Grand Rounds-Revascularization Techniques for Treatment of Complex Aneurysms

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- Hello ladies and gentlemen, and thank you for joining us. My name is Aaron Cohen. Our guest today is Dr. Amir Dehdashti from Cushing Neuroscience Institute. He's the director of cerebrovascular research there. He'll be talking to us about some of the more technically challenging procedures, which include a bypass and revascularization techniques for complex aneurysms. Amir, thanks for being with us.

- Aaron, thank you very much. It's a pleasure to be here. Thanks for the invitation. And I'm very happy to share my experience with you.

- You're welcome. Regarding our disclosures, Dr. Dehdashti has no disclosures, and my disclosure is consulting for Sysomatic Tech. So with that in mind, Amir, please take it away.

- Thank you, Aaron. So we decided to talk about the cerebral revascularization for complex aneurysms. When I look back at my experience over the last five years, of about 50 intracranial bypass surgery, about 22 are done for aneurysm. So it's not really half but close to that number, and I tried to pick a few of those cases that are in terms of the technical and decision making the more challenging and obviously, the achievement of the bypass per se and the post-operative outcomes are also a formidable challenge for us. So I'm gonna start here with the first case. This is a 45 year old gentleman who was actually recently moved to the U.S from London and had some headache and obviously did a CAT scan, and that identified, unfortunately, a large, rather giant partially thrombosed MCA aneurysm. We can see the image in here. So this patient is completely neurologically intact. Young, he's a lawyer, and he has this large giant, it's exactly 2.5 centimeters aneurysm that you can see on this imaging. I'll take the pointer here. So on the CT, you will see this aneurysm has some enhancements at the MC bifurcation. The rest is all thrombosis around the aneurysm and some enhancement of the periphery. You can see the extension of the aneurysm to the temporal base here, and you can see here exactly the part of the aneurysm which is filled by contrast, and the rest is all calcified thrombose. And this is the 3D imaging of the angiogram showing the patent part of the aneurysm. And obviously, we can not see the rest of the aneurysm, which is a huge mass here, the line here with the red dot. This is the whole aneurysm here. So in a young patient, we would like to treat this aneurysm, the natural history of this giant aneurysm, a navicular thrombose. Is not very good, unfortunately, and this will pose a different and difficult challenge because of the possibility of non-clipability of this aneurysm. So maybe I can just have your opinion, Aaron, on this particular case, do you think, or what would be the percentage that you quote the patient in this particular aneurysm, based on this imaging, that you or the neurosurgeon, would be able to clip this aneurysm, as opposed to other surgical alternative?

- Yeah, I mean, that's an excellent question. I would say the chance is extremely high. This is a very calcified aneurysm in a young patient. I completely agree with you that treatment on the aneurysm is indicated. I would say the chance of clipping this aneurysm primarily is almost close to zero. The surgeon has to be completely ready for a vascularization procedure. It's on the dominant side. I would say this is a very tough case.

