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Craniocervical Junction Abnormalities: Why, When and How to Treat?

Paul Gardner, MD

February 22, 2021

Transcript

- Colleagues and friends, thank you for joining us for another session of the Virtual Operating Room from The Neurosurgical Atlas. Our guest today is Dr. Paul Gardner from University of Pittsburgh, UPMC. He's a dear friend, a true pioneer in skull base surgery. He is Peter Jannetta Chair in Neurosurgery as well as the Director of the Skull Base Surgery at UPMC. I have always followed your career, Paul, your contribution to neurosurgery are transformative, your technical skills are second to none. I'm so proud to have you as a friend. I know today you're gonna be talking about endoscopic surgical management of craniocervical junction abnormalities, including degenerative disorders and basilar invagination. I'm very much looking forward to learning from you. So please, take it away.

- Thank you Aaron, it's a pleasure to be here again, and I wanna thank you for everything you've done with The Neurosurgical Atlas, as well as the Virtual OR. I know I myself follow the Virtual OR and there are many both live and also there's a huge library recorded, that I learn a lot from. So I would encourage everyone to check out the library that's available. Today, I'm gonna talk about a topic that is not covered very often I think, and that's craniocervical junction abnormalities and talk about everything from why to treat including all the way through what treatments to use. These are my disclosures, which are not really relevant to this particular talk. Another further disclosure is that this may seem odd for me to be discussing these, since I'm not a spine surgeon but rather a skull base surgeon, but they obviously do impact the skull base and I like this quote from Dr. Jho which is that, "the spine is most skull base of all." So I've extended perhaps my reach a little bit but this is something I've thought quite a bit about and I think I've learned quite a lot about. And to start with the craniovertebral junction, why do we treat lesions at the craniovertebral junction? Well, typically the severe symptoms are progressive quadriparesis, myelopathic gator imbalance. Occipital pain can be quite prominent, and even dysphagia. These are things that are often delayed in their diagnosis. Other more rare symptoms, it could be diplopia even from brainstem involvement, vestibular symptoms from similar as well as a Chiari type malformation, even vocal cord paresis, and an unusual one is palatal myoclonus which comes from olivary degeneration. But all of these are signs of ventral compression at the cervicomedullary junction. And typical indication rather, for a ventral decompression at least is an irreducible bony compression at the craniovertebral junction. This was a very clear indication to a ventral decompression in many of these cases. This can also be used after a posterior decompression infusion, if that doesn't provide adequate relief. And then finally, and perhaps a lot more controversial, is if there's a significant pannus with evidence of cord edema, severe myelopathy. I'll discuss my views on using a ventral approach for treating craniovertebral junction in this situation. When to treat? So, when do you decide these symptoms are bad enough? Obviously, you know these are dramatic surgeries. They often have high morbidity, especially in an elderly or debilitated population. And so the goals should often be to delay or avoid surgery when possible in younger patients who might have a craniovertebral anatomic anomaly. The fixation can have a dramatic impact on quality of life and of course, has downstream affects with adjacent level degeneration. So, I do try to avoid some treatment whenever possible if there's not significant cord compression or symptomatology. However, I think it should be treated when there are Overt Neurological deficits such as a weakness or quadriparesis, or vocal cord paralysis or dysphagia. Even early symptoms if they're progressive, is an indication for treatment. And then if there are significant radiographic disease but with progressive symptoms including pain So I think is an indication, because that often the pain is assigned to the patients' bodies trying to protect them from further harm. How to treat? This is a much, much more complicated decision and there's a lot of key anatomy to evaluate. There's a condyle joint which of course, involves assimilation. Here's an example of that. So, if there's assimilation of the condyle, then this is an indication to fuse to the occiput because that's already involved. But most of this disease is C1-2 disease, so actually fusing to the occiput usually not indicated, but when assimilation is part of the anomaly, obviously that fusion is inherent to the disease. Another thing to look at is the C1-2 relationship. Here you can see a case where there's subluxation of C1 and C2 which can be a common finding, especially in younger patients with basilar invagination. This changes that