I know they wanted to record this, so they wanted me to wait until that was ready, but I'll just say a few things. You know, some of this lecture will be a repeat from the point of view of anatomy, and I think that's okay because the anatomy of this region is fairly complex. You know, if I was going to look at the two things that it takes to be a really skilled skull base surgery, one is your knowledge of anatomy, but not your ability to look at a diagram and point out the anatomical structures. You have to be able to know 3D anatomy, rotate it around in your head, and the temporal bone takes it to a whole new level because some of that anatomy is created as you drill out the temporal bone. It's not just laying there out in the open, and so you'll see today in these courses the residents often have a little more trouble doing the temporal bone drilling and dissections than they have with the, say, anterior skull base. And so I guess in addition to just the knowledge of anatomy, I guess the second thing I would say is skull base surgery to me is a perfect example of this concept of lifelong learning. I mean, if I think about where I've learned the most of my skull base surgery, it's probably from these guys in these courses just presenting different procedures one after another. And you just, you keep picking up things from other surgeons time and time again. And if you think back to the early days of neurosurgeons, neurosurgeons used to do a lot of traveling. They used to go and watch other people operate. We just don't do that as much anymore, at least within the United States. But I think with what Jeff Sorenson's doing and his videos and the Rogan Collection, which you guys will have access to, you'll be able to go and see different surgeons operate. I just want to give a little recognition to Dr. Link. This is Dr. Link three weeks ago accepting the presidency of the North American Skull Base Society. So he's a man of influence if you want something in skull base. And then just finally, I want to thank John Robertson. You know, John has put more effort into resident education than anyone I know except perhaps maybe Al Roten. But he's the one responsible for all these resident courses, and so I thank him. And I have another thanks to him. He took me to his private fishing hole last time I was here in Arkansas, and it was so private it had this sign on the side of the river. And I'm not sure what it said because I didn't read it. But I just got to this part. But so this is kind of the skull base approaches that I do. And so looking at it really, kind of everything I do is 14 approaches. And so we've talked about, there are variations of each of these, but we've talked about these and we did these yesterday. So I'm going to kind of talk about these four approaches. Franco went over the infratemporal fossa, and I'll just say a little bit about that. But for this morning's session, we're going to focus on the extended middle fossa. And then this afternoon, I think you'll do a mastoidectomy and a posterior transmetrosal approach and have time to drill out the labyrinth as well. So we're going to just, I'm just going to kind of quickly go through these four approaches and focus mainly on the extended middle fossa. In terms of terminology, this is the one approach that has several different names. I think Harry Van Loveren, I think, was the one who wrote a paper that kind of coined posterior transmetrosal and anterior transmetrosal. But the name that's really stuck is extended middle fossa approach, I think. So that's how I think about it. All right, so infratemporal crani, just to kind of reinforce what Franco said, you know, for the ENT guys, the mandible is kind of in the way and the infratemporal fossa was always kind of a hard place to get to. But for the neurosurgeon, you know, we have access right here through this skull base bone. And I think it's a great way to get particularly to benign tumors, schwannomas. Remember schwannomas, once you get into the tumor and debulk the middle, the edges start to collapse in. And so it's totally different than doing a cancer case where you have to resect the tissue. So you can have kind of small approaches to schwannomas. This is a young woman in her 30s who presented with terrible trigeminal dysesthesia in the third division. This turned out to be a malignant peripheral nerve sheath tumor. But just kind of making the concept that you can get at these from above quite easily. So just a straight line incision down through the temporalis muscle, exposing the root of the zygoma. Looking right at this area of the skull. And in these cases, I don't even do a craniotomy anymore. I just kind of drill out the bone and work through this window for schwannomas. And so you can just get down, get through the roof, and just kind of showing the drilling. And this is the roof of the intratemporal fossa. And you can get into these schwannomas, debulk them with a cavitron, peel them in, peel them in, peel them in. And sometimes even save some of the branches of E3, maybe, if you're lucky. And just showing the post-operative section. So let's just move on to middle fossa and extended middle fossa. Now when we use the term middle fossa, most of the time people are talking about the middle fossa approach to intracanalicular acoustic neuromas. That's the big utility of the middle fossa. But you can also use it for small lesions of the geniculate ganglion. This is a cavernous hemangioma. I just have