see the veins that have grown to be quite dysmorphic and pathologic are all quiet. They're turning blue in their color. They're doing no harm. There's no need to do anything to those. And that finishes the job. So very simple to do a venous interruption, this is an indocyanine green, just to show you how the arteries now fill normally. None of the veins in these spaces back in here or back in here are filling. So we've done our job and we can go home. You can see the vertebral artery in the distance there. You can see the 11th nerve running up to the juggler foramen. You can see our stump of a vein. You can see how it dilates into these viruses. And again, because of the venous outflow problem, these veins are just searching for outflow for this arterialized shunt flow, and you can see how the veins respond accordingly. So let's move to the next slide and we'll move on to this topic of the tentorial fistula. So I really was perplexed by these, years ago. And so I studied these, I gathered up all my tentorial dural fistulas and wrote this paper. And I think it was really instructive, informative for me, because at the end of it came up with these six types of tentorial fistulas. You can see them listed here and we'll go through the key ones. So the beauty of this taxonomy is that, as you identified these, you can really separate them in to their pathology based on their regions. The Galenic ones sit right at this faucal tentorial junction at the vein of Galen, really at the anterior most end of the straight sinus, but at the end of the vein of Galen. There's the straight sinus fistula which lies anywhere between the vein of Galen, I'm gonna talk you up. The third type is the tentorial DAVF here. The tentorial sinus dural AV fistula is a fistula that leaves in the leaflets of the tents between the straight sinus and this transverse sinus, anywhere in between. The next type is the superior petrosal dural AV fistula, which is along this SPS. And then finally the incisural also. You see six very distinct locations, and each one has its own pathology, its own feeding, supply, its own unique pattern. And most importantly, each one has its own unique surgical approach. So you can see that if you identify the type of fistula, it's gonna lead you to the approach, whether it be interhemispheric approach, supratentorial infraoccipital approach, a torcular approach, a lateral supracerebellar-infratentorial approach, a retro sigmoid or a pterional subtemporal. So it's important not just for, you know, making these academic distinctions, but also for making your surgical decisions. So some examples, I'm gonna start with the Galenic. The Galenic is, I think the most complex and the most challenging, you can see from this diagram, how it's fed from the tentorial arteries wrapping around. You can get supply from up above, from the falcine vessels. You can get supply from back here from the post-term NGLs. And you also get these ranches off of the PCA, the artery of Davidoff and Schechter and also branches off of FCA at times. So supply from all over and drainage out. Usually one or a couple of these branches out of the vein of Galen. The approach that I prefer after having tried them all is this posterior interhemispheric approach with gravity retraction. So the midline is horizontal. We've got gravity that pulls down on the dependent hemisphere and that gravity retraction opens up this space here so that you can get all the way down to the faucal tentorial junction down here. And as you do that, you get to the Galenic region, which is right here. This is an illustration for the medial occipital AVM, but it's the same surgical approach. Now, an advantage of this approach is that if you have very complicated anatomy and you can't see what you need to see, you can make a dural window, you can cut the faults, you can cut the leaflets of the tentorium on either side, and you can really open up this territory for a completely unobstructed view if necessary. So that's an advantage. And here now is a video. So classic feeding artery anatomy here, you see that tentorial artery or the artery of scenario, it comes off of the MHT here. It continues along the inside dura and gets to the vein of Galen. And you can see a little blush right there of what's left of the vein of Galen. Another vein of Galen is not filling normally. So we don't see it's modal emptying into the straight sinus. What we do see here is some middlemen GL supply. You can see a little bit of filling, healthy, visible vein of Rosenthal on the right side. And so that tells us here that that's where we need to go for our approach. We can get down on the right side of the vein Galen. And interrupt that vein immediately. Treatment itself will be exactly the same as you've been seeing in all these other cases. So here's the exposure at say, torcular craniotomy. Here's the torcular here, but really what we're interested in is this quarter here and the patient's position. So that gravity is gonna retract down on that hemisphere. So torcular craniotomy, I don't use any Lamar grand because I go right away to this quadrigeminal cistern. As you release CSF that occipital lobe will fall and get a clear view of the falcotentorial junction. You can identify the arteries, you can go down to the veins, you'll work out your anatomy. And as soon as you find that arterialized vein, then you can interrupt it. And indocyanine green again, is very useful for these dural fistula in recognizing the pathology and verifying that you've interrupted everything. So here's the view. Here's the supra-sagittal sinus. Here's the transfer of sinus here. Top of the head is up this way. The feet are over here. And so that should hopefully orient you here. You can see that falcotentorial junction curving that way. And as we come down, this is getting into that quadrigeminal cistern. You can see a little bit of a fusion here between the occipital lobes we wanna free up. And as the occipital lobes come apart, you're gonna see this coming to view. Here's this of the Corvus closer, it ends right there. And as we dropped further down this way, you see the batches of the PCA