the indication for treatment or the mode of treatment, rather. And then the degree of anterior compression. Here's a case with a patient with a pannus that is compressing their brainstem in the sort of medullary junction from the anterior trajectory. And then finally, associated anomalies. These can be many things including platybasia, and Chiari, et cetera, which can often go together. How to treat? And again, the focus of this talk is going to be largely anterior compression and part of the reason for that is simply my bias as a skull base surgeon to discuss things from an anterior approach. And the standard anterior approach for cervicomedullary junction or craniovertebral junction as a transoral approach, but I'm gonna talk about advantages of a Endoscopic Endonasal Approach. This was something that was first reported in 2005 from our institution when this was first done endonasally and we actually have not done a transoral decompression for this type of disease ever since then. How low can you go? Or how do you know if you can access this? Well, two things I would say is that you can always access degenerative or basilar invaginative disease from an Endonasal Approach, but sometimes if there's tumor involvement and you're curious how low you can get, you can the most simplistic method, although there are others described, is to draw a line from the bony nasal septum to the hard palate and extend that into the depth. Usually you can get at least one centimeter above this line with your inferior access using some minor tricks. Operative techniques. I do all these patients in rigid fixation. One thing to be careful of is, you know, if you think about this, especially using image guidance which oftentimes is very helpful in these cases, you can't extend or flex or rotate the patient's head or you'll throw off the position of C1-2 because of the rotation reflection that occurs at those joints. Remember, the majority of head flection and rotation occurs at C1 and C2, and this is a C1-2 disease. So, I'll bump the patient's body over in order to, I'll keep their head aligned and keep them turned in line with myself. And then intraoperative monitoring. I use somatosensory evoked potentials, often we'll use brainstem evoke potentials as well, and not to forget about hypoglossal EMG in cases where the patient has anomalous anatomy. If an anatomy gets destroyed, the last thing you wanna do in a patient, you already may have dysphagia is give them a hypoglossal palsy. We're fortunate to have an Operating Room with a CT scan or something Dr. Lance brought to us over three decades ago, but this is something that we use on a regular basis, and especially was very helpful, when we first started doing these types of surgeries. I found that more lately, I'm very comfortable with this, but during my learning curve, this was something that was very helpful for me to get a complete decompression. Here's the anatomy. Very simply, we go directly down to the nasopharynx. And this was first reported, we talked about opening up the sphenoid. That's only rarely necessary with severe basilar invagination and platybasia. And the truth is you can often go directly down to the nasopharynx and open this up. You can resect the tissue, or now we've gone to an inverted U-shape flap, which can be very useful. Here's a case where we see a patient who had basilar invagination that progressed after a Chiari decompression. Is that video, I think is playing hopefully? And in this situation, of course, they would need a posterior fixation. That's part of the problem, but here we're gonna do an anterior decompression first, since that's the vector of compression. This was an irreducible invagination. And here you can see removal of the soft tissue. You'll notice the attachment point of the rectus capitis muscles. There's a rectus capitis anterior and a lateral rectus muscles. And here we're drilling out C1, but you can see that attachment point, this is at the supracondylar groove and then resecting the anterior arch of C1 and the joint between C1 and C2. That joint capsule, once that's resected, then we can visualize the dens and you can see as we pass by, there is an area on the hard palates been drilled down where the septum meets the hard palates called the maxillary crest. And that's a high point in the hard palate. It can push you up when you try to extend . So drilling down that maxillary crest is very important. Curve drills are also a nice adjunct. And here you see the key aspect where we drill from the tip all the way down in order to not disconnect the dens at the inferior aspect. So drilling from the tip down allows us to not leave a free floating bone attached to all of these dens ligaments or the apical ligaments and the transverse ligament. Here, we can see visualization, we've drilled all the way up to lateral masses of C1. And we're up to the tectorial membrane. You essentially never have to see dura. You just want to see pulsations of the tectorial membrane, or sometimes the periosteum. Here's the intraop CT scan