a question for the residents. What's the difference between a cavernous malformation and a cavernous hemangioma? Anybody know? The residents? Somebody? John, anyone here from your program? John's? What's it? Push on your speaker button. Thanks, Dr. Robertson. So are they the same thing? I always thought they were the same thing, but I have a feeling you're going to say no. All right. You want a consult? Yeah. I think they're often confused in the literature. In fact, Robert Spetzler wrote a paper about this. But they're, to me, totally different pathologies. Cavernous malformations are an intraaxial lesion that are not a tumor. They're a vascular malformation, and they often occur in association with developmental venous anomalies. I don't know if they occur anywhere outside the central nervous system. I mean, has any of the attendings ever seen a cavernous malformation outside the brain? I mean, they're a blood vessel abnormality. Cavernous hemangiomas are a vessel tumor. They're a benign tumor. And when neurosurgeons encounter them, this is the way I think of it, it's in an arc. Most of them are in the orbit. Some are in the superorbital fissure. Some are in the cavernous sinus, and the back edge is geniculate ganglion. I never saw one any other place than in that arc, which, I mean, you can have hemangiomas in the bone, but what they call cavernous hemangiomas tend to occur in orbit. Orbital guys do a lot of these. Cavernous sinus, superorbital fissure, and then for some reason, they can occur back here. So that's a cavernous hemangioma. That's a benign tumor. Totally different than a cavernous malformation. Now, when we start talking about extended middle fossa, then we're talking about lesions a little deeper than the internal auditory canal, and this is just kind of taking you through the spectrum. So you can do schwannomas in Meckel's cave. Obviously, if it was bigger and more anterior, then I would do some kind of orbital frontal approach, peeling the dura off like you guys did yesterday. But if it's purely in Meckel's cave, this is an easy-placed extradural to get to by the middle fossa. You can also use this for Petrus apex granulomas. What's the other popular approach to this these days? Yeah, endoscopic endonasal. So one of the beauties of the endoscopic endonasal approach is you can, through the nose, provide nice aeration and drainage. If you're trying to treat a cholesterol granuloma, the goal of treatment is aeration and drainage that stays open. If you do a middle fossa, you're just taking the whole thing out. It's really hard to maintain aeration and drainage, almost impossible. When I was a resident here with John, we were draining these infralabyrinthine, infracochlear, and they were kind of small little openings. And so now I think if you can get to it through the nose, a lot of people are doing these endonasally. But the problem is the smaller ones that need treatment that are symptomatic are tucked behind the carotid artery. So the issue is you try to come from the contralateral nostril through the sphenoid sinus behind the carotid artery to drain them, but sometimes you can't. So middle fossa, extended middle fossa, is a way to get there. How about bone destruction at the petroclival synchondrosis? What's that likely to be? What diagnosis? Pardon me? Push on your speaker there. Schwannoma? Well, when you have a schwannoma in the skull base, typically there is erosion of bone with smooth bone edges around it. That's one of the CAT scan signs that this is a slow growing, gradually expanding mass. When you have chewed up missing bone, you would think of chondrosarcoma, yeah. So we tend to say if it's chewed up missing bone in the midline, more likely chordoma. If it's along the petroclival synchondrosis, more likely chondrosarcoma. Which is better? Which would you guys rather have, a chondrosarcoma or a chordoma? Why is that? Or what would you just say would be the 10-year survival for chondrosarcoma versus 10-year survival for chordoma? 95 or 60? Not bad. I mean, I would probably say 80% to 90% chondrosarcoma and maybe 50% to 60% with chordoma. So it's one of the sarcomas that actually has a better prognosis than corresponding tumors. And then, petrous apex meningiomas, relatively small ones. You can also use this to get to the upper basilar, but I do a lot of tumors, so I don't do much vascular. But that's another use of this extended middle fossa. So middle fossa approach. There are a lot of acoustic surgeons who love the middle fossa approach. I'm a selective user of this approach. And the way I look at it is this. I pay a lot of attention to the coronal MRIs. Which nerve usually gives rise to acoustic neuromas more often, superior vestibular nerve or inferior vestibular nerve? What's the answer? Do you want a consult? I would say more are inferior. And John? In some papers, there's a, from the, sorry, the Italian guys, 90% they thought were inferior vestibular nerve tumors. I don't think that's right, but it's supposed to be more. Every time I do a suboccipital in a small tumor, I always try to say, is this inferior or superior? And they're always like, it's a high number, or inferior. But I pay a lot of attention to this image right here. One, does the enhancement, and I didn't pick out great images to make this point, but does the enhancement go out underneath the transverse crest or go out above the transverse crest? If it goes above the transverse crest and the middle fossa floor is very