Fully Endoscopic CP Angle and Brainstem Surgery

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- Colleagues and friends, thank you for joining us for another session of the virtual operating room. Our guest today is Dr. John Lee from University of Pennsylvania Neurosurgery. He is an incredible academician leader and neurosurgeon. He has contributed significantly to endoscopic skull-based surgery, as well as fluorescence in nerve surgery. Today, he's going to talk to us about the details and technical pearls of endoscopic surgery within the cerebellopontine angle. John, thank you for being with us and I very much look forward to learning from you. Please, go ahead.

- Thank you, Dr. Cohen-Gadol. That was a very nice introduction and I look forward to presenting some, a pet project of mine, which is using the endoscope and the CP angle and not just a endoscope assisted, but also just using only the endoscope for visualization. And that's been something I've been doing now for over a decade. So, it's a great honor to be asked to present for the, at this virtual setting. So, just as an aside, I do have, I have received research dollars from Storz and I have had stock options in another endoscope company. So I have some conflicts in the sense that I do believe that endoscopy and visualization is very important for neurosurgical success. With that said, however, all of these conflicts are resolved and no longer active and or- So I practice at Pennsylvania Hospital. Pennsylvania Hospital is one of the three main inner city teaching hospitals at University of Pennsylvania. Pennsylvania Hospital is also the first hospital in America established in 1851. And if you look up to the top floor of this historic building, you'll see the surgical amphitheater, and the surgical amphitheater is housed up at the top. And the reason is because of light. In surgery, so this amphitheater was used for many, many years, and you can see where the participants would observe, where the surgery would be done. This image of this gas light, now it's electric, but at the time it was a gas light. That light was only installed later. So if you look up from the surgical amphitheater and look up to the ceiling, look up to the high walls, you'll see these beautiful windows. And what you recognize is that surgery is the story of light. And I'm taking this introduction, I borrow this from doctor, my colleague and friend, Quyen Nguyen, who is at San Diego and is a wonderful surgeon herself. But surgery is the story of light. You have to bring light to the field in order to see. Our main revolutions, think about our great revolutions in neurosurgery, the introduction of the microscope in the 1950s and 60s, bringing light and magnification to the field. Think about the endoscope also bringing light to the field and panoramic non-invasive visualization. And the other aspect of the area where I work, is fluorescence, bringing new novel ways to visualize tumors using fluorescent dyes. So, today I'll focus on an aspect of bringing light to the field into the CP angle. So the analogy I give is that if the pituitary were the only place where the endoscope would be useful, it would be a adjunct. It would be, it would have still been adopted. But what really brings benefit, is using the endoscope to do more than just a pituitary. It allows you to see beyond the pituitary gland to the tuberculum, to the clivus, to the cavernous sinus, to the pterygoid fossa. So this is one of the main advantages of the endoscope, is that it's not just allowing you to tackle the simple, the simpler procedures like a transsphenoidal for pituitary adenoma, but also allows you to see beyond. The other amazing thing actually is, once you start looking at a screen to do your visualization, it opens up this potential for augmented visualization. And this is where you can now see beyond the visible light. So, and this is another area of my research where we do near infrared visualization. So, I was very fortunate, I started training almost 25 years ago in residency. And at that time I had the privilege and honor of working with Dr. Hae-Dong Jho. Dr. Jho at that time had just published his 1996, 50 case series of doing a fully endoscopic pituitary transsphenoidals for adenomas. He published a, he tried to publish in a neurosurgery journal, but it was rejected. And he could only get a published in laryngoscope and which is a high quality ENT journal. But when I arrived in 98 as an intern, he was giving plenary session talks, demonstrating how he could use an endoscopic approach and remove clival chordomas and chordomas. And it was a really exciting time in Pittsburgh where I trained. And it was really great to see the use of the endoscope and how it could revolutionize surgery. And that continues on with the tradition with my friend and colleague, Paul Gardner at Pittsburgh, and many, many others now, going, expanding the access in the sagittal plane and the coronal plane. It has many advantages. This is a case that I saw, and unfortunately I was not involved in this case, but by trying to retract on the frontal lobe to get to the tumor, you cause inadvertent injury, that could be avoided by doing an endoscopic approach. This is a patient