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Grand Rounds-Giant Aneurysms: Techniques and Tenets for Ligation

Michael Lawton

March 04, 2012


- Hello, ladies and gentlemen, and thank you for joining us. This session will review neurosurgical technique for surgical management of giant aneurysms. There'll be also review of bypass techniques. Dr. Michael Lawton from University of California at San Francisco will be our guest speaker. Again, thank you for joining us.

- Thanks Aaron. Well, it's a pleasure to be here with you again, and I'm honored that the double NS has invited me to two videos. So, I'm going to show you two cases, one is a clipping case, the other is a bypass case. So this is the first case here. And if you look at these actual and sagittal MRI images, you can see the aneurysm here is in the interperdicular fossa here. You can see layers of thrombus intraluminally. So this is a really classic example of a giant thrombotic aneurysm. Now, looking at the angiogram here, you can see this is a superior cerebellar artery aneurysm. It's on the right-hand side. You can see that the luminal component is really a small portion of the overall size all of this area here is filled thrombus and doesn't fill the contrast on the angiogram. This is a view just at the CT angiogram again, showing how the intraluminal component is quite small. The thrombotic component is quite large. These are postoperative angiogram showing the clipping, and I'm just going to take you from pre-op to post-op here. This is just to show you the nice reconstruction that we were able to achieve. Now, the synopsis of the case is that this is gonna require a transcavernous exposure to get the room that we need to do this. We're gonna need to open up this triangle between the carotid and the oculomotor nerve, the so-called carotid-oculomotor triangle. And, you can see now it's pretty much consumed with aneurysm and, in order to get proximal control and really define and visualize the aneurysm that we need to remove the anterior clinoid, we need to remove the posterior clinoid, go through the cavernous sinus and make that working space. This is just the anterior clinoidectomy This shows you the posterior clinoidectomy With that, the more you can now get proximal clips on the aneurysm here. You can open the aneurysm and thrombectomies, visualize the anatomy and place your clips. So that's just sort of an overview. And now Aaron, we can switch to the video.

- Okay, if I may ask you Michael, would you let us know about the clinical history, how old the patient was and the present symptoms please?

- She presented, she's in her mid-sixties, presented with the third nerve palsy and some hemiparesis due to the mass effect on the cerebral peduncle.

- Thank you.

- All right, so this is the video that's now playing. And you can see that this is a transsylvian approach. This is a right orbito-zygomatic cranial artery. And you see from the video that the carotid oculomotor window is filled with aneurysm. And so we're going to need to do some work just to get the exposure that we need. So the first step in doing a transcavernous approach is taking out the anterior clinoid process These are the dural incisions that exposed the clinoid. I like to just raise these flats to expose the bone. This is a diamond drill bit that we're using to cavitate and then remove the anterior clinoid. You can see a little bit of bleeding from the cavernous sinus, but it's you around the clinoid but you can then just pull right out of that dural pocket there. Now, because this is right on the roof of the cavernous sinus and you make a little bit of a hole in taking the bone out, you can capitalize on that, use it as a spot to inject some to seal, which can control further bleeding from the cavernous sinus. So the clinoid has been removed. This is just incising the dura down. This allows you to then incise the dura over the posterior clinoid processes. And now what we're gonna do is we're gonna continue our drilling into the posterior clinoid and back of the top of the clivus. That was a quick clip just showing how as you take up that bone, that dura that was on the clivus, now become soft and you can pull it forward away from the aneurysm. And now what we've got here, we've got working space to essentially match down proximal to the aneurysm and get control. This is the basilar trunk What we're looking at right here is the superior cerebellar coming from the base of the aneurysm. This is cerebral peduncle here. Third nerve here, and this is the contralateral anatomy, contralateral PI segment and these are just a little bit of the ipsilateral P1. Now, going back to the basilar trunk here, this is gonna be our proximal control, and we're gonna need that so that we can open up this aneurysm and do a thrombectomy. So that was our proximal clip. Only on the basilar trunk. There's the PI ipsilateral on the distal side of the neck. There's our second temporary clip. So, now the aneurysm is between two temporary clips. It's not completely trapped, but it's controlled enough so that we can incise the aneurysm. What you'll see here is just an incision in the wall and getting into that organized thrombus that's inside the aneurysm. That's a crusa the ultrasonic aspirator is a very nice way to de bulk and break apart the thrombus and essentially just reduce that mass. We're gonna hit the luminal component of the aneurysm. You can see a little bit of back bleeding, but it's easily controllable with the sucker. And now we have the ability to mobilize this aneurysm. This gives us a view of that, cleavage plan between the ipsilateral P1 and the distal neck. And we can see the opposite side of the neck there. This first clip is what I call 'a tentative clip. It's just gonna go under to control the bleeding and get those temporary clips off. It's not a perfect clip. It doesn't really sit where we want it to sit. And if you look here carefully, you can see a kink in the P1, but, it's a first approximation of our clipping. We see now what we need to see, and what I need to do is essentially back that clip a little bit further up off the neck. So in order to do that, I'm gonna need to take a little bit more thrombus out of the aneurism. So now the crusa comes back in. I'm gonna to take some more thrombus out of the dome portion of the aneurysm, and you can see here, the aneurysm now becomes much more mobile and soft. We can put a second fenestrated clip on here, stacked right on top of the first. And now, we can take that first imperfect clip and just slide it back a little bit, just to be P1 origin on the ipsilateral side and right across the base of that aneurysm. So now we have two clips on, this is our third clip. Just gathering up a little bit of extra portion of aneurysm. And now between those three clips, you've got a nice reconstruction. Here's the P1 ipsilateral, P1 contralateral, basilar trunk here. Nice view of that anatomy. We've taken that kink out of the P1. So that looks good. Now we're looking over at the contralateral SCA, and that also looks good. This is an indocyanine green dye injection. You can see carotid here, you can see the basilar trunk, the P1 segment, all those vessels fill out very nicely. And so now we've got a very good reconstruction. Here's a better view of the anatomy, the basilar trunk, contralateral P1, ipsilateral P1. Here's the base of the aneurysm.