- And for this reason, as you can see, I evaluated also the external circulation. You can see there is a very good torturous, but good parietal branch of the MCA. The frontal branch, unfortunately, is very bad. It's there, but it's very tiny. And it's obvious that if he wants to revascularize the SVA, we have to revascularize both MCA, distal to the bifurcation, something which basically needs to bypass. And by looking at this imaging, we have one good candidate for bypass, but the second one is really tiny. So this evaluation was done prior to surgery. And when I talked to the patient, that the same way as you described it. Try to clip the aneurysm, but be really ready to perform a trapping of the aneurysm and bypass if necessary. We also had the arm and the leg evaluated and prepped in case we need some extra graft for the bypass. So if you can kindly go to the first movie, which is the MCA movie. So here we have a left sided exposure to the pterional craniotomy. This is the frontal lobe. And this area is the temporal lobe. As you can see here, this is the thrombosed giant aneurysm here. One of the MCA distal into bifurcation after the bifurcation, the superior trunk and these small vessels, very important, lenticular striate or pre-frontal branches that are wrapped around the aneurysm. So, initially, when I exposed that, I felt that maybe this aneurysm is clippable. So I identify the left M1 here and the patient is on burst suppression, temporarily clip the left M1 and attempt clipping of the aneurysm that would have been an easier and much quicker solution if it was possible. And use a fenestrated clip to incorporate those perforators or important cortical vessels. And as soon as I checked with the doppler and then ICG this vessel has absolutely no flow. And I tried that a couple of times with weak positioning. So at this point I concluded that this aneurysm is unfortunately not clippable and decided for bypass, use the parietal branch, this branch, or the bypass to the inferior trunk of the MCA, which is done already here. And I'm not going to focus on that as, I guess, it has been already an emphasis on his CNC bypass, but for the superior trunk here, we did not have a good graft. Therefore I use the radial artery graft and hook the radial artery proximally to the stump of the SCA. And this way we had a good flow to the radial artery and then we brought the distal part of the radial artery to intracranial part to perform the bypass to the superior trunk of the MCA. So here, the technique of the bypass, the arteriotomy is performed. I, in general, prefer to use interrupted stitches by suturing the two and heat up the anastomosis first. And then if you consider this as a clock, then putting the stitches at six o'clock here and 12 o'clock here, this way the anastomosis will be set feed for stable sutures. And then, depending on the size of the graft, adding two or three sutures between each previous stitches for a total of between 12 to 16, sometimes can go up to 17, 18. And you can see here, this is a relative, rather large superior trunk of the MCA. And once this is done, the ICG is performed. That's the STA-MCA bypass, and that's the radial artery graft, the junk graft basically, which is from the STA stump to the superior trunk. And once this was confirmed to be patent, basically we tracked the aneurysm by putting a clip just proximal to the aneurysm and two clips distal to the aneurysm on both the MCA vessels. So this is the status after bypass, as you can see, this is the STA that was the good parietal branch that I showed you on the angio. And this is the radial artery graft. You can already see some degree of the spasm here, which is one of the problems with radial artery. And the aneurysm here is completely trapped. I did not open or do anything with the aneurysm, because this patient did not have any symptoms, no seizure. So I did not want to bother touching the aneurysm itself. And we have a post-op imaging showing that both branches are patent. You can see the severe spasm in this vessel. This is actually an interoperative angiogram, which was done. And we didn't put some on this vessel, and this is the postop CTA. This spasm was still present on the postop CTA, but the patient did really well after surgery with no neurological deficit. And I hope that it will be a permanent treatment for it.

- It's an excellent result, Amir. I congratulate you on this very tough case and the outcome. So it seems like you used the parietal branch to do a revascularize one of the trunks. And then you also used the interposition jump graft of the radial artery to revascularize the other trunk using the same STA stump. Am I correct?

- Exactly. Yes. And the reason that I used the radial artery, because it was a relatively short graft and the aim was only to vascularize the superior surface of the frontal lobe or MCA. So I thought taking a vein graft might bring too much flow or the demand on the vein graft might not be enough and cause the occlusion of the vein graft. So that was my basically decision process to take the radial artery, as opposed to vein.

- And where'd you connect your STA parietal branch, to which branch is that anastomosed to?

- The STA parietal branch is anastomosed to the inferior MCA.

- Okay.

- And because, and that was basically based on the match of the vessel size that I decided to do. So the inferior trunk was smaller. So I decided to hook that to the STA and for the superior trunk, which was a bigger trunk, I used the radial artery.

- It makes good sense. I think matching donor and recipient is always a key factor in having a thriving anastomosis. So, and that's really a great case, I think, good technical nuances there. So please go ahead to the next case.

