Challenging CP Angle and Petroclival Tumors

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- Hello, colleagues and friends. Thank you for joining us for another session of the virtual operating room from the Neurosurgical Atlas. My name is Aaron Cohen. Our guess today is Dr. Michael Link from Mayo Clinic. Michael is a tremendous surgeon who is the past president of the North American Skull Base Society. And currently is the co-editor in chief of Skull Base Journal. Michael has a huge experience. One of the biggest in the world with resection of posterior fossa tumors and skull base lesions. He gave us a lecture just about a month ago about a resection of tumors and functional and hyperactivity cranial nerve syndromes. And this second lecture will cover more of a complex skull based tumors that are recording a number of different technical pearls, which make a definitive difference in the outcome of the patient. So Michael I want to thank you again and I look forward to learning from you regarding managing complex petroclival skull based solutions. Please go ahead.

- Thank you, Aaron. It's really a pleasure to be back with you all. As Aaron mentioned, I'm at the Mayo Clinic in Rochester, Minnesota. I don't have any disclosures. None of the devices, techniques, anything. Do I have any financial interest in. And as Aaron mentioned, the last time we spoke, we discussed a microvascular decompression surgery for things like trigeminal neuralgia, geniculate neuralgia, which is very rare. Glossopharyngeal neuralgia also very rare, but just to get a sense as to how at least I approach operating in the cerebellopontine angle. And then we showed a case of a fairly large cerebellopontine angle epidermoid, and then resection of a small vestibular schwannoma and a more medium-sized vestibular schwannoma. But what I wanted to talk about today are some more complex. I'm gonna say, some more complicated tumors that we often deal with. This is just an example. This is a 39 year old woman from up the road here in Minnesota, who noted a four year history of progressive right-sided hearing loss. And when she finally came to medical attention, she had only 35% word recognition in the right ear, but fairly good pure tone hearing, she had a 24 decibel pure tone average. Also what really brought her in and which prompted imaging is she had several months of progressive headache, worse with Valsalva or even when lying flat. She found she wanted to sleep kind of propped up on pillows, and she did have some mild subjective dysphagia, but no episodes of aspiration pneumonia, Frank aspiration, or change in her voice. And this is just some snapshots of her tumor. And I'll go through this with you here kind of slice by slice starting inferiorly. You start to see the tumor develop there. This is probably, let me just change that, thank you. This is probably the hypoglossal canal. And then as we come up, you can see this is the jugular foramen that the tumor extends into. And then here it's into the internal auditory canal and it continues to extend superiorly up to the tentorial incisura. So this is what I would call a cerebellopontine angle meningioma. And one of the problems, one of the reasons why I certainly have never published my series of cerebellopontine angle meningioma or petroclival meningiomas or petrotentorial meningiomas is because nobody can agree on exactly what that tumor is. How do you really make a classification for that? But this is what I would call a cerebellopontine angle meningioma. And while there are many skull based approaches, the approach that I would use for a tumor, like this is just the same standard retrosigmoid craniotomy that we talked about last time. So this is a right suboccipital retrosigmoid craniotomy. We can see we've now opened the dura. This is one of the rare times that I use a lumbar drain because I don't think there's any way to safely access the cisterns. So before I opened the dura, I take CSF off through the lumbar drain to make sure everything is nice and soft and relaxed. And of course you can't really do anything until you debulk the tumor. And we know just based on the imaging and the general anatomy, that we're along way from anything important. So once I look at the posterior pole of the tumor and see there are no cranial nerves getting pushed posteriorly, I can coagulate and open and use the ultrasonic aspirator to try and debulk it. And like most meningiomas it's fairly fibrous. As you take the tumor off the petrous temporal bone, which you're about to see now is what always happens to me is you get some pretty exuberant bleeding from the petrous temporal bone, because a lot of the blood supply is coming through the bone. And so I can try and try and try to bipolar this, but I can never get this bleeding to stop because it's coming directly right out of the bone. So some different techniques is you can take the bone cutting device of the ultrasonic aspirator, or you can take a diamond bur or you can try bone wax, but still with a fair amount of tumor there, I could just put gel foam and get it to stop. This is now looking superiorly. This is the tentorium here, petrous temporal bone here. This is the petrosal vein here. which I try and leave intact, and I could get over the top of the tumor, and I start to see a nerve here. And as I stimulate this doesn't stimulate, but deep here, that stimulates as the seventh nerve. So that's the seventh and eighth nerves, and they're coming up over the top of the tumor, which in my experience is almost always the way it happens. So as we further debulk the tumor, and we can start to roll it in, we can see the eighth