Surgery of the Cerebellopontine Angle

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- Hello, ladies and gentlemen, colleagues and friends, thank you for joining us for another session of the virtual operating room from The Neurosurgical Atlas. Our dear guest today is Dr. Michael Link from Mayo Clinic. Mayo Clinic is a very dear place to me. That's the place where I trained. Michael has huge experience with resection of lesions within the CP angle, including acoustic tumors. So again, it's such an honor, Michael to have you with us and hear about your pearls of technique. In addition, Michael is the past president of the North American Skull Base Society, as well as co-editor in chief of the Skull Base Journal. Cerebellopontine angle is one of the most challenging locations to operate within. There is many decisions that go both into choosing the right patient for surgery, and in addition, avoiding complications. So Michael, we're all very excited, and I look forward to learning from your pearls. Please proceed.

- Thanks very much, Aaron. It's really such an honor to participate in this wonderful webinar. As Aaron mentioned, I'm here in Rochester, Minnesota, and I don't have any disclosures. I'm gonna talk about some techniques, including some devices and instruments and so on. But I don't have any financial interest in any of those things. This is sort of a big existential question I think we all ask ourselves, but why am I here? Well, over the last more than 20 years, I've sort of had my practice emphasis be tumors of the cerebellopontine angle. And I'd like to share with you today just some of my experience or how I think about operating in the cerebellopontine angle and some of the mistakes I've made and some of the things I've learned along the way. I really wanted this to be a very technical, hopefully interesting talk to a surgical audience. I've had a lot of various interests over the years regarding neurosurgical disease, and particularly vestibular schwannomas and other tumors. But hopefully I'm gonna bridge this gap between what you're really interested in and what I wanna say. Cerebellopontine angle, as Aaron mentioned, is somewhat of a complex compact area with lots of both beautiful and challenging anatomy, and we're gonna go through some of that in the next 45 minutes or so. This is just my general experience over about the last 20 years. I've operated almost 1,500 different pathologies in the cerebellopontine angle. The majority by far are vestibular schwannomas. I've operated almost 800 of those now. I've also operated quite a few meningiomas. And one of the reasons why I think you will never see my series of cerebellopontine angle meningiomas is because nobody can agree on what represents a cerebellopontine angle meningioma as opposed to a petrotentorial meningioma, petroclival meningioma, a truly clival meningioma. Epidermoids are rare, but they are the third most common pathology seen within the cerebellopontine angle. Of course we do surgery, not for tumors, but for a functional disease like trigeminal neuralgia or hemifacial spasm. And then there's lots and lots of other very rare pathologies that occur. Ependymomas, choroid plexus papilloma, metastases, chondrosarcomas and so on. This is just an example. So this is a great tumor to operate. Obviously, it's in the cerebellopontine angle, but it's behind all the cranial nerves. So this is a very low-risk straightforward operation. But this is also a cerebellopontine angle meningioma, but this tumor crosses the internal auditory canal. It crosses the jugular frame and so a much more challenging lesion of course. Some people would consider this maybe a cerebellopontine angle meningioma, but I call it a petrotentorial meningioma. It has a broad base from the tentorium here. Let me see if I can make this work there. So I think that's more of a petrotentorial meningioma. We can take it out. I usually leave the part that is within the sinus here and just take out the part in the cerebellopontine angle. This is more of the standard petroclival meningioma. And as you can see, it's very common that those also extend in the Meckel's cave. So some people would consider this a petroclival cavernous meningioma. This is I think a true clival meningioma. It's arising between the fifth nerves and between the sixth nerves. In my opinion, these are just awful tumors to try and deal with. So if I control the world, if I could say to our trainees and fellows and young neurosurgeons who are out in practice, I think the best way to get proficient in operating in the cerebellopontine angle would be to start doing microvascular decompressions for trigeminal neuralgia, and then move on to do microvascular decompressions for hemifacial spasm, and then do increasingly large epidermoid tumors of the cerebellopontine angle. Those are really nice because they are avascular tumors. And then I think operating meningiomas that are all posterior to the cranial nerves, and then start operating increasing size of vestibula schwannomas, and then finally operate meningiomas that are ventral to the cranial nerves like petroclival tumors. I'll just quickly go over how I do most of these operations. And everybody has their own way of doing a retrosigmoid craniotomy. Obviously there's lots of approaches to the cerebellopontine angle, but just for time sake, I don't wanna get into all of the post-year petrosal approaches and translab and transcochlear and anterior petrosal and so on. All the operations I'm gonna show you today, I did through just this standard retrosigmoid craniotomy. I put the patients in the lateral decubitus position because it keeps their head and neck neutral. You gotta really pad that down hip well, especially in large individuals, and we have a lot of those in Minnesota. I put the patient in some reverse Trendelenburg. I put the head in a three-point pinion fixation, and I slightly flex the head and neck. But you have to be careful, you don't want the mandible to come back and compress the jugular veins. I flex the head away from the up shoulder about 10 to 20 degrees to kind of open up that angle. And then of course we do EMG monitoring depending on the size and location of the tumor, and we can now routinely measure five, we often now monitor six, seven, I typically use an auditory brainstem response for eight, but we can do direct cochlear nerve monitoring. We monitor the 10th nerve for large tumors and 11 routinely. Retrosigmoid craniotomy is familiar to all neurosurgeons. It gives you a great view from the tentorium down to the frame and magnum. There's a low risk of