- The next case that I would like to talk about is, basically, the implication of this rather new technique is not really a new technique. This technique has been used in Europe for many years. It's recently got the FDA approval in the US about two years ago as the excimer laser-assisted nonocclusive anastomosis. It's basically the same concept of doing a anastomosis with the major difference of being able to do a anastomosis in a non-occlusive way and the indications, or obviously it could be for any high-flow bypass, but if you used that bypass as a replacement or as a protective bypass. The vessel size, how there should be at least 2.5 millimeter. And the reason for this, as you can see in the movie, is that there is a ring that we will use and we basically hook the ring to the graft and use that graft with the ring and bring it to the intracranial part and then sew the ring to the intracranial vessels. So that ring, the smallest ring that we have with this technique is 2.6. So you can come slightly smaller than the 2.5 millimeter for the vessel or anything smaller than 2.5 would be very risky to do this procedure. Some people have tried, but at least in my practice, I leave the 2.5 millimeter as the inferior limit for this technique. And obviously that has to be done in an area that there is no atherosclerosis or a calcification. So, this I felt that this is a real excellent case for this technique for the simple reason that this 64 year old woman presents with significant visual field feedback. And you can see there is a giant superior hypophyseal aneurysm. And obviously significant compression of the optic chiasm, but interestingly, if you can see here, that's the area this optic chiasm is completely compressed, but more interesting is here you can see that this aneurysm has the whole part here, which is the non, basically, the non. The cistern was part of the aneurysm and the aneurysm is almost double the size of what we see on the angiogram. The other interesting part is that the right ACA is non-existent. So the whole circulation of the left hemisphere and the right ACA and the left PCA, because there is also a left fetal PCA is on left carotid. So it's very obvious that this patient cannot tolerate, even for a few minutes probably, occlusion of the left carotid The significant visual deficit was one of the reasons that we consider surgery, and because of the fact that we had the capability of doing the ELANA procedure. And this will at least would give me the option of doing the bypass in relatively safe circumstances of not being obliged to occlude the carotid at any time, which for this patient, you know, with this patient, we did not even take her to angio suite for test occlusion, because there was no point of doing a test occlusion. So obviously this patient will fail within seconds, probably or minutes of. So this is the graft, and this is the ring that I was talking about. I always use the smallest ring, which is 2.6, because for intracranial vessels it's difficult to use anything larger than that. And we sew this ring inside to the graft, and that was a vein graph, as you can see, and this is the left Sylvian fissure that we open. Distal MCA vessels. Left frontal and left temporal region. So, at this point, the aim of the procedure is to find the appropriate recipient. As long as you would like to use the ELANA technique. Here we have the carotid artery. This is the PICA, and this is the anterior colloidal. The aneurysm's all behind. Everything we see behind this carotid here is, this is the partial calcified thrombosed aneurysm. Optic nerve. This is the aneurysm here. I also, at some point, the falciform ligament to decrease the pressure on the optic nerve. This is the carotid bifurcation, and we're looking for a good area of bypass, whether it's here or here, wherever the ring can fit, in terms of the size. And you can see I bring the ring. This is the smallest ring that exists. And you can see how limited you are with ELANA technique, because you need to have a vessel as large as this ring, or at least one or two millimeters smaller, but not more. So I decided to use the just, basically the entrance of the M1. That's the way the ring is sewn around the carotid. This is M1 here. The first four stitches has to go through the vessel, under a CPN and around the ring on the donor. It's very important that every time that we put the four stitches on the recipient, that you get a bleeding from the vessel, otherwise you will knot through the vessel and those stitch will not be strong enough to hold the ring to the recipient. So we start by one suture here, basically at three o'clock, if you consider that as a clock one at nine o'clock, and then at six o'clock. the same way through the vessel around the graft and around the ring. So you'll have to go beyond the ring. And then this is at 12 o'clock. Once this is done and you know that the ring is anchored to the recipient. And then the other stitches has to go only through the adventitia. Adventitia of the M1 here, and then just the adventitia of the vein graft. We don't need to go around the ring again. That four stitches at the beginning would be enough for that. And this is sewn here. So basically it will be the four initial stitch and about... eight others to just between, actually it could be between four to eight, depending on how large is the vessel to just keep the graft sitting nicely on the recipient. And this is the most important part of this procedure, obviously. Then on the graft I leave a small opening, oblique opening that's for being able to pass the laser, when we want to do the anastomosis. But before doing the anastomosis, you go to the neck and this is the proximal part of the graft and the performed bypass in the neck. This is the ECA always use the ECA for a variety of reasons. First; that you don't compromise the internal carotid circulation. And if you have any problem with ECA, it's easier to deal with, and if there is a problem, the complication of that would be less than if you have a problem with the ICA. And making an arteriotomy in the ECA. As you can see, I leave the graft with the tension here. It's very important to have the graft under tension. Now here, once the proximal part is- When the laser is in and we fire the laser, this is the intracranial part. And then that's basically making an anastomosis and we have the assistant ready to clip that area of the distal graft. And we have to make sure that we have this flap. If you don't get this flap on the laser, you have to go and look for it, because that might be a traveling flap around this area of the anastomosis, but if you get it that means that you're done with the bypass. And then you finally, you finish the bypass by closing that oblique arteriotomy at the distal end. Check with the doppler. And in this particular case, then the aneurysm was trapped. One other important thing is that when we performed the proximal anastomosis, and as I mentioned, you have to be careful to keep it on the tension, but at the same time, you have to always check in the intercranial parts that you do not put too much on the, on the ring here. So you need to have your assistant to check on the intracranial part under direct vision that the ring is not pulled over the recipient arteries. Now, if you can go back on the imaging, we can see that, I think we have a couple of post-operative imaging on this patient, that the graft is open, and then we took care of the aneurysm. So this, I think, in this particular patient, I cannot think of any other less invasive surgical way of dealing with this particular aneurysm, just because the ELANA will give us the option of doing this in a non-occlusive way. Now if, you know, if someone can perform this bypass in less than 10, 15 minutes, I think we can, we can cannot argue against that. But I would like to know your opinion on that as well.