and we can start to work through the pathology. This ends up being our arterialized drain vein, but you'd never know it. It's got exactly the same caliber as the branches of the PCA that are normal. And it's very important that you don't mistake them, because if you think that the clip is going on the drain vein, but it's in fact going on your PCA, you can end up with an occipital infarction and a visual field deficit. So very important again. Here's our vein coming down. It's arterialized so it looks exactly the same color as the normal arteries, but there it is. So that's our target. This is just some additional dissection to make sure we're seeing the right things. These are the normal arteries coming in. This is the vein leading out and here on our IC green. This is our vein draining retro grade. Our normal arteries are here going Antero grade. And this IC green is very helpful to make sure you got everything worked out. So vein here and arteries adjacent. So now that we have that worked out, our clip is gonna go right here. You interrupt that draining vein just as it leaves the falcotentorial junction at the bank of Galen. And here a second clip, just to make sure that you've got everything shut down. And now the pathology is interrupted. We can look down here and see an IC green on that vein, which is running right here, it is now dark. These are the normal arteries whizzing by, but the vein is dark and we can now cauterize and cut, just to definitively interrupt. So there's the cannery, there's the cut. And once again, this very deep, very complex dural fistula is very easily interrupted here. It's just this simple maneuver. So this was an example of this Galenic type, of the type one and a very simple one at that. Let's go to the next slide. This next one is an example of the type two lesions, straight sinus dural fistula. Now we were talking about the Galenic up here. You can see this one is now a little ways down the pike. So it's on the mid portion, typically of the straight sinus, but I've seen them everywhere from here, just adjacent to the triangular region and here just adjacent to the vein of Galen. But what differentiates these is that they typically will drain into a vein infratentorially going to the cerebellum. And the approach is gonna be under the tent. You wanna get to the vein, so you've got to go supra-cerebellar infratentorial. So here is the approach. I like to do these sitting because the cerebellum sags, you get this migration of the cerebellum downward, and it opens up this space very beautifully into that or supra-cerebellar cistern. And you can then have access to the fistula. So let's roll that video. Here you can see the pathology are straight sinus and exiting vein are right there. You can see a tentorial filling artery. You can see a little venous pouch here as it exits the vein. So this is a nice example of one of those remote viruses. You can see filling from the occipital artery on the backside here. And you'll also notice that this is not so far from the basically right here. And this is one that's just inside of that. Our approach is sitting position, torcular craniotomy. You want this craniotomy to get above the transfer of sinuses so that you can lift up on the torcular and widen your surgical exposure. These are the steps we did. Embolize this one with Onyx. We did our torcular craniotomy, sitting position, we recruited gravity to open up the plane. We identified two arterialized veins coming from the straight sinus. We confirmed the fistula site with IC green. We did a venous interruption with clips, and we did IC green to confirm. So this is the view that you get once the exposure is done, you can see this was a ruptured case, and you can also see how as we go supra-cerebellar, we get right onto this vein. This is the outflow vein here, we're following that forward. And we're looking for the place where this vein joins the dural. So as we follow that forward, we see it joining right there. So that's the spot where the vein exits the straight sinus. They were actually two veins exiting the sinus there. So we want both of those addressed. And you can see how there are oftentimes these arachnoid adhesion that lie between the outer edge of the cerebellar hemisphere and the cerebellum. And this just gives us a little bit wider exposure, but now we've brought all of this into our view, and this is gonna be our fistula site here. So this is the site of occlusion. We do our IC green, just to confirm, and you can see how the flow out of this thing is this way. And there's also some flow going out in this way. So we wanna make sure we get all of it closed down. And so here's clip number one. You can see how this first vein here is now interrupted. You cauterize and you cut. You can see internally a little bit of that Onyx embolization, but we still have some work to do. We've got this second vein that's coming out here. So we go on with the next clip and we, again, cauterize and cut. And now we've taken care of the arterialization of that cerebellum venous assistant. So that is the overview. You can see that's just a normal vein off to the side. That's straining cerebellum normally in the arterial great direction. Then a stagnation here in all of our veins, leading from the fistula. And so we have successfully obliterate things and you can also see that bluish color in the veins. That's an indication of that stagnation and the fact that the job is done. So we can go to the next slide here. And these, I think are just some slides just showing the other types of the torcular fistulas are a mixed bag. These are actually at the level of the torcular. They're in the dural. And so they're not in that supra-cerebellar space. The feeding supply is tentorial artery, middle meningeal artery, and the veins that drain this are usually super tentorial and into the occipital region. So that is the pathology of these. And these are tough because these are often not just a type three. If they are just take three, you can simply do the venous seclusion. But in this case, this had a lot of flow into the torcular sinuses as well. And so you can see that