Surgery Around the Anterior Clinoid Process

Siviero Agazzi

January 24, 2022


- Colleagues and friends, thank you for joining us for another session of the Virtual Operating Room from the Neurosurgical Atlas. Happy New Year. We wish all your families a year full of happiness, health and peace. We sure hope that the year ahead of us is much better than the last one. This evening or today we have a great guest, talented neurosurgeon, a dear friend, Dr. Siviero Agazzi from University of South Florida. He's the vice chairman as well as director of skull base surgery there. I've followed his career for many years, and have really been impressed with his contributions to complex intracranial surgery. He's going to talk to us about the surgery around the intracranial process, a very challenging area with a lot of neurovascular structures in the region and a complex anatomy. So I wanna thank you Siviero for being here, and I'm very much looking forward to learning from you. Please go ahead.

- Thank you Aaron, and thank you so much for this invitation. It is a great honor to be a guest in your world famous Neurosurgical Atlas. And I can tell you that I can not count how many times my residents and all the trainees, and other neurosurgeons that I talk to, sing the praise of your atlas, and that's where they go to get information before surgery, get videos, get an expert opinion. So thank you so much for what you do for the entire neurosurgical community, for our trainees, and I think it is an incredible work. I know it's a lot of commitment, and thank you for inviting me to participate. So, tonight I would like to talk a little bit about the surgery around the anterior clinoid process. And well, I have no disclosure for this talk, let me put this first. And when you called me and asked me to to speak tonight, I was recently coming back from the CNS meeting in Austin where you and I met and finally were able to see each other again after almost two years of distant learning and online virtual meetings. And if you remember, we had this very good presentation by Alex Honnold. He is the rock climber that was featured in a great documentary from the National Geographic because he was the first and the only rock climber that was able to climb El Capitan without any ropes and that style is called "free solo." And as I was putting together the slides for tonight's discussion, I was thinking that there is a little bit of... There is a lot actually, of similarities between the way we approach a surgery of the skull base, and the way he approached his climb. And I really encourage everybody to watch the documentary "Free Solo" because it's very captivating, and it's very fascinating to see how he prepared himself, the participation of his team to his success, but also, well, his own self dedication to this mission, his failures as well, and finally, his success in climbing this. And the reason why I wanted to make this kind of comparison or put the skull base and the anterior clinoid process next to rock climbing is because right around that anterior clinoid process, there are certain structures that if they're not gonna kill the surgeon, they could kill the patient. They could have a very bad, poor outcome for the patient. And the region of the anterior clinoid process is a region that in the documentary, Alex Honnold relates to as "The Crux." And so I would like to bring you back to that movie just for a second, and I will show a little excerpt of it. But this is the route that he took to climb El Capitan, and the little excerpt of the movie that I'm going to show you, that I downloaded from YouTube, talks about this Number 23, it's called the "Boulder Problem." And you will hear Alex Honnold saying how this is the most difficult part of the climb, it's what really determined if the climb is gonna be successful or not. And it took him a long, long time to figure out exactly how to deal with that part, how to finally decide which way to go, and it really made or was gonna make or break his climb. So it takes about four minutes and a half. Let's watch this part of the documentary together so hopefully I can get you in tune with the skull base.

- [Alex] Piece that I've always worried about the most is The Crux, the hardest part. To get past The Crux you have to climb either the Boulder Problem or the Teflon Corner, 2000 feet off the ground, each of which I have fallen off many times with the rope. The Teflon Corner is basically like a 90 degree corner of glass which is ultra slippery, it just fills me with terror. Pushing against the two walls of it with my feet on glass, my palms on glass, and trying to make these little micro adjustments to keep my balance centered so that I can push evenly on all four sides of it. And then I imagine 2,500 feet of air beneath my feet. You're like, that's just a crazy thing to think about. The alternative is the Boulder Problem, but the Boulder Problem has a 10 foot section that's incredibly difficult. It's a very intricate sequence. You've got your right hand on a crim, left hand on a side pole, and then you put your right foot onto this dimple thing. Right hand is up to a small down pulling crimp. Left foot goes into a little dish, and then you drive up off of the left foot into the thumb press. That's the worst hold on the entire route, so you get maybe half your thumb on the hold. Then you roll your two fingers over the thumb, switch your feet, left foot stems out to this really bad sloping black foothold. Switch your thumbs, and then reach out left to a big sloping red loaf type hold that feels kind of grainy. From there, either karate kick or double dyno to an edge on the opposite wall. In some ways, it makes more sense to do the big two-handed jump because you're jumping to a good edge so there's actually something to catch. But the idea of jumping without a rope seems completely outrageous. If you miss it, that's that. But then the karate kick always feels like you're falling into the other wall, which also feels outrageous for so long.

