Franco and I, together again, are going to discuss kind of what we're going to do in the lab now this afternoon. I want to start by pointing out, I'm sure you all know this, but it took me a long time as usual to kind of come to this epiphany, but if you think about what we do as neurosurgery, for most of our training, most of our careers, we think about that bone is in the way. We're just going through the bone to get to what we want to do to get to the operation. You know, you do a craniotomy to get to the aneurysm. You take off the lamina to decompress the nerves and so on. If you're an otologist, what you're interested in is in the bone. So you're really dissecting bone, and that's what we're going to do this afternoon. And so if you kind of have that mindset, I actually think it's somewhat helpful. Franco's going to give you the nuts and bolts of what we're going to do, and I'm just going to talk a little bit about the philosophy of when do I go pre-sigmoid versus retro-sigmoid. And really what we're talking about is doing the posterior petrosectomy, the retro-labyrinthine pre-sigmoid approach, so a hearing preservation operation versus just a straight retro-sigmoid craniotomy, which, you know, you've all done hundreds of times probably by now in your training. Again, I have nothing to disclose. So there's lots of ways to operate in the temporal bone, right? The old standard that we all know. Earlier this morning, we did a middle fossa and anterior petrosectomy. What we're going to move to now is posterior petrosectomy. And you can certainly add a partial labyrinthectomy. So some people talk about taking off the posterior semicircular canal to give you a little bit more room. Many people say you can do that pretty liberally and then you just pack it with bone wax and you can still save hearing. The otologists that I work with, you know, I would say we're more conservative. We're either going to take the labyrinth out or make an effort not to violate the labyrinth. And then, of course, you can go trans-lab, which is one thing I really want you to see this afternoon, the difference, the difference in the exposure between leaving that block of bone versus taking it out. I think you'll find it's really quite striking. And then as Jeff mentioned this morning, if you want to get more into the clivus, if you want to get more anterior, you can actually go trans-cochlear, but you have to transpose the facial nerve. And hopefully you'll all do that this afternoon. In fact, I don't have any doubt you'll all do that this afternoon because you guys are a fantastic group of surgeons. And to try and keep that facial nerve intact from where it's leaving the brainstem to where it's exiting the stylo-mastoid frame, and that's your challenge for this afternoon. And then as you move inferiorly, of course, you can go far lateral. And about the time I was in residency, everybody was coming out with these approaches, far lateral, extreme far lateral, trans-condylar, extra far lateral. It seemed to be you had to have your own perturbation on that if you were going to say you were a skull base surgeon. So I came up with the insane far lateral. So sometime that ear's just gots to go, you know. And we like to say we're so lateral, we're medial. This poor woman had a radiation-induced osteogenic sarcoma and we had to take out her whole temporal bone. So this is a picture I really like from Rob Jackler's book, and it just shows the different exposure that you get. So this is sort of the standard retro-sigmoid. And what I want you to pay attention to is this dotted line. So retro-labyrinthine, trans-labyrinthine, they start out the same back here, but something happens here. You've got to preserve this if you're going to preserve hearing, right? So you take out this bone, but then you leave this block of bone here. Of course, if you go trans-lab, you take that out. And then if you go trans-cochlear, you're way up here, and that means over-transsecting and over-sewing the ear canal, moving the facial nerve, and that'll get you even more forward. But what we're talking about is changing your angle, retro-sigmoid, pre-sigmoid, retro-labyrinthine. It doesn't look like it's that different. But there are some real advantages, I think. Number one, it does remarkably shorten your working distance. So if you're trying to get to something up here near the petroclival junction, being able to come this way actually really shortens that working distance. It doesn't seem so from this picture, but it actually does, and you'll get a chance to see that. It certainly gives you a more direct lateral view of the brainstem, and it communicates the middle and posterior fossa because you cut the tentorium, as Frank will go over, where you can cut the tent from a retro-sigmoid approach from underneath, but this is certainly, I would say, an easier way to do that. And it also allows a bit more ventral reach around the anterior brainstem. The disadvantage is you have to do it. So I work with a phenomenal otologist. I have kind of the same setup that John talked about, where we've been working together now since 1999, so going on 15 years. And I mean, he can do it in about 35, 45 minutes. You know, if we're letting one of the senior residents do some of it, I've seen it take up to two hours where you're kind of sitting around wanting to get in and start working on the tumor. You really got to remind the otologist, this drilling is not the operation, okay? It's just helping us get there. It certainly puts the transverse sigmoid sinus at risk because you completely decompress it. And