nerve here as it's running along towards the top of the tumor eventually to find the IAC somewhere out there. And so the trick so to speak, is to get the arachnoid separated, to free up the eighth nerve, and we can follow it all the way back to the brainstem. And you can see it's very adherent. This is a branch of vagal that's running with the eighth nerve. We have to preserve. And we know that the facial nerve is gonna be just deep in here, somewhere in this location, in this general area. Now thankfully, her hearing was already pretty poor going into the operation. We could not monitor an auditory brainstem response in this patient, and clearly I couldn't make too much progress. So I gotta further debulk the tumor, and this is now looking inferiorly. And as I work inferiorally here, this is the 12th nerve way in there deep. So I can stimulate that. And then I can come back and find the lower cranial nerves. So after I've located those, this is once again, now I'm trying to get the eighth cranial nerve and the seventh cranial nerve to come off the tumor. So I can safely debulk more tumor to try and get down to the jugular foramen. And as I work here, this is still all eighth nerve. It's very splayed out from there to there. So I thought, "Well, maybe that's the seventh nerve." But it's still eighth nerve. So that's just stimulating. And then once I get that more freed up, then the facial nerve comes into view hidden on the other side of the eighth nerve. So that's all eighth nerve that we're seeing in the field here. And that's the facial nerve there as it leaves the brainstem under that sucker. And so once I get the arachnoid separated from the eighth nerve, then we can follow the facial nerve from proximal to distal, from brainstem all the way out to the internal auditory canal. So there are now facial nerve comes more into view as it's running along the deep side of the eighth nerve. So now we can stimulate it at the brainstem. So that allows us to more safely debulk tumor in the cerebellopontine angle. And then we wanna come down and get the lower cranial nerves freed up. And certainly that, in my opinion, is the biggest risk. The lower cranial nerves, even though majority are motor nerves, just like the facial nerve, they tolerate the manipulation less in my experience. So here some lower cranial nerves heading up to the jugular foramen, including this one that's kind of wrapped up there stuck in the arachnoid. That's the ninth nerve here. So we can be a little bit more cavalier with that guy. Then we can see more of the 10th nerve, fascicles coming up like this. We have to get them freed up from the tumor capsule so they'll swing inferiorly. So there we go now finally, we're getting the ninth and 10th nerves completely freed up from the tumor capsule. And I periodically stimulate as I go and make sure that I'm not injuring them as we're working. This is the ninth nerve and the 10th nerve here. Fascicles coming up knowing the jugular foramen and is somewhere around here. And so I'm giving the jugular foramen which is approximately here kind of a wide berth. I'm gonna intentionally leave this cap of tumor here so that I am not tempted to coagulate too close to the nerves 'cause certainly in my experience, the two things that cranial nerves really hate is stretch and heat. So I try and leave myself a little bit of an insulated buffer there of tumor at the jugular foramen. And certainly, earlier in my career, I always left more tumor than I intended to. And then you can go back and before you finish the operation and take more out, but it's more efficient if you can kind of estimate it correctly the first time around. So after we get the majority of the tumor out of the cerebellopontine angle, now we can take this bone cutting device on the ultrasonic aspirator. And just like with an acoustic neuroma operation, take off the bone over the internal auditory canal. So this is now the internal auditory canal that's been opened here. That's the eighth nerve in the internal auditory canal. And using these Cueva dissectors, Roberto Cueva who's an otologist in San Diego, developed these and we really like them. So now this is the seventh and eighth nerves in the IAC and just detaching the tumor from around the porous, this is the superior porous of the IAC and the inferior porous, and just taking this bone off, not only does it take some of the blood supply of the remaining tumor, but it really improves your working space. So now we can just roll that tumor down and completely free up the seventh and eighth nerves here now. And it also allows us to mobilize the seventh and eighth nerve superiorly and get the tumor along the ventral aspect of the IAC in a very safe manner. And so that's the facial nerve at the brainstem, as it's running here, These are the lower cranial nerves as they're running there, we'll get a better look at them here. That's sixth nerve there. That's 10th nerve there. That's more 10th nerve fascicles proving that everything's okay. And we can look down and find the 12th nerve again. That's right there. So we can go back to the slides. So this is just what the post op image looks like. You can see this is the, you know, pay attention to this area. This is that little bit of tumor that I leave at the jugular foramen and to make sure that I don't injure the lower cranial nerves. And as we come up, we can see that we did well with the internal auditory canal there. There's a little bit of dura enhancement. There's the seventh and eighth nerves going into the internal auditory canal. Then we see the trigeminal nerve there as it goes into Meckel's cave. And that's that case.