shallow like this, then middle fossa is really straightforward and very easy. But if the enhancement is, if the tumor's in the distal canal and the enhancement goes out under the transverse crest and the skull is much thicker, sometimes there's a long way down. And I'd much rather do that by a suboccipital approach. If you looked at facial nerve results, at least in the short term, what's the difference in outcome that's been published between small intracanalicular tumor, middle fossa approach versus suboccipital approach? Which one do you think has better facial nerve results? Yeah, suboccipital, the, you know, to me, if you're doing intracanalicular tumors by suboccipital approach, you should have hardly any patients wake up with a weak facial nerve. Maybe once in a while you'll have a bad one, but they should just come out without much facial nerve. But if you're doing middle fossa, most people have published 10% problems with severe facial weakness. Now, the papers have said by one year later, the results are the same. So most of these end up being temporary. But you can have cases where you have an inferior vestibular tumor underneath the transverse crest, facial nerve rolls right over the whole top of the IAC. And to me, suboccipital approach is fine with bringing an endoscope. You can see all the way out to the distal part of the interauditory canal. So the ability to see to the end of the IAC, in my mind, is not an advantage for the middle fossa because you can't really easily see to the very end of the inferior vestibular nerve by that approach. So I just want to say a little bit about where is the interauditory canal, just from kind of what Jeff talked about. This is a surgeon's view of a right middle fossa floor. And remember the old, the standard teaching was if you take the GSPN and you take the arcuate eminence, this actually is this right here, and bisect them, that's where the interauditory canal is. But in my mind, it's almost always a little more posterior than that. It's not a perfect bisection. And so I never use that or think about that ever during a case. I never look at this angle and this angle. To me, the solution is make sure you have the entire area exposed. So for a middle fossa approach, usually I don't divide middle men and GOR, your framus spinosum. You only really need to get your retractor blade right to right here. And to do that, you can get the dura elevated from the superior petrosus sinus up to framus spinosum. When we're doing extended middle fossa, then I divide this, peel the dura up off of V3 and we'll say more about that in a minute. But if you can expose all the way to here and look at all of this bone, it's really by seeing the petrous apex and knowing, okay, what's in the petrous apex? What's the answer? I'll give you two choices. Something or nothing? Okay. Air cells or bone marrow. Okay, that's it. Air cells or bone marrow. So basically, to me, a landmark that is crucial is this trigeminal depression. Once you know where the trigeminal depression is, all the rest is easy. Air cells, arcuate eminence, meatal plane, petrous apex, trigeminal impression. So I use that to decide where to drill. How far am I from this area back? And I just found that more useful than drawing any angles or trying to figure out where's the external ear canal and such things. Now, this is a drawing from Rob Jackler's book, just kind of showing the typical exposure for middle clostrid case. And I'm going to show a video of a patient that I did. I've worked with five neurotologists in my life, but this was a time where I didn't have a neurotologist. So I did this case by myself, and I'm just going to show the anatomy of the facial nerve, the labyrinthine segment, geniculate ganglion, and the tympanic segment. Now this is a patient who had a hemangioma. This is a cavernous hemangioma, but the video I'm going to show, I lost the films on. But it's just the hemangioma that was in the skull right here. So we're going to see after this hemangioma was in the bone right here, and we're going to see the GSPN, the labyrinthine segment, going into tympanic segment, the distal part of the facial nerve. There's a straight line incision again. And so here we've lifted up the dura, and we're looking at, this is the hemangioma in the skull here. You can see the hemangioma right over the facial hiatus. Stimulating with a facial nerve stimulator. And basically what I would do is stimulate, see if there are any nerve fibers, then drill away a bone if there was nothing to stimulate. Now she had a recurrent Quobel's palsy and had a grade 5 facial nerve function pre-op. And so still had a tiny little bit of movement that had kind of progressed over several years. And so my thought was, I'm not going to try to resect the facial nerve and graft it. I'm going to try to decompress it, see if she can get better. And so here's just the GSPN coming back. Still some bone I'm going to drill out over the distal part of the internal auditory canal. So here we're going to find the dura. And we just keep irrigating, keep drilling slowly, peeling away pieces of this hemangioma in the skull. Again checking what's a nerve fiber and what's not with a nerve stimulator. Here's the dura, the distal part of the internal auditory canal starting to show up. So here we see the facial nerve, jumping around a little bit, but dura coming up to geniculate ganglion and turning and go down into tympanic segment. And so just a case that shows that