- This is a very wise way to deal with this problem. I really liked the way the technique was designed. It's just right application of the right technique. So my question is when you want it to trap the aneurysm, I assume you trap the aneurysm distal to the opthalmic artery. Is that correct? And also proximal- Go ahead.

- The aneurysm was trapped proximally in the neck, obviously, and it, in this study, was trapped just proximal to the PICA and actually some of, because I had to two clips on that area. There was a little bit of a, maybe, kink on the PICA, which was the fetal PCA, but we did also need to have imaging that shows that fortunately with the vertebral injection, the fetal PCA is fed, basically, in a retrograde fashion. So although during the surgery we had the impression that the PICA is open, although it was a little bit kinked because of the clip, there was no other way to track correctly the aneurysm without kinking the PICA a little bit, but there was a good retrograde flow to it. So... That will allow us to be confident with this opening, which was just proximal to the PICA. So this 50 year old woman present with the giant right, ICA bifurcation aneurysm that you can see here, you see aneurysm is partially filled with contrast and the rest is all thrombosis, as you can see. This patient had significant left-sided weakness and headache. Obviously it was the swelling and edema around. And this is the angiogram shows that the part of the aneurysm, which is filled, but as you can imagine, that whole aneurysm is basically here, around. So this patient actually presented a couple of years ago. I was done involved in her care and it was felt at that time that the safest way to deal with this aneurysm is to treat it endovascularly. And the patient was treated with a stent coil, which seemed appropriate as a first option, because this aneurysm obviously has a high chance of recurrence. So you use a stent, probably the chance of remission or recurrence would be larger. So this aneurysm was coiled and initially the patient, still was suffering from the mass effect. And left sided weakness, was on steroids for a while, and came back about six months, nine months later. And you see there was a small recurrence around the neck and the treating team at this time, because the patient was grossly stable, decided to continue the endovascular treatment by adding some coils here. And we can see here, that's another view of the recurrence. The aneurysm was further coiled and, angiographically, that seems to be a good result. And the patient still had the left sided weakness, but at least angiographically this aneurysm seems to be completely gone. The patient did not have any new neurological deficit and was again followed up regularly and came back a couple of few months ago. And this is the follow up. We have an MRI and we'd like you to pay attention to this here. This is a new MRI of the, if you remember previous MRI that we had did not show any enhancement this far. That was the first MRI that this patient had. This repeat MRI about, I would say, 16 months after the first treatment you see that this area is pretty good, but there is enhancement here. So that was really worrisome for us. Plus the fact that the patient had significant worsening of left sided weakness and headache and seizure. And we'll repeat the angiogram here. And you can see that this is the new area. That's basically completely an aneurysm. So this is the second obvious recurrence over less than two years in this giant, partially thrombosed, ICA bifurcation aneurysm. And obviously we felt that this has to, this segment has to be sacrificed. There is no other way to protect this patient from the recurrence of this aneurysm. And this was during the time that I was going away. And so we wanted to preserve this area, make sure that this will not cause her any problem or bleed, because the patient's neurological status was rapidly progressing with a significant left sided weakness. So we temporarily treat that area with coil, wait for about 10 days or so to plan for a bypass and try to sacrifice this segment. Now I would like to ask your opinion on how would you...would you agree with this option or would you still wait to see if you see another recurrence before bypass and, if so, what would be your bypass option?

