Chordomas and Chondrosarcomas: Surgical Anatomy and Technical Nuances

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- Colleagues and friends, thank you for joining us for another session of the virtual operating room for Neurosurgical Atlas. Our guest today is Dr. Juan Carlos Fernandez Miranda from Stanford University. Juan Carlos does not require any introduction, not only as being one of my best friends, my incredible collaborator, Juan Carlos is a spectacular surgeon for the skull base and complex intracranial surgery, as well as truly the most outstanding protege of Dr. Rhoton. He has truly carried the tradition of Dr. Rhoton better than anyone else, and I cannot find anyone who can really claim his legacy, the legacy of Rhoton as much as Juan Carlos can. He is the chief of division of skull base surgery at Stanford University. He's also the director of Neuro Training Center, where a lot of amazing operative neuro anatomical research occur. Obviously, his expertise in skull base surgery and endonasal surgery more specifically is second to none. I have been incredibly honored by working with him along the years as one of my dearest colleagues, and I'm so honored to have him with us today talking about resection of chordomas and chondrosarcomas. Juan Carlos, thank you so much and please proceed.

- Thanks, Aaron. It is my pleasure to be again with you, and setting time to contribute to your amazing Neurosurgical Atlas. The best resource we all have as surgeons I think, from the younger students to the most advanced and experienced surgeons, we rely on your work, Aaron to continue learning. So thanks a million for all these years of friendship and collaboration, and for many more. So today, we'll talk about chordomas and chondrosarcomas. I gonna review some of my clinical experience and some technical perils and surgical anatomy that is key for removing these tumors. These are my conflict of interest. This is my team at Stanford. As you see, I work very closely with my ENT colleagues, and this is very important when you do a skull base surgery. I have three three ENT - Rhinology colleagues. I have actually another three lateral skull base surgeons, And this is so important to develop your good skull base practice. As Aaron mentioned, I also run what we call the Neurosurgical Training and Innovation Center at Stanford, where I have the privilege to work with young fellows that wanna explore the surgical anatomy and learn as I did years ago. And it's so stimulating learning from them as they made amazing contributions. And we actually collaborate very closely with Aaron Cohen and the Neurosurgical Atlas to produce the best possible anatomical dissections and operative neurosurgery pearls for all of us to learn. So today we'll talk about clival chordomas and petroclival chondosarcomas. As many of you know, these two tumors have very different biological behavior, and it might be a mistake to put them together, but I do this because they share similar surgical anatomy and technique for the removal. One major difference is that clival chordomas arise from the center, from the nautical remnants in the clival bone here, while petroclival chondosarcomas, they arise from the petroclicval fissure here. And are paramedian. They rise from the foramen lacerum, and the fissures are confluent to the foramen lacerum and therefore, they are paramedian, as you see here. Now, endoscopic endonasal surgery was introduced almost 20 years ago for the treatment of chordomas and chondrosarcomas, and experience was built over the years. And these are the first large clinical series from the Pittsburgh group, the French group and Italian group. So in the feasibility of the approach, how is highly effective and probably reduces the morbidity, increase efficiency of the operation in comparison with open approaches. And therefore, it became a very important approach for clival chordomas and chondosarcomas. For chordomas in particular, we realized, and this is our paper at University of Pittsburgh that there is a significant learning curve, and the resection rates and the complication rates are very much related to the experience of the surgical team. You can see here how in the first decade in Pittsburgh, the first five years, I meant, the resection rate was about 36%, while in the following years, it jumped to almost 90%. This is for primary chordomas, first operation. While the complications remain the same approximately. And if we look at the experience and the learning curve, you can see how there is a continuous increase in the resection rates that we are able to achieve as we increase our experience, and we are moving along the learning curve. When we look at the more recent series from my experience with the team in Pittsburgh, we look at 106 patients, 151 operations, you see that many of them were previously treated, and that's unfortunately, common with clival chordomas, as they tend to recur. But you can see how the gross total resection for recurrent tumors was significantly lower than for primary tumors. But also, we're gonna see how this depends on a number of factors. And among them, are as you see, years of experience of the surgeon. Even more so for recurrent tumors means you need more experience when the tumors are more complex or recurrent. This is something obvious, but there are other factors like previous multiple surgeries. And of course, when it's a larger tumor that involves at least two thirds of the clivus, and especially the lower third involvement was a significant risk for not so good resection rates. It was more difficult. The same, involvement of the craniocervical junction was another factor that influenced resection rates. But we can see how the learning curve also applied very much so for recurrent tumors. The resection rates, complete resection rate, gross total resection rate, I meant, increased from 27 to 53, to 56 to 83%. And these are my middle years in Pittsburgh, we were doing many chordomas and improving the resection rates as we went along. And I think the reason for this improvement is not only the experience, but also more knowledge that we acquire by working in the lab or learning the anatomy. And that's what I wanna share with you today. Why is this so important? Because the resection rate on chordomas makes a difference and has a significant impact on the outcome. And you see here the lines for progression free survival when you have gross total resection, is very different than when you have a subtotal or a partial resection. And this remains true also for recurrent tumors, where gross total resection rate is sometimes possible and actually often possible and it also involves a better prognosis. Therefore, there is a steep learning curve for clival chordoma surgery. This is definitely an operation that should not be done by surgeons without enough experience. Should be done at centers, multidisciplinary with the proper training. And this is what is gonna make a definite impact in the quality and outcome of these patients. Another thing we also sort of discovered at University of Pittsburgh at that time is that, of course we all know all chordomas are different. And we realized, and this the work of one of our previous fellows, a now a faculty, Dr. Zenonos, excellent work, where we realized that you can stratify in three different categories, clival chordomas, based on the Ki-67 index. And you can see here, the different groups. And then on fissure studies. And the reason of this deletion, or this other one, or this other abnormality. And the percentage of this would really influence the survival in these groups. So we categorize Group A, B and C from low, medium and high risk chordomas. And you can see how the curves are so dramatically different. So the biological behavior of this chordomas is different. And we can actually do these studies now and sort of stratify your patient into three different groups. And that actually is influencing the way I counsel my patients. For example, if I have a patient, what I've done a complete tumor resection. And I'm very happy because I even got some . It's a tumor that is relatively focal and it can do a very good clean resection. And the patient is in the group A where there is a low, Ki-67 is low lower than 3%. And we have low rate of these fissure abnormalities. In this case, I might actually recommend observation and non-radiation and leave radiation as a possible tool in the future if there is a recurrence, but this group of patients has the lowest risk for recurrence. And therefore radiation might not make sense. I know this is a bit controversial because many experts in the field recommend radiation for all patients across the board. Now, we have the second group with intermediate prognosis. And in this one, if you get a gross total resection, still, usually you recommend radiation because there is some concern for higher risk of recurrence. If there is incomplete resection, you should try to remove it completely. Now, would you think that's too high morbidity, then radiation is definitely indicated. I always counsel patients, if you had another operation and there is residual tumor, please get a second opinion with an experienced surgeon or surgical team to see if that residual tumor can be removed relatively safely. But not all chordomas can be completely removed. So it's not always possible. But often, it's the experience of the surgeon that determines