- So this is the end of the karate kick that he's showing. And so we're gonna retake control now of the presentation. So as you can see The Crux. And if you can make my picture a little bit smaller here. The Crux is the hardest part, and I think that in a lot of the approaches to the middle skull base, the region of the anterior clinoid process is probably the hardest one of all. And there are structures around there that can make or break an entire surgery, whether it's an injury to the carotid artery, or an injury to the optic nerve. Now, to get around that anterior clinoid process there are different ways of doing it. Some people like to do it in an intradural fashion to remove the clinoid, some people like to do it in an extradural fashion. I will talk to you about how you can do it both intra and extradural. But the important thing is that in order to do clinoidectomy correctly and safely, you have to follow very delicate, and he calls it, "intricate sequence of hand movements and feet position," but it's something you have to master ahead of time so that when it's time to do it you can do it safely and knowing exactly where you put your drill, just like he knows exactly where to put his hands and his feet, always in the same spot. So let's look at this sequence. What is the sequence of events? Well, in order to understand the sequence of events for the clinoidectomy, you need to understand the exact anatomy and in particular how the anterior clinoid process is secure to the remainder of the skull base. And there are three roots to the anterior clinoid process. One is this one here, which is the lateral root, which is probably the easiest one to understand and the one that we're more familiar with. The lateral root of the anterior clinoid process is the lesser wing of the sphenoid. The lesser wing of the sphenoid is what separates here the middle fossa from the periorbital. And in a subsequent video, we're gonna see that a little bit better. In addition to the lateral root, we have the medial root. This is the part of bone that connects the anterior clinoid process to the posterior sphenoidal and to the tuberculum sellae. Aside from the medial root and the lateral root, we have a third root. So, this is another view of the two roots. We have the third root, which is the optic strut. Now, the optic strut is a root that is very well visualized endoscopically, when we come transnasally, we know that the optico-carotid recess corresponds to the optic strut. But when we come transcranially from this location here, the optic strut is completely hidden by both the optic nerve as well as by the bone of the anterior clinoid process itself. This is another view of the optic strut from the intra orbital view. And you can see how when you come transcranially, which is on the other side of this, this part of bone is completely obscured by the presence of the anterior clinoid process. So this is a little bit of the real difficult part to remove when we try to resect the anterior clinoid process. So there are two ways of doing the clinoidectomy. One is intradural, the other one is extradural. And there is also different ways to approach the anterior clinoid process. And we are gonna talk a little bit about these different ways to approach the anterior clinoid process. You can approach the anterior clinoid process from the anterior aspect. Now, this is usually for meningioma of the tuberculum sellae. I would like to come subfrontally, mostly for tuberculum sellae meningioma and meningioma that are located in this region here. And that then kind of spill over to the anterior clinoid process, but they stay above the optic canal and especially above the carotid artery. You can also approach the anterior clinoid process from the anterolateral route. This is a route that comes from here and that's usually everything that relates to the spenocavernous meningioma that start along the middle sphenoid wing, involve the anterior clinoid process and then eventually extend in the cavernous sinus. This is the anterolateral valve. Now, every now and then we approach cavernous meningiomas straight from lateral with the middle fossa approach. And because these meningiomas are meningioma of the cavernous sinus, in order to unlock these meningiomas and separate them from the superior orbital fissure, we also need to deal with the anterior clinoid process so that we can remove it and unlock the entire dura relationship. And you know from ventral here, there is no real surgery of the anterior clinoid process from the endoscopic side. So I just put that to show that yes, we deal with the optico-carotid recess, we deal with the optic strut when we remove craniopharyngiomas or sometimes tuberculum meningiomas, but we don't really do any kind of surgery of the anterior clinoid process from the ventral route. So let's look at the steps of the extradural clinoidectomy. So the first step and probably the most important step that we need to understand is how to expose the anterior clinoid process. And the most important part to understand is that the meningo-orbital band that is here, that bridges the temporal lobe dura with the periorbital prevents us from actually seeing the anterior clinoid process. So the only way to expose the anterior clinoid process when you come transcranially is to section the meningo-orbital band. And once we section the meningo-orbital band, you can see how suddenly the temporal lobe dura right here can be pulled back and expose the superior orbital fissure and the cavernous sinus right here. And I wanna call your attention here to that famous lateral root that we were talking. This is the lateral root of the anterior clinoid process. This is the sphenoid wing, that lesser sphenoid wing that we were talking about. And so you see in this cadaveric dissection, you have here the periorbital right here, you have here the cavernous sinus right here, and you have here the temporal lobe dura. And you see that as long as you don't have a completely soft space between here and there, you have not disconnected the anterior clinoid process. So you need to absolutely disconnect this so that everything is soft from here to there. Now, you can also appreciate that as soon as you have cut the meningo-orbital band, which is here and there, this has been cut, suddenly you can expose here the optic nerve and you can see very well the media root of the anterior clinoid process which is the roof of the optic canal. And so you understand that up until the time where you have soft here over the optic nerve and then you have soft all the way here to the periorbital, you have not completely disconnected the anterior clinoid process. So all of this from here, soft periorbital, to here, optic nerve that starts piercing the dura, all of this has to be soft to be certain that you have disconnected the anterior clinoid process. Now, this is a kind of an old video that's gonna show you how to cut the meningo-orbital band. And you see, it was a teaching video because I purposely here made the cut before coagulating the band just to show that there is always a small little arterial branch in the meningo-orbital band that is gonna start bleeding. So obviously, you can coagulate it pretty easily. It's a very small branch but I find it a bit more elegant to coagulate the band first and then make the cut so you don't have this type of bleeding. Now, as soon as you have cut calculated that vessel, you can cut the band and then you can start peeling of the temporal lobe dura from the cavernous sinus right here and start exposing here the clinoid process. Let's go back to the presentation. There we go. And so once you have done this, you have removed the medial route, you have removed the lateral route, then you have to start dealing with the optic strut. So how are we gonna do that? In order to deal with the optic strut you have to see, this here is the view that you have transcranially. There is no way you can see the optic strut. Why? Because the optic strut is deep to the actual bone of the anterior clinoid process. So one way of removing the optic strut would be to drill right here at the edge between the optic canal and the anterior clinoid process. Okay, this is the exact location of the optic