- That's very nice job, Michael. I have a question for you. Number one, one thing that personally has worked for me that you can often openly dura over the distal portion of the third nerve to release the nerve a little bit if you need to, just to decrease the tension on the nerve. The second point is, if this patient did not have any mass effect and the lumen was so small, and most of the aneurysm was thrombosed. How do, you know, discuss the option of the treatment with the patient? What are the risk of hemorrhage when, you know, 80% of the aneurysm is thrombosed and there's only a very small amount of lumen is present, and there is no evidence of mass effects?

- Well, there's really no good natural history data for thrombotic aneurysms. They're rare enough to begin with that, to gather a group and follow them prospectively, to gather us natural history data is, it would be a challenging study. So that study has not been done, but we do know from giant aneurysms, many of them have thrombus intraluminally, they grow like tumors, I think probably if I have to guess, I would say the rupture risk is gonna be less overall, but they're dangerous in their growth rate in their behavior like a tumor. And so, I think that even though most of it is thrombosed, I still think that these need to be treated because they progressively grow. Even though that intraluminal component is a small percentage overall. Now, in terms of other options, you could discuss coiling with the patient. I think in this day and age coiling options need to be presented to patients. But this is a giant aneurysm, this is a thrombotic aneurysm. Those two features in combination make these aneurysms particularly refractory to a durable endovascular cure. The data from many groups has shown that reccurrence rates with thrombotic aneurysms are really quite high. So, I don't think the endovascular option would be a real durable cure, it would be a relatively safe treatment, but I think you would have the patient needing treatment over and over again as this thing progressively enlarge.

- Thank you very much. Please go ahead with your second case.