including, as Jeff showed this morning, the vena libae can be at risk. There's certainly a bigger risk of CSF leak because you're going to open the antrum of the middle ear. That's a really important landmark, and you're not going to be able to close the pre-sigmoid dura, so CSF can just wash in there out the eustachian tube, and you're off to the races if you don't close correctly. The question is, you know, does it put the hearing at greater risk because you're working around the inner ear? And you need a fat graft, which you don't need with a retro-sigmoid operation. So when I think about am I going to use this or not, I sort of ask these questions. Well, where's the pathology? Is it middle fossa, posterior fossa, both? What's the relationship to the IAC? Is it in front of the IAC, behind the IAC? Is the pathology intraaxial, extraaxial? Is the temporal bone specifically involved in the pathology or just a bystander? And of course, what deficits does the patient already have, and what are they willing to accept? And is the approach I choose going to be the difference between a curative and a non-curative operation? And probably, you know, that's the most important question. What problem am I solving by increasing the complexity of the operation? So here's just an example. You know, this is tumor in the middle fossa, right? So you don't really need to work in the posterior fossa to take this tumor out, and likewise, you don't need to work in the middle fossa to take this tumor out. You know, where is it in relation to the IAC? So this is the same pathology, right? Anybody want to shout out what this is? Does nobody want to shout out what this is? Epidermoid. Yeah, right. So epidermoid. So this is, you know, this would be easy through a retrosigmoid, right? It's posterior to the IAC. This is kind of high and ventral to the IAC. So for me, this would be a good case for a posterior petrosectomy. You know, this is an intraaxial lesion. This is a completely extraxial lesion. Anybody want to take a guess if that one's intraaxial or extraxial? Yeah, I didn't know either. Yeah, intraaxial, that's the winner. This turned out to be a gangliocytoma coming out of the brain stem in a 12-year-old child. And then, of course, is the temporal bone involved? So this is just a chondrosarcoma in the temporal bone. So being able to drill the temporal bone, obviously, is very important because that's where the pathology is. CT scan is really important in terms of your surgical planning in relationship to the inner ear structures and the petrous apex. And then I also honestly think about some of the other radiographic findings. So you know, when you look at this tumor here, you look at this whole picture, is this a good skull head for a pre-sigmoid approach? And I would say, no, it's a terrible one because this guy's got tiny little petrous bones. You know, if you look at this line from petrous bone to petrous bone, it's nearly a straight line across, whereas, you know, if it was coming back like this, you'd have a much better shot of working here. You know, you're going to have a very steep angle with just a little bit of pre-sigmoid dural. So this is one that I would say I would not consider some type of pre-sigmoid approach, trans-lab or posterior petrosectomy. Same thing, I think Jeff alluded to this. You know, so this was a much bigger tumor here in the posterior fossa, but this is just the inferior extent of the tumor. And as you can see, if you're coming pre-sigmoid, the jugular bulb is going to be right in your way because this is a relatively high jugular bulb. So you want to come in and drill through here and you're going to run right into the jugular bulb. And I will say that some people talk about no worries, you just decompress it and push it down. But in my experience, what that means is you drill into it, venous blood starts shooting out, you pack Surgicel into it and push it down and then work around the Surgicel. So you know, you can try this afternoon, try and take off that thin shell of bone over the jugular bulb and not see blue latex today. It's extraordinarily difficult. I think that the dura that makes up the top of the jugular bulb is basically the periosteum of the bone. So I'll just show a case that I think illustrates all those examples. So this is a woman originally from Lebanon, now living in Kansas, who had a six-month history of ear fullness, tinnitus, not feeling well, myalgias, headache. And she did have an ancient history of vertigo. She had a normal neurologic exam and she got an MRI for all these complaints and showed a lesion and then it was followed and seven months later it had actually grown. So this is what it looked like. So if you know, go back to the original questions, you know, it's posterior fossa and middle fossa, temporal bones just kind of a bystander. It doesn't actually go into the IAC but some of this dura enhances. So I thought this was a very good case to operate through a posterior petrosectomy. So that's what we did. It turned out to be just a WHO grade 1 meningioma, as you might expect. And this is what the post-op scanned. So these are the pre-op and these are the post-op. And so we were just basically able to take all that dura out with the tumor. She does have a little bit more of a conductive hearing loss because I like to put a little fat in the antrum to prevent CSF from coming out. So that probably affects that. Some other tumors I think that are really good for posterior petrosectomy. So these epiduramoids, trigeminal schwannoma when you want to work in the posterior fossa, in the middle