the completeness of resection. Unfortunately, we have the group C, that has the worst prognosis with really unfavorable features as you see here, and this ones are always radiation and actually, this will be a consideration for further surgery. Some in new therapies like immunotherapy, trials, et cetera. These are behaving almost like sarcomas, very aggressive and malignant tumors unfortunately. Now, just a word on chondosarcomas. They are different animals, as we said. The majority of them are more indolent and not as aggressive as chordomas, although we see some bad players occasionally, of course. Our initial experience, and this is a bit outdated. You see 35 patients, 42 plus six, 48 operations. The extent of resection was a bit lower for chondosarcomas, but that was also on purpose, and is because sometimes these tumors encase the carotid artery, encase cranial nerves, and if you think you are dealing with a lower... A tumor with lower morbidity, perhaps some residual tumor is more acceptable, although we always try to achieve a complete tumor resection in chondosarcoma patients. Now, after that introduction about our surgical experience, especially during my time at University of Pittsburgh and now into Stanford University, I want to share with you what I think is very important surgical anatomy and technique that really, I believe was key and instrumental in improving our resection rates and decreasing, or at least maintaining an acceptable risk of complications. We developed this classification of the clival and petroclival region in three levels, and this was following Professor Rhoton's rule of three of the posterior fossa that many of you know. We developed this rule of three of the clival region, in upper, middle and inferior clival region. And you see the upper clival region entails mostly the dorsum sellae down to this bony prominence, I'm gonna explain later to you. This bony prominence is located right here. And it's this little slope that touches the petroclival fissure and the petrous apex. This is called the petrosal process of the sphenoid bone, and it's actually where the sixth nerve runs to enter Dorello's canal. So that is all lower limit of the upper clivus. And if you look at it on the sagittal view endonasally, it correlates with the floor of the sellae right here. So we call this area, the sellae clivus, because entails the sellae, the dorsum sellae, the posterior clinoids. And the pituitary is in front of us. So we need to deal with the pituitary gland in this upper clivus as I'll show you in a few minutes. Then we have the middle clival region right here, goes from Dorello's canal down to the beginning of the jugular foramen here, and it is the part that is facing the petrous apex on both sides. And usually, for open approaches, use a transpetrosal approach to get here, but now working endonasally, you have a direct access to this, what we call a sphenoidal clivus or the sphenoid portion of the clivus, because this is mostly done by the sphenoid bone. Goes from the floor of the sellae, down to the level of the floor, of the sphenoid channels right here where the choana starts, where the pharyngobasilar fascia comes here and attaches to the bone. So the mid clivus is this portion of the sphenoid. If you drill it, you get access to the prepontine cistern, where often chordomas extend. And finally, we have the lower clivus. Lower clivus includes from the foramen magnum and condyles, and jugular tubercle, after jugular foramen here, and this lower part of the clivus includes the craniocervical junction, and as we said, is one of the most tricky areas to work because the tumor can actually involve the C1 junction and make the resection more difficult and more morbidity because of the craniocervical instability that can be caused by this. Now, in the upper clivus, as we said, is the cellae clivus from the petrosal process to the posterior clinoids and dorsum sellae. We have the pituitary in our way to get to dorsum clivus. To get here, we have the pituitary. So we need to learn how to do mobilization of the pituitary gland. And this was an original description by Amin Kassam. One of the most original technical nuances. I was fascinated when I saw him doing it. What a beautiful approach to remove the pituitary gland of the sellae, so you can get access to the dorsum sellae behind. This technique was described initially as an extradural approach, where you dissect the dura of the dorsum sellae, so you can get access to the bone here and to the beginning of the posterior clinoids here. The problem with this extradural approach is that it's quite limited, because the dura of the interior wall of the cavernous sinus right here is gonna be preventing the displacement, superior displacement of the pituitary gland and therefore is limited. Now, that's why Dr. Kassam developed this technique where he would open the dura and mobilize the pituitary gland out of the sellae, put the pituitary gland out up here into the interpeduncular, into the suprasellar cistern, excuse me, in the suprasellar cistern, and then gives access to the dorsum sellae and posterior clinoids here. You can remove all of this, and you can open this and get a parallel view of the interpeduncular cistern. This is a technique that is highly effective, and I like to employ it especially with intrinsic tumors like craniopharyngiomas that have a lot of retro clival extension. And I do it mostly again for intrinsic tumors, where the risk of pituitary dysfunction is significant already, because I worry about this mobilization of the pituitary gland causing pituitary dysfunction. Now, some years later, we describe this transcavernous posterior clinoidectomy, or what we call the interdural approach to the posterior clinoid or the upper clivus. Interdural because we use the layers of the cavernous sinus to get access to the posterior clinoids and before. And this is the original technique we described. As you remember, the pituitary gland has an outer layer of dura, and then there is an inner layer of dura. And this bifurcation here is what forms the cavity of the cavernous sinus. So we open it right here as this diagram shows. We mobilize the medial wall. So the pituitary gland is still protected by that medial wall, and we can have direct access through here to the posterior clinoid so we can drill it. In a way, we're working between the carotid on one side and the pituitary gland, medial wall, the cavernous sinus on the other side. And here you can see how this technique is the equivalent of the Dolenc approach. Dolenc described this transcavernous transellar approach to get to basilar tip aneurysms to be able to remove the posterior clinoid. And this is the other way. This is a transellar, transcavernous approach. It is the opposite to get to the same area. These are the different steps of this approach. You see the two layers. There is the cavernous sinus starting right here. Now, what we're gonna do is open the anterior wall. We're gonna open this anterior wall right here. So then the medial wall can be mobilized, and then we work within the medial wall and the carotid artery here. And gives us access directly to the posterior clinoid right here. So we can remove it with direct visualization. The posterior clinoid is often quite tall and it has very severe adhesions of ligaments. The petroclivus and the ligaments, and postherpetic ligament. And this ligament has to be dissected, and that is difficult, unless you have good access as this transcavernous route provides. Very important, we describe how in this route to the posterior clinoid, you this artery, which is the inferior hypophyseal array. So if you're not careful in this route through the cavernous sinus, you can potentially abolish this artery and start seeing arterial bleeding. And it can turn really bad if this avulsion is proximal from the wall of the carotid. So you always need to be very careful. And I like to coagulate this artery upfront, so I don't have to fear a hole in the carotid artery wall. Once you take the clinoid, you have this excellent exposure. You're now seeing the oculomotor triangle laterally, the posterior wall of the cavernous sinus here. And you could open the dura along this line, if needed, for tumor that is extending interdurally, and as you do so, you can see the third nerve that is entering the oculomotor triangle right here. And this is your interclinoidal ligament, this is the posterior communicating artery. You get phenomenal access to this lateral recess of the interpeduncular cistern. So as we learn more and more the anatomy of this area, we realize that as we go through the cavernous sinus, we encounter often these ligaments, and we call this deep parasellar ligaments. These ligaments are attachments from the medial wall of the cavernous sinus to... From the middle wall of the cavernous sinus to the carotid, and to the other walls of the cavernous sinus. And we describe a number of them. The most important one is this one here. This is the so called carotido-clinoidal ligament, and is the same as the proximal dural ring. The ventral aspect of the proximal dural ring. This ligament that you can see here comes in the medial wall, and then it goes on front of the carotid, forming like a collar around it, that's the proximal ring, and then goes behind the carotid like this and like this to meet the anterior clinoid process, the tip of the anterior clinoid on the