CSF. We've become quite fond of doing what we call the internal petrosectomy. I think Professor Samy deserves a lot of credit for really sort of popularizing this, but basically you can drill the petrous apex from within the cerebellopontine angle. And you can even cut the tentorium and communicate the middle fossa with the posterior fossa. The disadvantages of retrosigmoid craniotomy is it is a long reach to the petroclival junction. The presigmoid exposures shorten that distance significantly, and it is harder to get tumor out of the middle fossa through a standard retrosigmoid craniotomy. This is just typical positioning. This is a big Iowa farmer who had a meningioma in the cerebellopontine angle. So positioned laterally, we've opened up this angle here by flexing the head and neck away a little bit. I've marked out where I estimate the transverse sinus is by connecting a point between the in ear and the root of the zygoma, and then where the sigmoid sinus is, just lateral to the digastric groove. And then I typically make this C-shaped incision here about three finger breadths behind the digastric groove. And this is just a reminder that down hip, if you don't pad it well, this is a patient, this is as a different patient, but a large man who actually got a Piriformis syndrome from edema in his gluteus muscle from laying on his hip all day during a long operation. Typically, what I do is take the skin and pericranium laterally, and then take the muscle inferiorly, leaving a cuff for later closure. So you've got this kind of two-layered exposure down to the bone, put a burr hole right over the junction of the transverse sigmoid sinus, and then do a craniotomy. And I do an actual craniotomy. Sometimes we do end up drilling a little more bone here to expose the medial sigmoid sinus. And I usually trough this with the acorn bit so I don't run the footplate down here and risk injuring the sigmoid sinus. This is just what it looks like. We just use fish hooks so there's nothing in the way of your hands. I do always attach the Budde Halo retractor, but we don't often use fixed retractors as you'll see. But it's kinda nice to have if we need it. To start with, I always open the dura inferiorly here. I just make about a two-centimeter durotomy, and then have your assistant just hold the dural flap open, and then you can sneak in here and see this glistening arachnoid. That's just a more magnified view. And then you can incise that with the arachnoid knife and that releases CSF. And then even in a large person, this posterior fossa is nicely relaxed. You can get in there and do your operation. At the end, we just close up the dura, put the bone back, sew up the muscle cuff and then sew up the scalp. So let's look at some video of surgery. So this is the most straightforward operation. This is a patient who had intractable right face pain consistent with trigeminal neuralgia. You know, there's lots of ways that people do MVD for trigeminal neuralgia, including some really slick ways with small incisions. But I have to admit that I want the residents and fellows to kind of learn one way to safely get in and out of the posterior fossa. So I'm kind of a one-trick pony with these operations. I kind of do it the same way all the time. I overheard the residents a couple of years ago joking that, you know, if I had operate an L5 disc, I do a retrosigmoid craniotomy. I don't think that's quite true, but that's kind of the idea. For this operation, for trigeminal neuralgia, I actually open the dura a little bit differently. I learned this from Dr. Tew in Cincinnati when I did my fellowship in 1997. So for this, we open the dura along the sigmoid transverse sinus. So I'm leaving a little bit of a cuff of dura here, and this is the sigmoid sinus over here. And then this just I think helps protect the cerebellum a little bit. I think Aaron likes to do kind of the old dandy incision for these operations, that works well. One of my colleagues, Dr. Polik, does just a straight linear incision and a small craniectomy and, you know, some people now do it with the endoscope and do a about a quarter sized opening. But I find this gives you enough room, and it also gives you the kind of reassurance that if a petrosal vein tears or a vein over the cerebellum tears or something, you have the ability to open the dura wider and you've got great access to everything in the cerebellopontine angle, and that'll really give you the ability to do any operation you wanna do. So we can tack up the small dural opening, and we can actually even use the dural flap to protect the cerebellum a little bit. You don't need much more of a dural opening than this. That's about the smallest dural opening that I do for this operation. And the first thing I do as we enter the upper cerebellopontine angles. I'm looking for that petrotentorial junction. So this is the tentorium here, this is the petrous bone here, and this is the junction. And of course, the first thing I wanna look out for is the petrosal vein. You don't wanna put too much stretch on that or tear it. I like this case as a demonstration because the arachnoid was not very friendly. The arachnoid was very thick in this patient. And so getting in there was not all that easy. I have to say, when I started doing this operation, I was very cavalier about taking the petrosal vein. And for no particular reason, I've gotten more conservative about that. I try and preserve it if I often can. And I have found over years, one of the ways to preserve it is to take the time to sharply remove all the arachnoid around the petrosal vein. Because it's often that arachnoid that'll put it on tension and potentially run the risk of evulsing it out of the petrosal sinus just from a little bit of retraction on the cerebellum. So now we've opened up the cistern and you can see down here is the trigeminal nerve. And now I'm exposing the eighth cranial nerve, just getting the arachnoid off of it. So again there's no traction whatsoever on the eighth nerve. Now this is just finishing up, getting all the arachnoid off the petrosal vein so it's not gonna be stretched as I wanna gently retract it to get a better view of the trigeminal nerve. I know a lot of people monitor, for instance, the ABR while they do MBDs for trigeminal neuralgia. I'll just say I don't. It's one of the operations I don't use neuromonitoring for. I just try to not obviously put any stretch on the eighth nerve. So now, this little artery here is the subarcuate artery. It's going into the subarcuate fossa just above the eighth nerve. It's not going into the internal auditory canal. It