- The second case, is a different type of treatment strategies using bypass. And I think it's important to show a video of a bypass because, when I looked at my giant aneurysm series, there's a very high percentage of patients that ultimately need bypass. And I think what bypass gives you is the ability to treat a lot of these very difficult aneurysms in a very controlled way, and in a way that avoids other more aggressive maneuvers. Like what I showed in that first one with an opening of the aneurysm, with the thrombectomy, but also with things like hypothermic circulatory arrest, I think, you can be very creative with your bypass solutions to these problems and it provides another route. So let's switch to the video now and I'll show you an example of the PICA to PICA bypass. So this next case is an example of the in situ bypass. And what I mean by that is instead of an EC-IC bypass that uses an extracranial artery as the donor, it uses these in situ bypass, it uses an intercranial artery as the donor. So, what you're doing is you're bringing together, two arteries, the donor and the recipient in a way that spares you the need for having to harvest the extracranial vessel. And, I've been trying, as I've developed my bypass practice to do more and more of these, because I think they're very elegant reconstructions. They have a lot of advantages which we'll get into in the lecture portion later. But, this is a really nice example. This is gonna be a PICA to PICA bypass for a giant PICA aneurysm that just does not lend itself for direct clipping. So rather than try and open the aneurysm, take out the thrombus and then clip reconstruct it. What we're gonna do is we're gonna bypass the PICA and then trap the aneurism. So Aaron, you can start the video at this point. So, this is a lady who's middle-aged, she presented with this aneurysm, which was unruptured it's giant, mostly thrombotic. And the view that we have here is the far-lateral approach. This is a right far-lateral craniotomy. You can see PICA there, the caudal loop of PICA coming out just below the tonsils. What you're seeing there is the contralateral PICA, and it's important to mobilize those tonsillar loops of PICA together so that they really approximate with one another. Now, this clip just shows you an attempt at direct clipping and every effort to place that clip resulted in the clip sliding off. So, they were joined to the bypass and you can see how the two loops of PICA come together very nicely, temporary clips around the right PICA. The left PICA is shown here. We're gonna to put temporary clips on that one as well. And we're gonna make two arteriotomies, one in each vessel. And we'll basically bring them together in a side to side connection that will allow flow from the left side to feed over to the right side. These little arteriotomy scissors that allow you to make a nice clean cut in the vessel. Here is our first stitch. This is tenno monofilament nylon. We're gonna place, one of these approximating sutures on each end of the arteriotomy and tie them down. And again, as you tie that knot down, you wanna make sure that the vessels are not nice and freely mobile, so that there's very little tension on the suture or on the vessel wall. This is our second bite in the opposite end of the arteriotomy. And I like to just bring those two ends together so that everything's lined up. And so, you don't have to worry about spacing your bites, you have everything in front of you. And it's just a matter of just lining things up at that point. Now that last bite is very important because you've got to get the needle from the outside or extraluminal side to the inside. And this first suture line is really a continuous intraluminal suture line. So, you're sewing from the intraluminal side of the PICAs, and it's a running continuous suture. There's no knots to tie along the way, you just take these bites over and over again. And you can see how the two inner leaflets or inner walls of the PICA come together very nicely along that suture line. Now, as we get to the other end of the suture line, we once again have to pass the needle from the intraluminal side to the extraluminal side so that we can tie down our knot. And here's that bite. We're basically gonna pass that needle from the inside to the outside. So that that needle becomes opposed right next to the knot that's already there. And then we can go back and we can tighten down or snuck down these various loops of the suture line and get everything snugly together. So, the sutures have been tightened. Now we're gonna tie these together and that completes half of the anastomosis. Now, the second suture line is much easier, instead of working between two layers of arterial wall to get to two additional layers of arterial wall. This last layer is just bringing two walls together. So this is a running continuous stitch. You can see how, as you place the loops, you can keep everything loose. It allows you some mobility of the tissues and of your instruments. And then once all the sutures are in place, you can just tighten those down loop by loop. And, anastomosis comes together very nicely. So, we're just gonna snug those down, again, you knots at either ends serve as a tail for you to tie that suture to. So there's the knot going in, we completed the anastomosis. We're gonna take off our temporary clips and get things reprofusing now. And, I like to see a little bit of bleeding through the suture line just shows you that everything's flowing and flowing right. And here's our indocyanine green dye that shows flow from one side to the other across the anastomosis. So we know we've got a patent bypass. So now, we're turning our attention to the aneurysm. This is a clip on the distal vertebral artery, as it exits the aneurysm. We're now gonna put a clip on the proximal vertebral artery and the proximal side of the aneurysm. And then lastly, we're going to close down the PICA at it comes from the aneurysm. So three clips, complete trapping of the aneurysm, and now our bypass is taking over. So, we've got flow from left to, right. You can see a retrograde filling of the proximal PICA and that takes care of all those perforators that go to the middle artery segments. The aneurysm can not be opened just to remove some thrombus and take a little bit of pressure off of the brainstem, just to release some mass effect. So that's PICA to PICA bypass. It's a very elegant bypass. The vessels, both donor and recipient are right next to one another. The aneurysm is right in the field. So everything is right there for what you need to do to take care of that otherwise difficult aneurysm.

- Thank you, Michael. I have a question for you. Now, there're some people say, you know, when you do a PICA to PICA bypass, you may place both PICAs at risk. So there is an advantage to do the occipital PICA bypass versus PICA to PICA. I want your thoughts on that, number one. Number two, I wanna restress what you said about retrograde flow in the trapped PICA to irrigate the perforators, that's very important to be obviously confirmed on ICG. What are your thoughts about the issue of occipital PICA bypass?

- Your question that, when you do these bypasses, you, bring in an intercranial vessel that wouldn't otherwise have been at risk. And so in this case, the left PICA is now potentially at risk. If something were to happen with anastomosis and you were to get some distal thrombosis of the vessels, you could lose an additional territory. But, I think that, for anyone who's tried to do an occipital of PICA bypass, the harvest of the occipital artery is not fun. It's not always a very good vessel to work with. And I think ultimately what you want is a patent bypass. And, you know, I just think that, working with another intracranial vessel is a nice way to increase your patency rates because you can see everything, there's good tissues to work with. The caliber matches, if the vessels is good. The same can't always be said of the extracranial donors. You sometimes get some, mismatch in the donor and recipient. Sometimes there is trouble harvesting the vessel. So, you know, you do have some problems there as well. It's a personal preference. I think everybody has to do what they're most comfortable with, but for me, in most of these, there have not been problems with the additional artery at risk.