other side. This membrane, carotido-clinoid ligament separates the cavernous sinus cavity, which is all this. All this is cavernous sinus here, from this clinoidal space up here. And this clinoidal space is a much narrower space, but it's important to understand its anatomy. When we are working through the cavernous sinus to get to the posterior clinoids, usually you don't have to cut this CCL. You have enough access to get the posterior clinoid just behind. But there are occasions where you have tumor extending up and you need to cut through the ligament, even through the diaphragm to join your retro sellar exposure here, your retro sellar exposure right here with a suprasellar exposure. And you can do this what we call an extended transcavernous approach to get to the interpeduncular cistern and suprasellar cisterns. Now, we also describe very important, we said the CCL but we also describe the... Excuse me, this ligament here. The inferior parasellar ligament. And this one is very important. We just cut it from here. Is very important because this ligament is the first one you encounter when you open the anterior wall of the cavernous sinus, and is the one that you need to cut first to start making your way within the medial wall and the carotid. You cut this ligament, you can start separating both, mobilize the carotid, mobilize the pituitary gland and just get your access directly into the posterior clinoid here behind. Of course again, remember the inferior hypophyseal artery is in your way and has to be sacrificed. Sometimes, you can actually dissect or mobilize it but I don't hesitate in sacrificing this artery. This anatomy of the medial wall on ligaments is so relevant for a transcavernous approach. This is the paper we published about this. This is very relevant about pituitary surgery too. We talk about this in a different webinar, but it's also very relevant as you see today on working through the cavernous sinus to get to the posterior clinoids. So I'm gonna show you a couple of examples of the posterior clinoidectomies using this technique. This is a 14-year-old patient I did here at Stanford and approximately two years ago, and they had done first an orbitozygomatic approach for what they thought was a brainstem lesion. They didn't realize this actually was coming from the clivus. You can see this is post-op and there is tumor left in the posterior clinoids, dorsum sellae and even in the brainstem right here. So this whole dorsum sellae has tumor on it. Now, as we said before, what do we do with this? Do we just go for radiation in a 14-year-old or do we wanna do a complete resection? So my recommendation, of course was complete resection, so we went for it. And here you will see this is what we have done or opening of the sphenoid sinus, the sellae has been drilled. I drilled the hole middle clivus. So I've cleaned all the area and you see there's the dorsum sellae, and I cannot remove it and it has tumor inside. So I'm using a Doppler ultrasound to map the carotid artery, and I open directly through the anterior wall of the cavernous sinus, and now the carotid is a bit more lateral. Once you open up an anterior wall, you of course get your venous bleeding. And this is the hemostatic agent that we use. It's highly effective, you can inject it. We're using the special suction tube to inject it. It is the right angle knife that is so important to open these dura. That's the inferior parasellar ligament. And I can transect this ligament. You see, this instrument is key because it has a blunt tip and an upper surface that is sharp. And now you enter the inferior hypophyseal artery. Once I cut inferior hypophyseal artery, I can separate the carotid more and I can get excellent access to the posterior clinoids. And see how big this posterior clinoid is. And it's very difficult to remove without opening the cavernous sinus. Now I'm removing the posterior clinoid on the other side. In this side, I did not open the cavernous sinus wall because I had enough space and I could bring that posterior clinoid down. So in this case, I open one cavernous sinus to remove this posterior clinoid, and this way we completed our resection of the posterior clinoids and dorsum sellae. I'll show you more of that case later but I wanted just to show you the posterior clinoid portion. Now, this is another case. A recent case I did. 74-year-old patient, presented just with nasal obstruction. You see a panclival chordoma, mostly extradural, with some interdural extension, as you will see, but in this one, there is not so clear invasion of the posterior clinoids, but the tumor is displacing the pituitary gland up. And I'm worried the posterior clinoids are gonna be involved. So I'm gonna go after them, I'm gonna take them. You see, again, the right angle knife opening then through both the cavernous sinus, inferior parasellar ligament is almost always there. Once I cut the ligament, I can start separating artery from medial wall. That is a nice view of the inferior hypophyseal artery. I dissect it, coagulate, transect. After I do so, I have much more space to safely remove the posterior clinoid. You see this particular ones are smaller. Taking the dorsum sellae and I'm gonna open in the other side because it's big. I don't have enough access. Same operation, Doppler, right angle knife, identify the medial wall, find the inferior parasellar ligament, another beautiful example. Look at that very robust ligament. I cut it with this right angle knife we designed. And then we have our inferior hypophyseal artery, in this case, we didn't find it. There was no inferior hypophyseal artery in this side. But I have excellent access to get this whole posterior clinoid, which is very robust, and it seems to have tumor inside. Believe it or not, there was tumor in this clinoid, and we can remove it completely. Look at that ring, osseous ring. The posterior clinoid sometimes forms an osseous ring with anterior clinoid, and you have to break it so you can remove it completely. And then we're taking the dura, but we finished all bony portion of the resection for this case, by taking those posterior clinoids. Now, when we started doing this technique, we were wondering if by going to the cavernous sinus and mobilizing the gland and coagulating inferior hypophyseal artery, we would have any increased risk of pituitary dysfunction and the answer was no. All of our initial, a dozen patients we did initially, none of them had pituitary dysfunction. These include both unilateral and bilateral sacrifice, but most of them was unilateral. Years later, we review as we evolve and apply this technique more and more often, we reviewed 20 consecutive patients where we did this bilaterally in all of them. All of them had bilateral posterior clinoidectomy, bilateral sacrifice to the inferior hypophyseal artery, and only two patients got DI. One patient got hypercortisolism. I do believe those are not related to the sacrifice of the arteries but of manipulation of the pituitary gland in some of these very large chordomas or skull base lesions. So bottom line, we believe that the inferior hypophyseal artery can be sacrificed safely because the superior hypophyseal artery will compensate. As long as you preserve the superior hypophyseal artery, the perfusion of the pituitary gland globe would be preserved. Now, can you always do this transcavernous approach? No, you cannot. This is a case I did while at Pittsburgh, and in this case you can see this patient has kissing carotids. Residual tumor left at the dorsum sellae posterior clinoids, but you look at that, those carotids are kissing. Which means I'm not gonna be able to develop a corridor between the pituitary gland and the carotid. It's gonna be really difficult. And getting to that posterior clinoids and dorsum sellae is gonna be a challenge. So what do we do in this case? Do we give up? Do we just go for radiation? Do we take to remove the tumor? So what I did is I modified the technique. You can see the carotids are here and here. There is a few millimeters only in between. So what I did is I opened the dura in the midline. And if you realize, the two carotids are actually tethered by the dura on the floor of the sellae. So if I coagulate, and cut the floor of the sellae, all the way back to the dorsum sellae, I'm gonna be able to get more space, separate those carotids. So I'm not going to the cavernous sinus. It's like a combination of the intra and extradural, cutting to the floor, exposing the bottom of the pituitary gland allows me to separate both cavernous sinuses. And then I can get access that way to the posterior clinoids. I know some of my colleagues, for example, in Japan use this technique routinely for all their cases. I prefer to open the cavernous sinus directly when I can because I have better control, and I believe, in my opinion, better visualization, but the technique can be modified according to the anatomy of each individual patient. In this case, we have to go through the floor of the sellae, cutting the dura to get to the posterior clinoid. So now let's move to the mid-petroclival region. As we said, this is an area where endonasal has made dramatic changes, because in the past, transpetrosal approaches were the only option to really do an effective operation in this area. But now endonasal provides just such a direct access to this region. In this area, we need to understand very well the anatomy