fossa there's the post-op. So you can open up Meikle's cave as Carl showed this morning really well. I got to say I don't like operating into the posterior fossa from the middle fossa. But you could easily have done this all through the approach that you all did this morning. And then this is a pathology that I think lends itself really well to posterior petrosectomy approach. This is another small town in Iowa, John. So this guy has this problem. So anybody want to say what that pathology is? Yeah, cavernous malformation, sure. That's no surprise. I thought this was going to be all just a big clot. It turns out this thing was hard as a rock. This was a big calcified rim down here. But he'd had two clinical and radiographic hemorrhages over about two years' time. He had left hemibody numbness and rare dysesthesias. So I thought that he's a young guy that we should operate on that. So we did that. And that's just what his post-op scan looked like. So we could come in this way and do a little corticotomy between five and eight and get into this thing and work around it and take it out. So I've really become a fan of posterior petrosectomy for brain stem cavernous malformations that come to present to a lateral surface. The final comment I'm going to make is, so when I finished my fellowship with Dr. Tu, of all the approaches that we've done and we're going to do, this was really my favorite, the posterior petrosectomy. I really like this anatomy and I really found this useful for things. And I thought this was going to solve the problem of petroclival meningiomas. So I was initially very enthusiastic to operate every petroclival meningioma through this approach as long as they had hearing. And it occurred to me as I went along, so this was one I did through posterior petrosectomy, but look. So why did I leave that tumor there? What was in the way that prevented me from doing a better job, do you suppose? A lot of crickets. So the fifth nerve, you know, the fifth nerve was on the wrong side of this tumor and so I didn't want to bang up the fifth nerve anymore. And how about this one? Why didn't I get more aggressive right there? What nerve was I worried about injuring? In fact, what nerve, for extra points and a chance at the bonus round, what nerve is at most risk, do you suppose, with taking out a petroclival meningioma? It's the most common cranial neuropathy after... Well, at least I got answers, yeah. So it turns out it's the fourth nerve. So as the fourth nerve comes into the tent, you're a little bit stuck because, you know, if you keep resecting tentorium, which is what you want to do, you're going to take the fourth nerve with it. So that's the issue. And in fact, you know, when I looked at, you know, my first series of probably 25 of these, I only had one patient where I really thought I cured them. This was a young woman who presented with trigeminal neuralgia, relatively small tumor going into Meikle's cave and now you can see Meikle's cave is clear. So I, you know, I've only had, that was only one out of about the first 25 where I thought I really made a difference. You know, and then it occurred to me that, and this is interesting because of what Jeff said earlier. So this was a case I was contemplating doing a posterior petrosectomy on, but the vena labia came in very early into the tentorium and basically was right in the way of where I wanted to cut the tentorium. So we just went retrosigmoid and took the tumor out. You see I operated her in 2003. I just saw her back last month in routine follow up 11 years later and so far so good. So I've really tempered my enthusiasm, I would say, for posterior petrosectomy for petroclival meningiomas. I think it's a great approach for brainstem cavernous malformations that present somewhere to a lateral brainstem surface, epidermoid tumors, trigeminal schwannomas, and if I'm really going to tackle a bad petroclival meningioma, I talk to them about giving up hearing in one ear and doing it extended trans lab and then you've got a short working distance, a lot of exposure, and I think I can do a little better or just do it retrosigmoid. And just to point it out, so just over, you know, about seven, eight years, you know, I do, for every posterior petrosectomy I do for a tumor, I do seven retrosigmoid craniotomies and I think there's kind of a trend here where I'm doing it a little bit less. I have just a couple final things to say. One is that if you like this stuff, if you're not just completely tortured by now, I'd invite you to come to the 25th annual North American Skull Base Society meeting. It's going to be in Tampa, Florida, February 20th to 22nd. There's going to be a pre-meeting course at the Camels Lab, it's called. It's a fantastic lab there in Tampa. And then finally, I just have to thank Dr. Robertson for the invitation to come here. If you talk about somebody who refuses to rest on their laurels, I think it's Dr. Robertson. You know, he's been president of the AANS. He was president of the North American Skull Base Society and he really got, I think, all the faculty involved and it's just a treat to come to Memphis and if the Nobel Prize Committee called me tomorrow, it would not be as big an honor it is to get an email to will I come and help with this course. It's just great. And you guys are doing a phenomenal job, by the way, and you're kind of, one of your big tests is going to be this afternoon to keep that facial nerve intact. Thanks very much.

neurosurgery

posterior petrosectomy approach

otologists

advantages and disadvantages

brainstem cavernous malformations