- I think this patient needs surgery. There's been multiple failures and there will be more failures if you persist on the same treatment, which has failed multiple times. So I think, in this case, trapping and revascularization is ideal. I think doing a radial artery bypass graft to the revascularized MCA tree is most reasonable in this case. I just don't think STA adequately can revascularize the whole MCA tree. The flow, or like more likely than not, is not adequate. So that would be my plan.

- And just to emphasize on the point, you just mentioned, the STA in this patient was really, really small. Really not a good size to be able to carry the responsibility of all these MCAs here. Now, interesting point is that we waited only one week. You see, that's the coiling that was done, for example: Day one, and then just the day before the surgery, we did an angiogram and you can see how the aneurysm is recannulized within one week. So that shows how unstable is this area. We've also recannulization at the neck. So we all agreed that the bypass is necessary in this case. And here comes the interest of deciding for a short graft bypass, as opposed to a longer graft, like the previous case that I showed. And this patient had a very potent internal maxillary artery, and this technique has been described before and published by St Louis University Neurosurgery, namely Dr. Abdulrauf. And we actually recently sent that for publication, because this is a modification of that technique, and I'm going to quickly go over that. So if we look here, these are schematic illustration, the drawing, you can see, this is the area of this aneurysm, looking from the left side. This is the internal maxillary artery here. So if we can bring this internal maxillary artery in hook with an interposition graft to the MCA, that will give a very short graft without a need to expose the carotid artery in the neck. And it's a much more, I would say, elegant and probably a better bypass in terms of the patency rate, because of the fact it's a shorter graph, as long as we can get these internal maxillary artery. So if you look at the- That's the procedure is done with a, whether it's depending on the location of the aneurysm, or because of zygomatic craniotomy or temporal crani, at least you would like to have a good exposure of the middle fossa and we set the bowl of the middle fossa, as you can see around here, identify the internal maxillary artery. At its exit from the muscle, basically when you have the middle fossa exposed. Original technique identified the internal maxillary artery to the middle fossa. But in our technique, we expose the whole middle possible, remove the bone, and that will give us more ample exposure of the internal maxillary artery. And this way you can basically use it as an end to end graft with your graft and then bring and connect it to the MCA and that's all. So that's, I have to give the credit in our center to Dr. Langer who thought about this and performed this procedure. And... then... I decided to do this case with the same technique. And as you can see here, the graft is hooked to the MCA, and this is the schematic drawing that we can see here. So here we have the temporal base, the middle fossa is drilled. And as I said, the difference that exists is that we drilled the whole middle fossa and removed it and identified the internal maxillary artery inside the muscle, basically, and this will give us a good exposure of the internal maxillary artery, because we do not need to deal with this small opening in the bone. This part of the bypass, and here actually I'm using the brachiocephalic vein, that part of the bypass is performing end to end way, and then the Sylvian fissure is opened here, as you can see. We identify the MCA vessels, and you can see, this is the proximal MCA M1, and you can soon see the stent inside the vessel. That's the M1 here. Right temporal lobe. Right frontal lobe. And here we're looking for an appropriate recipient. This is the MCA here and the bifurcation. And... I find a vessel here, which is appropriate for a bypass and identified this vessel and made sure that the length of the graft is