runs right through the superior semicircular canal, and it dead ends in the bone, so that's a safe artery to take. Now that I freed up all the arachnoid, I can push that petrosal vein superiorly. I don't have to take it and I'm getting a pretty darn good view of the trigeminal nerve. This is the right trigeminal nerve. It's much deeper than the eighth nerve. And if I open up this arachnoid just above, you can see this is the motor root under my instrument, and then the sensory root. And so we open up this arachnoid to get a look to see if there's a vessel here compressing. And of course the most common vessel we find is the superior cerebellar artery. And sure enough, the superior cerebellar artery is definitely loping down in contact with this trigeminal nerve near its dorsal root entry zone. And as I try and mobilize it, there's this vein here, right there, that's kind of in my way. So the artery behind and the tiny branch contribution to the petrosal vein is in the way and he's gotta go. So with the bipolar on very low power, we just make sure we coagulate that. I have to admit, I really like this lighted bipolar. At first, I thought it was gonna be kind of a gimmick, but I really like it. I think it's really beneficial. So let me just cut that vein. You noticed I started using straight micro scissors, but I couldn't see the tips well. So then I went to a curved micro scissors, and that helps when you're working in a kind of a small place. Now you can see I can really elevate both divisions of the superior cerebellar artery out from away from the trigeminal nerve. And now I can get a really good look at where the trigeminal nerve is leaving. I can look at its superior side and now its inferior side. There's a tiny little vessel running along the superior side, but clearly that superior cerebellar artery is the culprit. So now the last thing to do is just to pad that up. This is just some shredded Teflon felt, and we just wedge that in there. Here in Minnesota, I call this making a sweater for the nerve. So that'll just keep that superior cerebellar artery basically mobilized superiorly well away from the trigeminal nerve over its entire course from the brainstem to where it enters Meckel's cave. I like to leave this little bit of arachnoid up superiorly there. Right up there, to kind of hold that Teflon in place. Now, as I mentioned, there's that little tiny artery. I don't really hold out any suspicion that this little artery here is a culprit in causing trigeminal neuralgia. But if, for instance, the patient doesn't get better from this operation or the pain recurs at a later time, I definitely wanna make sure that I feel I have completely 360 degrees decompressed this nerve. So I do put a little piece of a Teflon felt between that guy and the trigeminal nerve as it leaves the brainstem. So for me, that's a pretty standard microvascular decompression of the trigeminal nerve in a kind of a great way to get introduced to operating in the cerebellopontine angle. So it gets a little more complicated when you start dealing with the other cranial nerves. And the next video we can go to is a 54-year-old woman who has neuralgic ear pain. So she's thought to potentially have geniculate neuralgia, which is a rare diagnosis. I've done six of these operations in the last more than 20 years. It's hard to know why people have neuralgic ear pain, and so frankly, almost always I do everything I can if I'm going to explore them to make sure, number one, this isn't a rare type of trigeminal neuralgia. So I always explore the trigeminal nerve, just like the last operation, that's what we're doing. There is no vascular compression in this patient, but I'm gonna put a piece of Teflon felt between the superior cerebellar artery here and the trigeminal nerve here just to make sure there's never any in the future. And now I'm gonna go down and look for nervus intermedius. So this is opening up the arachnoid between the lower cranial nerves, nine, 10, and 11. There's nine, there's the roots of 10 there. And this is the flocculus of the cerebellum. There's always thick arachnoid holding the flocculus to the lower cranial nerves. And I think it's a very important step to release that. Dr. Rhoton always used to lecture about the infrafloccular approach to be able to see the facial nerve where it leaves the brainstem. And I have found that is the absolute key to look at seven and eight at the brainstem, and certainly to find nervous intermediate. So now I'm pushing the flocculus superiorly and I'm opening the arachnoid between the flocculus the ninth nerve. And as I do that, you can see the eighth nerve here and the facial nerve easily comes into view here right to where it leaves the brainstem at the pontomedullary sulcus. And now what I've done is I've just reached in with a one millimeter otology hook and I've hooked the nervus intermedius, and now I'm gonna cut it, and I'm trying to not cut the tiny little vessel that's running with it. So I'm holding the nerve with my right hand and I got the arachnoid knife in my left hand, and I just wanna cut that nervus intermedius, and there it's done. And then the last thing I do is I cut the ninth nerve in case it's a rare form of glossopharyngeal neuralgia. And so that's the conclusion of that. So a little bit trickier. Now this is a patient with hemifacial spasm. So this is a second most common functional disorder after trigeminal neuralgia. So very similar exposure, also on the left side. So in this patient, interestingly, I think this is instructional because the arachnoid was very unfriendly. The patient denied any history of meningitis, but had very thick opaque arachnoid. You can see this really large vertebral artery swinging up a little bit in our exposure here. Ninth nerve here, and just trying to get all the arachnoid separated so I can do this infrafloccular exposure here and obviously worried about making sure I don't injure any of the little perforators off the anterior inferior cerebellar artery, that is often running with seven and eight. Seven and eight are kinda hidden in this thick arachnoid up here. So it takes a bit more effort in time to get that exposure I just showed you for the geniculate neuralgia case. And you can see one of those little perforators here that I was worried about that you have to kind of go slow and protect. So now when I release all that, I can follow nine and 10 back, push the flocculus superiorly. There's some choroid plexus, and now we really see the culprit. We see this loop of the posterior inferior cerebellar artery and a branch of the anterior inferior cerebellar