of the cranial nerve six. Of course, as we said, we go to the clivus, we drill the clivus, we get access to the prepontine cistern, where we have the basilar artery and the perforating branches, but the sixth nerve is on each side. This is external segment, this is the interdural segment, that goes into Dorello's canal, goes behind and lateral to the carotid to get into the cavernous sinus. I'm gonna show you again, let me reemphasize the anatomy. So the sixth nerve has a cisternal segment right here. Here starts the interdural segment. Follows the same trajectory, same direction, goes up. And then as I'm gonna show you, it bends on top of this bone right here, which is the petrosal process of the sphenoid bone that continues with the petrous apex, and here where the sixth nerve enters, changes its direction, it becomes almost horizontal. It goes behind the carotid, then lateral to the carotid right here and then goes up into the inferior compartment of the cavernous sinus. So let's look at this case. It is a nice case of a clival chordoma that is settled in the mid clivus. This is just below the sellae, there is an extradural component and an interdural component that is compressing the basilar artery and the pons. You see what I do in this case, is instead of going to the tumor, I start sucking tumor out. I really spend a lot of time going around the tumor, drilling all the bone around it, from the foramen lacerum, as explained later, up to the sellae, to both carotids. And only when I have the tumor well surrounded, I go into the tumor and I do intracapsular debulking. So we cannot do en bloc resection in clival chordomas for the most part, but we can do an equivalent of en bloc resection, which means surrounding the tumor completely, getting clean margins, debulking it inside, and then progressively going in the outside. And that's the best way to get a clean, methodical resection in these patients. So now we got all the way to the dura. And I live in the interdural component. But you see, at this point, I've exposed both carotids completely from the foramen lacerum to the sellae. There is no bone left of the clivus. No, in this case, I didn't take posterior clinoid, there was no need. There's no invasion whatsoever. But after the dorsum sellae. Now we go into the intedural portion. And we're opening the dura and you see the tumor invading there. You see the basilar artery displaced to the side. You get basilar artery displaced to this side, I worry less about the left side sixth nerve, I worry about the right one. Because here, the basilar is probably protecting the sixth nerve. These tumors are usually soft but centers are possibly calcified, and they can be quite adherent. But in general, if this is the first operation, the tumors can be nicely resected. The problem is recurrent tumors, radiated tumors, the planes can be really unfavorable. But in this case, if you do a careful dissection, you take your time, you're meticulous, then you can do excellent resection. That is the tumor being peeled off the AICA, anterior inferior cerebellar artery, and we can finally remove the tumor completely. Always in this area, we worry about the sixth nerve. And in this particular case, the right sixth nerve. I was very careful with sealing these tumors. Truly, the risk of sealing is actually very low. I've only seen it with tumors that are highly aggressive in the Grade C category. You can see here sixth nerve right here, and we're gonna trim the dura close to Dorello's canal. You can see the third nerve superiorly. I'm looking for the arachnoid. Sometimes, there are tumor cells trapped in the arachnoid. So I'm opening the arachnoid, making sure there is no tumor left anywhere. And I actually, I'm gonna send dural margins. I like to send superior, lateral, medial, inferior dural margins, even sometimes arachnoid margins to make sure I'm not leaving any tumor behind. I really think these tumors need to be treated like a cancer. This is a type of bone cancer, is a type of bone of sarcoma, and we need to achieve complete tumor resection. Now, I showed you this case previously, and I showed you how we took the dorsum sellae but there's also brainstem invasion. So what do we do in this case with brainstem invasion? And this as I said, you saw a case that we nicely dissected off, but this case is recurrent. There was no recurrent, is recurrent, there is regrowth but also previous abrasion. So these planes are not so febrile. And you see them in the brainstem, I have to dissect and work between these perforating branches, these pons and perforating branches. You can do this very carefully. And then thankfully, the tumor remains soft so I can gradually debulk it, working within the tumor cavity in the pons, and using for this case neuro monitoring. I didn't mention before but I routinely use cranial nerve monitoring for these cases, especially for nerve six, which is the one at risk most often. But in this particular case, going into the brainstem, I would also use potentials, and those remain stable throughout all of resection. You see how the instruments we're using are micro dissectors, similar to Rhoton but especially designed for endonasal endoscopic surgery. We barely use ring curettes because this is more microsurgery than anything else. And here we're using the two suctions to look for any residual tumor. And again, I'm gonna remove that last layer of tissue and I'm gonna send it to the pathologist. I wanna hear from them that this is negative for tumor, and then I'll be ready for closing. So remove everything, very clean resection. And this patient did great. We'll talk about reconstruction later, but this is multi layer always. Fascia lata, fat graft, and the large extended septal flap that covers everything, is the best guarantee for success in these cases. And this is the postop intact patient, no complications, complete resection. Now, we said understanding the sixth nerve is so important, and especially understanding it as it gets into Dorello's canal. That is the most difficult area right here. And what we've learned is the petrosal process of the sphenoid bone is a key landmark, and the dural fold that covers it. You see this dura right here. And this is equally important for chordomas and for chondosarcomas. Gruber's ligament is less relevant because this is Gruber's ligament is behind the sixth nerve. So I find Gruber's ligament after I find the sixth nerve usually, but I can find the petrosal process before I can find the sixth nerve. And therefore, that is the real good landmark I use in surgery. So what I do is I expose the carotid completely, and then with my dissector, I feel this bony slope right here. When I feel that bony slope of the petrosal process, I know the sixth nerve is gonna be just behind, just above that dural fold. I then usually use my stimulator to confirm, and I use that in surgery all the time. I'm gonna show you now how we work around the sixth nerve for tumors that are more invasive. This tumor extends more laterally. You see here, the sixth nerve can be seen actually right here, on the FIESTA sequence, and we lost it here. So it's somewhere there. So it's very difficult. So in this case, I'm working the interdural space and right within Dorello's canal. This is the sixth nerve right here. This is the sixth nerve right there, and this is the petrosal process. So a trick I've learned is if you remove the petrosal process, the sixth nerve becomes more free, and it always manipulation better. You can see here the sixth nerve intradural cisternal segment, I can stimulate and I can swing the dura up to its entrance in Dorello's canal. Then I'm working in between the two layers of dura, so I can trim both, under direct visualization of the sixth nerve trajectory. This dura is always involved, so that's why I'm removing it. And then I'm gonna keep following the sixth nerve and trimming the dura parallel to the nerve. And I use that blue tool, is that my stimulator. And I use it to track the nerve and to see if the nerve is tolerating well the dissection we are doing. Now, this is the very important anatomy I was trying to explain, which is this petrosal process right here. You can very well identify this in surgery, and the sixth nerve runs just in there. In this dissections, you can see, this is the petrosal process and the petrous apex. Petrosal process and the petrous apex. One of our fellows in the lab, Julius was studying this carefully, and showed me how actually it's not always the petrosal process. It is here because this is the petroclival fissure, but sometimes the petrosal process is very short. And actually, what you have here is the petrous apex. So the sixth nerve could be on top of each of those structures. But regardless, what really matters is identifying this slope. Because this slope behind the carotid canal is what tells you where is the sixth nerve. So when you come endonasally, you come this way. You find this slope, here is the sixth nerve. It's always, always like this. It's a very, very reliable landmark. And here it is in surgery. I'm going endonasal. These is our dissection. This is the sellae right here with the pituitary gland. This is the carotid is coming down. And this is the carotid coming up. And you see I'm displacing the carotid in this direction laterally. And then you can see the bone right here. That is the petrosal process. And the sixth nerve is right here. And if I