the dura has been skeletonized along the transverse superior sagittal sinus junction, along the torcular here, we've cut the dura on all sides to try and dearterialized this. And this is one of the ways that you can treat these volume type one components of these fistulas. So I don't have a video to show you on that one. And I'm gonna skip the video on this tentorial sinus one. But this, as you can see, these tentorial sinuses live in the leaflets of the tentorial. Usually the veins are draining into these tentorial sinuses, which then go antegrade to the transverse sigmoid junction. But if you have a fistula that forms, you can see as a drawing, it's right here. And the venous outflow becomes retro grade and it looks something like that. And so the treatment of these is usually through a supratentorial infraoccipital approach, which you can see as the similar craniotomy to what I showed you for the posterior interhemispheric approach. You slide underneath the occipital region and you get full exposure of the tentorial surface. You hunt that vein as it comes out of the dura and then you put your clip to interrupt. Moving on to the superior petrosal sinus, this is a more common fistula. You can see the lens along the SPS here. This is Dandies vein, dandies vein gets hijack and the flow becomes retro grade into the veins. Normally draining the cerebellum. Our approach for this is typically a extended retro Sigmoid, just as you would say in a microvascular decompression. The extended retro Sigma is a skeletonization of the sigmoid sinus, mobilization of the dura forward, and a really extensive opening here that gets you into that CP angle. So that's the exposure. Here's an example, we can roll this video. We can see this circuitous venous outflow that leaves or originates right there at the superior petrosal, sinus right in this region here. And you can see that the outflow is out this vein and it's working its way through the Galenic region. So we wanna get to this point here and do our interruption at that point. Here's our positioning for the extended retro sigmoid. It's just a simple supine position. Head turned, you can see the opening there, and that's gonna be all that we need. So here now is the view. We are in the CP angle. This is the petrous zone over here. And as we come into the CP angle, you can begin to see our pathology right in this region here. So this is our arterialized vein. You can see that was just a little branch of it. Now we have a much clearer view, you can see that whitish, this colorization of the vein as it exits the falco of the petrotentorial junction. Here you can see how red it is, indicative of the flow. And now we're just kind of bisecting our way along its course. You can see how it continues on this way. It had a very medial direction. It was working its way over to the vein of Galen. And you can see that as we go more immediately there's dilation. So this is where we're gonna occlude this thing. This is the fistula site up in here. This is the outflow over here. Here's a little branch of the SCA kind of sliding by, and now we'll occlude this with this clip. So this is my fellow, I'm applying the clip. Now what you wanna try and do is you wanna try and get this clip as close to the fistula as possible. The fistula is up here, so we have left a little bit of a pouch here, which we'll wanna address in a minute. But at this point, we know that we've interrupted the fistula and just putting this second clip on there. And now you can see that the fistula no longer shunts. So we've done our job. This is just looking to make sure all the arteries are good. You can see, I wasn't happy with the amount of venous pouch that was left behind. So this last bit just eliminates most of that remaining venous pouch and getting the blades as close to the fistula in this direction here, in this direction here. So that we really strangulate that venous outflow. There really isn't much left of that venous pouch now, and I'm cutting across the vein to disconnect it. And now you see that petrous bone is here, tentorium is here, our fistula is in that little attic and we completely isolated this. This last one, the incisural is the rarest of the six types. This leaves along the inside dura here between the sinus and the vein of Galen. Typically drain supratentorial to those medial temporal veins or nasal vein and Rosenthal. And this is typically approached with an oversized automatic Transylvanian approach. So just as you would for an aneurysm, you can see we go into this carotid ocular modal triangle here. This is our normal working space for the vascular apex, but instead of going immediately as we would for the vascular apex we wanna go laterally this way, and we wanna work our way along the inside dura back in this direction. So we get into that oculomotor tentorial triangle and we'll find our fistula there. So this is just a summary slide showing you the six types of the dural fistulas of the tentorial. You can see the frequency, the most common ones being SPS, straight sinus and Galen. You know, those being far less common you can see that each one has its own unique location, dural based venous sinus and venous drainage. And importantly, each one has its own surgical approach. So classify it to find this type that will lead you to the best approach, it'll lead you to the best position, and you can make your surgical decisions. The results are good, angiographic occlusion, 96%, no morbidity, no permanent neurologic morbidity, sorry. Mortality was also zero and this was the follow up. So really we do well with these and these are really quite enjoyable lesions to take care of. So my final slide to some, these are acquired lesions, fascinating pathogenesis with this sinus occlusion, venous hypertension and angiogenesis mechanism. The high restoral fistulas or the volume type ones, sorry, type threes are the ones that should be treated. Endovascular therapy is generally first line, but if there's any difficulty or any incomplete treatment, then surgical interruption is the second line and effective treatment of choice. So with that, I will stop. Thank you.