strut. Now, this can be done, this has been done, some people advocate doing that, I usually prefer doing a coloring out of the anterior clinoid process. So I make a hole into the cortical bone and expose the cancerous bone here of the anterior clinoid process. And you will show in the video how with just a diamond drill this cancerous bone can be slowly removed, pushed. And you will see under the microscope. It doesn't come through very well on the video but under the microscope you can see very well the cancerous bone of the anterior clinoid process. And then suddenly, the vertical bright white bone that is the cortical bone of the optic strut and that allows you to drill it safely. Now, also keep in mind that the optic strut is always going to be underneath the optic nerve, okay. Again, this is the optic nerve right here. The optic strut is gonna be underneath the optic nerve. So if you kind of lose a little bit of orientation, if you find the optic nerve, which you will see transcranially and you start drilling underneath the optic nerve, you will be drilling the optic strut, okay. Whereas if you go in this direction right here, and let me clear this for a second. If you go in this direction here, you're gonna come down into the carotid artery. Instead, if you go in this direction here underneath the optic nerve, you will cut the optic strut, okay? So this is a video that is gonna be fairly quick, it is a little bit accelerated video. So what you will be seeing on the video is the funny situation. This is the optic canal roof that has already been drilled out, okay. So the medial connection has already been drilled out. This is the lateral sphenoid wing, so there's sphenoid wing. So this is the lateral root that's already been drilled out. The first thing you will see is a cutting bur. The cutting bur is used just to take out the cortical shell of the anterior clinoid process. And as a matter of fact, I've stopped now using a cutting bur, I just use one of those coarse diamond or extra coarse diamond. They do a great job at removing the cortical bone. As soon as the cortical bone is removed, then a diamond drill will start kind of shelling out the cancerous bone of the anterior clinoid process. And then you will see that the drill is gonna start drilling in this direction, which is underneath the optic canal. And you'll see that I drill a little bit in this direction and then I stop the drill and I push in this direction a little bit until I see that the anterior clinoid process starts moving. Okay? So you first drill in this direction, then you can stop the drill and push in this direction. And once you feel that this clinoid is moving, then you are ready for the final maneuver, which is gonna be grabbing it with a pituitary rongeur. So now we're ready to get the movie started. There we go. So you're situated. So this is just to open up a little bit of the cortical bone. And now we reorient the microscope. So we are looking really underneath the optic nerve and then we drill a little bit and then we push. You see how the drill is pushing back? So it's pushing back right now. Drill, then push back. And then at some point the clinoid starts moving and then we grab it with a rongeur and we do disrupting movement. Now, keep in mind this rotation movement, okay, because later on I'm going to show you another instance where we do this rotation movement and I will try to remind you at this exact part of the movie where the rongeurs grabs the clinoid and then kind of turns the clinoid in one direction and then turns it in the other direction until the clinoid comes out, okay? So let's go to the next slide. So when do we take out this anterior clinoid process? Well, for practical purposes we talk about vascular problem and tumor problem. So in the vascular world we used to have to always remove the anterior clinoid process when we used to clip ophthalmic segment aneurysms. Now, they're pretty rare nowadays because most of them are coil, but we still need to be able to clip ophthalmic aneurysms whenever the ophthalmic artery takes off from the aneurysm itself and therefore cannot be safely coiled. And then I wanna talk a little bit about Pcomm aneurysms because I think that anybody approaching a Pcomm aneurysm should be ready to take out the clinoid process if it is necessary. And most of the time, starting the CTA will give you that answer, but sometimes we have to improvise. So this is an example that I will show you a little bit later on the video of, but I wanted to point out to you, this is a patient that had an unruptured incidental ophthalmic segment aneurysms. We can see here on the angiogram, it's very standard aneurysm. The ophthalmic artery is taking off right here and that's the aneurysm, okay? And this is the postoperative CAT scan. And you can see on the other side this is where the anterior clinoid process is. This is the carotid artery. So the ophthalmic artery takes off right there and you see where the clip has to sit right here. The clip has to sit right here, which corresponds to this area right here. And in order to reach it transcranially, well, you have to remove the anterior clinoid process. And then the clip is sitting here like you see on this particular picture. It's sitting right on the carotid, right on the neck of the aneurysm. Okay, so we're gonna see the video of this and on this Roton's picture, you can see exactly the location here of the anterior clinoid process and the ophthalmic artery... Sorry, the anterior clinoid process here, the ophthalmic artery. And then you see why when you come transcranially, if you want to have access to the ophthalmic artery you need to remove the anterior clinoid process, otherwise it's all obstructive view. So the other picture, the one that draw your attention to is this posterior communicating artery. So you see this is the PComm right here, it is going in this direction and it's coming down and my face is kind of hiding it here, but whenever you try to clip... There you go. Thank you very much. Whenever you try to clip a posterior communicating artery aneurysm, you have to anticipate that this anterior clinoid process can be small like in this case, but the anterior clinoid process can be a lot more prominent that it can sometimes reach all the way to here. Usually, it never prevents you from seeing the posterior communicating artery, but it can prevent you from getting proximal control on the carotid in case there is a rupture of the aneurysm. So whenever you clip a posterior communicating artery aneurysm, you might need to take out at least part of the anterior clinoid process. In those cases, the easiest thing to do is to take it out intradurally and to take it out intradurally, you simply make a cut right in the middle of the clinoid process and you push the dura medially so it protects the carotid and you push the dural artery so it protects here, the nerves going into the cavernous sinus. And then once you have this dura removed right here and it clears, once you have the dura that is reflected this way and is reflected this way, then you can take the drill and then you can start coring out your anterior clinoid process. This allows you to do a much more tailored resection of the anterior clinoid process because since you have direct view of the carotid, you know whether you have to remove maybe just this little corner of the anterior clinoid process or maybe you have to remove it all the way back to here, or all the way back to there, or maybe you need to do a complete clinoidectomy if you want to open up the optic canal as well. But since you have a complete visualization of the carotid and the aneurysm, it allows you to do a tailored clinoidectomy to just remove what you need. Now, again, in this picture here you see that if you want to see the takeoff of the ophthalmic artery which is right here, you often have to remove the clinoid completely and you have to then open up the optic nerve sheet in order to expose the ophthalmic artery safely and put a clip on that aneurysm. So one comment. So theoretically, extradural clinoidectomy, intradural clinoidectomy, but in practice we often end up doing a little bit of both. Okay? We start extradural, we finish intradural or we cannot go back and