that I took care of. She required two approaches, both endonasal and craniotomy, but it allows the endoscope, allows us to tackle these types of tumors. Here's a pediatric craniopharyngioma where I worked at the children's hospital, to resect this tumor with my colleague, Dr. J Storm, as well as of course, my ENT colleagues, Dr. Adappa, Dr. Palmer, Dr. Newman, and the endoscope allows for a gross total resection. And this is the case that convinced Dr. Storm, my colleague, that we need to, he needed to switch from craniotomy to endoscope for these types of cases. So working in the endoscope, I was able to participate in this landmark paper published by Priscilla Brastianos, identification of the BRAF gene and its implication in craniopharyngiomas. Tuberculum sellae meningiomas, of course I tackle all through the nose. And so I've been very fortunate to experience, to be part of this endoscopic ventral endonasal approach. I published this paper over 10 years ago, at least a decade ago, where we went through the clivus. And at that time, this was probably the first publication of a brainstem, brainstem cavernoma resected through the nose. And we published that case report back then, and that was, it's a very successful approach for a young basketball player. So, the real question now that I started to ask as well, it's so successful in the nose for the ventral clivus, can we extend it to the lateral approach? And what's interesting is that when you go to the skull-based meetings, there's so much activity and so much interest in the ventral endonasal approach, but the lateral approaches are kind of neglected. And it's kind of unfortunate because I do a lot of acoustics, I do a lot of retrosigmoids for MBDs. I've done almost over a thousand of these surgeries now. And it's somewhat neglected because there hasn't been as much of an advancement in the lateral approaches. Nevertheless, I decided to, I saw this being done at Pittsburgh, Dr. Jho was using the endoscope for MBD surgery, and I wanted to explore it myself when I got, when I started 15 years ago at Penn. And so I love this slide by Jacques Morcos, He talks about approaches to the clivus by clival level. So traditionally, if you're approaching the lower cranial nerves, you use a far lateral approach. If you're going mid clivus, you use the posterior transpetrosal. There's also the subtemporal. And then some of it's variance, subtemporal transtentorial subtemporal transpetrosal or enter causal approach. And then of course you have transsphenoidal, orbital zygomatics. But one thing I love is that the retrosigmoid gives you access to all of this, albeit at an oblique angle. So it's not quite direct lateral because your posterior lateral and nevertheless, this retrosigmoid approach can give us a huge, huge advantage and access when we're doing this type of surgery. So that's one of the advantages of the surgery and approach. So if we could use the endoscope and expand our approach, perhaps we could accomplish even more. So I was very fortunate, Dr. Jannetto was a professor at Meridas when I started in Pittsburgh, Dr. Jho, was there as mentioned. Dr. Jannetto was doing, well we would do eight to 10 MBDs a day, Tuesdays and Wednesdays when I was there. So I got to very familiar with the microvascular decompression. Then I moved over to UPenn, and then I ran into this historical figure, Charles Harrison Frazier, and now Charles Harrison Frazier also did a lot of trigeminal neuralgia surgery. There's a very famous picture of him standing next to a sign, and it says total number of major procedures for tic douloureux, 837. And of course his procedure though, was derived from Harvey Cushing and not from Walter Dandy, but rather it was the subtemporal retrogasserian rhizotomy. And so the Spiller-Frazier operation, so Charles Harrison from Frazier being the neurosurgeon and Spiller being the neurologist who would identify which patients need to have surgery. The Spiller-Frazier operation was basically the subtemporal retrogasserian, no longer performed procedure. So I have been at two Pennsylvania institutions, one with a very strong Walter Dandy, Peter Jannetto tradition for a retrosigmoid microvascular decompression. And then you can now, which has the opposite tradition of the subtemporal rhizotomy. So it's fun though, because I continue to innovate in the field of trigeminal neuralgia. So I was not the first to do this, there've been many others. I mean, Shahinian the plastic surgeon in LA has talked a lot about doing endoscopic MBDs. And then of course, Dan Piper, the late Dan Piper in Michigan, had done this as well. Even Laligam Sekhar has publications, there's a French neurosurgeon who's done many of these. So I was just following in their footsteps, but I continue to push these steps. Now, the other thing is I don't believe that just doing an MVD, I think the MVD is very similar to the pituitary adenomas in the ventral skull base. So the analogy that you learn how to do endoscopy with simple procedures like MBDs, and then you can do expanded. So what are the expanded approaches from a retrosig? So I credit Madjid Samii for publishing this paper many years ago, where he described the suprameatal approach. Basically you identify