- Hey Mike, I really like that technique. Something that I wanted to just emphasize that I completely agree with you in this case, it's use of lumbar drain. In these cases, if you don't use lumbar drain, you're gonna come into brain and is gonna be so tight and it's posterior fossa, it's gonna toothpaste out. You cannot get to the root of the tumor. You cannot devascularize it. Because you didn't devascularize it, it becomes a vicious cycle. You have to debulk it. And then you're gonna have bleeding and a little bit of removal, hemostasis, removal, hemostasis. The length of surgery is gonna be significantly increased. And by the time you get to the critical part of the operation, you're so fatigued, the outcome is affected. And it's a classic example of how in skull based surgery, one detail that was missed can really lead to a series of events that cause a poor outcome. Even if it was a minor, you know, maybe omission, the cascade of events of a minor omission can really lead to a problem. So I always say in a small space of posterior fossa, if you can get this tension down early, if the obstructive hydrocephalus is not present and you really can bring the tension down. They say a relaxed brain is a relaxed surgeon. And so just try to calm everything down with decreasing tension when you can reach the cisterns early on and therefore be able to devascularize and find the neurovascular structures very early on, because everything is relaxed and that can be a huge advantage for the later steps of the operation. Thank you.

- Yeah, I agree. Thanks Aaron, for those comments. We'll just move to what I think is a little bit more challenging of a lesion because now it's ventral. It's in front of all the cranial nerves. And this is I think a pretty classic example of a petroclival meningioma. This is a 40 year old woman from just south of us here in the state of Iowa, who noted shortly after she delivered her second child, a healthy baby boy, that her right face had persistent tingling. And then about two months prior to presentation, she noted persistent headache with no nausea or vomiting. And those two symptoms prompted evaluation. And once again, I'll just run through the imaging. So again, starting inferiorly working superiorly, you start to see here's the internal auditory canal. Here's the tumor of course. And you know that the cranial nerves are gonna be between you and the tumor. As you go in, you can see the basilar artery there. And as we go up, it becomes really very difficult. In my opinion, to find the trigeminal nerve, the tumor extends right up to the back of the infundibulum to the pituitary stalk. It pushes the basilar artery. Fortunately it pushes the basilar artery with the brain stem. The really scary ones are the ones where the basilar artery is separated from the brainstem. So in a way, this is a bit favorable in that regard. You can see it extends superiorly up to the optic chiasm, which is here, and a little bit higher yet. And so, you know, there has been just decades of debate about what is the best approach for a tumor like this. And I would say to you that I think all of the approaches here would be very reasonable. And I think very thoughtful, talented, experienced surgeons might use any one of these approaches and achieve excellent results. Of course, when you get into these approaches where you're opening the inner ear, there's no chance of saving hearing. In this patient had normal hearing going into the operation. This is a picture from Rob Jackler's book. It's a very, I think, a famous picture, but it just shows the different bone removal. You can go retrosigmoid like we did in the last case, you can go retro labyrinthine or posterior petrosal. Or you take this bone away, but you leave this, you leave the inner ear and this remarkably shortens the working distance to the petroclival region. But you have to look around this block of bone. If you go translab you take this away. If you go trans cochlear, you take even this away, but in the standard trans cochlear, the true trans cochlear, you also have to mobilize the facial nerve, which is not only a big undertaking, but it puts the facial nerve a lot of risk. I will say how I like to approach these lesions is through the posterior petrosal approach. And I learned this when I was a fellow in Cincinnati in 1997, 98 with Dr. John Chu and Harry van Loveren and the rest of the crew there. And these are pictures from Dr. Chu and van Loveren's atlas, Tonya Heinz, as the artist, she's remarkably talented in most atlases, most papers talk about doing this. They talk about putting a burr hole above and below the sinus and above and below the sinus, and then connecting the burr holes to do this kind of L-shaped craniotomy. I would say to you that I don't think you should do it that way. How I do it as I make a trough, I drill a trough over the transverse signal junction, and I drill a trough over the mid part of the transverse sinus. And then I put two additional burr holes in, and then I just connect the dots. And that can be very safely done to give you this craniotomy. And this is just what it looks like. So you do the craniotomy and that exposes the transverse sinus. Then you do a wide mastoidectomy, the horizontal semicircular canal and the mastoid antrum, and you take off all that presigmoid bone. You leave the facial nerve and the fallopian canal. You protect the posterior in the superior, in the horizontal semicircular canal. So you have a chance of preserving hearing, and it exposes the superior petrosal sinus. That's kind of the schematic of how it looks. And then you will open the presigmoid dural here in the subtemporal dura here. And then you clip and divide the superior petrosal sinus, and then you can cut the tentorium all the way to the tentorial incisura being careful of where the fourth nerve is. And that gives you this kind of panoramic view of the posterior fossa. You have the trigeminal nerve, you have the sixth nerve, the basilar artery, the seventh, eighth cranial nerve complex. And you're limited inferiorly by where the location of the jugular bulb is. So sometimes you can see the lower cranial nerves, but if it's a high jugular bulb, you sometimes can't. This is just what it looks like in a real life person. So you have the transverse sigmoid sinus decompressed. You have the jugular bulb down here. This is the labyrinth, this block of coated capsule bone. You have the temporal dural here, the retrosigmoid dural here. And then of course, the presigmoid dural here. Just a more close up view. And when you open the dural this is the view you get. So there's the motor root of five, the sensory root of five, the seventh, eighth cranial nerves there. And then you can look in and see all the way down to the basilar artery there. There's a very zoomed in view, eighth nerve here, fifth nerve here after the tumors out. So let's