remove this bone, and sometimes this bone you can remove en bloc, and that completes your clinoidectomy, you remove this bone, the sixth nerve has no bone underneath now. And this sixth nerve is now more free and you can do better dissection. You have two more around this sixth nerve and you have to work above and below the sixth nerve. Having no bone underneath is ideal, and patients will tolerate that better. So I'm gonna show you an example. Now this is an example of a chondrosarcoma. These tumors are even more often involving the sixth nerve because as we said, they have a location that is more paramedian on the petrous apex. This tumor goes from the foramen lacerum that is expanded here, down into the jugular foramen, up through the petroclival fissure into the petrous apex and cavernous sinus. Go to the next please, Luke. So we've done a lot of work here. The transclival approach, removal of tumor, but I'm going to show you how we find the sixth nerve. You see this bone we're removing here is what is left of the clivus. That is the petrosal process of the sphenoid bone right here, clearly involved by tumor. And the sixth nerve is gonna be just above that. You see that dural fold I'm cutting right here. That's the dural fold that covers the petrosal process. This here is your sixth nerve. You can see it clearing out the sixth nerve here, and how we were able to identify it early in our operation using this very reliable landmarks. Now, I'm gonna move a bit more into some important anatomy. And this is the anatomy, the transpterygoid approach. And this is so important for mid clival chordomas and inferior clival chordomas. So first, as you know, this is this sphenoid bone and the sphenoid bone has the body of the sphenoid here. And then we have the pterygoids. We have a medial plate, a lateral plate, vidian, V2. So in front of pterygoid, we have this bone, the palatine bone and they form together, the pterygopalatine fossa in between. So the pterygoid here, vertical plate and horizontal plate, and then this pterygoid bone has two processes that are very important to understand. This process here is the sphenoid process of the palatine bone right here. Sphenoid because it touches the sphenoid floor. This process here is the orbital process, because it forms a small part of the floor of the orbit. In between, we have this foramen, which is the sphenoid palatine foramen right here. It is the foramen that is used by the sphenopalatine artery to go from the pterygopalatine fossa into the nasal cavity. So understanding this configuration is key and also look what is vidian canal? So vidian canal is inside the pterygopalatine fossa. You want to find vidian, you need to open the pterygopalatine fossa. You need to remove the sphenoid process, you need to remove the orbital process and then you can find vidian nerve. This is a recurring question. How do you find vidian nerve in an operation? Is not with too much guidance. Is by using anatomy. And this is the key anatomy to understand it. So here we see again, the palatine bone, this is the sphenoid process. This sphenoid process covers an artery, which is this one right here. These very important artery is the palato-sphenoidal artery. It goes from the pterygopalatine fossa down into the nasopharynx. It's covered by this palatine bone, sphenoid process. If you remove the sphenoid process, you can see and identify the artery. Once you identify the artery, you can coagulate it and transect it and you can move it in a superiorsal fashion, and you will find the vidian nerve. That is the best way to find vidian nerve. Once you find the vidian nerve, you can start drilling the pterygoid above the vidian and below vidian as you get closer to the foramen lacerum. As you get closer to the foramen lacerum, you wanna stay on the lower aspect of vidian canal, as Dr. Kassam described many years ago, just to be safe and not get into the carotid. Something that we've learned that is very important landmark these days is the pterygo-sphenoidal fissure. This pterygo-sphenoidal fissure is located right here, and is the fissure between the sphenoid sinus floor and the pterygoid bone. It still is not the clival bond. The clival bone is a bit more posterior than this fissure. So the correct name for this is the pterygo-sphenoidal fissure. The sphenoid bone is one single bone, but they have different embryological origins. The pterygoid comes from one place, the sphenoid body come from other. There is a junction in between them, and that junction is the pterygo-sphenoidal fissure, which actually you can see very well in children. When I do surgeries, I've seen this being like cartilage. Pterygo-sphenoidal fissure right here. So the importance of this fissure is that if you drill the pterygoid lateral to the fissure, you drill the sphenoid floor medial to the fissure, you follow this fibrous tissue and it's gonna confluence, it's gonna have a conference directly, take you directly into the foramen lacerum. And to me, this is the safest way to expose the foramen lacerum. The exposure of the foramen lacerum, it really is difficult. And it took me years to master this exposure. But it's so important, because it's the most inferior aspect of your exposure and your carotid canal. And you wanna expedite the whole carotid in many of these cases. That's why it's so relevant. So the foramen lacerum is this opening here. It's this gap that is in between the sphenoid bone, the petrous bone and the clival bone. So three bones come together, they leave a gap, that is the foramen lacerum. Now, at the same time is formed by three different fissures. So there is the pterygo-sphenoidal fissure, the petroclival fissure, the petrosphenoidal fissure. These three fissures comes together right here in the foramen lacerum, and that is what it is. The vidian canal takes you there, the pterygo-sphenoidal fissure takes you there. These are your two landmarks. Pterygo-sphenoidal fissure and vidian. For those with more interest, we describe this anatomy in great detail in this paper. This is difficult anatomy to understand, but I'm gonna try to give you the most important tips that I think can come up of this work. We found out that between the pterygo-sphenoidal fissure, which you can always see in a CT scan, you can see it right here, and the vidian canal right here, there is usually a 45-degree angle. And that is helpful because you can follow both structures as they come together, as they converge into the foramen lacerum. The foramen lacerum, as you know, is what we call a ventral skull base crossroad. From the foramen lacerum, you can go so many different places. So you expose this area right here and the carotid right here. You have the most difficult part of the exposure completed. Then you you can go up into middle fossa, up a lateral, I mean. You can go directly up into the cavernous sinus. You can go behind the carotid into the petrous apex and petroclival fissure. You can go low and a bit median into the jugular tubercle. You can go low and lateral towards the inferior petroclival fissure and jugular foramen. So there are so many areas around, but the starting point is the foramen lacerum exposure. That's why I put so much emphasis in studying this very carefully. As I mentioned, vidian canal and pterygo-sphenoidal fissure, form a 45-degree angle. You can see these in your bone specimens, and you can see this is the skull has been flipped over. We're looking at the base of the skull from behind. So this is the choana right here. The choana. That would be the front. This is the back. So you see this the pterygoid medial plate, lateral plate. Floor of the sphenoid sinus. You see, this is clival bone. It starts here, clival bone. This is the sphenoid bone right here, all this. And then you can see how there is this line right here between the pterygoid and between the sphenoid. And this takes you directly into the foramen lacerum right here. And you see this opening, that little hole right here, that little hole right here, that is the opening of the vidian canal. You see the 45-degree angle. And at the confluence of both, we have this bony prominence right here that is there. And when I was writing this paper, I was thinking about how do we call this? What is this? And I looked into it, and "Grey's Anatomy" actually had described these many years ago, and this is called the pterygoid tubercle. Of course, they didn't know the surgical relevance of this pterygoid tubercle. Now, we have the surgical relevance, but that is the name of this bony prominence between vidian canal and pterygo-sphenoidal fissure. This is the pterygoid tubercle. So you remove the pterygoid tubercle, you get access directly into the foramen lacerum. So more dissections. So I knew these landmarks. I'm just gonna pass through this, but this is now looking from the front, and this is an open dissection. You see this is Eustachian tube. So this is the choana right here. Choana. The sphenoid centers would be here and now we're seeing the carotid going down. And again, this we're seeing vidian nerve and we're seeing the pterygo-sphenoidal fissure, they form this triangle, which we use as our landmark. If you remove all the bone here and the apex of the triangle here is a pterygoid tubercle, you remove it, this is where the pterygoid tubercle was right here. And it gives you access directly into the foramen lacerum. Inferior aspect of the foramen lacerum if the