forth. Now, the trick to easily doing this combined is to open the dura in what has been called, "the Dolenc approach of the dura opening." And this is because he's the one that taught us how to do that. And in this opening, you start over the Sylvian fissure down there and you take your first cut over the Sylvian fissure down there to fairly proximal on the Sylvian fissure and then you tear that cut over the temporal lobe right here and then over the frontal lobe right here. This cut has several advantages in particular for the surgery around the clinoid process. One of the biggest advantages is that you can leave all this part of the brain here completely covered because the tumor or the aneurysm is not here. So by leaving the dura here, you do not expose the brain, the brain does not get dehydrated, it doesn't get injured because you can put either your cottonoid or your retractor right on this edge. And because there is an opening here, it'll retract this way and then it'll retract that way and you will become intradural right in this spot right there. The other advantage I'm gonna show it to you, let me see, on this picture here, is that you will be both intradural and extradural. So again, this is just a picture of the video that you are going to see later. So we're gonna stay on this picture for a second. So this is a Dolenc opening. Remember, we are on the left side, so this is the aneurysm that I showed you earlier. We are on the left side here. So this is the frontal lobe, this is the temporal lobe, okay? This was the Sylvian fissure and this was our opening that went down the Sylvian fissure and then the dural cut went this way and the dural cut went this way. Now, you see that because there is just a very short segment of dura. We are intradural here and we are extradural here. It's very easy to flip back and forth. And what you see here, you see here the anterior clinoid process right here and that anterior clinoid process, we started removing it extradurally and I will show you that the dura here over the optic canal, so the medial root had been removed. This used to be the sphenoid wing, it has been removed so the lateral root has been removed and we had also removed part of the optic strut, but not all of it. And I will show you exactly why. So the next slide is the actual video. Let's get it started. Okay, so you see this is the situation. So we're taking a look. So now we're gonna start mobilizing that clinoid and please take a look at this aneurysm right here. You see how much every time I move the clinoid how much this aneurysm moves? And every time I try to push on the clinoid, the aneurysm moves. What does that tell me? It tells me that the dura that is attached to the clinoid is also attached to the dome of the aneurysm. If we try to make that famous movement, you remember that movement where we grab the clinoid and then we rotate it one way and then we rotate it the other way to try to to pry it out? If we try to do that with the dura attached to the aneurysms, we're gonna end up very likely with the rupture of the aneurysm very early on. This is why in the case of an ophthalmic segment aneurysm, I never remove the clinoid completely extradurally because I do not know how stuck it'll be to the dome of the aneurysm. So you will see now what we do. So, we become more sophisticated. So we take the part of the dura that is between the clinoid here and the aneurysm and we cut it. So we cut it so that we can separate this part here of the clinoid from the aneurysm and remove the bony part safely without having to pull on the aneurysm. Okay, so you see how here we leave this part of the dura attached and we remove this part right here and that allows us to then gently separate the clinoid from the dura and proceed with the clinoidectomy without taking the aneurysm out. So this video, I had a lot of trouble with 'cause it wouldn't play on the PowerPoint. This is why I kind of edited in a funny way, so I apologize for that. But you'll see it, this is the whole video of the clipping and I just wanted to focus it on the clinoidectomy, but this is what you see. Once you have removed the clinoid, then you can dissect the aneurysm. And here we have the optic nerve that is exposed. Yeah, again, I apologize. I tried to do this very quickly and editing very quickly. So here this, you can see the optic nerve and this is the falciform ligament right there. And we're gonna take a knife and cut out the falciform ligament and then cut the dura of the optic canal roof. Again, in order to be able to manipulate the optic nerve without strangulating the optic nerve while we do that. And so that allows us to have a much better view of the aneurysm and eventually to identify the ophthalmic artery and then eventually to put a clip. Very good. So here we finish up opening the optic canal. And again, and then this video continues to show you the clipping, but that is not the topic for tonight. So we're gonna go back to our presentation. So this is a funny case, this is a case that actually happened to me when I was still in fellowship, but it's so unusual that I just wanted to show it to you to tell you how sometimes you need to deal with this clinoid and you really don't expect it. So this is a patient that presented with the subarachnoid hemorrhage. This is the CAT scan. It's pretty clear. And this is the angiogram. And you can see this is a carotid artery, this is the ophthalmic artery right there, you know, that is probably Pcomm aneurysm or some type of carotid aneurysm Pcomm, but nothing really terrible. So we said well, okay, we're gonna go and clip it. So we did a pterional craniotomy and lo and behold, we were not able to find the aneurysm. There was no way we could encounter the aneurysm. And at some point we'd removed the anterior clinoid process. We said, you know, we're gonna find it, maybe it's closer to the ophthalmic... We were kind of confused to the point that we cut out the radio-opaque little string that is on the cottonoid, on the half by half cottonoid. We cut it out and we put that cottonoid right at the level of the distal dural ring. Again, this is the anterior clinoid process right here that was removed. So this is kind of the region of the distal dural ring. So we put the cottonoid as close as possible to the distal dural ring and then we got an angiogram. Okay? And you can see here on the angiogram that the little marker here shows us very, very clearly that the aneurysm that is here is proximal to the distal dural ring of the periorbital. So this was able to confirm that we were not just blind, but that really, well, we had misrepresented the location of the aneurysm. The aneurysm was actually an extradural aneurysm and that patient, really, had an angio-negative subarachnoid hemorrhage. So had like a spontaneous subarachnoid hemorrhage but that aneurysm was not the reason. So every now and then you find yourself in a situation where you need to deal with that anterior clinoid even if you don't anticipate that. One last word about the posterior communicating artery, as I said, always study the CTA please. It's very important. I found this study in the literature from 2009 where over the whole series of Pcomm aneurysm, about 94 cases of Pcomm aneurysm, they had about a 6% of the time the need to drill the anterior clinoid process. So it's not very frequent, but if you clip Pcomm aneurysms you're gonna have to do it a few times. So you better be ready for that and be familiar with. Let's switch gears real quick and let's go to tumors. Okay, so which kind of tumors would require you to take care of the anterior clinoid process? Well, mostly meningiomas and we're gonna call them periclinoidal meningiomas. And these can be separated a bit artificially, but some of them are mostly in the sphenoid wing and then they go into the clinoid and they have a small extension to the cavernous sinus, okay? Some of them are really clinoidal, they don't really go into the sphenoid and then they go from the clinoid and into the cavernous sinus. And then there are those that are tuberculum sellae meningiomas that kind of extend lateral into the anterior clinoid process. So those are the kind of broad categories that we're going to talk about. But really in all