showing a nice low decompression and the width of decompression. The trick here all is with any minimally invasive approaches that you tend to narrow in, as we want to keep our exposure nice and wide. A simple tissue closure is essentially all that's necessary. Here's a picture taken in clinic showing healing, not the best picture, but what we see is that you essentially can't tell anything was done if this is done properly. We go on to the next video. This is a case of a child who had a basilar invagination and had a posterior fixation. Unfortunately, using a BMP in a child. This was back when BMP was just brought out and very, very popular. And what happened is they developed a worsened compression, even from the posterior bony fusion, and didn't decompress their anterior vector enough. And so we had to do an anterior decompression as a simple solution as patient ready has an occipitocervical fixation. And here again, we're resecting the soft tissues. Again, now we use an inverted U-shaped flap and tuck that down towards the oropharynx in order to try to avoid any problems with CSF leak or feel powerful and sufficiency. Here's the anterior archs C1 being defined. And we can see very clearly here, the anterior tubercle of C1, that's very useful midline landmark. In this case, there is an increased atlantodental interval. And here because the basilar invagination were all, but got all the way down to C2. So that allows me to just use a Chiari in here. I don't have to even drill off again. There's a big space between C1 and C2 because of increased atlantodental interval. And this patient's already fixated, or perhaps someone we could have considered trying to do a reduction. They did try to reduce this child preoperatively part of the fixation unsuccessfully, but there are some who will try even for several days in traction. And here we can see after a resection now of C1, there's actually a lot of intervening soft tissue between C1 and the dens. Once we remove that, we start to see the dens come into view, removing the joint capsule and some other intervening connective tissue from the invagination. And we can really see the entire dens all the way down to the body of C2. Again, critical here to drill from the top down. This is the most challenging part to access. You can see there can be some overhangs. So sometimes Chiari sending away some of that soft tissue or removing even part of the foramen magnums necessary. You can see here, the profile of this drill is a little higher because it's a curve drill is designed to occur downward. And that gives us a little greater access. And here appealing way. The tip of the dens is a lot easier when there's a small amounts of it left of the inner cortex, rather than trying to remove the whole tip of the dens. Again, critical or not disconnect that tip, but rather drill it flush with the tectorial membrane or the apical ligaments first. Here you can see the apical ligaments coming into view, and then a nice white or pale tectorial membrane, which is again, the rostral extension of the PLL. Here we can start to see that come into view. And what we're looking for is a nice wide and low pulsatile tectorial membrane. Here's the final view, you can see those pulsations and a beautiful decompression, and here's the postoperative MRI. The next slide. Here's the postop views. You can see we're able to because of the degree of basilar invagination, you get all the way onto the body of C2 and completely decompressed the cervicomedullary junction. This is an older patient, and often as we know, older patients can get a ectatic arteries. Here's a very ectatic carotid artery. This patient doesn't have a six carotids as it looks like on this right-sided picture here, but rather has rather just has a very ectatic one, which you can tell from the coronal. This creates a whole new challenge, even more difficult from a transoral approach and creates a whole other kind of limbo when we're trying to get low down in the upper cervical spine. If we can play the video. The trick for this is simply to come in above it. Remember, the carotid artery lies superficial to the basal pharyngeal on the fascia. And if we, here we can look endonasally, there's a little bit of a posterior septectomy is always helpful, but you can see here the pulsation of the carotid artery on one side and then on the other side. So clearly if we just Bovie right down here, this could be a complete disaster. But this is sitting right under the mucosa, so if we simply make an incision above the level of the arteries, we can get down onto the area and simply come in behind it. So if we Bovie down here, we can access the basal pharyngeal fascia, and then dissect down onto the anterior ring of C1. Much like the other cases then, we drill out the anterior ring of C1. And once we remove the anterior ring of C1, identify the dens, drill the tip of the dens down, et cetera. I think we can skip this video in the interest of time, but it would basically show that we can access directly down behind the carotid arteries, and