- Thank you.

- So let me transition to this presentation. I just wanna begin by saying that it's clear if you review the literature that more and more endovascular centers are trying to treat giant aneurysms with endovascular techniques. And I think, that's a reasonable effort to pursue. I think that ultimately as our techniques and our technology endovascularly improve, we may arrive at things that provide a durable and lasting cure for these aneurysms. But if you look at the current state-of-the-art, this is a study from the Buffalo group, one of the most innovative and aggressive groups for endovascular treatment. You can see that in their giant aneurysm series, 38 patients, 39 aneurysms, the complete occlusion rate was really just over a third of their patients. Stents were needed in many of these patients, multiple sessions were needed. And if you look at the final M and M, you're talking about a greater than 50% late morbidity and mortality rate. So, I think that endovascular therapy for giant aneurysms has a ways to go. I'm very supportive of it in general, because I think it will evolve and get better. But I think as things stand right now, I'm cautious. This slide just sort of summarizes the problems with coiling. You have anatomy, that's not favorable. You have intraluminal thrombus. You have the problem with incomplete obliteration, which then leads to issues of rehemorrhage and aneurysm occurrence and the need for new treatment. So, what you're effectively doing is taking an aneurysm here that's difficult for no matter which way you treat it, but you're taking away some of the surgical options by coiling it and you're converting this patient's course in the chronic relapsing problem that they really never will have a chance of cure. These are some of the notable surgical series on giant aneurysms. And you can see that these are the kinds of lesions that really challenge our great technical masters. But, the bottom line is that if you look at what's achievable surgically, good outcomes are in the 80% range for a lot of these surgical series with M and M rates that are between five and 15%. And thinking back on the endovascular results, I think that these really, still compare favorably to that. Now, this is data from my experience. It's 12 year review period. I did 141 giant aneurysms in 140 patients. And you can see some of the demographics there. I just wanted to kind of boil out some of the lessons from USCF experience. First point is that these aneurysms happen in all locations. There really aren't any particular locations that are spared and there's, you know, maybe a little bit more in the posterior circulation than you would otherwise expect. A lot of these aneurysms, even though they're giant in size, I still like to try and treat them with the clipping techniques that we all are familiar with. Sometimes you get away with simple clippings, but for most of these, you need more complex or sophisticated clipping techniques. And, this is an example of one of those that required just a simple clipping technique. You can see it's a giant thrombotic, middle cerebral artery aneurysm. There really is just one inflow here and not much in the way of outflow. There used to be a serpentine aneurysm that the serpentine channel thrombosed and that caused presentation. And so this really lends itself to a very simple, single clip occlusion. And this is the view that surgery, you can see the aneurysm here in the temporal lobe. The inflow is right here at this point. It just takes a single clip here to occlude that inflow and take care of the aneurysm. We can then de bulk it and take that mass effect off of the patient's temporal lobe brainstem. Now, the Drake technique of tandem clipping is very useful for giant aneurysms because you can use multiple clips to sequentially close down the neck. And, these fenestrations allow the transmission of branch arteries, perforating arteries, or using them as booster clips. So, tandem clipping is a really nice strategy in general for these giant aneurysms. This is that case I showed the video out that thrombotic superior cerebellar artery aneurysm. And that's an example of the use of these tandem or fenestrated clips. We've gone through this video, so I'll just advance to this. These are other clipping techniques for periclinal original aneurysms. You often need these angle fenestrated clips, which you're gonna apply heel to toe. You can apply clips facing one another, or you can apply them heel to heel a variety of different ways that these clips can go on. And really, it just depends on the anatomy of your lesion. This is a giant posterior communicating artery aneurysm. You can see the anatomy here. And for this one, it's a combination of straight fenestrated clips and these right angle fenestrate. Thus the key being these perforators, and particularly the intra caudal that comes off the back in the aneurysm. If we look at the interoperative view, you can see that here's the carotid, here's the middle cerebral vessel. And the carotid is adherent to the back wall, so much so that it was impossible to develop a plane and separation between carotid and this back wall. So, what was done here was just to apply the clips, starting proximally working distally, and to use the fenestration to send those branches of carotid through the fenestration. And that is the way to preserve them when you were unable to actually separate or strip them down from the aneurysm wall. These are other examples of fenestration tubes. We've written about this, but you can stack these fenestrated clips and create essentially a channel through the fenestration for an antegrade branch vessel, while still closing the neck, and also using the heel to close up this portion of the neck, which is against and often adherence to this branch vessel. You can use a retrograde tube that turns the floor around and out the tube where you can use these fenestrated clips to stack as a picket fence that closes the dome of the aneurysm. This is an example of these stacked fenestrated guts. You can see a giant ACA aneurysm here. The neck is actually quite manageable, but you need to create this little right angle connection between A1 and A2. And, the best way to do that is to stack these fenestrate clips around this right angle junction, and then close the fenestration at the top. So, you're essentially here building this little pocket here for that flow to come in, bounce off the clips, and then head up the two segment. Here's another clipping technique where you transect the aneurysm and then use a stack or roll clips to close down the neck. There's a giant middle cerebral artery aneurysm. You can see the thrombotic component here, and our strategy for this is going to