exact same anatomic structures. Now what is the most narrow part of the facial nerve's course from the brain out? It's that labyrinthine segment. The thought is that's where Bell's palsies come from, inflammation or swelling that gets into the labyrinthine segment. And our facial nerve recovered to, depending on how you use the House Brackman grading system, a grade three or a grade four. What's the difference between a grade three or a grade four facial nerve palsy? Who can tell me? You guys know what the House Brackman grading system is? So there's six grades. Grade one is perfect. Grade six is no movement. Grade two is you have to study the patient, look at them, and after a while you decide there's a tiny bit of asymmetry in their face, but that's about all you see. And grade five is they barely have any motion, but you can see when they try to activate the facial nerve, some little fasciculations are moving. So one, two, five, and six are easy, but grade three and four are always confused in the literature. What's the difference between grade three and grade four? Anybody? Yeah, I mean that's what a lot of neurosurgeons use. If they close their eye, it's a grade three. If they don't, it's a grade four. I heard Darryl Brackman himself answer this question, and that is not what he said. He said grade three is independent ability to elevate your forehead. So independent ability to elevate your frontalis muscle. And to me that's crucial because anytime you do a nerve graft, anytime you have a complete shutdown of the facial nerve and get recovery, you get synkinesis, and with bad synkinesis people cannot independently elevate their frontalis muscle. So he said to have a grade three, you have to have both complete eye closure and independent ability to elevate your frontalis muscle. So that's a lot better function than, as you'll see in talks all the time, people cut out the facial nerve, sewed in a nerve graft, and they recovered to a grade three. To me that should be impossible if you stick by how Brackman invented this grading system. But anyway, so she didn't have independent frontalis function, but she had complete eye closure. So you could call it grade three slash four, whatever you want for that. Now let's move on to extended middle fossa. And this is a good way to approach petrous apex tumors. You could do this by a suboccipital approach. But the middle fossa is largely extradural, and so not a bad way to go. Now there are several different skin incisions for this. I just use a straight line, but a bunch of people make a question mark incision. The beauty of the question mark incision, you can kind of get the temporalis muscle more forward. So you have a little more room to push it forward than if you make a straight line. Sometimes at the anterior aspect the temporalis muscle is kind of bunching up and it gets in your way to kind of get and see the foramen ovale. Or you could do an upside down U-shaped incision, but I don't know many people who use that. Now you want to turn a bone flap that's based on the middle fossa floor. You can think of it either way. It's one-third in front of the root of the zygoma and two-thirds behind, or two-thirds in front of the external ear canal and one-third behind, whichever you tend to pick. So just kind of showing where you draw this, if the root of the zygoma comes into the skull right here, you make about one-third of your bone flap in front and two-thirds behind. Here's the ear canal and you can make about two-thirds in front. And I just, one thing you don't want to do with the middle fossa is tear the dura. Okay, and this is an extradural case, the case is kind of depressing if you turn the bone flap and you tear the dura over the temporal lobe right at the beginning. So what I do is I just start out with a match head and just drill down through the bone here until I see the dura and then strip the dura up this way, make a little burrow here and turn the bone flap down. To me that's a way that you almost always end up with perfect dura in this case because you don't really need to go intradural at all at that stage. Now this kind of sequence I go through, identify five structures in a straight line, so posterior petrous ridge, and this is something you'll see in a lab today, a false petrous ridge. The superior petrosus sinus makes a groove in the back edge of the temporal bone. If you think the posterior aspect of the temporal bone is the first groove made by that superior petrosus sinus, you end up shifting your thinking about where the middle fossa floor is a couple of millimeters forward, and that can make it hard to find the internal auditory canal. So you want to make sure you see the true petrous ridge, arcuate eminence, medial plane, and trigeminal depression. So kind of these five things I look for right down the line. Then start to go forward, dissect the dura forward, and find the GSPN, middle meningeal artery, foramen ovale. So kind of five in a line, and then go forward. And what is the reason that you don't want to just go extra durally, front to back of your exposure, and dissect and go from lateral to medial? What would you guys say? What's that? So what would be more specific than facial nerve? You could pull the GSPN and it involves the GSPN with the facial, genital ganglion causing the facial nerve palsy. Yeah, I mean, I've never seen yet a facial nerve palsy caused by that, but that was, yanking on the GSPN can cause a facial nerve palsy, and I think that