these meningiomas that are centered around the clinoid, the goal is to turn that skull base meningioma into a convexity meningioma, okay? And how do we do that? Well, once again we have to remove that clinoid so that the dura layers can be peeled off. Again, like we peel it away from the cavernous sinus to then be able to excise it just like a convexity meningioma. Now, what are the problems? It's that every time you have meningioma, the anterior clinoid process is always hypertrophic, okay? And it's often very attached to the tumor. So do you remember what we said earlier? That okay, theoretically, there is an extradural clinoidectomy and then there is an intradural clinoidectomy. From a practical standpoint, it is very often a combination of the two because you are unable to do all the work extradural, okay? So what do we do? Well, we do it kind of in a hybrid fashion. So how do you actually approach the anterior clinoid process? Well, listen; the standard approach, the approach that will always work, the approach that will always be safe is the frontotemporal approach. So okay, it's the standard pterional approach. It gives you an incredible view that is subfrontal, an incredible view that is subtemporal, an incredible view that is transient. You can go back, forth, you can expose the entire clinoid from front to back, almost like 270 degrees of the clinoid can be exposed. You can really never go wrong if you go with the frontotemporal craniotomy, okay? Please remember that. Now, obviously because we always try to improve our technique, to be less invasive, the pterional craniotomy has been kind of separated, okay? And so now you can decide to do a supraorbital approach which is called the eyebrow approach. You know, people say, well, I'm gonna do this through an eyebrow. That's pretty much the frontal extension of the pterional, or you can do a mini pterional, where you're gonna come mostly from side. And then in between the two, you can do a lateral orbital approach which can usually be done through an eyelid approach. And those three together, they represent the standard frontal temporal, but you can tailor your tumor to the exact craniotomy that you want to do. And so in the next few slides we're gonna go through some of these examples to try to figure out exactly when and how you can approach this. Now, I would like to take one second to talk about orientation. Why? Because as soon as you start going minimally invasive, as soon as you don't have the entire 270 degree exposure of the clinoid, you run the risk of becoming disoriented. And if you become disoriented and you forget where the carotid artery is or where the optic nerve is, or you get confused that can lead to a catastrophic outcome. So to illustrate this point, I would like to show you this example of this aneurysm, okay. This is clearly an anterior communicating artery aneurysm. And if you look at this aneurysm, it is pointing forward, okay? Pretty clear. It's anteriorly pointing anterior communicating artery aneurysm. It's probably one of the more easier aneurysms to treat because the perforating vessels are posterior and so it's more favorable, I would say, for clipping. Now, let me clear this. If you are the surgeon, and this is a picture taken from one of our skull base courses a while ago. This is Dr. Robertson here who was teaching one of our participants. So if you look here at the surgeon operating on a patient, you see that this is the way that is anterior for that surgeon, okay? Now, let's look at the patient and let's put the patient in the surgical position . And now let's put this patient right here on the table where these two surgeons are operating. Now, what happens? Let's put this aneurysm who is pointing anteriorly in the head of this patient, this aneurysm once in the head of this patient is gonna be located this way. And if you look at this, the anteriorly pointing aneurysm now is pointing in this direction. As you can see, an aneurysm that points anteriorly depending on what the position of the patient is, or the position of the head is, or the position of the surgeon is, can be pointing posterior when you look at the surgeon operating. So it is also important because we are looking at what? The carotid artery inside of the cavernous sinus and it's very important to understand that depending on how you look at the patient and depending on how you approach that area, what appears to be anterior, posterior, up and down can be completely different and you need to keep that in mind so you can stay safe. Okay? So let's go back. So, where is the carotid artery? So whatever you decide, which approach you're gonna choose to come and take out a meningioma in the clinoidal area, you have to remember, where is going to be the carotid artery? So in this case, if you take an eyebrow incision, so this is the eyebrow right there. So if you do an eyebrow craniotomy, it's usually like a small here, subfrontal craniotomy and you come and you look this way. Now, let's put a tumor in there. The same tumor we saw before, let's put it on the anterior clinoid process. The ICA is behind the tumor. Now, is that a problem? Well, it is not a problem if the tumor is on the tuberculum sellae. It is not a problem if the tumor is on the planum sphenoidale right there. It is also not a problem if the tumor just is on top of the anterior clinoid process. But when is this a problem? It is a problem when the tumor is kind of like herniating over the anterior clinoid process and behind the anterior clinoid process. If you pay attention on this picture, you'll realize that the carotid artery here is deep, is lower, is more into the skull compared to the anterior clinoid process. So if the tumor is at the clinoid process and above, you are safe. But if the tumor kind of spills over into the space underneath the anterior clinoid process, it could engulf the anterior carotid artery, it could engulf the Pcomm, it could engulf the anterior choroidal artery, it could engulf the superior hypophyseal artery. And those are all arteries that if you are reaching around the tumor to kind of deliver it into your view without being able to control this artery, you might end up with an injury. And I'll be honest with you, I did have once a problem with evulsion of a small vessel, an evulsion right at the level of the carotid artery that I was able to fix, but that certainly could have been avoided if I had had a better view of that relationship between the tumor and the carotid artery. So if that same tumor, you approach it with the mini pterional craniotomy and you kind of have an approach that is more from the side, okay? More from the side. This was the subfrontal straight down, the mini pterional comes from the side right there. So this is a view of the Roton and the best view, this is a sagittal view, okay? This is the sagittal view, this is the anterior part right there, this is the posterior, okay? So this is sagittal view. And so the way you come, you come at it a little bit from the back and from underneath. And as a matter of fact, you can also come from the top but it's mostly from the back. So if we put now our same clinoidal tumor, you can see that the anterior clinoid process and the tumor that sits on the anterior clinoid process are on the other side. So when you come from a mini pterional, you are going to be able to see and control the carotid artery, to see and control the optic nerve because they're gonna be between you and the tumor. So some people will argue that, well, that's not a good situation to have the optic nerve between you and the tumor. I understand, it might not be a good situation to have the carotid between you and the tumor. Well, I would argue against that because I think that having those two structures in direct view allows you to sharply separate the tumor from the structures with a much more accurate precision rather than coming from the front and having to reach behind the tumor to separate it from the optic nerve or from the carotid artery. So this is the mini pterional. So let's take this example. The next video that I'm going to show you, it's a video that was done in tumor, it was done just with a standard pterional. What are the downsides? Well, people criticize the standard