be the simplify clivus anatomy. This is really just a portion of the aneurysm but, by transecting it endarterectomizing the thrombus at the neck, and then closing down this portion here. We can then reconstruct those middle cerebral branches. So, this is some of the data from my experience. You can see that for direct aneurysm occlusion, it's still under 50% of the total aneurysm cases. So, for these others, you need indirect techniques, which involve either closing down the parent artery or some sort of a bypass strategy. You can see here also, it's important to note only four cases with hypothermic circulatory arrest. So, one of the points of this is to show that you can move away from these high morbidity procedures like, hypothermic circulatory arrest with the use of bypass. So, I talked a little bit about intracranial bypass, and these are the various techniques involved. There's in situ which uses a side to side anastomosis. There are reanastomosis techniques which excise the aneurysm and bring them together end-to-end. And these are ideal for simple aneurysms that have one in flow vessel and one out flow vessel. Reimplantation techniques use an end-to-side strategy where you take a vessel off of the aneurysm, and then you reimplant it on a parent vessel in a different location. The fourth technique is the intracranial bypass, which uses a graft. And these are the various sites that you can do the bypass. And I'll take you through these different sites. We'll start with the intracerebral artery. The interhemispheric fissure is a very nice fissure to open and create working space. And because there are so many vessels here in the fissure, it provides you with a lot of opportunity for the bypasses. The in situ bypasses are shown here, bringing the pericallosal vessels together side to side. Here's an example of a reanastomosis. Here's an example of a reimplantation. And then you can do an intracranial bypass graft which jumps from proximal to distal. So, as an example of that, here is a giant thrombotic ACA. You can see it's very calcified on its wall. It's got lots of thrombus intraluminally. And if you look at the angiographic anatomy, it feels entirely from the left, the right side doesn't contribute to the aneurysm flow. And you can see too, that there are two branches coming off the base. So this is not one that's very easily reconstructed because of how thrombotic and calcified the tissues are. So what we're gonna do is we're gonna to build an azygos intracerebral artery territory. We gonna go down the interhemispheric fissure. We're gonna use the uninvolved right-sided pericallosal artery as our donor. We're gonna put an anastomosis there so that we now have a live bypass graft. We're gonna bring the graft around to a second vessel on the opposite side. So the two vessels on the other side that lead the aneurysm, and we need to look each one of those to the bypass graft. So here's our first anastomosis which is a side to side connection. And then we do a third anastomosis, which is end-to-side to be close to the marginal. So, we've now done three and anastomosis, one is our donor and then two for each of our recipients, one here and one here. Once the bypass is in place, we can then proximately occlude the aneurysm. We can distillate through the aneurysm and that effectively traps the aneurysm. So this is the postoperative angiogram, which you can see now, the flow from the left side that used to fill the aneurysm has been shut down. The right side, now, fills this bypass circuit, and we've got all of our ACA vessels of the bypass. So, that's an example of the azygos bypass. And that's an example of the graft techniques. So, moving to the middle cerebral artery, this is again, Sylvian fissure provides you with a very nice working space with lots of different branch vessels for bringing things together. So, there are in situ options that bring two vessels together. In this case, the anterior temporal artery to the inferior trunk, you can excise and reanastomos as shown here on the M1 segment. You can reimplant or take a vessel off of the aneurysm and bring it down to the other, or you can use these bypass grafts. Now, this is an example of a graft. The aneurysm here is dolichoectatic there's an inflow on this side, there's an outflow on the other side. And there's simply as no good way to clip reconstruct the tissues between them. So, what was done here was to put in a little graft from the M1 proximately, connect that to the M1 distally right before M2 segments begin. And that, repairs the defect. Here's our view interoperatively. This was a sub hemorrhage case, temporal lobe is here, frontal lobe is here. And this is all aneurysm. This shows you the outflow, an attempt was made to try and clip reconstruct this, but it just would not keep the parent vessel patent. So, here's the radial artery coming in. We're gonna sew this end-to-end to the distal M1, we then gonna sew this to the proximal M1. And now we have this connection from M1 to the graft to M1 distally and unload to anterior segments. This is indocyanine green dye, which shows that the bypass is patent. Now, the basilar artery bypass are some of the hardest ones, because it's such a depth in the surgical field, but again, you have the same options available to you. The in situ bypasses can connect the SCAs and the PCAs. You can do anastomotic techniques. You can use reimplantation techniques, or you can use an intercranial graft. So let me show you some examples. This is a giant basilar bifurcation aneurysm. This was treated over a decade ago with rapping and Nephilim attack relate. This was done from the right side, but you can see that this aneurysm has continued to progress. There's intraluminal thrombus, this is a giant incise now, and you can see the mass effect and distortion of the midbrain. So for this one, our strategy will be to come on the opposite side, away from where the prior surgery was. So coming from the left, revascularize with the bypass, and then simply proximately occlude this and a lot of bypass to supply the basilar circulation at its basilar apex. So this is the view of interoperatively. Again, left sided approach because of the prior surgery on the right. This is the carotid, this is the M1, this is our transsylvian exposure. Here's our P2 segment, third nerve cantorial suture So, we get a very nice pre-temporal exposure of the anatomy that we need. This is our PCA that we're gonna use as our recipient. Our radial artery graft is shown here with the connection to the P2 segment. This is after the bypass has been completed here, and we bring this end up to the middle cerebral, since it's already transsylvian, those middle cerebral donor vessels are right there in the