look at this video of that petroclival meningioma. So this is after the craniotomy towards the end of the drilling. This is the endolymphatic duct in sac coming out of the posterior semicircular canal. This is my colleague, Dr. Driscoll, the otology partner I work with completing the drilling. And this is what it looks like at the end. Once again, we have this block of preserved labyrinth, the sinuses here, and obviously you have to take great care of the sinus. So I cover it with a little surge of cell and want to keep it moist the whole case, because we aren't going to retract on it. We're gonna move it around. And we want to make sure that it's not going to thrombose and we're not going to rub an instrument along it, or tear it open or something disastrous. So this is just opening the presigmoid dura right in front of the sigmoid sinus. And I'm cutting across the endolymphatic sac as distal as I can. And then I turn the cuts anteriorly just above the jugular bulb which is here, and just below the superior petrosal sinus, which is here. And what I'm doing here is I'm holding onto the endolymphatic sac. I'm trying to hold it closed because I don't want the endolymph to leak out and make the patient deaf. So I'm gonna sew it closed. I just put a figure of eight, three old silk stitch. I think the risk of deafness in doing this is very, very low. So this is kind of the technique or the way I've always done it. So you can just tack that up, have a little retractor here on the sigmoid, and now we can open up the arachnoid and get into the cistern. Because this tumor didn't extend far inferiorly, just to the point that Dr. Cohen made, I know I can get into the cistern and get things relaxed. So I didn't use a lumbar drain in this case. This is now opening up the subtemporal dural. So the transverse sigmoid sinus junction is here. So I opened just above it. You can see the vein of Labbe here, which obviously we have to protect. And now we can gently lift up the temporal lobe working right on the tentorial surface. Once again, this is the labyrinth here. This is the tentorium, and I'm looking for the tentorial incisura, 'cause I want to know the trajectory that I'm gonna use to cut the tent. So we adjust our angle here and right there is the edge of the tent. So I know that I can then cut in this direction. So I have to clip ligan the superior petrosal sinus. If it looks like a small sinus, sometimes I just coagulate it with bipolar and cut it. But usually it's pretty big. And I think it's good to put these little clips on it. And you really only have to leave yourself just a wide enough aperture that you can get the scissors across and cut the tent. So I'm also looking, is there a large superficial petrosal vein coming into the superior petrosal sinus and fortunately in this case, there is not. So then I can put my second clip on the superior petrosal sinus. And now we can just cut the tent. And it's always a little bit of a more difficult undertaking than I want it to be. The tent is extremely vascular. So right now, no problem 'cause I have my wet clips, but the minute I extend past where my clips are, you always get pretty exuberant venous bleeding from the edge of the tent, which you can just coagulate and help shrink the edges back. It's amazing how much tension the tentorium is under. You saw how close I put those clips together, but immediately as I start to cut the tent and certainly once I get it completely cut it really springs open. So now we just wanna continue our cuts all the way to the incisura. It's tempting sometimes to say, "Oh, we don't need to go all the way to the incisura we have enough room now, we can see supratentorial." But it's really important to complete that cut. And of course, as I mentioned, the thing we're worried about is where is the fourth nerve? Sometimes the tumor will push it against the edge of the tent. If we cut too far anteriorly, we could cut the fourth nerve as it's entering the edge of the tent. So I'm always looking as I'm cutting. And right there is the fourth nerve protected in its arachnoid. We could cut the tent and not injure the fourth nerve, and now it just widely opens up this space. So there's the brain stem down deep in the cerebellum, more superficial. And so now we've really widely, widely opened up our working room here for this deep tumor. So this is now looking in, this is the trigeminal nerve sensory and motor root, and you can see the tumor kind of surrounding its entrance in the Meckel's cave. And I just want to point out, even with all that work, we still have to work kind of under and around the labyrinth if we're gonna save hearing. There's the eighth nerve down there. So now we're looking below the eighth nerve. I wanna see where the sixth nerve is running. We just saw a glimpse of it down there and now we follow it above. So this is the sixth nerve making a turn into Dorello's canal, completely surrounded by tumor. And besides the fourth nerve, it's the sixth nerve that is really at risk with petroclival meningioma surgery. So we wanna free up their rachnoid and really see where that six nervous is turning into Dorello's canal. Now this is gonna be our main working window above five and below the fourth nerve, which is way up there. Now this, because we cut the tentorium, gives us this really nice open window to work in to debulk this large tumor. So now this is, we can coagulate and open the tumor capsule really aggressively. As most meningiomas, you know, it's moderately fibrous. it won't go up the sucker. You have to open it sharply and debulk it with a punch or the ultrasonic aspirator, but we've got a fairly decent view here. So now we can make a good window in the tumor, just like we did with the CP angle meningioma. And we can start to more aggressively debulk it with the ultrasonic aspirator. Of course we gotta be careful or think about where's the basilar artery? Where are the branches of the basilar artery? We don't wanna inadvertently come through the deep, the deep part of the tumor. I find once the deep area of the tumor starts to move with the sauna pet. That's when we have to be careful and slow down a bit. So this is now looking more superiorly. Here's the fourth nerve, here's the superior cerebellar artery coming around. We wanna release all the arachnoid holding those structures. So when we move them around distally, they're not gonna be tethered back here and have traction put on them. So now this is once again, there's the eighth nerve and the fifth nerve, and we can debulk the tumor in between there because we removed a lot of tumor up here. So now we can mobilize the trigeminal nerve superiorly and give ourselves a bigger window between five and eight. And now we can lift up the tumor. Now that we've got it debulked and find the basilar artery here right down against the brainstem. And this is working along the superior