pterional because it's a long incision. It is true, it's longer, it takes longer to open, it takes longer to close, but I would argue that it's all behind the hairline, okay? So once it's done, the patient is never gonna have an ugly scar no matter what. Whether he heals well or whether he doesn't heal well, he's not gonna have an ugly scar. Now, the biggest problem I really find is that yes, I mean it does lead to some temporalis muscle wasting. Now, there are techniques to avoid this. You know, we all know them, but in the end it's a little bit of, some people are lucky and there is no temporalis atrophy and some people have a significant temporalis atrophy. Now, you can pay attention and focus on the reconstruction. And in those patients that really end up with a lot of atrophy, injection of fillers can be very, very useful. And plastic surgery or ENT can do that for you and it can be very satisfying from a cosmetic point of view. Now, some people say that you expose a lot of brain and certainly, the counter-argument is that well if you do an opening of the dura like I showed you, like with the lens opening, all that brain is covered with dura or with cottonoids. So that's not necessarily a valid comment, but anyway, it is still a much bigger exposure, much bigger craniotomy. And so let's take a look at that. Now, do you need an orbitotomy? Often, no. Okay, and again, this could be like a completely other lecture, but most of the time if you do, in my experience, all of the time, if you do a very good flush craniotomy where you take that cut very, very flush with the orbit, the advantage of removing the orbital rim is very minimal. Now, should you do a zygomatic osteotomy? Well, once again, this is a completely different lecture. We have published something about that a couple of years ago to try to explain our thought process for that. In the end or sometimes, it just depends on your patient. These are two pictures from the internet. Those are not patients of mine this is why I didn't hide their eyes, but you know, if you have a nice lady here that has a very, very thin temporalis muscle, probably taking out the zygoma is not that useful. If you have a person here that has a big huge temporalis muscle like this gentleman here, well, it's probably gonna be in the way, so a zygomatic osteotomy might be useful. And then there is a lot of other details that help us determine whether we need to take out the zygomatic arch, but I will not go into the details right now. But I have to admit that for large spheno-cavernous meningiomas, the zygomatic osteotomy can be quite useful. So let's go back. So this is the example of this tumor you see on the left side. You see, it's a fairly large meningioma centered over the anterior clinoid process. And this was FTOZ, okay? We took out everything here. We took out the orbit, we took out the zygoma, it was a full complete FTOZ. And here we start peeling off the dura from the cavernous sinus to separate this tumor and to devascularize this tumor so that we can start debulking it. So you see, this is what we call also the front to back. So Hakuba style where we separate the temporal lobe dura from the cavernous sinus from anterior to posterior. Now, this is the clinoid process, and again, it's a very short video of the clinoidectomy, but you see this is the clinoid right here. And so you see, in this case we are still extradural, okay? We have not entered the dura, but we have not removed the clinoid completely. We have started the clinoidectomy, we have cut out, we have drilled out the clinoid, we have cored out the clinoid, but we have not completed the clinoidectomy because as I was saying earlier, the clinoid is often stuck, is often hypertrophic and it's very difficult to remove in one piece. So we start extradural and then as soon as we get to that and the tumor has been removed, we go back intradural-extradural and finish up the removal. Now, a couple of concepts here. So obviously, the part that nobody ever talks about is the debulking of the tumor. So every time we focus on all the steps to remove meningioma but don't forget that debulking the tumor is always very important because as you see, we operate without retractors. This is again, like a real case. And you try to bring the tumor into your field rather than retracting the brain away from the tumor. And to do that, you need to debulk, debulk, debulk. Now, here you can start seeing here the optic nerve right here, okay? Remember we're on the left side, so this is the frontal lobe right there. And then we're going to open again the falciform ligament right here to allow us to manipulate the optic nerve without strangulating it. And then here, you have the carotid artery right there. This is probably the posterior communicating artery, I suspect, unless it's . I think it's the posterior communicating artery. Yes, because here you have the third cranial nerve right there. This is the so-called Dolenc cut, and we actually have a publication coming out where we kind of criticize it a little bit, this Dolenc cut. We have slowly, slowly abandoned this particular cut in favor of what we call the final cut, but maybe we'll talk about it a different time. But this is all supposed to, again, disconnect this tumor from the cavernous sinus, disconnect this tumor from the tentorium. And as you see here again, we are intradural-extradural, okay? So we are both intradural and extradural and we are able to then remove and resect this tumor completely as a convexity meningioma. And how are we able to do that? Well, we start it all by taking out the anterior clinoid process that then allowed us to unlock all these neural layers. And once again, this is intradural here, this is extradural here. This is intradural where the scissors are, this is extradural. And this is the insertion of the tumor that is cut. This is the edge of the tentorium, and we slowly, slowly, slowly come across this insertion of the tumor just like we would do for a convexity meningioma until the entire tumor is then removed. Again, this is extradural, this is intradural and this is the dura that now is almost like a convexity meningioma and it is completely removed. And then this is like the situation with the optic nerve and carotid artery. Sorry, the third nerve and the carotid artery. And here, a complete resection, at least, of the part that is outside of the cavernous sinus. Good. We can move to the next slide. So now we saw a big tumor, we did a complete OZ, orbit, zygoma, everything. Now we're gonna go a little bit into the variation and we're first gonna talk about a mini pterional. I have two small examples, two short examples of a mini pterional. The first one is a 48 year old male that presented with very, very significant visual loss. So we had to take him quite rapidly to surgery because he was losing vision very, very rapidly, which is not very common, I would say, for this clinoido meningioma but it happens every so often. So this is the MRI that he has. So you can see here, the anterior clinoid process is quite hypertrophic, okay? It's right here. This is the carotid artery and this is the carotid artery that appears to be engulfed by the tumor, okay? So this is again the carotid artery right here and there is tumor all around. So we were anticipating having to dissect all the carotid artery. Again, this is a sagittal view. Once again, I call your attention here on the anterior clinoid process that is quite hypertrophic. And then here, once again, anterior clinoid process is hypertrophic. We get CT angiograms in most of these cases to try to figure out exactly where the vessels are. And like here, you know, obviously the A1 segments here are stretched behind the tumor. And then here, I was trying to show that the carotid artery was here. This is a lobe of the tumor right here, and there is another lobe of the tumor right there, and the carotid artery was right here in the middle. So there was a little bit of, the carotid was surrounded by the tumor. Now, whenever we do the mini pterional we have to anticipate where the Sylvian fissure will be. And there is very sophisticated ways of trying to anticipate where the Sylvian fissure is that you can see here. So you have to cut three quarter from