the seventh, eighth nerve, and then you drill away that pechous tubercle that often can block you when you're doing a fifth nerve approach. And then by doing that, you get much deeper, you can get much closer, more access. It's in effect, it's in a way it's a reverse colossae approach. You can also cut the tentorium. And so here's an example of a paper where Fukushima describes cutting the tentorium. And with that you get beautiful access to the third nerve, the supracerebellar artery, the PCA, posterior cerebral arteries. It's a wonderful approach. And I've done that very successfully in removing meningiomas. So, here's an anatomic study using the endoscope and the CP angle. So here are some examples of my, what your visualization is like. So here's a video, this is just a classic microvascular decompression for trigeminal. With the endoscope, I try not to sacrifice these veins as much, but many times, I would say about 30 or 40% of the time, I do have to sacrifice some branch of petrosal vein. Here you can see, this is a classic MVD with a supracerebellar artery on the medial cephalad side of the trigeminal nerve. When I see this, I know the patient's going to do great. Obviously, if you can predict this on the preop MRI, it's even better because then I have even more confidence that the patient's going to do great. So with this, I'll do this decompression and then I'll also then turn to that vein and then I'll push the nerve back, and I'll put Teflon on that side as well. And so, and of course here, you can see Dorello's canal. You can see the third nerve up, up higher over there. You can see the sixth nerve in the depths, mark that six nerve, of course, over here, we saw the third nerve earlier, but I'll also do distal vein decompression as well, because sometimes this is not something you see easily on the, with the microscope because of this tubercle in the way. So next slide please. So, I do often get this question. What is the value of MRI? How do I choose who to go to the operating room? Almost always I base it on clinical presentation only. So this is the Peter Jannetto way of doing it. If you have our classic way, if you have sharp shooting lightning bolt pain, I will offer MVD microvascular endoscope. I call it E-MVD or endoscopic microvascular decompression. And this is really based on Burchiel's paper where the negative predictive value of MRI was only 30%. So if you didn't see it, yeah, on MRI, 70% of time, you still found vascular compression when you went to the OR. I also do Gamma Knife, percutaneous radiofrequency rhizotomy. I also put facial pain stimulators, but I'll do that for atypical facial pain and not for typical pain. So, now my technique involves the use of an endoscope holder. So, unlike in the nose where you might have an ENT colleague across from you or able to hold the endoscope, I tried that in the beginning, but it was horrible. I can't, it's too tight of a space. And the structures surrounding you are much too delicate to have somebody holding your endoscope. So just imagine when you're in the nose and you accidentally move to one side or another, you just hit a middle turbinate. Or if you don't like that middle turbinate, it starts bleeding, sometimes you just cut out that middle turbinate. You just can't do that with the eighth nerve or the petrosal vein or, so it's much, I find it a little bit too harrowing experience to have an assistant hold the scope. So instead what I do is, I use a pneumatic endoscope holder. Here you can see it's mounted to the bed and I always create this figure four and then extend it over. A patient is positioned the park bench. In this picture, you'll see the patient is positioned in MAYFIELD headpins, actually for the last year now, I no longer use MAYFIELD headpins, I just tape them to the bed. And I've done that in over 50 cases now with no problems. I used to use a micromanipulator to go up and down. Now, one thing that's a little bit disconcerting when you put the endoscope in, it's so far deep, you can't actually see your hands going in, your instruments. Unlike the microscope where you have that whole periphery, which is out of focus, but at least you could see your instruments coming in. You can not see that with the endoscope because everything's in focus generally, but the endoscope is parked deeper. So in the beginning I would have this micromanipulator. I would roll it, roll it down, just so I could see my instruments. But at this point now having done over 500 of these endoscopic MBDs, I don't use that. You just kind of memorize the, where your hands need to go in and out, and then you don't need that. Here's kind of just a little demonstration of how I set up the Mitaka holder. Here's a clamp to the bed and here's the figure four, here's it extended over the skull. So I use a 2.7 millimeter OD endoscope. So your standard nasal scope is four millimeter OD outer diameter. Your laparoscope is 10 millimeter outer diameter, so 2.7 is pretty small, 2.7 is like a pediatric endonasal scope. So, the company has a these options. And then what you see is that I just put my hands underneath that and I teach my residents, this triangle approach, basically keep the endoscope high and then your hands come