surgical field. So we can complete the anastomosis. And once that gets completed, they can then go to the basilar apex, and simply do a Hunterian ligation from this aneurysm. It's all through the same exposure. There's no extracranial component. We've got a very short segment, a bypass graft, and this is very well tolerated because his basilar circulation at the apex is now being set from the bypass graft. Here's our post-operative angiogram. You can see filling at the graft. You can see flow across the aneurysm, which is on its way to thrombosing and is good feeling of the PCAs and the SCAs. This shows you how the clip has effectively shut down flow into the aneurysm. So, summarizing the trends and surgical management are these conventional clipping should remain the first-line therapy. When that fails, then the second line therapy is some sort of a bypass strategy. It was about a little more than a third of the cases in my experience. The need for hypothermic circulatory arrest is shrinking if not gone. And I think that the endovascular adjuncts, the endovascular techniques that are available currently can be used as adjuncts to surgery, either to perform your parent artery occlusions, to the delayed in a delayed fashion, or as part of your planning and doing VTS and other maneuvers. So, these I think are some of the things that have changed today as compared to 10, 20 years ago. These are some of the outcomes just to show you that we've looked at our outcomes. There really are quite good. The M and M figures really, I think, compare favorably to what we saw on the endovascular side of the equation. And, these numbers speak to the durability of the surgical repair. These are the bypass results, generally very favorable patency rates and only one patient with a late occlusion. And we did quite well with our aneurysm occlusions, even when we don't completely trap the aneurysm and instead of the line and some thrombotic element to complete the thrombosis. But, I will say that a bypass surgery is not without its complications. And these are some of the complications that we've had in these 140 patients. You can see that there are some postoperative hemorrhages, there are some bypass occlusions, there are some thrombotic occlusions of perforators, and there can be occlusions of branches. And these, I think are some of the more frustrating things because technically, it's surgery and things may go very well for you. But these are things that are very difficult to control postoperatively. This is an example of such a case with the giant basilar trunk aneurysm, just distal to the vertebral-basilar junction. This was treated with one of these MCA/PCA bypasses. very similar case, good occlusion of the aneurysm. And we achieved a very nice closure of the aneurysm. You can see the minimal filling now. Here, this is on its way to thrombosing, the bypass fills the upper basilar complex, but he had a small perforator infarction and had an ultimately poor outcome because of that. This is another example, two large aneurysms one here, giant the other lodge, and you can see the anatomy here. This is one that was treated with the bypass first, the MCA and the proximal end is to be external carotid artery. And this was initially very well tolerated. What we see here is good filling of the middle cerebral territory, very sluggish flow inside the aneurysm. The aneurysm itself has been occluded approximately here. And what we've done here is we've taken this giant aneurysm and we've induced this thrombosis intraluminal. So at day one, you can see just the beginnings of thrombus falling on the wall, by day five, you can see this serpentine channel that's forming, but the problem is that we've got a loss of the inter cordal territory. So we've got a branch occlusion. The intercradal artery came off the base of this aneurysm that is now occluded because of the way in which this aneurysm is thrombosed and the patient went on to have hemiparesis as a result of that complication. So again, technically well done operation, but a complication because of our inability to control the subsequent thrombosis. So, we can use computational fluid dynamics to try and give us some idea of where things are likely to thrombose. We studied velocities. You can do that. We can also study residence times or how long the blood hangs out in an aneurysm. And if you have areas of low velocity and high residence time, and also low shear that ultimately leads to intraluminal thrombosis. And so we try and define some of those things preoperatively, and we looked at the various bypass options that are available. And we then look at where our critical branches are, where are these danger zones for postoperative thrombosis were like. And we can use this information to inform our decisions about which option is preferable. These are examples of that case I just showed you. And in this particular example, when you close off the carotid artery that fills the aneurysm, there's a dramatic change in the flow dynamic. However, the areas where the carotid originates back here are in the blue zone, where there's a higher risk of thrombosis. This option here of trapping the aneurysm distally and doing the bypass just to the MCA territory, I think would have been safer. It keeps flow right along the inter cradle, but it doesn't dramatically change the flow dynamic compared to the pre-op. So, I think that what we need to look for is maybe not so much dramatically changing the flow dynamic, but preserving those critical perforators. So again, to recap that you want to eliminate the shear stresses, the high pressure variations, the turbulent flows that form aneurysms, but you also want to preserve the perforators and you have to carefully look at these flow analysis to help yourself figure that out. So these are my conclusions. Conventional clipping is the preferred treatment for giant aneurysms, but again, it's often inadequate or too difficult and is only used in about half of these cases. Hypothermic circulatory arrest is rarely indicated in this day and age, the alternative way of dealing with these are with bypasses. I think coiling is ineffectual because of the rates of incomplete obliteration and recurrence. Flow diversion with pipeline and other devices may offer another alternative for us in the future. We're gonna have to wait and see as we gain more experience with that. But in the meantime, I think surgery is still the freedom of choice. So these are tough aneurysms. There are a variety of different ways that you can deal with them. I've tried to just sort of summarize the range of options, but again, each one you just need to sit down with an individual case by case basis and see what's going to work best for you and for.