artery that are both crossing the facial nerve where it's leaving the brainstem. And by pushing the flocculus superiorly in that direction, it protects the eighth nerve. You don't put any traction on the eighth nerve that way. I do monitor lateral spread and I monitor the auditory brainstem response when I do these operations. So once I get the vessels mobilized up and off, then just like with the trigeminal neuralgia, we put some pledgets of Teflon felt in there to keep the vessels mobilized up off the brainstem. It's obviously a nice prognostic indicator if the lateral spread seen on the intra-operative EMG goes away. But if it doesn't, I've still had success with this operation. I don't do too much in terms of other exploration. I think we get a good lock and the bigger the vessel, I think the more padding you need to try and get it mobilized and padded up. So that's for hemifacial spasm. So now let's look at some tumors. I think these tumors are the best way to start operating tumors in the cerebellopontine angle. This is a very pathognomonic, of course. This is diffusion weighted imaging, bright diffusion. Signals kind of like CSF on T2. This is a young woman who only had some hearing loss and tinnitus, but this is characteristic of an epidermoid. And we can show this video. So this is the right side, same exact opening and exposure. Some surgicel covering the cerebellum and I always start inferiorly. So I look at the inferior aspect of the cerebellopontine angle. And when we start, as we're looking in, things look pretty darn tight. We see the 11th nerve there and the 10th cranial nerve fascicles up here. And so what I really wanna do is exactly the same thing that I did for the other cases, and that is widely open up the arachnoid so I can separate the cerebellum from the cranial nerves and get a good look around. I once heard a seminar where they asked a lot of prominent surgeons, you know, "What two or three instruments would you want if you were stranded on a desert island and had to do neurosurgery?" I have to say for me, one of them would be this arachnoid knife. I use this a lot. It's just a curved beaver blade, and I find that really is a valuable instrument. The other is the Sundt suckers. They're variable suckers, come in different sizes. Of course developed by Dr. Sundt, former chairman, and very famous cerebral vascular neurosurgeon here at Mayo Clinic. So when we open up all this arachnoid, all of a sudden, the cerebellum relaxes back, and we get a good look at the lower cranial nerves, and you can see the typical pearly appearance of an epidermoid deep to the cranial nerves. So now we can continue to open up the arachnoid and we'll look superiorly here in a moment. So very characteristic appearance of this kind of pearly silver looking tumor. Now, this is superiorly, this is actually the trigeminal nerve. She did not have any numbness preoperatively, but you can see how intimately involved this epidermoid is in her trigeminal nerve. This is the eighth cranial nerve back here. And so I'm just trying to separate the tumor capsule, which is the actual sort of neoplastic portion of an epidermoid. Most of this is just sloughed off skin of course. This is all the stuff that's at the bottom of your shower at home, but it's the lining that's the thing that generates this that you wanna try and separate from the nerves and the vessels and the dura and the cerebellum and remove. So it's often hard to tell what's arachnoid and what's tumor capsule, but I try and remove it all. Once you get into it, you can see, you can just suction away the contents. It's avascular, so it's really nice. And then you can see the basilar artery comes into view. Again, through just a standard retrosigmoid approach because the tumor pushed the brainstem back, I've got this great view of the basilar artery. Obviously, you wanna be very gentle because of these little perforators coming off the basilar. Obviously, if you injure any of these perforators, the consequences can be devastating for the patient. So I always take a lot of time. Now, you know that there's no important vessels up here then. You're in a kind of a clear zone, but there is a nerve that runs up there, the sixth cranial nerve. So I can't be too aggressive yet until I find the sixth nerve. So now I go back, this is the eighth nerve. This is nine and 10 here. I'm working in that window between eight and nine, and you see this vessel here and you know this has to stay with the brain. There you can see the facial nerve, gets kind of pulled out from behind eight as I manipulate the tumor. Couple of these epidermoids don't really have feeding arteries, so to speak. So every artery you see has to stay with the brain. This component of the tumor was really stuck. And then now I can see the sixth nerve. This is the sixth nerve here, and this tumor was really adherent to the sixth nerve, but just with some time and fussing, we're able to get it out. This would be the other instrument I would take on my desert island that I'm using here. This is the Rhoton number six. It's not sharp, but it's got a nice fine end to it that's great for dissecting tumors, nerves, and vessels. So as we meticulously kind of get this out in pieces here, now you can see the six nerves that enters Dorello's canal and comes back. This is the vertebrobasilar junction there, and I can manipulate the sixth nerve off and then sharply cut the attachments to free it up. I'm a little bit more, let's say cavalier with the motor nerves. They tolerate this manipulation much better than the sensory nerves, particularly the eighth cranial nerve. But I would not expect this degree of manipulation to cause the sixth nerve palsy. And in fact, in this patient it did not. So we can remove this tumor here between eight and nine and get it freed up from the brainstem. Now this is superiorly, this is the tent up here. This is the fifth nerve, this is actually the third nerve. So that's the oculomotor nerve, we have a good view of that. This is the fourth nerve and we just wanna release the tumor capsule in the arachnoid from the fourth nerve, and it kind of springs up behind the tentorial inside dura a little bit. And all this is at the end. So again, this is the third nerve way down here, and I'm just looking to make sure I did not leave a little tumor up above the edge of the tentorium. I don't doubt, Aaron, you're kinda laughing at me for using a mirror. It makes me look like an old guy. But honestly, I find it works fine. If, you know, really slick people can stick a endoscope in here and look around and get a great look as well.