underneath it, and then form an equilateral triangle. I think that's a way to be safe. I borrowed this from Kaufman, from Canada. It's not that different from the conventional open surgery, in experienced hands because you still do small openings. But I do have a paper where I compared my first hundred microscope MPDs that I did as an attendee, and then my first roughly hundred endoscope procedures. And we definitely, we found a statistically significant drop in the number of headaches reported at one month. So I do think making it smaller, making your bone opening smaller, making your dural opening smaller, does provide some benefits. So you can see here how we look up at the screen and the endoscope is mounted and draped across from the patient. And that's how I do the surgery. More recently, I mean, over 50 patients, I've done it now just by taping the head. Modern anesthesia with propofol and is so, so good with TIVA now that the risk for movement is much, much less, especially for a short procedure like this, which can be, you know, 80, 90 minute procedures, I think we've been- And on top of that, I do my, I've started doing now all my acoustics now. I don't pin them either. And of course, translabs, we don't pin. So all my retrosigmoid at work now we're doing without a MAYFILD headpins. So it's been very safe. You can do very small bone openings. This is an example of using the sonopet to remove a small, tiny bone flap that you can play back later. My dural openings are generally under a centimeter, so a subcentimetric openings in order to get in, I've published extensively on this. And with these drawings again, the equilateral triangle, the approach to the posterior fossa. And I think this really does help our residents to learn. So, here's some just examples, this is a lower approach. You can see I'm coming a little bit more inferior to seventh, eighth nerve, here's the left side, a fifth nerve case where you can see the nerve being bowed out at you. And then the decompression. This is a different case where the AICA seems to be pushing on the caudal surface of the fifth nerve. And then you can see that and then decompress that. Here's additional examples. And this is, I often put these pictures in because sometimes I don't trust that the video will work, but this case you can see it clearly, lots of vascular conflict with veins and arteries and lots of work to be done here. Sometimes all you find is this vein, this distal vein, and you have to, you decompress that. And here's an example of that. But with the endoscope, you can see so much better. You just put the endoscope deeper, you see it, you come back out, then you do your work. And then double check by putting it back in. This is a glossopharyngeal neuralgia case, where it is either a PICO or a branch of the firt pushing on the medial aspect of the ninth cranial nerve. So I'll push that away and then put the Teflon in there. Here's a classic hemifacial spasm case. I love it when you find this classic vessel, right at the root entry zone, it becomes so simple the surgery to place it right in that groove there. This is an example of geniculate neuralgia. So here I'm cutting the nervus intermedius. You can see the sixth nerve belly of the pons, and I'll do this for deep ear pain. One thing is sometimes my openings are so small that it can be hard to use the standard bipolar. And so in those situations, it helps to have different options. I no longer use this massive, this is for the nose. This is another version where I would where it's a pivot where you over compress and it'll open. So that was sometimes useful. So there are different options for how you can do that. Now actually there's a small single shaft bipolar that's a really useful, the endopen. So we published step-by-step guides. Storz used to distribute these silver guides. This was kind of over a decade old now, so I'll just move on. So here's my clinical series, I've done almost 700 MBDs and of those, the endoscope has been used as the only visualization fully endoscopic and over 500. You could see here, mostly trigeminal neuralgia, but also, this reflects, I think, the incidents of the disease in the United States. I also do a lot of acoustic neuroma surgery. This is a mal 300 acoustics. Now for acoustics though, I'm still mostly just using the microscope and the endoscope is just an assist. And actually sometimes even there, what I'll do is, I'll just ask for the endoscope and light and not the full tower, because then I'll just literally put it up to my eye and then look in just to double check, just basically look out the fundus. Sometimes it's a blind sweep of the fundus with that canal dissector. And so with the endoscope, you can see it just a little bit better. I find that with acoustic, I need to open larger. And especially like, for example, if it's a trans lab, it's going to be a big opening anyway. Even with retrosig, if I open it too small, then it's hard to drill out and look out lateral toward the IAC. And then my ENT's will complain. So, I find that for acoustics, it's still a bigger, bigger surgery. I know that there's people who talk about doing endoscopic acoustic neuroma surgery. I think in my hands just binocular surgery, I'm