- Great work, Mike as always, really enjoyed it. A lot of good technical pearls there. May I please ask you how'd you make a decision for endovascular versus surgical treatment of most of these classes? As you know, currently there's a number of endovascular techniques that do a relatively good job. And so if you could comment on that I'd appreciate.

- Yeah, so even though I love doing these cases, and even though surgery does a wonderful job, I usually give the right of first treatments to the endovascular team. So I essentially give it up and when they can't do it or can't completely do it, then I step in. Hold on one sec. Hello. Yeah. Okay, great, thanks. That's the carotid.

- You have two more minutes, we need to wrap up.

- Yeah, let's do our recap and then I'll be through.

- Okay. So I start again if you don't mind. How about we just start with a question. Mike really illuminating great lecture, really enjoyed the technical pearls as always. Would you comment about your selection criteria for endovascular versus surgical treatment? As we know there is a number of endovascular therapies for these lesions. So I assume you give the first line of fusion to endovascular and then proceed with surgical therapy. Is that correct?

- Yeah, so as much as I love these lesions and as effective as our treatments are, I turned them over. I give the endovascular team the chance to cure these things and you know, if they're not successful, then I'm ready and waiting.

- The other question I have is there about, the spinal arterial venous fistulas, those are obviously are becoming more and more endovascularly treatable. Do you still continue to treat those, especially a class one dural spinal fistulas?

- Yeah, I'm a believer in the efficacy of the surgical treatments for that one. You know, we've gotten to the point now where a single level laminectomy, a really directed clip occlusion is incredibly effective and a very low risk and low morbidity with no recurrences. And so I'm still a believer in that. So those are generally... I will present surgery as a equal option. And, you know, I let the patients decide. If the patient preference is one for endovascular, then we'll let them be treated in that manner. If their preference is open surgery, then we'll go that direction. But, you know, I think the options there in my mind are equivalents. There really isn't a superiority of endovascular for those patients.

- Can you comment on maybe the top one or two points topics that are most controversial for surgeons in treatment of the dural venous fistula?

- Well, yeah, I guess the biggest controversy is the one we just touched on is what's the first line therapy. This used to be a surgical disease. And now with the navigability of the current catheters and the Onyx agents that are available, the efficacy has found a way out. The risks of endovascular therapy have gone down. So I think, you know, we've got ourselves to the point where we've got a really great endovascular option for a lot of these intrepreneurial lesions. So I've done over a hundred of these, but clearly there's been a dip in the frequency that I do these. And that's one area of if not controversy, some contention. But we've always done a great job with these. And it's hard to give up on something that you do so well with but if you can do it with a less invasive approach, then, you know, patients often look for that. That's the one area of controversy. I think the other is just not so much controversy, but the real teaching point is that these lesions are often difficult to decipher on angiography. And I can't tell you the number of times that people have encountered the dural AV fistula thought it was a brain AVM, gone in with a certain mindset of resecting an AVM within brain tissue and then completely the wrong operation, or not been able to find what they were looking for. And so I think to be able to recognize a dural AV fistula for what it is, and differentiate that from a brain AVM is really an important lesson. It was my first slide, and I think if you walk away with anything from this lecture, if you can just recognize a fistula for what it is and make sure that you don't think of it as an AVM, then you'd be on the right track and you'll do the right operation.

- Beautiful, thank you again, Mike. We sincerely appreciate your contribution to this series.

- My pleasure, Aaron. Congratulations on the success of the Atlas in this series. And thank you for having me.

- You're welcome.

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