- Thank you so much, Michael. Therefore you're very useful talk. I wanted to raise a couple of questions here. Number one is, use of adenosine. I think it has really almost exclusively replaced the issue of the hypothermic cardiac arrest. How often do you use that for giant aneurysms? Because I really think it's very low risk, it's effective and works well.

- Yeah, I think it's, I agree with all those statements. I think it's a much better tolerated option than stroke arrest. The problem with the adenosine is it gives you a couple, well, it gives you about a minute or 30 seconds to a minute of low flow or no flow. And sometimes you just need more. That case I showed you up front where we're entering the aneurysm. You need more than just that 32 second window together with the adenosine. So, I think that for short occlusion times where you just need to apply to clip or perform one last little maneuver, I think it's very useful. I think if you need to really open an aneurysm, it's not very useful. I think in those cases, you really need to resort to temporary clips and, you know, isolating the aneurysm as best you can. And just working through whatever residual bleeding that you get. I still think in my view, that's a better strategy dealing with the inconvenience of some in bad bleeding, then resorting to hypothermic circulatory arrest which has all that associated morbidity.

- Okay, also to reemphasize your great point about those issues. When you have a very giant aneurysm, the next sort of looks clippable using the fenestrated clips to create this little lumen for the blood to be able to circulate and to then pack it off and sorta finish it off with a strict clip at the bottom. One of the biggest enemies of, you know, a giant aneurysm surgery is really a perfection in clip application, just because what you see in the lumen could be a lot narrower of what you see on the outside because of the amount of calcification of atherosclerosis. So, leaving a little bit of extra lumen, there probably can be very helpful. Any other last pearls of technique you have in managing these extremely difficult lesions, Michael?

- Yeah, I think with giant aneurysms, like you said, you just, you can struggle getting the aneurysm close with one clip or with the perfect clip, you really need a lot of clips to distribute the forces and to really bring the tissues together. And you really have to be generous with the intraluminal reconstruction that you do, you really can't judge how things are gonna be on the inside just by looking at the outside. So, when in doubt, I think error on the side of leaving a little extra tissue, so that there's good flow rather than trying to, you know, have the perfect angiogram with just the right lumen. Because if you error on that side, I think you run the risk of branch occlusion.

- Okay, I have another video you wanna share with us Michael.

- There is one other we could show a PICA or MCA to PICA, sorry, NCA to PCA bypass. If you would like.