still faster to do doing it with a microscope and use the endoscope as an assist. For meningioma, same thing, I think it's still faster for me to do it with the microscope and then use the endoscope as an assist. So here's that picture of Charles Harrison Frazier, the UPenn chairman, total major operations for tic douloureux, 832. I'm approaching it, but not quite there yet. This is my first paper where I compared outcomes published in journal neurosurgery. And we found less headache, 21% versus 7% at one month when we used it. We found vessels more often with the endoscope. We found vascular compression compared to, with the microscope, but I couldn't find actually a significant difference in pain outcomes. We are actually publishing, preparing for publication right now, a paper where we, because everything's stored on video, we're able to retrospectively look at location of compression and to determine that outcome. That paper still, we're still working on it. So actually it's a little premature for me to present that. I'm going to take a very brief aside because one or another area of interest of mine, has been the measurement of pain and trigeminal neuralgia. So I'm seeing all these patients for trigeminal neuralgia, but I recognize that we don't have good outcome tools. So, imagine doing a blood pressure trial, you have a new drug and you haven't measured their blood pressure before surgery, you just say, ah, they're high blood pressure. And then you just measure it afterwards, you call them up and say, how's your blood pressure? So here with pain, it's the same thing. We haven't measured their pain. We just took them to surgery. And then you apply the BNI scale, or you just call them up and say, Hey, how are you feeling on a scale of one to 10? Or how are you feeling on a scale of zero to five? And that is not an acceptable outcome technique for anything that you want to get FDA approved. And so what I recognize is deficiency in our literature and our practice when I first started 15 years ago, was that we don't have a way to measure pain and we don't have a reliable and validated outcome tool. So in conjunction with my mentor, John Farrar, who's a pain neurologist expert. We created the BPI, brief pain inventory facial. And what we've done is that we've administered it to every patient before the procedure and after. So we're trying to measure their pain before and after. And actually multiple companies have approached me now. They all are licensing our tool to use in their studies. So, Biogen has a new drug that they're testing in trigeminal neuralgia patients. So they're using our outcome tool. Stimwave has a new stimulator that they're doing for placing for facial pain and they're using our outcome tool. So I think this is important if you measure what you treasure, if you care about something, you're going to apply techniques to measure it. So, pain relief is not a binary outcome. So, I basically modify the brief pain inventory. I created a reliable and validated outcome tool. We published this many years ago. We validated it. Basically we measure pain intensity. So how bad is it now, or how bad was it last, in the week? So that's easy intensity. We also then looked at it's, how it interferes with your activities of daily living. So this is part of the standard BPI. And then I just created by querying and talking to patients, we created, we asked, added seven more questions that focus specifically on facial activities, like touching your face, brushing or flossing your teeth, smiling, or laughing. And we then published this, and this has been very valuable. We published, for example, that atypical facial pain patients report much higher pain interference. And I think actually that's a bigger need in some ways than classic trigeminal neuralgia, Classic trigeminal neuralgia, we have actually good ways to treat them. We've also published the MCID, what's the minimum clinically important difference for patients to feel that it's a benefit. And then if you measure pain before and after, you can also then look for differences. So, what's very interesting is Gamma Knife has a decay rate, right? So the lesioning of the nerve is faster in the beginning when you have hot sources and then as the half-life of the cobalt decays, and you got slower sources, it takes longer to lesion the nerve. Well, interestingly, there is biologic physical biophysical reason to believe that lesioning of, can have differential effects based on how fast you are lesioning it. And this was shown in spinal cords when you lesion the spinal cord. So, well we tested this hypothesis, is it possible that our effects of the Gamma Knife for lesioning of the nerve are less successful if you do it with cold sources. And I was able to show that in this paper. We've renamed it the Penn facial pain scale revise. But the beauty of this is, I apply this to my patients. I get outcome measures and I study them and we try to correlate that with their vascular compression. So some of the nuances of this surgery, so hopefully this video will play. So one thing you'll see here is that when you have a tight space and you put the endoscope, you can get condensation on your endoscope. You never had this with a