edge. There's the fourth nerve. We got to separate the arachnoid to get the traction off the fourth nerve. And there's the sixth nerve coming into Dorello's canal, which to me is always a little bit of an Achilles heel of the operation. I'm always very cautious around that entry point. This is looking supratentorial now. This is the hyper vascularized tent there, and I'm lifting up the temporal lobe gently with a broad spatula. And I'm finding all this supratentorial tumor that we looked at on the MRI images. Here's the fourth nerve as it's heading to go into the edge of the tent. So we got to keep separating the arachnoid and get the traction off the fourth nerve. And we know there's gonna be one more nerve we're gonna encounter here in deep. Once we get supratentorial part of the tumor further debulked, we're much deeper than the fourth nerve, which is there. And this is right where the fourth nerve enters the tentorium. So we can keep kind of digging it out of the tentorium. And this is always also a very tricky part is, you know, you have to debulk the tumor deep to the fourth nerve. So this is the fourth nerve here. So we're working inferior now to the fourth nerve. And I don't know how to do this other than it takes a lot of time and patience to free things up. So I'm gonna try and leave a little bit of tumor, right where the fourth nerve enters the edge of the tent right there And get the rest of it detached so I can move it out of the way. I use a lot of Papaverine soak gel foam I don't actually know if the Papaverine is really that helpful but I think it's helpful. I use it a lot for vestibular schwannoma surgery as well. The gel foam also nicely protects the nerve from the heat of the bipolar. Then we can detach the tumor from above it. Now we can come up over the apex of the tumor as it was extending high up into the supratentorial space. And what I'm looking for is the third nerve. So I know it's gonna be about at the level, of course, as the basilar apex, the superior cerebellar artery, it's gonna run right underneath it. And there it is. So there's the third nerve coming forward. Now we can free up the tumor from that. This is just a band of arachnoid here. You'll see we'll disconnect. That'll take us back to where the third nerve is leaving the brainstem. So there now we can see the third nerve as it leaves the brain stem and heads forward. This is just releasing it's a rachnoid and this is the third nerve here, tumor underneath it. So there's the superior cerebellar artery. There's the third nerve freed up from the tumor. So now we can debulk it. This is still working beneath the temporal lobe, working out towards the petrous apex. So a little bit frustrating with this labyrinthine bone in the way here, but we can work around it. Fourth nerve again, as it's entering the tent here, trying to free that up to get more of this tumor out here, right at the petrous apex. And this always has to be done sharply. It seems like there's always thick arachnoid adhesions holding the tumor to the fourth nerve. I think these Roatan instruments work so nicely. Just one of the countless things Dr. Roaten did for us. So this is now looking superiorly, looking at the bottom of the optic chiasm. Just to show that we get a good look at that. We're actually kind of did a reverse third ventriculostomy here and got some CSF out. That's again, looking at the bottom of the optic chiasm, and we can just keep working forward along the tent to get that aspect of tumor out. It's up towards the basilar apex. Of course the subtemporal approach is well well-known described by Dr. Charles Drake to fix basilar apex aneurysms. And so now what's really remaining is the tumor that's right at the very peak of the petrous apex. This is tumor here. And with the labyrinth in the way our angles are a little bit limited. But we can still look in there and be able to get this tumor off. And further debulk it, and then roll it in. And I have to say the temptation to just grab it and pull is sometimes overwhelming, particularly as you've had a long day struggling with this tumor, but of course, none of us would ever really do that because of the risk of what's attached on its deep side. So we can further debulk it. And then we can roll it in further. This is the fourth nerve, very superficial there. And get a freed up from its medial arachnoid adhesions. As you recall it was up against the back of the pituitary stalk. So we don't want to pull too hard or not be able to see what we're gonna cut for fear of injuring that. I can debulk it further and so on and keep rolling it in. And finally, a lot of it'll come out. It's absolutely worth the time. I think we're often surprised by how much tumor is hiding out there. And you can see it's got such a broad attachment on both sides of the petrous apex. Once we get that out, then we can get a look around. So there's just more of the papaverine gel foam and take out. Fourth nerve still intact as it extends into the tentorium. This is the third nerve in here deep going forward. Just underneath that is the basilar artery. See after the gel foam has been in there for a long time, it doesn't want to easily come out. You gotta be careful it's not stuck to the fourth nerve and do something regrettable. So there's the superior cerebellar artery there. That's running below the third nerve origin, and then we should be able to see the posterior cerebral artery running above the third nerve to prove that that's what we're looking at. So we'll get a glimpse of it here. The third nerve was pushed up, but there, we can see the posterior cerebral artery, Right. We can go back to the slides. So this is what the postop scan looks like for this type of case. And I have to say all my postop scans for this type of tumor look like this. And by that, I mean, there's a little bit of residual tumor here where the sixth nerve was entering Dorello's canal that I don't wanna coagulate and pull on and hurt the sixth nerve right where it enters Dorello's canal. And as we come up, we can see a little thickening of the clivus dura and a little bit of tumor here in the back of Meckel's cave. I think. And we're a little bit limited again, because we had this labyrinthine bone back here that we kind of had to look around to see that direction, but that's basically, you can see, we did get the, a lot of the supratentorial component. You can see the infundibulum's decompressed, the optic chiasm as well decompressed. This is her postop audiogram. Because we didn't drill into the inner ear, she has good hearing and that's basically kind of the pre and post. And again, it shows even that very anterior tumor that was up here under the chiasm against the pituitary stalk is gone and there's our pituitary stalk intact and so on. So even from kind of a posterior lateral approach, I think you can get pretty far, pretty far interiorly.