pterygoid tubercle sits is the safest entry zone to the foramen lacerum in my opinion. And that's what I use in my operations very often. Another example of the relevance of the pterygo-sphenoidal fissure, not only for exposure, but also if you need to access the inferior aspect of the petrous apex, you need to cut, transect the pterygo-sphenoidal fissure so you can access the bone behind in this area. And Luke, please play this video. As I was reading this dissection, as we transect this tissue, we can get access to this whole corridor here, which is the inferior petrous apex, where you can see here is the inferior petrosal sinus. Right there. So this is the jugular foramen. Is the ventral aspect of the jugular foramen. So this is our avenue into the jugular foramen. And this gives you the exposure from the sixth nerve here, the top of the petrous apex, the whole petrous apex down to the level of the jugular foramen. If you could go as lateral here as the anterior aspect of the internal acoustic canal. So you can get a lot of the petrous apex exposed and tumor removed from this area, by doing this, what we call this translacerum approach, which means we cut the foramen lacerum tissue right here, which is no other than the pterygo-sphenoidal fissure. And that allows us to swing the carotid laterally, gently and gain some access to the petrous apex. Extremely effective technique, very much so for chondosarcomas and for some chordomas. So I'm gonna show you an example of all these important anatomy I just described with this chondrosarcoma I did recently. This young lady, international patient that came from South America to have these removed with me, referred by a kind surgeon in her country. You see the carotid has been displaced laterally. So our first exposure is gonna be finding the vidian nerve. So that is the vomer, that's the choana. This is this sphenoid process of the palatine bone that I'm removing. This is the palato-sphenoidal artery and palatovomer artery, there are sometimes two arteries here. So once we coagulate first the palatovomer artery then the palato-sphenoidal artery, we can mobilize the pterygopalatine fossa contents laterally. I didn't show it, but the first step here is open the medial wall of the maxillary sinus and remove the posterior wall to access the pterygopalatine fossa. You see, we are coagulating the palato-sphenoidal and palatovomer artery. That is what is anchoring the pterygopalatine fossa. You can see nicely, the palato-sphenoidal being displaced down into the nasopharynx. Now you have the pterygoid. And now here's my vidian canal right there. So easy right here. The arteries I coagulated and identified are the key for finding vidian nerve. Once you have the vidian nerve exposed, now I drill the sphenoid sinus floor all the way to vidian. And I keep drilling the sphenoid sinus floor until I find the beginning, as you see right here of the pterygo-sphenoidal fissure. You see tissues starting going there. Right here. Pterygo-sphenoidal fissure, vidian, and I'm gonna follow them towards the foramen lacerum. In this case, I'm coagulating and cutting vidian. When I really have to expose the foramen lacerum well, I cut the vidian nerve. Because then I can mobilize pterygo-sphenoidal fissure more, I can drill the sphenoid and I can get so much more access. If I just need to expose the foramen lacerum, I don't need it, but I have to go and work around it. I need to really sacrifice the vidian nerve, which has actually no significant functional consequences. That's a middle clinoid that I just removed. Quite prominent. So I'm gonna expose the carotid from the cavernous sinus and clinoidal segment, down to the foramen lacerum. That is abnormal bone. And you can see my pterygo-sphenoidal fissure down here, vidian, pterygo-sphenoidal fissure coming together all the way to the arotid. In this case, these landmarks were very important because the carotid was very displaced. So it's difficult to identify the carotid because it's so destroyed, but I used this landmark to find it. And I cut the pterygo-sphenoidal fissure so I can get access to tumor that you see right there. They're existing inferiorly into the petrous apex and towards the jugular foramen. Once this is done and once I have the foramen lacerum exposed, the rest is actually quite easy. Just with a you can completely expose the carotid and all the tumor invading the carotid canal. And now I'll clean all the bone around it, getting a clean margin of tumor. That's my cat two stimulator, I'm finding the sixth nerve. This is a stitch I put in the pterygopalatine fossa, simply so I can have a bit more of space. Then I just get it with a mosquito outside. And this again, look at my pterygo-sphenoidal fissure, how I can use it to follow and get into the carotid canal at the level of the foramen lacerum. Doppler ultrasound always key. That was the superior orbital fissure below V2. And I'll take in all the tumor. Now, we're starting to see the carotid in the cavernous sinus. You will see it slowly. That's cavernous sinus wall and carotid. The carotid has been displaced, and the cavernous sinus in this case was not invaded, which is an excellent feature for this tumor. So carotid and cavernous sinus identify and stimulating the sixth nerve. This patient had a sixth nerve palsy pre-op, almost complete sixth nerve palsy. And I know now that she's three months post-op and she has completely recovered her sixth nerve. It's back to normal. We're now using an angular scope, where you see we transected that pterygo-sphenoidal fissure. So I'm into the petrous apex and I can drill all the way. This is the petroclival fissure. You can see it very nicely. So this is clival bone here, clival bone here, petrous bone here. Petroclival fissure in-between. And all these completely clean. I have drill even with an extra volume to get a complete tumor resection beyond even tumor invasion. A patient like this, favorable pathology, usually I would not recommend radiation. Now, some tumors, if they go too lateral, they might be more difficult to access all the work into the nasal cavity. In this case, we developed at Pittsburgh, and this is a phenomenal idea, but Dr. Karla Schneidermann of going through the maxillary sinus in a contralateral fashion. Contralateral, transmaxillary approach. Great design by Karla Schneidermann. And you compare it with the endonasal approach, this gives you a better, much better angle of attack to the petrous apex. You almost pile to the petrous carotid in this direction, and this allows you to reach more posterior. And I've used this approach many times, and it's a great agent for selective cases. This one, for example. This patient had a previous orbitozygomatic approach for this chordoma and all these tumor was leftover in the cavernous sinus, in the posterior clinoid, dorsum sellae, even next to the basilar artery and pons. And the patient was sent to radiation. And the radiation oncologist asked me, this is something we could resect. And I say, yes, of course, this is something we have to resect because there's a lot of tumor left in there. So first step, you see a vidian and pterygo-sphenoidal fissure. The carotid is being exposed right here. Pterygo-sphenoidal fissure, as it goes up into the carotid canal in the foramen lacerum. This is the pterygoid tubercle right here, and then this is gonna be vidian right there. V2 is gonna be lateral, and this is gonna be where the lingual process is located. You can remove it if you wanna get a bit more lateral exposure. And this gets you, you can see here, this is something called Vesalius vein, or sphenoid emissary vein that I'm coagulating. And it goes just medial to foreman or valet for V3. Now, removing the tumor here. And this is the very involved and abnormal petrosal process of the sphenoid. The sixth nerve is gonna be just above that, but this is full of tumor. So the sixth nerve presumably is gonna be displaced. Now I'm going through the cavernous sinus. Open the entry wall of the cavernous sinus really well. You get significant venous bleeding, of course, but we use this hemostatic agent. I also use the trick of simply reverse Trendelenburg to decrease venous pressure. That's very effective also. With this right ankle knife, we open along the carotid canal. And I do that because I need to see the carotid to effectively remove this tumor. I do not like to just blindly aspirate tumor out. I like to see the carotid, and imagine this is a large piece of tumor. That is the posterior clinoid heavily involved. I need to directly see the carotid when I'm doing this. And opening the control cavernous sinus. Same anatomy, inferior parasellar ligament, inferior hypophyseal artery. Posterior clinoid is being mobilized, clearly involve dorsum sellae here. And then this is completed all my... All my bony resection. And now we're gonna go intradural. Oops, sorry. I wanted to move this a little bit forward for you. And then, so we're gonna go intradural. I'm working inside the cavernous sinus. I wanted to show you this. I'm using this transmaxillary approach, and then going through the maxillary sinus in a contralateral fashion, I can get deeper into the petrous apex. This is the sixth nerve up here. This is sixth nerve. And I'm working on removing all this petrous bone inferior to the sixth nerve that is so involved. This patient also had a sixth nerve post-op that completed recovered months after