was something that was seen in tick de la rue cases where people did this approach to go in and rub on the trigeminal nerve. Remember, they were doing that without microscopes, probably without headlights, dissecting the dura up, and once in a while someone would have a facial nerve palsy. But the main thing is that if you're elevating anteriorly from lateral to medial, you can get your instrument underneath the GSPN. And then when, and you don't really want it there. You want it to be down along the skull base. So then when you go back and dissect it off the skull base, it could be injured or traumatized. So it's much easier if you just have it stay down all the time from the beginning. So if you work from back to front as it comes out of the facial hiatus, it just ends up staying down against the bone rather than getting elevated up by your elevator. So I want to go back to this diagram again because this is kind of the workhorse diagram of the extended middle fossis. So remember, we've done our craniotomy laterally. We're going to start, and we're going to start posteriorly. Just because if you come down here, you could get your instrument underneath the GSPN. This particular patient's facial hiatus is pretty close to the trigeminal nerve. Some of them are here. So you can easily elevate that, and then you have to try to get it off the dura, and you might injure it. So start posteriorly and make sure you find the true Petrus Ridge. In this diagram, here would be the false Petrus Ridge, and this line would kind of continue up along the anterior edge of the superior petrosal sinus. But make sure you find the actual true Petrus Ridge because in these courses very often, residents will dissect back, see the first edge, and that just shifts your thinking just a couple millimeters back, and it can make you start drilling the wrong place. So make sure you find the true Petrus Ridge, arcuate eminence, mieto plane, Petrus apex, trigeminal impression. Now, when you're doing a real patient, sometimes it's hard to get all the way to here without dissecting the GSPN off. It's just the dura is just hard to elevate up. So after you get to the mieto plane, then you're going to start working forward, working forward, working forward. Then you get to the Petrus apex, work forward, work forward, work forward. And then you'll start to see the GSPN. Now, in some patients with a freer, you can just dissect that plane. I tend to bring in a micro-scissors and just as I'm elevating the dura, cut any little adhesions between the GSPN and the dura. It just tends to be a little gentler on the GSPN. Now, then you want to divide the middle mendual artery, and the dura is still kind of tight at this point. You're still kind of having trouble lifting it up. There's CSF in there. But once you peel the dura up off of V3, so you can, sometimes you can just dissect and keep rolling the dura up. Sometimes you have to take a 15 blade and cut a little bit through the dura right here. But once you elevate the dura up off of this area, all of a sudden there's lots of room, and the retractor's not that tight. And you can see the whole Peter's Apex. And it's very easy to know your anatomy at that point. So that's what we want you to do. Come down this edge, then go forward, then cut this, then peel the dura up off this, just like you guys did from the front yesterday, but coming right from V3 on this side. And just showing this. Now, then we're going to start to drill. And I like to think of drilling the Peter's Apex as five anatomic structures that are not all in the same plane, but five lines of a pentagon. Posterior Fossa Dura, Trigeminal Nerve Edge, Internal Carotid Artery, Cochlea, and IAC Dura. Cochlea is the only one you can't see. Every other one you can see. So you can see the dura, the IAC. You can see the Posterior Fossa Dura, Trigeminal Nerve. You can drill right along the carotid. And then you have to kind of estimate where the cochlea is. But once you've drilled out those five sides, that's all there is to drill. So we're going to, again, do that same thing. So here's, this is in Roten's diagram, it's kind of five sides, but they've drilled out probably over the dura, the IAC here. But we want you to do that today and keep drilling until you see this. What is this blue structure in the bottom? Inferior Pitrosa. Inferior Pitrosa size. And that's when you're ready to open the dura. And when you're ready to open the dura, you want to open it below the Trigeminal Nerve, above the Trigeminal Nerve, divide the Superior Pitrosa Sinus, and then peel the dura back. Now, so this would be kind of the view you would get, and Jeff showed some of these. What is this? These two nerves? Yeah, so how often is the sixth nerve in a couple fascicles? I don't know a percentage of that, but it definitely happens. I've probably seen that five or six, seven times in my life where the facial nerve is two different fascicles. Here it's going around what artery? What artery is that? Ica. So sometimes the facial nerve will, I mean the sixth nerve will divide up into a couple different fascicles. And look, in this patient, they stayed as two separate fascicles. What's the name of this canal? Dorelus. Dorelus Canal. And what's the name of this ligament? Duber's. And what's it connecting? Pidger's Apex. Pidger's Apex to what?

skull base surgery

anatomy knowledge

3D anatomy

temporal bone

surgeons' techniques

middle fossa

extended middle fossa approaches

facial nerve