- Sure let's go ahead and do it. I think that will be exciting, obviously very challenging operation. Here we go.

- So I showed you this case in the talk. So this was that basilar trunk dolichoectatic aneurysm. And again, we're working through this carotid ocular motor triangle. Here's the third nerve here, here's the carotid artery. And you can see that aneurysm looking down the clivus. This is our P2 segment here and that's gonna be our recipient. It's lateral to the third nerve. I've attracted the temporal lobe just enough to give me a working space. And, by really freeing up the temporal lobe, you can really open that up nicely. So, this is that segment of the P2 that we're gonna use. It's the same techniques that I showed in that other bypass video. Temporary clips go on. We use a bevel needle just to make a small puncture in the artery. And then we can come in with these right angle microscissors that make a nice clean incision or arteriotomy. And, because it's a single shaft, you can rotate it work in both directions. It's a really nice instrument. We're gonna use the radial artery graft, which is shown here on the top of the screen. And for this one, this is a 9-O nylon suture. And again, I just start by bringing the vessels together, bringing one end of the arteriotomy together with the graft. And then with our second stitch, bring the opposite end together. You can see that the radial artery graft is kind of lying flat and on the superior side. And I do this anastomosis first, so that I can have some morbidity in that graft. Let's see for the second suture line, we're gonna flop everything the other way. And you can only do that when you've got the other end of that graph completely free. So I always do the deeper, harder side first and look my way out. So those are the two sutures at the arteriotomy ends. And now, we're just gonna do a running continuous stitch from one to the other. And you can see that, you know, the technique is the same. You wanna minimize how much you touch the tissues or pinch the tissue tissues and just try and manipulate the needle. It's a very deep and very narrow working channel. So, you have pretty good view of things, but it's very difficult to get that super nation of your needle because you're really so limited. But, in any event, you know, you can see that it can be done. It's, I think one of the most challenging bypasses that there is, because of those limitations. But, you can place these sutures very nicely. We tighten them one loop at a time and then tie it down on the other side. So, that really completes one suture line. And now, as we tie this down, we'll be able to flop that artery towards us and get a view of the other suture line. So now you can see the radial artery graft has been pulled towards you, and that gives you that view that you're trying to get on the opposite side. So, again, it's, you lose some perspective at that depth that makes taking each bite a little bit more challenging, but there's the completed anastomosis. We're now kind of bring this radial artery graft up the Sylvian fissure. We've already split the Sylvian fissure to get down to the end of the aneurysm. So, we're just gonna use the frontal branch of the middle cerebral, and we're gonna trim the graft. We're gonna strip it of its adventitious and fat here. And this is now gonna be our recipient on the MCA. So, everything's cut to size, again, use that beveled 27 gauge needle, bringing the microscissors, extend our arteriotomy in both directions and flush everything that hapenz sailing and there's a first bite. We've got a nice view of everything. This is so much easier than what we were just doing down deep at the PCA. So, you just bring the vessel together with the radial artery graft. Once again, this is a 9-O suture. And tie everything down.

- Michael, do you use etomidate during these clamp times? How do you protect the brain?

- So, a good question. The patient is in EEG burst suppression. We use either arbitorates or protocol, and that's an anesthetically what you can do. Surgically, what you can do is just hurry. And you know, these anastomosis take about 20 to 30 minutes, there are two suture lines. You know, you just got to take those bites carefully and not make any mistakes, but move it along as quickly as possible. The temporary occlusion times on the M2 segment are very well tolerated. If you're done the M1 segment where the lenticular strikes, you can get into trouble. So I think the key is just placing that anastomosis in just the right spot. So you want it to be distal enough so that your clamp times are tolerated, but you don't want it to be so far out the tree that you don't have good recipient calibers. So I see green show that we have good patency in the graft. We can now go down back to our aneurysm. So we're gonna go into that carotid oculomotor triangle here, we gonna go back to the aneurysm and you can see normal basilar trunk coming out of the aneurysm right there we'll perforate it right here and we're gonna carefully select our clip spot and close this aneurysm distally. Now, the advantage of this is that it now eliminates the flow through the aneurysm. We see our perforators very nicely. You can see good pulsation in the bypass graft. It's doing its job profusing things. And, that provides us with the flow to the vascular apex. And so, it's all in the same surgical field. We've got everything in our view and it really is a nice way to deal with an otherwise difficult case.

- Michael exceptional job as always. We really enjoy watching the videos and your work. I appreciate all you do, and we hope to have you with us in the near future again. Thank you.

- Thank you Aaron. It's a pleasure and I'm glad I could share some of my thoughts with you.

- Thank you again.

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