enough. And we have to also make sure that the graft is not too long. We would like to have a little bit of tension. And here the MCA is clamped. And arteriotomy is performed, as you can see, with this backcutting knife. Again, here, we can use interrupted sutures or running. I decided to use the interrupted sutures. I have had good results in interrupted sutures, and I'd rather continue that for all the inter-sci, but here, the vessel is clearly large enough that you can run that as well. And... once one side of the graft is closed, we performed a bypass on the other side. So this part probably took about 35 minutes, 30 minutes to have the bypass. And then the distal and proximal clips were removed. There was a little bit of ooze here that had to be fixed with a small stitch, the last stage. And that will fix the ooze around the bypass. And you can see here, the bypass here is open, but it's not of a spasm and not too much flowing the graft. But as soon as here, we put the demand on the bypass with clipping the M1 and this clip is going over the stents, you see that the bypass becomes very potent and we check obviously the flow with the flow probe. And there is about 70ml per minute of flow in the graft coming from the internal maxillary artery, which is to be enough to cover the circulation of the MCA. So this is what we see. The status after the bypass, you can see the graft coming from the subcranial fossa to the MCA, and there is no spasm anymore, but at this point, there is a demand on the graft. As you can see, the brain was a little bit swollen and also very fragile, because of the fact that this brain has been under significant swelling of this giant aneurysm for a couple of years and so, very vulnerable, but this patient did very well after surgery. And you can see here, this is the bypass that we can see after surgery connecting the internal maxillary to the MCA. And look at this, you can see here the aneurysm is still completely patent, because I did not trap the aneurysm, I just put a distal clip on MCA. It was almost impossible to get to the proximal here, because of the swirling around, and the fact that this coil mess we're pushing on the basically surgical exposure off the Sylvian fissure. And what we did afterward what was relatively easy, go in endovascularly and occlude the proximal MC just proximal to the neck of the aneurysm. And again, I hope that this will be, this is a case that I did about six weeks ago, and I hope that this will be the permanent treatment, hopefully for this patient.

- Excellent result. A very challenging case. Go ahead please.

- So here I have the case of a sixty year old woman who presents with this large, rather calcified basilar type aneurysm, as you can see. This patient had gait disturbances and interesting features of this case is this patient does not have any carotid artery. So bilateral quartered occlusion, the whole brain is fed by the basilar artery You see this and this huge left PICA, that you can see here. And then if you look at the imaging of that 3D imaging here, you can see that the aneurysm incorporates, this is the left PICA, which we did a normal MRI on this patient, and it showed about a hundred CCs of fluid or about 80ml per minute of blood flow in this, this is taking care of the whole brain, basically the left PICA, and this is the left P1 here. And then you see the right P1 on the other side. So obviously the basilar type aneurysm in a relatively young patient, a patient in had very significant history of, you know, hypertension in the vascular disease. But you would like to treat this aneurysm, the natural history of this aneurysm is not good. So, and if you looked at the, this imaging here, you can see that the right P1 here is completely involved with the aneurysm. So I would like to know, Aaron, what would you suggest to this patient, considering that I can tell you what our endovascular team felt, that if they treat this aneurysm endovascularly, which would have been definitely my first choice, they would have lost a hundred percent the right P1. Would you worry about losing the right P1 or not? And if yes, then what would be your suggestion?