microscope. So what do I do? You apply that solution that they give you, but I think that's a placebo, but they make some money off of it. So simply what I do is, you'll see me periodically as it gets condensation, I lift up my endoscope. I mean, I've seen my suction in my left hand and I suction, I bring in cold air into the field so I can keep working. Now, obviously that's gonna be more problem if you have bleeding, but my attendedness don't create bleeding, do beautiful, beautiful dissections, careful dissections, and don't create a lot of blood in your field. So, this is another video. Sometimes you have a very tight posterior fossa, so you can see how it gets a little bit tight. Maybe it's a young brain. So, sometimes you don't have a lot of space, but you still work and you're still able to get the surgery. The other thing here you can see is this pechous tubercle, is blocking my view of the fifth nerve. So, I'll sacrifice the Dandy vein, or petrosal vein to get a cephalad. And that will help me to skirt and see the nerve. And I carefully do my dissection. But the there's obviously there's so many anatomic variance and you have to be prepared to deal with these. But here what you see is, I'm looking only at the root entry zone, but putting the advancing the endoscope deeper, I will be able to get further along and do the decompression. Same thing, you can see that vein that I'm decompressing as well. Sometimes what you have to do, or what I'll do is, I'll actually go one-handed. I will put the endoscope on one hand and no suction in my left hand, just endoscope in one hand and the instrument in the other. Next slide, please. So, actually we'll go to the next slide. So, yeah, and this is a redo case, so you can still do redos with this. You just have to be careful with the bleeding. I've been fortunate, I've had two covers of the journal neurosurgery with this endoscopic technique, one for hemifacial, one for trigeminal neuralgia. Let's see, this is an example of hemifacial spasm. So you can see the seventh nerve on the pons and here's that branch of this. So let's watch this video. I think for hemifacial spasm, the endoscope is even more useful because you can put a 30 degree angled scope along that pechous stirrer in between the eighth and the ninth cranial nerves, and you'll see beautifully. So this is a zero degree. And what you see is a, it's a little bit hard to see because of the floccules of the cerebellum. And so what I find, and then I don't want to pull directly against that. So here, I'm just searching with the zero. What are we going to see? Where is my vascular compression? It's not usually up here. There's the seventh nerve visualized there. It's usually at the root entry zone near between eight and nine and just medial to it. And there, I can just start to see it. So what I'll do here is instead of taking out all that arachnoid or the floccules, and then trying to retract even more, what I do is, I just put a 30 degree angle and look how beautifully you can see the vascular compression there. I mean, it's just gorgeous. You know, this patient's going to get better. But once I parked that 30, one tricky thing is getting my instruments in and here's where you just have to be delicate, careful, and then slowly get your instruments in without the spearing anything. And then here I can just lift up that nerve. And then now I'm going to bring in the Teflon and decompress that seventh nerve and this patient will do great. I measure lateral spreads during these surgeries. I think that that has some predictive value, if I've done an anatomic decompression and the lateral spread is still present, I won't necessarily go back to change that. But I think for hemifacial spasm, this is an excellent, excellent procedure. This is the old way of closing, putting this titanium burr hole cap. Now what I do is, I just fill it with bone putty. Next slide, please. So this is our paper, we have an 85% clinical success. Lateral spread was a good predictor. I did have one hearing loss and three temporary facial palsy, but that that's usually a delayed facial palsy that gets better. Here you can see an example, you can see the bone putty and my typical openings now for these surgeries. And this is the old days with the burr hole cap. You can see it on this side. Now the next slide is someone I got as a redo, and this was done elsewhere. And if you have to put a plate, I'm still shocked at how much variety there is and people doing these surgeries, even for an acoustic, I wouldn't open it this big. But, actually what I did with this is, I just cut the titanium plate from here to here, because I didn't need any more, all of this for my surgery, so. Now, one other beautiful thing about the endoscope is that, unlike the microscope, you can position yourself in a very comfortable position and you can put the monitor in a comfortable position and you can operate with low tension with excellent dexterity in your fingers and wrists. Seeded posterior fossa surgery is challenging I find, just because of this, if you're using the microscope, you're in a very awkward angle, you have a lot of tension in your shoulders, and I have to give a lot of credit to the Samii trainees and Marcos Chadha