the operation. So we were able to get a clean resection on the petrous apex. And now this was really problematic, because this tumor was severely attached to the brainstem, to the basilar artery and the perforating branches. And these took me a lot of careful work to remove this tumor completely from the brainstem and basilar. And you see here, the problematic situation when there's been another operation and there is significant adhesions. The natural planes are not there anymore, so you have to find them. And here is dissecting the tumor carefully, to see two different perforating branches from the basilar. And as you know, you injure one of those that is a significant risk of severe deficits, such as hemiparesis. But we were lucky with careful technique, we were able to completely remove this tumor. Even the dural attachment all the way lateral. And here what I saw was the anterior petroclinoidal ligament. The beginning of the tentorial edge. You're seeing it right here. This is the tentorial edge with the fourth nerve just behind. So we cut all the way through the tentorial edge. Superiorly, we cut the oculomotor triangle all the way until we see the pecum right here and the third nerve. When you cut this dura up here in the oculomotor triangle, the pecum can be at risk. So always be very careful with that. You see the third nerve running all the way to enter the cavernous sinus. So this is as extensive resection as I can make. All bone, all dura, all interdural tumor has been removed. And then we proceed with our multi-layer reconstruction. You saw collagen, fascia lata, fat graft and our septal flap. And this patient had an excellent outcome with no complications, other than the sixth nerve palsy that recovered completely. But this shows how difficult these cases can be and how effective this resection was all the way in the petrous apex, all the way to the trigeminal nerve, all the way to... Thanks, Luke. So here is the post-op. You see the complete tumor resection. And with this, I like to bring the concept of supratotal resection, because you're gonna get, if possible, extra margins, such as the newest low grade literature, where they advocate for resection with margins when possible. In chordoma, I would advocate for the same. Whenever it's possible, let's get extra margins. Now, another example of a chondosarcoma. Young patient, 19-year-old, also coming from abroad with very large tumor. In this case, can we do all endonasal? And the answer is yes, you can do it all in endonasal. You can see the beauty of this case growing through the petroclival fissure into the cavernous sinus and into the jugular foramen. And you can see here, different sequences, a lot of tumor extending into the middle fossa, but this is going from inferior to superior lateral. So you follow the tumor, you can actually remove it. This is another example of using a contralateral transmaxillary approach, so we can get to all that tumor. And this is the post-op. With a complete tumor resection, you can see all the tumor, the carotid preserve, petrous carotid. All the middle fossa tumor has been removed. And this is our happy patient. So just to finish, the inferior petroclival region, a few words on it. As we said, very difficult area, challenging. We described the anatomy of the, what we called at that point, a far-medial approach. Is the approach to the inferior third of the clivus, that you extend more lateral into the jugular tubercle or the condyle and hypoglossal canal. As we said before, when we studied these, there was a significant learning curve when dealing with tumors in this area. Complex anatomy. We studied carefully how to expand our approach more lateral, especially how to do a condylectomy. And I'm gonna show you briefly this case of a chordoma extending to the nasopharynx. When this tumor is extending to the nasopharynx, they are sometimes embedded in the soft tissue and they are more difficult to deal with. And you need to be very careful not to leave residual tumor around. When they also extend intradurally in the lower clivus, those are the most challenging one. And some of them perhaps is better to do a anterolateral approach or an extreme lateral approach better than an endonasal approach. In any case, we are seeing here how the vidian nerve is being dissected and transected, and I can follow it all the way back. Again, the pterygo-sphenoidal fissure is being found to take me to the foramen lacerum, including the pterygoid. Again, there is tumor everywhere, but I need to find my landmarks. That is the carotid or the foramen lacerum. And I wanna keep this as in block as possible. I wanna work around the tumor as much as possible, not within the tumor. Only within the tumor, once I have the outside very well, delimited and the anatomy will line up. Now, I'm transcending the tumor from the pharyngobasilar fascia and from the nasopharynx, and finding that clean plane of dissection posteriorly. It's very important for us skull base surgeons to be familiar and comfortable working in the nasopharynx. That's the pterygoid tubercle within the vidian, pterygo-sphenoidal fissure and then again, finding my other carotid. Once I find my other carotid, I can transect the tumor from each pterygo-sphenoidal fissure. That is the upper limit. Both foramen lacerum are being exposed and transected. So I can detach the tumor. And this is working, transecting the nasal pharyngeal tissues and deep to the tumor. That is C1 arch. That was foramen magnum, sorry. And then this tumor is removed and block for the most part. As I said, might look unusual for a neurosurgeon to work in the nasopharynx, but I truly think that is an area that we need to master when we do these exposures, so we can really know how to do a wide nasopharyngectomy, know where to find the parapharyngeal carotid. It is always tricky, but we have some fix for that. You see, in this case, this tumor is invading all the... There's a panclival chordomas, which is invading all the bone here. This is the interval extension. Very limited in this case, but you see how I'm mobilizing the carotid artery and doing all the bone that is next to it. And I can even move the carotid artery out of the canal. I use the bipolar coagulation to shrink carefully the venous plexus around the carotid so I can have a bit more space. So I can drill all the bone and remove it completely. This is one of the new instruments we designed to dissect the dura in an epidural fashion, and then taking the other carotid. So at the end, you are removing everything. There has to be no bone left. Again, I'm finding my petrosal process, landmark for the sixth nerve, enters into the cavernous sinus, down to the jugular tubercle, towards the petrous apex and complete resection. So, and that's gonna move it to the end because I show you part of this, and this shows you an example of... Okay. So, for example, these are, as we said, very challenging tumors going into the lower clivus. You can see here I did in Pittsburgh with a nice, complete tumor resection and the interval portion of this tumor. You want to play this video quickly. It's just a short clip, Luke, showing, if you remove all these tumor at the level of the jugular tubercle, you can end up seeing the lower cranial nerves. The beauty of this is you're coming from the front. So the lower cranial nerves are located posteriorly. The 12th is located inferiorly. That's the hypoglossal canal. This is the vertebral artery. This is the sixth nerve. Actually, sorry, it's not, it's up here, but these are the nine, 10 and 11 nerves going down. So ideal, and here, we remove all the jugular tubercle as this is showing here to get access to this area. That's the benefit of doing these cases endonasally. And just to finalize, I think it's important to put a few words on reconstruction. Of course, we always worry about the morbidity of CSF leak, meningitis, et cetera. So we adopted this technique of multi-layer reconstruction. The first layer is a collagen that goes in lay. The second layer is a fascia lata that covers the clivus, the fat graft sort of buttresses these fascia lata graft on the clival recess. And then the flap on top. And then very important, a lumbar drain. We like to keep it for about three days at five to 10 ccs an hour. Now you would wonder about the lumbar drain. And this is something that has been always controversial and debate in the literature. So we use a lumbar drain or not after endonasal cases. So the answer is, depending on the case. For example, in this particular case, this is a phenomenal study we did in Pittsburgh. And Paul Gardner was the champion of this study. For two or three years, we were analyzing patients in this study. So this is a very, very well done and valuable study. And we saw that we have to stop the study earlier because we were seeing already significance, more leaks on the no lumbar drain group than on the lumbar drain group. But when we studied final patients by location, for posterior skull base cases, mostly chordomas, and some meningiomas, 50 patients we had. No lumber drain, risk of CSF leak, 30%. Very high. With lumbar drain, 12%. And this was statistically significant. So definitely, I would encourage all of you, you do these cases to use a lumbar drain post-op to decrease the risk of a spinal fluid leakage. Now, these numbers have now gotten better, because at the beginning, we were not so consistently using multi-layer