- Yeah, I don't think there is a good endovascular option in this case. This is, most likely, one of the most challenging cases in our surgery in general. And in this case, I was thinking you do need a revascularization backup plan, undoubtedly. The problem is really the revascularization techniques in this area are sort of limited. I think one option to consider would be potentially an intracranial to intracranial bypass, such as a MCH PCA bypass. I think that will be something to strongly consider. I think that's pretty much, most likely the only option you have. I can't think of anything else. How did you manage it?

- So the, exactly, the right PCA was my only worry here. I knew that that this, in my hand, exploring this aneurysm for clipping has a very high risk of mortality or morbidity. This aneurysm has a calcified neck, it's very large, involving the vessel. So my only goal here was to preserve the P1 and let the endovascular guy go in and treat the aneurysm. The patient was not really suffering from the mass of the aneurysm. And I thought the aneurysm was not ruptured. So I thought this is the safest way. And obviously I started thinking with the safest way of going there, easiest way to do a bypass from STA to PCA. Unfortunately, the patient's STA was almost non-existent on that side. The other option would have been to bring a higher flow graft from ECA to PCA, but for that as well, I felt that this is a more challenging, because I don't know how much flow this P1 needed, and, actually, the Nova couldn't really show, there was about 20 ML or 18 ML. So a high flow graft would fail on this small amount of demand. So that's why I felt that going from an intracranial to intracranial have several advantages, is it in short graft is an ICIC bypass, intracranial intracranial bypass, and probably has a better chance of success in this case. And with via radiologic graft that we got. So that's what basically we decided to do and expose this aneurysm to a right orbito-zygomatic craniotomy, If you can kindly go to the movie four. Okay, so this is the video of the procedure. You can see the right side of the approach, the Sylvian fissure here. Temporal lobe, frontal lobe. The temporal lobe is pulled backward. We used a retractor in this particular case. It's basically a half and half approach and allow us a good exposure of the posterior cerebral artery here. This is the P2, which is just after the PICA. Some sepial resection of the gyrus rectus is performed. The aneurysm is here and this is the P1 and all the important perforators. I used a, tried to see if we can do an ELANA, but the vessel was too small. I clipped the P1 and measure the flow, dramatically dropped compared to the flow before clamping. So that's why I decided to the bypass thinking that this patient needs a bypass. An arteriotomy was performed on P2, as you saw, and the graft, which is a regular artery graft, in this case, is sewn to the P2 and the same technique, heat onto the anastomosis. Then the easier side, I always do the easier side of the bypass first, because if you do that then the more difficult part becomes easier. So, and then this is a more difficult part, but once the easier side is done, then you only have to deal with one side and make your bypass easier. Maybe you realize when I'm trying to say, but it's... at the end, when you have the difficult side as the last side, it make it a much more amicable for suture placement. The graft is closed, just distal to the bypass here. And now we go to the MCA. This is the MCA branch. Distal MCA branch. The clips are on MCA and M1. Arteriotomy is performed on the MCA, as you can see here, and the same technique is used. Here, again, as mentioned before, we can do a running suture, interrupted, and I prefer for end to site to do interrupted in general. And this will take about 30, 35 minutes to do a not very deep bypass. The one on PCA took longer. On the MCA, probably 35 minutes, 40 minutes, nice single. And then the clips are removed. It's very important to leave the graft with clips on until you have the flow circulate. You don't want to have blood with the end on the graft, otherwise that will thrombose. So once you have the flow circulating, clip the P1 here, we preserve this perforator. These are crucial, absolutely important perforator. And then the clamp on the graft that we moved. And we have a flow now nicely in the graft, and we measured it. It was about 18ml per minute, which was basically comparable to the flow that we had seen before on the right PCA, which was about 20ml per minute on the Dove MRI. And we accepted that as a good result there, the ICG showing the flow and the patient was planned for an endovascular procedure after that. So here, the post-op imaging shows, this was done a week later, we