the Nasion to Inion line. It's really complicated. What I usually do is that I find here my suture. Okay, this is the front zygomatic suture right there, and then I go just a little bit below, okay? This is pretty much kind of the angle of the orbit and this is the frontozygomatic suture. So kind of like in between the two. And then I go about six to eight centimeters above the IVC. And again, there is no real science or studies out there, it just works often. And I have to say that in the end, we often have a navigation system when we take out these tumors. So it's a very useful tool to figure out exactly where the Sylvian fissure is 'cause then the next point is to make this cut behind the hairline as far anterior as we can that straggles where we think the Sylvian fissure will be. Now, I have to say that I don't have good pictures of that because I never... Well, I should probably get some, but I follow the hairline and so, you know, some people have a hairline that kind of goes like that and I try to make my incision as far anterior as I can and I kind of stay right behind the hairline. And so the incision is not necessarily always in the same place. If people have a nice thick hairline, it's more anterior, which is more favorable for a clinoido meningioma. And then if they have a receding hairline, well, then sometimes I make a little bit of a longer incision so I can kind of stay behind the receding hairline and still get enough to make my mini pterional. But the concept is that once we have opened the skin, we expose temporalis muscle. Instead of separating temporalis muscle like in a standard pterional and then reflecting it inferiorly, I'll just make a cut here anterior, push the temporalis muscle posterior and then usually put here a cerebellar retractor that retracts this anterior and this posterior and then I have plenty of space to make a small mini pterional craniotomy. So, we're gonna watch the video here. So this is the tumor. So remember it's on the right side. So this is the frontal lobe, this is the temporal lobe, this is that hypertrophic line, you see how big it is? And so even it is a mini pterional, it's a fantastic approach. So you see here now I use the diamond drill, the course diamond drill to do most of the work. I think they are better and they do just as good of a job as the matchstick cutting bur. And then here again, I am opening up the optic canal right there to separate the medial root of the anterior clinoid process. Again, here you can barely see a little bit of the optic nerve that is gonna be pushing right here. And here we open up the optic canal along the optic nerve. Okay? And now here, we're drilling out the inside of the clinoid process. And as you see in the case of a meningioma, there is a lot of kind of bone and spicules of bone. And then it's because the anterior clinoid process is often invaded by the meningioma. Now, this is again the Dolenc cut, so this is the Sylvian fissure. We have a cut right off the Sylvian fissure and then we take right here temporal, and then right here frontal, and then we slide our cottonaids right here. So I'm gonna take this opportunity to talk a little bit, while this video runs, about resecting the meningioma. And you will see, I try to never coagulate the area that's the dissection plane between the brain and the meningioma. Why? Because meningiomas, they almost always very often have a very good dissection plane. And even in areas where they don't have a good dissection plane, there is probably an area next to it that has a good dissection plane. And if you coagulate that interface between the brain and the meningioma, you're gonna fuse those two layers and you're gonna lose the dissection plane. So let it bleed a little bit, but keep the dissection plane. Now, second comment. Some people that take out anterior clinoid process meningioma recommend not to open the Sylvian fissure because these meningiomas, they never invade the Sylvian fissure. Now, they are absolutely correct. Those meningiomas rarely invade the Sylvian fissure. You see how the arachnoid here is preserved, okay? So the meningiomas does not invade the Sylvian fissure, okay. Now, the reason why I like to open the Sylvian fissure is because it allows me to identify very early on here the MCA and then later on identify the ICA early on in my dissection. And I think that is extremely important to allow me to identify where the critical structures are and then to proceed faster because I know where they are. Now, here the same thing. You see how it is a little bit bloody here, okay? This is the interface between the optic nerve and the meningioma. And I tried to do a sharp dissection so that I can keep that plane. Now here I was talking to earlier, because you have a very short piece of dura, it is very easy to go intradural-extradural. And here we are cutting the dura towards the falciform ligament in order to then cut the falciform ligament, open the optic canal dura, and be able to manipulate the optic nerve, I would say with less chance of strangulating it against the dura of the falciform ligament. And you will see that in this case, this patient was losing vision dramatically. And as a matter of fact, I never thought we were actually gonna save vision in this patient. So you will see that... I admit it, when I watched this video, well, it's kind of an aggressive dissection of the optic nerve. Let's put it this way, okay? But the patient, actually, his vision improved dramatically. So you see here again, always trying to do a sharp dissection to separate the arachnoid and without using the coagulation here. So yeah, that's what I'm talking about. So, I would say that if I saw this video, I would say this is a very, very aggressive dissection of the optic nerve, which I would not necessarily recommend, let's put it that way. I think we were being very aggressive in this patient because we thought that his vision was gone anyway. But anyway, so please just keep that in mind. We probably could be a little bit more careful, but we got lucky. So here again, we go back and we can identify here a one segment and once... Sorry, the carotid artery. Yeah, this is the point that we switched the view. We switched the view already, but everything that is close to the edge of the tumor. I stay a little bit bloody, I keep on using the sharp dissection, I do not coagulate. Now, once I am away from the dissection plane, 'cause the dissection plane is down here and I have the tumor bleeding up there, then it's okay. Then obviously you can coagulate so that you get a clean feel, okay? So this view here of the carotid artery and the tumor, this interface is extremely favorable view when you come from a mini pterional craniotomy. But it is not a favorable view, if you come say for example, for an eyebrow craniotomy. So this is why my default, I would say craniotomy, my go-to craniotomy is mostly mini pterional. Okay, we can move to the next slide, then the dissection continue. And this is the post-op picture. We say we got a complete resection of the tumor. And really, I'm honest, I'm serious that the patient really recovered his vision dramatically too. I think it was 20/100 or 20/70 something, extremely good. This is the post-op picture. So you see here, this is where the clinoid was, on the other side the clinoid was extremely pneumatized, on the other side it was just all invaded with tumor. And then here, we had the clinoidectomy, the tumor, and this is the incision that we did, you can see it here. So right behind the hairline, a small incision, very cosmetic. All right, perfect. So this is another example of a mini pterional craniotomy. So this is again an anterior clinoid process meningioma. And I'm gonna call your attention on the hypertrophy here of the anterior clinoid process as well as here the vascular structures that are involved. This is, you say, it's a pretty long incision, not necessarily too small of incision but simply that it was sufficient for this patient. And again, so here you see the clinoidectomy that is extradural, most of it. And then you will see how we're gonna end up taking out the clinoid in a pleasing fashion, both from intradural and from extradural. Here we are able... So again, this is the right