Cheever in Germany who continues that tradition for doing it like this. I think that with the microscope, it can be quite a challenge, but I think with the endoscope, you don't have to be quite so stressed, you can position yourself beautifully. So, then after MBDs, it's very easy to move on to epidermoid cysts, because these are nice, beautiful cases. The avascular, very easy to use the endoscope to remove tumor. Small acoustics, I've tried to do all with the endoscopes. So, here you can see an example of this tiny tumor, just barely put you on the CP angle. Here is just some debulking, peeling it off the eighth nerve. And then what I do is, sometimes just use to see how far out the CP angle or at the IAC. Now, let me see if this is the same. Okay, this case is a little different case, over here I actually tried to scoop out the IAC portion of the tumor just from the CP angle, using an angled scope. I have the rotatable endoscope as well that allows even more than 30. And the optics are not great, it's kind of a blind scoop. Then I had the NT drill open the IAC, and you still see that I left tumor behind. So I was hoping one day that we could just do the entire IAC with an endoscope. I don't think we're there yet. But looking out the fundus is a beautiful thing with an endoscope, because you can be sure you're clear. You can see it still see your facial, your cochlear nerve intact. Trigeminal schwannomas is another great case to use. Again, this is the Madjid Samii supraglenoid tubercle approach, drilling off. So, this video is not quite as good as I would like, 'cause it's a little bit bloody, and it's not the prettiest technique, but here you can see the porus acusticus. One of the challenges here is that, I'm kind of doing it blindly. I'm just scooping out tumor with, in this case, a canal dissector, you can use pituitary ring instruments. But you can get some of the tumor out this way without doing any significant excess work. So, over to the next slide. So, but as you can see here, I can get a lot of that tumor, just kind of blindly scooping out to Meckel's cave and to the caesarian ganglion. And so it's nice. I follow this guy now for five, six years, I just saw him back. This is an interesting patient, she presented with facial pain and she had this meningioma. So you can see how far up into the middle fossa it extends. And can see it's going to the level of the midbrain. And here it looks like, oh, it can easily do it retrosig, but I think it's cephalad extension would probably influence some people. But what's beautiful about this is, I do this all retrosig, I cut the tentorium. And once you cut the tentorium, you get these beautiful views of the third nerve of the tumor extending up into the ambient cistern. And you can take the whole tumor out. This video did not work well last night, so I just eliminated it. So here's the results of that approach. So I didn't even drill open that IAC. I just spend more time just getting super tentorial. So great result, her pain's better, she's very happy. So, midbrain cavernoma, this is a woman actually, interestingly I operated on her father from meningioma. And she then developed this symptomatic with diplopia and hemibody numbness. And this is just a variant of the retrosigmoid. And I just open up the retrosig to drain CSF. And then I come supracerebellar paramedian, here's the fourth nerve. Here you can see the staining of the lateral midbrain and there's the cavernoma, and I can resect that with the endoscope. So, what I'll do in these situations, I want to drain CSF to, there are different ways you can do this. You can do the seated, here in this case, I just did this lateral, just like an MVD. And then I just turned cephalad. And then after I drained this here, she's pretty young. She was a 20 year old female. And so now you can see. Now, interestingly, where do you put your endoscope in this situation? In this case, what I did was I worked above and below. 'Cause every time you're working with endoscope, you have to think about where's my endoscope and where my hand's going to be. Is very different than microscope. Microscope, you only have to worry about your hands, but what you do have to worry about is your neck. Your neck position can be a real challenge. Like what awkward angle are you going to be? Because that microscope stack is so large. So, anyway, we just proceeded with a fully endoscopic resection here. We can move to the next slide. So, that went beautifully. She did great. I'm still seeing her and her father for followup. So, in conclusion, what I'd like to say is that, using the endoscope, it brings light to the field. We're carrying on the tradition of great surgeons by bringing maximal light to the field, maximal visualization, you sacrifice stereo imaging for 2D imaging, but you gain panoramic views. I think in the CP angle, we still have a lot to learn and do. And I'm going to continue to keep pushing the envelope in the CP angle. I have some ideas of even more or less invasive ways to do this surgery, but I think that it requires dedication. And I look forward to the next generation of neurosurgeons building, doing even better surgery than me. And with that, I'd like to conclude my talk. Thank you.