went to coil the aneurysm and we don't see the bypass. So I should assume that this bypass got occluded, because the demand was not enough and there's collateral circulation took over. Now for how long this bypass was necessary, it's difficult to know. I think at least the interoperative investigation proved that it's necessary, but obviously a week later was not. The patient did not turn in her in terms of not having the bypass and did well with her return in her policy. And now we go to this last case, because we are talking about the pursuit of possible aneurysm of the PICA and the dissecting dangers and what they internal cerebral artery. This is a 38 year old woman presented relatively recently with sudden collapse and subarachnoid hemorrhage. And you can read the history yourself here. And the physical exam was a patient who was left-sided weakness and otherwise agitated, not obvious neurological indices. And the CAT scan shows a bleeding in the fourth ventricle and subarachnoid as well, as you can see here. And the angiogram shows this fusiform dilatation of the third segment, which is the tonsillomedullary segment of the PICA. And after evaluation of this, we decided that this aneurysm is not a good candidate and this patient for endovascular treatment, because that would sacrifice the segment. And we know that the third segment of the PICA can have perforators. So that's why we decided, after discussion of the treatment strategy, we decided for surgery and it's a treatment that could save that segment of the PICA. And... initially we took the patient to the OR. The patient was highly unstable with the high ICP during positioning. We took the back, waited two weeks until the patient could be completely stable, almost neurologically intact. And we decided for the PICA PICA bypass, which was felt to be the best option here, because we had a good PICA contralateral, and an insight to bypass. And whenever I can do an insight to bypass ICIC I prefer than ECIC. So here we have the midline exposure. This is the right sided PICA. Here is the left sided PICA. The aneurysm is on the right side somewhere here. The PICA in this region, this is a tonsillomedullary segment of the PICA. And that has to be completely dissected to allow the two PICA to be completely mobilized and come together. Once this is done, we mark the area of the arteriotomy, and perform the arteriotomy. Here I do it with two different techniques. One is with 11 blade and micro scissors and on the right PICA. And the second is with the backcutting knife that I prefer. Actually, just to show them how different and easy it is with the backcutting knife. There was these two small perforators that had to be preserved, because they have the backup to the bypass area. The first stitches performed in the back wall, the needle is brought from the back wall and once it's brought from the back wall, it's simple running sutures going this way from the left PICA out into the right PICA, in, out. Out into the left PICA, in, out the right PICA, all the way to the end of the bypass, where we close the deep wall off the bypass. And once this is performed, then the front wall is the same way closed with running sutures, leaving just one small area. And that you check with the hook to make sure that the bypass is patent. And then close that last stitch. Use the gel foam for hemostasis. And then the clips are removed from the from the distal PICA, from the proximal PICA. And then this is the aneurysm that you're dealing with here. Trapping the aneurysm, all the cranial nerves, nine and 10 branches are here. The aneurysm is trapped. And ICG shows that this bypass is open all the way down to the distal clip on the aneurysm. So this way, this aneurysm is completely out of circulation. And we did not sacrifice the third segment of the PICA, which is the segment that still has perforators. And here you can, we could see that there are some perforators under segment on the left side that were preserved due to this procedure. And this is the aspect of the clipping after surgery. And you have the post-op angiogram showing this area. You can see this X shape bypass basically they are the two kissing PICA. They were very close to each other here, and this patient did not have any neurological deficit after surgery and the post-op. Yeah, it's kind of stroking that posterior fossa.

- I really want to thank you for presenting these almost impossible cases. Being very honest about them, sharing your technical nuances as bypass intravascular position is going to remain a very, very critical port of managing difficult aneurysms in the endovascular era, especially in the future. So Amir, thank you.

- Thank you very much, Aaron, it was a pleasure to be here.

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