- You know, it maybe, It's actually more difficult to use the endoscope by the time you bring the whole setup. But sometimes it's worth it. So if you really have to really feel like there is a tumor and you really need to look panoramic, I think then an endoscope. But if you have a hunch that there is no tumor, you just wanna confirm, the mirror works beautifully.

- Yeah, yeah, it's much better to work with an endoscope if you're gonna to do additional dissection. Let's go on to a few maybe a little more challenging chores. This is just the pre and post-op DWI imaging. So you can see at the end we have a diffusion negative scan. We were able to maintain her hearing. This is a preoperative on your left, and postoperative, it suggests the hearing got better. I don't know that I believe that so much, but at least we didn't make the hearing worse. I think she just studied for her hearing tests so our word recognition score got that. Of course this is kind of the quintessential tumor for the cerebellopontine angle. 80% of all cerebellopontine angle tumors are vestibular schwannomas. And we might as well start with a small one. This is a patient that had really just a primarily unilateral tinnitus that brought him to medical attention. His audiogram does show some hearing loss here in the right ear at the highest frequencies. He's actually got some high frequency left side in hearing loss as well. Some of that could be just hereditary or noise exposure, but he's pretty young to have an audiogram that looks like that. And let's have a look at this operation. So this is a small right-sided tumor looking into the right cerebellopontine angle here. We're looking at the eighth nerve. This again is the subarcuate artery. You have to worry, is that the labyrinthine artery or the artery to the internal auditory canal? But it's actually going into this little fossa here in the bone. So it makes me confident that I can take that. I'm not gonna put hearing at risk by taking that vessel, and I feel I need to do that because I need to get this loop here of ICA down away from where I wanna work, 'cause I wanna see sort of the crotch in the nerves where the tumor is coming out of in order to safely get this tumor out and try and preserve the cochlear nerve function, and of course the facial nerve. So just as before, we wanna release all the arachnoid so we can work around in there. And I wanna get that vessel out of the way. Also, so it's not in the way in my ontology partner when he comes in to do the drilling. So now we can really get a much better idea of the landscape of this tumor coming out of the eighth nerve here. And we can see some superior vestibular fibers here. I think you can get the sense that there's a nerve coming up this way. And so this is a small tumor, so there's no point in starting to work on the CP angle component until we get all the drilling done. So this is just opening the IAC about five to six millimeters. Here we make a good trough above and below the IAC, and the otologist thin this bone down, and then just kind of flake it off. I'm really lucky to work with a group of just super talented neurotologists here in Rochester. And now I'm just gonna open the dura of the internal auditory canal to really expose as much of the tumor as I can and the relevant anatomy. And again this arachnoid knife just works real nice for that. Then we can fold that back, and we really get a good idea of the superior vestibular nerve running here. So now I wanna go back and develop a plane between the vestibular nerves and the tumor capsule, as I hope I can. That little feeding vessel on the tumor is gonna have to go so I can kinda get in there and actually do the work. So again, this very fine tipped 0.5 tip lighted bipolar works great for that. You want the bipolar on very low amplitude so you don't get heat spread to any of the nerves. So now this is a Rhoton number 11, which I think works great for separating tumors from nerves or vessels from tumors. So here I can get into the plane between the superior vestibular nerve and the tumor capsule and kinda separate that. And ultimately then I can just look around the corner and see the facial nerve there, that white nerve there. So I obviously wanna verify that I haven't made a mistake and thought the vestibular nerve was the facial nerve. Because in this case, I elected to cut the superior vestibular nerve so I could better define the plane between the tumor and the eighth nerve. So there I cut the superior vestibular fascicles, and that allows me to fold that back. And now we can get a really nice look, I think at the plane between the tumor and the eighth nerve. This, I'm gonna say, is a nice tumor because it's fairly firm. So now I can elevate it up out of the eighth nerve and get it to kinda deliver itself and that'll make it easier for me to also see and dissect it away from the facial nerve. Because of course the worst thing we encounter is any facial weakness in a small tumor like this. So now you can see the facial nerve underneath here, right there, and I can dissect the tumor nicely from it 'cause I've cut the superior vestibular fibers already. And so once I get it freed up all the way out as far as I can into the internal auditory canal, this is a superior vestibular nerve, this is facial nerve, that I'm able to dissect the tumor off of. And now basically I wanna just flip it the other way and do the exact same thing with the inferior vestibular nerve and the cochlear nerve. Those nerves were pushed way down along the inferior margin of the IAC, but I can dissect this tumor. Sometimes it's helpful to bulk some of the tumor, but in this case we could kind of just keep it intact and keep working. You can see the dura on the deep side of the internal auditory canal, that blue down here, that's just dura. The inferior vestibular and cochlear nerves are along here, kinda hidden out of the current angle of the microscope. And here, I just wanna make sure I'm getting out to the very end. I'm not leaving any tumor in the fundus. At the end, we always look with the mirror or the endoscope, but here it looks like these are just some residual superior vestibular fibers. I think this was a superior vestibular nerve tumor. And so now we can just cut those and deliver the tumor. And now we have a good look. This is facial nerve cut into superior vestibular. We're gonna change our angle of the microscope. And now we're gonna see this is actually, the cochlear was in there, and this is just looking at the eighth nerve coming back to the brainstem. So that's a small of vestibular schwannoma. We can go to the next slide. This is just the postoperative MRI at three months. There's often this kind of linear enhancement that you see here. We don't think that means anything. And this is just the postoperative audiogram. He did lose some hearing with that adventure there, but still a very aid-able ear with 90% speech discrimination. This is a little bit of a larger tumor, but still not a large tumor. This patient had a tumor that only measured 2.4 centimeters as we look across here. It does have this cystic component up here. And interestingly, he'd gone deaf in that ear several years earlier, but what was really bothering him was trigeminal neuralgia. And otherwise, this would be a tumor that would be quite appropriately treated with stereotactic radiosurgery, for instance. But because of his trigeminal neuralgia and he was already deaf, we counseled him that probably we should remove this. So we can just go with this video. So this is looking into the left cerebellopontine angle. This is a nice demonstration. Everybody I've ever operated on has a small vein that goes from the inferior cerebellum and brainstem to the jugular bulb, and that's what this vein is doing. This is the jugular bulb there. And you just wanna make sure you don't tear it out of the jugular ball when you're getting access to the cerebellopontine angle. So if it's in my way, I just coagulate it and cut it, and I make