- You know, Mike, this is a treacherous case, very difficult, I mean, petroclival lesions are so extremely difficult because it's not only because of technique. It's the marathon that you have to run to get this tumor handled. Really what you've demonstrated is such an honest appraisal of this, because no matter how much you try and how many hundreds of hours you sit there, there's tumor between the sort of layers of the clival dura. There is fair amount of tumor in there. That there's no way you can access because of the sixth nerve that people underestimate. And you can do an incredible job on come out and there is thick sheet of the tumor there. And that's because that's not even within your operative field of view, it's really anterior almost to the clival dural and infiltrated the clival dural swing tensity that's impossible to remove. At the same time you're limited by the cavernous sinus and a fourth nerve. So there's always tumor there as well. So it becomes almost disheartening after all that work. Why doesn't my MRI look like that? But that's the reality. And that's something we have to accept if we want to preserve function. I completely respect you for what you do. And I think that's an excellent way to do it. Along the years, I have just transformed my approach to a retrosigmoid approach with a second stage subtemporal approach. I think I'm not saying that's better. I don't think anybody can say that it's better. I think your approach is absolutely excellent because nobody knows what the right answer is. So much of our resection results is dependent on the anatomy of the cranial nerves, the texture of the tumor, fibrous versus suckable, that those, and obviously vascular encasement. And so, and again, how far medial it is, does it displace the perforators of the basilar? Which you very well mentioned. Because those factors are so overwhelming in terms of recenda resection. That's the approach almost is a much smaller factor. And because of that reason, I have gone through doing a more conservative posterior fossa versus sigmoid approach with tiny resection of the lateral edge of the cerebellum. As you remember Mark Hebrosol used to do that at Mayo Clinic and it gives me a beautiful approach. I knew you were resecting a little bit of abnormal cerebellum, but very small, and it's extremely benign, and it gives you that extra angle that you need to go, and then you'll have to cut the tentorium from below, which is also challenging. And then you close and then come back and do it from above and almost, you know, as you know, 80, 90% of these patients, at some point we need radio surgery