reconstruction or extended flaps, and I think that makes a difference. We were not using . That also makes a difference. Now, what happens when the nasoseptal flap fails? And I'm sure many of you have had this occurrence, and this is really unfortunate, but it happens. A flap could be necrotic or the flap maybe is transected, or simply there is no flap because you're doing a reoperation in a patient with no septum. Because someone else damaged it in a previous operation. So what are your options? So I wanna review these two with you. One is inferior turbinate or lateral nasal wall flap. And that is a very important one. This is a flap that is pedicle of the inferior turbinate and of the lateral nasal wall. And it is so important to work with our ENT colleagues doing these cases because this is something they can do very well, and they really master this technique of raising these flaps as you see here. So let's go to the next, please, Luke. At the end, this flap, depending on how you raise it, the inferior turbinate is your conduit. And then the floor of the nasal cavity and part of the lateral wall can be your area for reconstruction. Sometimes it's not large, but regardless, it's very useful because it's providing vascular supply to your reconstruction. Here you see a fascia lata, and then the inferior turbinate flap reaching this area. And this in this case was enough to solve these difficult problems of an inferior clival leak. Let's go to the next one, please. Now, a necrotic nasoseptal flap is something that is really problematic. Patients may present with many injuries and not necessarily a CSF leak. This is a patient with a very large meningioma I did. And unfortunately, the flap wasn't closed. The incidence is higher in patients with not good health, poor healing, et cetera. But in this case, the flap is clearly necrotic. You see it's not well vascularized, it doesn't adhere. This patient developed meningitis without a CSF leak. And in those cases, it's not enough just to do antibiotics. This is dead tissue. You need to go there, you need to do debridement, and, let's go to the next one, please. You need to do debridement and then you need do develop another reconstruction technique. You can use a contralateral flap if you have it, but sometimes you don't have it. In this case, I use a temporoparietal fascia flap. This is something that I've done just a few times, thankfully, because it's like one of your last resource. So in this case, what we're doing is we are working through the pterygopalatine fossa right here, and coming from the inferior orbital fissure through the pterygopalatine fossa, we transpose this temporoparietal fascia flap. This flap is based on the STA, and is the tissue that covers the surface of the temporalis muscle. By transposing it, you are bringing this large vascularized tissue into the nasal cavity. You can use this guide to this dilator to increase your corridor. And as you see here, we are now using again, fascia lata and fat graft and all the same multi-layer reconstruction in the clivus. These are fat, but the key part is now bringing the vascularized tissue. Remember, this is a panclival defect, really large defect. And this is, or temporoparietal fascia flap that you were bringing, through the pterygopalatine fossa, in front of the pterygopalatine fossa right here. But this provides fantastic reconstruction, highly vascularized tissue to the whole clivus. And this patient healed very well after this reconstruction. So if you're gonna get into these complex cases, you need to learn how to have backup options to solve the many problems you can get into. So just to finalize, remember, endonasal endoscopic study is, in my opinion, the best approach for chordomas and chondosarcomas in most cases, but not all of them. In our series in Pittsburgh over the years with over 200 cases or patients, about 15% of those would still require open approaches. And that's when this comes out of the six plus one skull base approaches fits into it. I like this idea because you have the one approach, which is the endonasal approach that can access all these places. You can have endonasal approach to go from the anterior skull base, all the way down to the craniocervical junction. But as tumors start getting lateral, endonasal approach might not be enough. Then you can use a combination of your orbitozygomatic approach, transpetrosal approaches, far-lateral approaches, to go to more lateral access if needed. So it's important as a skull base surgeon to combine both approaches, integrate it into your armamentarium and apply them wisely. This, for example, a transpetrosal approach. This is the classic approach where you have the foramen spinosum, this is B3, and we are pealing the temporal lobe dura. We are gonna find the GSPN, I'm gonna drill the petrous apex where all this tumor is located, where in fact isolate, I isolate the petrous carotid and remove tumor around it. You see, that's your petrous apex, the estimated location in the internal acoustic canal, and you're drilling. I'm gonna skip this video, just the GSPN. Actually in this case, it's interesting, because this GSPN, we had done an endonasal approach before. So the vidian nerve had been cut. So now we're cutting the GSPN and this give us better access to find first the tumor. We can mobilize B3 better, and then to drill the bone and expose the carotid. And here is gonna record a complete scrutinization of the petrous carotid to remove the tumor around it. You see how we are using a diamond drill. The petrous carotid canal is being being opened. We are dissecting it. And at the end, this anatomy is the same open, the same endonasal it's all about what route you prefer to use? A tumor goes very lateral, endonasal approached might be limited and you might need to use a transpetrosal approach. Tumors like this is a recurrent giant chordoma. Terrible case. You see this recurrent tumor here at the level of the jugular foramen. So how do you approach this? In this case, we chose to go one endonasal approach for this portion, stop at the level of the jugular foramen where the nerves are located, then come through a transpetrosal or transmaxillary approach to get the remainder of the tumor. So two approaches for this patient. One endonasal and the other one transmaxillary, and this, you can see endonasal approach this way, transmaxillary approach this way, and you can combine approaches. They're not exclusive. They are complimentary to achieve your goals. And as I said, often, these patients with recurrent chordomas, chondosarcomas, they are involving deep paravertebral space in this area. Can you do this endonasal? Maybe you can do some work endonasal, but it goes too lateral and it goes too posterior. And in this case, you might wanna have better access using your extreme lateral approach, working within vertebral and carotid artery here. This is your corridor to get into the tumor and work in through your neck approach laterally. That's usually a better approach for this tumor sustained to the paravertebral space, and you can see this mobilizing the vertebral artery, taking C1 and C2 masses. This patient will need a fusion and we'll be able to work from C1 mass towards the midline, towards the odontoid process and achieve as complete resection as possible. The beauty of this is we are keeping all this approach extradural. If you have to remove the dura, you can, and you can then just suture a patch north and what other type that you can bring your muscle flap to cover the reconstruction and use also fat graft that will really help preventing the risk of pseudomeningocele and CSF leakage. So I believe with this, we finalize our tour around chordomas and chondosarcomas. This is a lot of surgical anatomy and nuances. As I told you at the beginning, I believe many of these are key and fundamental for making progress in improving our resection rates and decreasing the morbidity for these very complex cases. Go to the next one, please, Luke. So you saw, this is a steep learning curve. Outcomes are definitely related to expertise, experience of the surgical team. It's so important that these are treated at skull base centers of excellence with high volume and lots of experience doing these cases. I've reviewed many of the multiple anatomical nuances that we have in these areas, starting from the top posterior clinoidectomy to the cavernous sinus, petrosal process for the sixth nerve, transpterygoid approaches to find the vidian nerve, pterygo-sphenoidal fissure to get to the foramen lacerum. From there, going down into the jugular foramen and jugular tubercle, up into the petrous apex. Of course, the important issues of reconstruction. Remember always multi layer, extended flap, lumbar drain usage is very important. And as a skull base surgeon, it's so important to combine with transcranial skull base approaches when appropriate. I wanna end that by thinking again Dr. Cohen-Gadol for his kindness, inviting me again, and his team. Luke, thank you for another wonderful webinar. Thank you.

- You're welcome, Juan Carlos. Spectacular lecture, incredible expertise. Thank you for joining us. I really enjoyed it. A lot of learning pearls and a lot for us to learn from, including myself. So with that, I wanna thank you again and look forward to seeing you in one of our future webinars. Thank you.

- Thank you so much.

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