sure I don't injure the lower cranial nerves with my coagulation. This is the 11th nerve coming up and I'm just opening the arachnoid, and now some of the 10th nerve fibers are coming into view. And just like before, we've separated the arachnoid. There's been really decades and decades of discussion about our vestibular schwannomas intra-arachnoid tumors, or inter-arachnoid tumors, meaning is there a layer of arachnoid on both sides of the tumor? I think Dr. Yasser Gill probably gets credit for bringing this up first in his book about brain tumors. Professor Kano from Japan and Professor Sureshnia from India have also written extensively about this. It's an interesting question I don't know the answer to. But what I would say is I find it's important to try and release all the arachnoid off the tumor and get right down on the tumor capsule. This is now the ninth cranial nerve here and the 10th cranial nerve fascicles. Now we can see actually this is some eighth cranial nerve that we were just seeing there. This is now looking at the kinda dorsal aspect of the tumor. Again, just trying to get the arachnoid freed up, which allows them the cerebellum to relax back. Often just stimulate the 11th nerve to make sure that the patient isn't pharmacologically paralyzed and the monitoring folks are paying attention. For a tumor like this, we just make a wide opening into the capsule and internally debulk it, and then we can start working around the margins. I really liked this case. I'm showing you this case because people rarely talk about the vasculature as it relates to vestibular schwannoma, but this patient had several findings that made this no very large tumor challenging, and this is one of them. So this is a loop of ICA here that's running up on the sort of deep side of the tumor. It's gonna make a loop up here, and then it's gonna head back to the brainstem. And up here somewhere, it's gonna give off the artery to the internal auditory canal. And you don't wanna make the mistake of seeing this vessel here and then saying, "Oh, that's the artery to the internal auditory canal," or, "That's a feeding artery to the tumor." It's definitely not, that artery belongs to the brain. And if it's injured, it can result in a stroke that can cause a defect in the middle cerebellar peduncle. And that can cause some hemiataxia. It's not a devastating stroke, I have to say, but it can affect patients. And if this is his dominant hand, it can have some real implications. So we wanna free this vessel up and we wanna free up all its little perforators that are going back to the brain stem. And you can see also now the facial nerve just poked its head into view here. If I change my view again to this infrafloccular approach, then I've got the eighth nerve here, and around the corner, I've got the seventh nerve there, and this little guy here is actually nervus intermedius, right there. So now I can see all three nerves. And once again, I wanna get that vessel separated. I don't wanna make a mistake and coagulate that guy. So we have to get it freed up from the deep part of the tumor capsule before we can work on that aspect of the tumor. And one of the, I'd say, common mistakes I make as I leave too much tumor bulk before I start to work on the capsule. So now I'm coming back inside. I really like the Sonopet for this. And I just internally debulk the tumor. You don't need a very high setting. It's also nice, as you recall, this patient had a big cystic component superiorly, and right there we enter that so we can inspect inside that cyst. Just take away a little more tumor, and that gives us a nice, good view, and I can say, "Oh yeah, that's the inside of that cyst." That must be compressing the trigeminal nerve. And now that I've really got it thinned out, I can work on the capsule much easier. And you can see that there are some important perforators that are coming off and going back to the brainstem. And so we have to dissect those free and protect them. And this just gets harder and harder the bigger the tumor gets. But for a tumor this size, we've at least got a good fighting chance. So that's some eighth nerve fibers I'm retracting up on. The patient's already deaf so I'm not so gentle with that. This is one of the rare times we use a fixed retractor. So this is just the interface with the tumor and the middle cerebellar peduncle, and you can see this branch of ICA really wants to stay stuck to the tumor, the planes are not really favorable. Finally, we get it freed up. So we've protected this vessel here in this other branch. This is the eighth nerve on stretch here, and because the patient's already deaf, I don't see a, there's certainly no reason in preserving any of those fibers. So I just come across them. And you can see, and, John Golfinos taught me this a long time ago at a course in Memphis we both participated in, that there's almost always this branch here that runs between eight and seven. And if you're cavalier and really aggressive in cutting the eighth nerve, you can injure this artery. So you have to be, even when the patient has no hearing, and you know you're gonna cut the eighth nerve, you have to be careful of this guy here that runs between seven and eight. So now I can lift up the tumor capsule and start the meat of the operation here, dissecting the seventh nerve off the tumor capsule. This is the nervus intermedius here, which I'm trying to save but it's having a bad day. It's really not cooperating. It's very adherent to the tumor capsule. And oftentimes the tumor capsule will just elevate up off the brainstem. But in this case, it's really adherent. As you can see, I got that loop, Whoops, sorry. I got that loop of ICA down off of the tumor, so that's clear. But just getting this tumor to come up off the brainstem is really getting difficult for me. And you can start to see also the facial nerve is starting to do this. It's starting display out here, which is an indication that this is not gonna be an easy day. It's very common course for the facial nerve to run kind of inferior to superior. This is the Rhoton number two, which sometimes is a nice instrument to help develop the plane between the tumor capsule and the facial nerve. But again, this one is really difficult here. It's not wanting to come. So now when we stimulate, we stimulate proximally here and we get a good signal. Then we stimulate these fibers over here and we get firing from the facial nerve at low amplitude. And then we come across. And even when we stimulate over here, we also get firing. So it indicates it's starting to display out there. So now I'm gonna try and find the superior edge of the facial nerve. So I'm working superiorly, just releasing the arachnoid over the superior aspect of the tumor and trying to separate the superior vasculature. So we know the branches of the superior cerebellar artery and some of the petrosal venous system will be in here. So we gotta be a little bit ginger about how we do this. Now we can separate that and get a good look and see if we can see that leading edge of the facial nerve as it's coming up over the top of the tumor. And it's running here and it's not very friendly. So since I know the facial nerve is coming up over top of the tumor, I can come back here and be a little bit more cavalier on the inferior aspect. And now basically I'm stuck. I can't go any farther here 'cause the facial nerve is doing this, and it's stuck. So I ask my colleague, Dr. Driscoll, to come in and start to work from distal to proximal. So this is the Sonopet. Again, this bone cutting aspect of the Sonopet works great to open the IAC. So this is Collin Driscoll here, and he's gonna find the facial nerve out, distal in the IAC after he's done with the Sonopeting away all the bone. And he can free it up, and now we can see the facial nerve and the IAC. I have to admit it helps that he's left-handed and I'm right-handed. I think you're left-handed, Aaron. So you gotta work with a right-handed orthologist then.