- Yeah.

- Because the, or radio therapy, because the tumor, all these tumors are in pluck there's no, I don't think I've ever seen maybe that's me, but I've never seen a petroclival tumor that is actually really a full call meningioma that aura and plaque, and therefore go all the way up and down and even a gross total resection, which is absolutely impossible. So this is just a different perspective. Doesn't mean it's better.

- Yeah. I think it's a great point, Aaron, and I mean, so many people have talked about evolving to do it that way. And I think, you know, Majid Sammy talks about also, you know, you can do kind of an internal petrosectomy and we're great fans of that approach here. Where you do a retro-sigmoid craniotomy, and you can drill the suprameatal tubercle around the fifth nerve from, from a retrosigmoid approach, which works well also.

- Yeah, that's right. I think that he's described that. I can tell you that that bony removal, which actually we're writing, finishing a paper on about right now, is through using the endoscope, you can expand it more and really do well. However, it's really gonna be difficult to do microsurgery way above, you know, sort of the tent without getting, or anterior, without getting subtemporal.

- Yeah I agree.

- So this stage approach of retrosigmoid, cutting the tent, do the best you can then coming back later, doing this subtemporal approach has worked well for us. It's just the amount of work of a postherpetic sectamy, and number of structures you have to mobilize is so immense that then I think, and if I get the variables that are so important in extent of resection or beyond the approach. Again, this is just one philosophy. Doesn't make it better. I think both works well. Thank you.