side. This is the frontal lobe, this is the temporal lobe right here. This is a Dolenc cut to open. And then here you see, whenever you need to move this dura back and forth for extradural here, intradural there, just put a little stitch and that allows you to move the dura back and forth, back and forth. And here once again, we have a lot of sharp dissection around the arachnoid. And then here, the optic nerve. I think probably if we are a bit, you know, in a hurry, we can... Yeah, I thought I was gonna be able to fast forward just a little bit. And this is again, we're gonna... So we were extradural before, we became intradural, now we're back extradural and we finish up the work to remove the clinoid, open up the optic canal here, open the falciform ligament with a hook knife. There we go. And here once again, opening up the Sylvian fissure. Why don't we advance for the sake of time since we're getting a little bit late and move to the next slide? And again, the reason why this video was shown is once again, to show the exposure of the carotid artery from the mini pterional, which I think it's a lot more favorable than from the subfrontal. Now, let's talk real quick about the lateral orbital approach, which is an eyelid approach. And I think that it's a very, very elegant approach that allows you to go straight to the anterior clinoid process. Now, one thing that you have to be careful is that in the lateral orbital approach, which is in a project, is right along the sphenoid, the lesser wing of the sphenoid, an anterior clinoid process meningioma will be hiding the carotid artery a little bit. The way you get around that is that that lateral orbiter approach can be extended a little bit more temporally. And so you can see behind the tumor and find the carotid artery right here or can be a little bit more frontally. And that's not gonna expose the carotid artery very well, but can expose the top part of the tumor. So this lateral orbital approach is a fairly versatile approach that we usually do with oculoplastic surgeon with an eyelid approach, which is a very elegant approach. And we were able to get there very, very nicely. This is the history of a patient that had a left rhabdomyosarcoma treated in childhood and developed an orbital apex tumor that really grew in about one year, one year and a half. And so we were afraid that this could be maybe malignancy. So you see it's a very small tumor. We really need to get a biopsy or a resection to make sure it was not a malignancy. And there we go. And this is the video. And if we can launch the video, this is gonna be the last video of the presentation. So again, you can see here it has eroded the anterior clinoid process. The tumor has eroded the anterior clinoid process quite a bit. This is our incision right here over the eyelid. And this is the part of the orbit that we are going to remove. And again, this approach is right along the sphenoid wing. And again, you see here with the extension of the navigation, it takes you straight down to the anterior clinoid process. And this is the exposure after we have done here the incision. We have removed here the lateral orbital rim. And then here we're gonna have a little bit of the frontal dura right here. This is temporal dura right there that we start to peel away from the superior orbital fissure. Again, this is the little temporal extension. So if you drill out here, you expose more of the temporal extension, which allows you to see a little bit better the carotid artery. And again, this is the orbital rim. We try not to remove completely the lateral orbital wall if it's not necessary. And we try to leave as much of the lateral orbital wall with the orbital rim so that there is no enophthalmos after the surgery. So this is what is left of the anterior clinoid process. So you see that, you see the anterior clinoid process from laterally. You don't have a perfect view over the carotid artery. Okay? At the time if you remove this anterior clinoid process. And this is why in this case we're able to remove it completely extradural, but sometimes you have to go extradural as well as intradural. Again, this is here a little bit of the frontal lobe dura that has this small little hole right there. And this is the temporal dura right here. And here again, we drill out the same roots of the anterior clinoid process. So this is the lateral root. And then we were reaching over here where the optic nerve is to remove it. And then here we are dissecting it away. This is the optic strut right there below the optic nerve. And then we're able to gently rotate it to detach it from the adjacent dura. And there you go, remove the anterior clinoid. So this is a clinoidectomy, I would say from the lateral orbital approach. And this is the tumor that we are going to now gently remove. And we were exposing the cavernous sinus right here because it's not the tumor really in the cavernous sinus. I mean it is a small tumor, we have some bleeding from the cavernous sinus that can be very easily controlled with injection of Floseal and a little bit of a cottonoid. There you go, right there. We're gonna control that. And so I think the advantage of this approach over the transorbital approach is that there is hardly any retraction on the orbital, the retraction is on the temporalis muscle right here, and we don't have a retractor on the orbit. So I think it's a very elegant approach that does not expose the orbit to any risk. This we're gonna see V2. Okay, this hook is in the foramen rotundum. Okay, so the foramen rotundum and then this is the maxillary strut right here. And this is the superior orbital fissure. And you see here foramen rotundum right there. Okay, with the navigation, just to demonstrate the point of what you can expose. So superior orbital fissure, maxillary strut, foramen rotundum, this is the optic nerve, and this was the clinoid process here and this is the tumor that now we're going to remove. And again, the tumor resection, I think it's not the point of this lecture, but this is the tumor right here. We're gonna express it. Again, we just wanted to get a biopsy. This turned out to be just a simple meningioma, WHO Grade 1 meningioma. It was invading the cavernous sinus so we did not completely remove it, we just took out the part that was outside of the cavernous sinus and the rest we're going to observe it and maybe eventually use radiation. But this was the goal of the surgeries to obtain a tissue diagnosis. There you go. So we can advance the video now. So, you know, I hope I was able to give you a little bit of a tour of this region of the skull base, which I think is a very key region of the middle skull base that we should all be familiar with because it needs to be dealt with for tumors as well as vascular lesion. And there are different ways of getting around the anterior clinoid process. They're all good, they all have their own dangers. And failure to understand this can lead to potentially catastrophic consequences. Make sure that you remember the sequence of steps that you need to take to safely remove the clinoid process. Maintain your orientation, this is paramount. Always know where the ICA is, and in my opinion the ICA is really the one that dictates where to come from. Whether to come from lateral, whether to come from anterior or whether to come from posterior. And you know, if in doubt just do a big frontotemporal craniotomy, you can never go wrong. You're gonna have a beautiful view. And then once you're a bit more experienced and you can tailor your approach a bit better, you can start doing it in a minimal invasive way. And thank you very much for your attention. I'm sorry that I went over a little bit in time.

- Siviero, thank you for a great lecture. We really appreciate it. Definitely the operations around the region are very challenging, just like you mentioned. I think there were huge number of nuance of techniques that are critical for success in this area. And I want to really thank you again for your time and really great pearls of technique and we look forward to having you with us in the near future.

- Thank you very much. Have a good night. Thank you.

- Thank you. Thank you.

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