- Yeah, I am left-handed. My orthologist is right-handed in fact, so that's a good thing, it works great for a special endoscopy procedures because I stay on the left side of the patient, he stays on the right side and it's like a beautiful dance, it just really works beautifully.

- So this is at the end. Here's the facial nerve running out like this. This is the trigeminal nerve here, including its motor root there. And as you recall, this patient had trigeminal neuralgia. And sure enough, just like the very first video we looked at, he's got a big loop of the superior cerebellar artery that's running down and compressing the trigeminal nerve, and probably the tumor was also elevating the nerve up against that. So just as before, we put some Teflon in there and make a little sweater for the nerve, and that's the end.

- Did you leave some tumor on the nerve, Mike, or were you able to take off the tumor all the way?

- It's a great question. I think there's a tiny bit of tumor right there. So this is what we would call a near total resection, meaning we can't see this on the postoperative MRI, but I think there's a little tumor capsule there. So in a 65-year-old, we stopped there. He had some, I'm gonna say, mild facial weakness. He was a House-Brackmann three postop, and he was a House-Brackmann one by three months, and his trigeminal neuralgia was gone.

- Beautiful work, beautiful work.

- So that's kind of my tour through the CPA angle there.

- Yeah, these are great pearls of technique. The videos are very superb. You know, Michael, you started with more basic principles, and escalated to the more difficult ones. I think that's great value. I think that dissection techniques are so important. Some of the techniques that I use very frequently, which again is a matter of preference, doesn't mean one is better than the other, is a bimanual technique that a lot of European colleagues use. I use a tiny tumor forceps, grab the capsule, and then I use a very fine forceps and grab the arachnoid sheath, then pull away the nerves very gently. That really works, it's, in my opinion, a lot more efficient, but it's also a little bit more tugging and pulling if you know what I mean. I think your tech-

- I use that technique also, Aaron. Dr. Lenzino actually developed some forceps, and so I use those, he's got a really fine one and a one that's just a little bit bigger. And I agree with you. Again, I think we have to give Professor Samy credit. You know, him and his disciples, Marcos Tatagiba and Florian Roser in Abu Dhabi, those guys I think, I've really become a convert to that technique.

- Yeah, I do believe, especially in the sitting position, which we know is so valuable for these acoustics, obviously it's more difficult for the surgeon. But using the bimanual technique in combination with the fine forceps, you know, peeling off things, it's just such an extremely quick way to do this operation. But again it may not be always as gentle as the videos you showed here. I really like the way you handle the cerebral vascular structures. It clearly demonstrates your utmost respect for normal anatomy, for preserving the arachnoid membranes, for avoiding significant traction, which really is a sinequanon of good outcome for these patients, especially in the posterior fossa. One has to be patient, one cannot lose his or her patience. And it's critical to remain, you know, energetic. And some of these more complex tumors, really the fatigue can set in later and can really compromise the technical expertise and really in fact affect adversely the surgical judgment, something we don't talk about. But I do believe that fatigue is a major factor in major complications and poor outcomes later in the operation. But again the surgeon can himself or herself not be aware because really our decision is so tainted that we're not aware of when we're fatigued. Don't you agree?

- I think that's such an important point, Aaron, I think it's right on and the really the voice of experience, I think. I've mentioned Collin Driscoll, my ontology partner. He's always fond of saying that it's hard to make good decisions after 5:00 PM.

- And it is the truth.

- And I think that's true. Obviously we don't try and rush these operations. I always tell my residents and fellows and young neurosurgeons that nobody cares how long the operation takes the next day. It doesn't matter as long as you have a good outcome. But I think there is absolutely a role for learning to be efficient with your movements so the fatigue is less.

- Yeah.

- And probably too, I have to admit as I've gotten older, it's gotten harder. And so I think that's such an important point.

- Yeah, this is one of the unspoken pearls that I think we don't talk about. Surgeon fatigue, surgeon lack of, you know, focus, and all of us have different days. There are days that I feel like I can do anything, and I do, and I walk on water and can do any major operation with better outcomes than anyone else. And there are days that I just feel like my processor's not just as sharp as it used to be. And that's what we call situational awareness. Such an important point. Surgical intelligence of a surgeon watching himself or herself. And when you're so good at surgery, you have a wider bandwidth to watch yourself. When you have less experience, your processor is so overwhelmed with every step of the operation that you really don't have the bandwidth to step away and really monitor your own movement. What we call emotional intelligence in regular daily activities. But I believe there's a surgical intelligence where the surgeon becomes his or her mentor, and that's something that I have personally worked on and I lecture a lot about, is that developing that automatic steps where you have extra bandwidth to monitor yourself and make good decisions. I also believe like Collin that after 5:00 PM there has to be an extremely good reason to operate. In fact, I have no fear and no sense of disappointment in terms of staging an operation. If the surgery is going after 4:00, looks like fair amount of work left, we're gonna close. We're gonna come back a day or two later. Nothing wrong with that, and it is absolutely fine. We just can't let our arrogance or ego to get on our way. Surgeons fatigue is an extremely important in outcomes. The other techniques that I really like to do is you have made a lot of your exposure standard. That means the Lenzino fellow knows one way to do it that saves you energy. You don't have to be there because every time you're doing something different, that takes a variability out of the equation, which is again is another sinequanon for lean. In other words, when you take variability out of system, you make it a lot more efficient, there is a much less error-proof, and I think that's a factor that I always use. I always position three positions in my surgeries, supine, lateral, and you know, it's supine, lateral and three quarter prone. That's really it, I don't do anything else besides that. I always position the patient exactly the same. Always I'm across the table, no matter, you know, a left or righted, or use lateral if it's right-sided to the scrub nurse. So when they set up my room, there is so much sort of least variability that it makes it a lot less for people to call me, to be confused, to know what's going on. And so every time I do almost all the exposure standard, and so when I come in, there's much less chance of problems. And I think this allows me to take more time to be efficient and have people help me out without me directly supervising everything at every moment. Does that make sense?