- Yeah. Yeah. Yeah. I think it's a great point. I'm just gonna show one more shorter case just to, I just want to emphasize the difference between leaving the labyrinthine bone in place and taking it out. So this final case is a 41 year old woman who originally was from Ethiopia. She and her family immigrated to the United States and she had a four year history of progressive left sided hearing loss to the point that she was fairly profoundly deaf in her left ear, but really had no other neurologic complaints. And finally it came to medical attention that she was completely deaf in one year, which of course is not a normal course of events. So she ended up getting imaged. In her MRI scan, going from inferior to superior shows this. So you can see this broad base of the tumor and extending into the internal auditory canal, again, similar to the first case. But the difference of course, compared to the first case is that there is a lot of middle fossa tumor here, including some that gets in the Meckel's cave in the cavernous sinus. So a much different tumor than the first one there's as much tumor in the middle fossa. I feel as there is in the posterior fossa. And I think your point Aaron is right on that. I think a very, a very reasonable approach is to first tackle the posterior fossa component with a retrosigmoid operation, then come back with the middle fossa operation. The way we chose to do it is a combined operation. Basically what I just showed you for the posterior petrosal approach. But this time we completely remove all of the bone over the internal auditory canal. So this is now the craniotomy has been done. This is the left side. So this is temporal dural pre signaling dural. And once again, this is my partner, Colin Driscoll, he's removing the bone of the labyrinth. So now this is the internal auditory canal becoming exposed here. So he can make really deep troughs, inferiorly and superiorly to the internal auditory canal. And that allows him to drill way out into the petrous apex. I know this is only a 2D video, but that's a really deep hole. So this is kind of a more broad view. And this is a case once again, I did not use a lumbar drain, but what I did do is first I opened up retrosigmoid. So this is just a small retrosigmoid opening here. So I can look in and just open up the inferior cerebellopontine angle, cistern and arachnoid, and drain off a lot of CSF. So now I've got things very relaxed. So now I can open up pre sigmoid just like we did in the last case, identical posterior fossa dural opening. This is the endolymphatic sac there in my, in my pickups. Of course, I don't really care about it because the patient's deaf. But we can get into the posterior fossa and get the plane with the brainstem early on. This is the eighth nerve. So you can see, we can open up the dura all the way out to the fundus of the internal auditory canal, because we got rid of the labyrinthine bone. And so this is now the eighth nerve decompressed, and this is working just superior to the eighth nerve. We can go ahead and debulk the tumor and look for the trigeminal nerve. So now we've debulked tumor. There is the trigeminal nerve, as it leaves the brain stem, there's the motor root of the trigeminal nerve coming into view there. There it is, motor root there. So now I was actually able to resect a lot of the posterior fossa component of the tumor just through what was really a trans labyrinthine approach, a presigmoid approach. Now I'm opening up the subtemporal dura again, we can gently elevate up the temporal lobe and we can see this large middle fossa component of the tumor. We want to release the arachnoid adhesions that hold the temporal lobe to the tumor capsule. Make sure there isn't a big subtemporal vein that we have to look out for. And now we can just debulk that component of the tumor really nicely. And we can get on the posterior aspect of the tumor and see around it, but there's so much tumor. We can't cut the tent in the typical fashion. We have to cut out the tentorium kind of in a piecemeal fashion, but now I've gotten across it, and there is my fourth nerve, nice and safe. And we can just keep peeling it off the tumor as we go. And I think the advantage of this approach is it then allows us to much more efficiently take out large amounts of tumor. So we can further get that big piece disconnected. Get the little feeding vessels that go to the tumor from the superior cerebellar artery. Probably just unnamed dural branches. And then now we can get a lot of tumor out. We've got this big wide opening now, 'cause all the bone of the labyrinth is gone. So I think that is really, really helpful. And this tumor extended far anteriorly, and we know the fourth nerve is up here under this gel foam protected. So now we can also very efficiently debulk this amount of supratentorial tumor. That's extending anteriorly towards the cavernous sinus. So there goes the fourth nerve. We can keep advancing our retractor anteriorly and keep working subtemporal. This is the petrous apex here, a lot of bleeding from the arteries that run through there to the tumor. So we can just take the drill and control that. We've got a much better working angles, view more light in the wound because we've basically gone trans labyrinthine. This is extending forward in the middle fossa here. The cavernous sinus will be right on the other side of that. So we can keep debulking a lot of tumor in a very efficient manner. And again, this is where the fourth nerve is gonna enter the edge of the tent. And so we're a little bit limited. We kind of have to cut on either side of the fourth nerve to keep it intact And we can keep going and debulking tumor and moving anteriorly along the floor of the middle fossa. Go forward again around the front of the brain stem and we can find the third nerve again. And then this is just basically at the end, we've got a big broad view into the posterior fossa and the middle fossa. We can go back to the slides, I think. And this is what the postop scan looks like. So this is a fat saturated image. So this is all fat packing in the mastoidectomy labyrinth, ectomy defect. There's our internal auditory canal. The cochlea is still there. We did not mobilize the facial nerve, but the labyrinth is gone. Some residual enhancement at the distal IAC. And once again, that's where the sixth nerve is running in Dorello's canal. So I left that tumor there and I left this tumor within the cavernous sinus here, but the rest of it, we were able to get out. So that's kind of a modification of the, of the posterior petrosal approach. If you add a labyrinth ectomy, it really in my way of thinking makes it a lot easier or it gives you a much better working, working room just to make you homesick Aaron, this is what it looks like most of the time that we're in Rochester.

- Well, maybe it was a great place. I missed a place. So it's not about the weather. It's about the people. Thank you so much, Mike, a tremendous lecturer, amazing pearls of technique. I can't thank you enough for spending the time editing these videos, which I can tell you, it's many, many hours of surgery, very, very time consuming and requires so much effort. So it means so much to me and our viewers for you to give these tremendous short, tremendous cases and provide us with your pearls of technique, which I personally have learned a lot from as well. So we thank you again and again, and hopefully we can have you with us in the near future Mike.

- Thanks so much, Aaron. And what you're doing with the Atlas is, is amazing. It's a great service to neurosurgery around the world and I'm honored to be able to participate. So thank you Aaron.

- You're welcome and thank you.

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