- Great lecture, really enjoyed it. John, you've truly being a pioneer in the endoscopic CP angle surgery. And that's just so respected, I'm sure globally. Something that comes to my mind that I like to really hear your opinion is, which is not very much related to endoscopy with a CP angle, but rather general to the mechanism of pain generation in trigeminal neuralgia, is if you do an exploration on a younger patient, especially, and all you see a vein touching the nerve, I just have questioned, if that's really the cause of the pain and I pinched the nerve just to do a mild rhizotomy. Do you believe that an isolated vein can potentially cause trigeminal neuralgia and be the sole cause?

- So, I referenced some of our paper that's coming that we're working on with video review, and we certainly have found that distal vein alone, so the vein that's hidden behind the pechous tubercle that alone, if you decompress that, those patients seem to have worse results, not as strong. The other thing that's born out in all of these series is that younger patients don't do as well. I've done some of these in the children's hospital and they generally don't do as well, which is certainly true. Patient selection is so critical for trigeminal neuralgia. What I would say is that I want to guide patient selection by data. And on the other hand, you also get a general gestalt and sense of who's going to do well, and who's not. And I would say, you know, the teenagers, the 20 year olds, those are hard patients to be sure that they're going to get better, but sometimes even the 30 and 40 year olds, I'm always questioning. But vein alone, I do the same thing. If I see minimal compression or no real anatomic, I'll do what Kim Burchiel recommends, which is just take the round knife and do a small neurolysis of the nerve. I don't squeeze it or pinch it, like some have recommended. I know Jannetto used to be pretty rough with the nerve. If he didn't see anything, he would pull, push, look, damaged a lot of, really searching for something to decompress. I almost always put Teflon. I don't think there's a case where I haven't put Teflon, because I, you know, you wonder, you know, if the brain is sagging or the CSF fills back up, maybe that would be a compression. So, trigeminal neuralgia can be very challenging because you want to help these patients, but we don't always have all the pain generation answers or the source, the answers for pain generation. Yep.

- Very well said. I also like your approach, I think for microvascular decompression surgery or cranial nerve hyperactivity syndrome surgery, the endoscope is really useful. But for bigger tumors, I think when things can become more blood and a lot of additional movements I think could be a good adjunct,

- Yeah. but not as a primary tool.

- Yeah. I don't advocate it as the primary visualization tool for complex tumors. Small, tiny acoustics, like those little ones that you could, I've done them. And it's not, those aren't tough cases, but big tumors, complicated case, I just did, you know, these NF2 cases. I going all microscope and opening it wide. I really want to see, have visualization access. Friday, I have a jugular tubercle meningioma involving the lower cranial nerves. That's going to be all done with the microscope. And the endoscope is really just an adjunct at that point. So, I think endoscope fully for practice, for visualization for, and it really works for MBDs, because you're looking for vascular compression. You want to see around the pechous tubercle, you want to see down into the brainstem for hemifacial spasm. And I don't need to bring out the microscope because the anatomy is all normal. I know where to expect things. And I know how to handle myself. I know relative positions, okay, right? H should be proximal and five should be deep. And nine, 10 is way low and petrosal can be variable. So you already know where to expect things. So the 2D doesn't interfere with my ability to perform the surgery, but with tumors, tumors can push the fifth, I mean, I've done these meningiomas. The fifth nerve, not that that's such a critical nerve to preserve, but you do wanna, where is it? Is it pushed down? Is it pushed up? Is it pushed medial? Is it in your face, lateral? So, identification of where things are, and then of course, where are the vessels? Because the meningiomas can wrap around them. And then if I have real bleeding, the endoscopes not the ideal tool, originalization tool for that at that time. So yes, I think that this is probably why the endoscope has not yet been adopted widely. I think there's not a lot of people with a large MBD practice where they can practice and practice, practice a lot with the endoscope. That was the thing endoscopes were still, is still in evolution. I was early, I showed you I was a stock options and vision sensor, early interest in the 3D endoscopes. And I know Storz now has a 3D endoscope, and I was hoping that that would provide major advantage, but it compared to your own retina and optics, I mean, it's a hard to, hard to beat, so.

- I want to again thank you for your significant contributions to neurosurgery, and look forward to having you with us in the near future as well, John, thank you.

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