- Yeah, absolutely. And I'm the same way. And the other thing, you know, when you talk about sort of that situational awareness, the other thing I found over the years is, you know, it's been really helpful to operate, and especially early on, where, you know, Collin and I were both sitting at the microscope talking to each other. Either he was operating and I was assisting or I was operating and he was assisting and saying, "Do you think I can pull this harder? Do you think we can cut here? You know, why do you think we're getting stimulation here?" And I gotta say having four eyes and two brains thinking about the operation doesn't double the efficiency or the expertise. I think it quadruples it, it really makes a difference. And I have to say now, you know, we started Skull Base Fellowship several years ago, and that's just been fantastic to have fellows come from other institutions and teach us things. And I think your point also about staging the operation is also very important point. Jeff Jacob, who was our first fellow, who's now with the Michigan Ear group up in Southfield, Michigan may stage all their large tumors and he has fantastic results doing that. I have to admit, we haven't done it much here, but I think it's an important point. And particularly if you're doing complicated skull-based exposures, there's I think real value in saying, "You know, we're gonna do an extended petrosectomy approach one day and we're gonna bring the patient back and start operating on the tumor early in the morning the next day.

- Yeah, no question for petrosectomy approach, especially post the petrosectomy, I routinely stage. I never actually in fact do both together because by the time you're done with the exposure, in that case, it's one o'clock no matter how good you are.

- Yeah.

- And this is the reason why I personally don't favor a translab approach because by the time you're done with the exposure, it's 1:00 PM. And I do believe there is an extremely important cortisol curve for a surgeon when you're really fresh between 8:00 to 11:30. That's just when you have lunch. No matter who you are, even if you're sitting in the office, it doesn't matter, you're gonna be overwhelmed, bombarded with questions from everywhere, unless, you know, you're taking a rest at home, which not all of us ever do. So by 1:00 PM, even though if you haven't operated, you're not in your sharpest, you know, sort of mode. And so that's why I think translab either way puts you sort of at a critical part of the operations for a giant tumor sometime around or a big tumor, we shouldn't really be doing that for giant tumor, for a sizeable tumor, around 3:00 or 4:00 PM, which is just when your cortisol curve start dropping. And that's actually the most, the highest number of accidents I found that appears to happen at that time. And there's a good reason, because we're just less sharper. And if you can't drive as well, you better not be doing your complex brain surgery, you know what I mean?

- We do about 60% of our vestibular schwannomas retrosigmoid and about 35% translab. And then we do about only 5% middle fossa. But for a really giant tumors, we, really, I strongly prefer the retrosigmoid approach. And one of the reasons is just what you said, we get to the tumor sooner. It also is a more panoramic view of the cerebellopontine angle.

- I agree, I'm gonna close with a statement that somebody, I think one of the Queens of England said when the surgeons were barbers and butchers, in fact. As you know, it was Royal College of Barbers more than 200 years ago in England, where we come from. We're not really technically physicians in England or in UK, they are in fact called nestors, not doctors, as I'm sure most of our viewers know. And as a barber at that time, which we all are from barbers, hopefully from not butchers, although some of the butchers at that time did surgery too. I think the Queen in 1601, one of the Queen Elizabeth mentioned that the surgeon, the best surgeon has to have three characters, and this important fact from 1601 to today really holds up so extremely well. They said there's three most important character in a surgeon and I'm sure you know all three. The first one is eyes of a hawk or an eagle. We all know that, visualization is such an important factor. What we really she meant is that you have to expect. It is so important as in skull-based surgery, this statement that I'm gonna to say right now is to, I'm okay to be wrong 1,000 times to say there it is and be wrong, but I don't wanna be even right once to say there it was and I was right. And I think that is so important in skull-based surgery to be important. So eyes of a hawk or an eagle is number one. Number two is hands of a woman, and obviously for them is to be very gentle, to really be light when you handle these tissues, and it's so important, so well-characterized that doesn't get respected in our surgery. And the last one, which also I think is important, it brings myself to the closure, was the hearts of a lion. And I think hearts of a lion means that we have to learn from our mistakes, do not dwell on them. In other words, keep it as a memory. I think Ronald Reagan had a pretty good statement maybe you can tell me that comes to our mind, says that trust, but verify.

- Yeah, right.

- And I think that's a such important thing in posterior fossa surgery, that when we make a decision, we wanna make sure we have made a good decision, at least one or two ways before we complete things. And I think at the end of the day, hearts on the lion also comes back to the point that you cannot, by any means, let your mistakes get on your way to so much affect your future that really compromise the care of future patients. And ultimately, it's the passion. The passion you have to have for microneurosurgery. Nothing is more important for you to get better self-reflect as I have said 1,000 times, to be better every time you do this procedure. So with that in mind, Michael, I wanna sincerely thank you for being a dear friend, a good mentor, superb surgeon, and such a great academician, and spending the time today to share with us your incredible personal technique.

- It's my pleasure, Aaron and I'm so grateful that you invited me and the work that you do with the Atlas is just amazing. It's such a great service from the neurosurgical community. So thank you very much.

- You're welcome, thank you, Michael.

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