then flip up the nasopharyngeal mucosa and nasopharyngeal fascia with the carotid arteries intact at the end. And that U-shaped flap certainly helps us do that. So what are the advantage of this approach over a transoral approach? Well, one obvious, one is the patients can be fed immediately with a transoral incision. For fear of the dehiscence, usually wait to feed the patients for several days may be these patients are already debilitated or malnutrition and so the ability to feed them quickly is very important. This also completely avoids any need for tracheostomy for access. If there's a limited jaw opening or difficulties with the transoral approach, you can have to do a tracheostomy. Very, very important as well is our access is above this area called Passavant's ridge Passavant's ridge is where the soft palate contacts the nasopharyngeal, oropharyngeal mucosa. And if you lose soft tissue here, either through incision or through loss of volume from resecting, it, you can get below palatal and sufficiency or palatal incompetence, because the soft palate doesn't have enough soft tissue to contact. But with an endonasal approach, we are inherently above the point of Passavant's ridge. And with using this inverted U-shape flap, we have an even greater ability to prevent loss of retropharyngeal tissue volume. This is a very important piece and can have a dramatic impact on patient's quality of life, avoid dysphagia and avoid nasal regurgitation, or hyponasal speech. VPI, velopharyngeal insufficiency can occur still in the postoperative period related to swelling or dissection and this can be transient in the endonasal approach was often permanent. In a transoral approach, we had no cases of permanent VPI in our patients. We looked at 34 patients relatively recently. I think we're up to about 50 patients with endonasal odontoid at this point. And many of these had a basilar invagination disease or had irreducible compression. There are some with other types of tumors as well. And many of these underwent posterior fixation, the vast majority did and should. The only cases where they wouldn't were patients who were either too sick to undergo it, or were treated in a collar. You can see the length of surgery dramatically changed over time. There was a big learning curve. No one was teaching us how to do this. When we were first doing it, we were learning how to do it ourselves. And we were still under our endoscopic learning curve as well. And now it's down to around two to three hours, even a great case for my fellows to do by themselves and can still get this timely fashion with fixation the same day, all within about four to six hours. We were able to achieve appropriate decompression for all these diseases in every single patient. There was no tracheostomy immediate as part of the surgical procedure. There's no reason that you would need this. And no patient required a repeat surgical intervention importantly, with the one exception of patient who develops further progression of subaxial disease and had to be treated, but no disease at the level of the odontoid had to be retreated or re-decompressed, or et cetera. The main follow-up was over three years and every patient had stable or improved symptoms of their myelopathy. Very important piece of all of this is dysphagia, I mentioned one of the symptoms that patients can often have, and about half of our patients have documented preoperative dysphagia and six of these even had lower cranial nerve dysfunction, vocal cord paralysis, or a complete loss of gag for example. As a result in both of the surgery and also of these pre-existing problems, a high number of these patients will have transient postoperative dysphagia. The vast majority were mild, but those who actually have pre-existing dysphagia can have more significant postoperative dysphagia. Again, as you might expect, this essentially only happens in the setting of significant preoperative dysphagia or especially with pre-existing lower cranial neuropathies. You should expect the patient to have worsened problems after surgery from having from intubation and from dissection in the area. Another piece that we often don't discuss is occipitocervical fixation, is a clear source of dysphagia as well. Even in the absence of any ventral surgery, there is a chin tuck maneuver that many patients and many of us use without thinking. And once you have an occipitocervical fixation, you have no ability to do that type of a neck flection and this can dramatically affect your swallowing until patients get used to it. Partly because of this, strongly recommend avoiding occipital fixation when possible. Fortunately, everyone who had perioperative dysphagia improved and all patients were tolerating oral diets. No patients suffered for velopalatal insufficiency. Of course, there are complications, pneumonia is a big complication. These are often elderly patients who are quite diminished in their function. They may have swallowing difficulties of course. We had two patients, intraoperative CSF leaks, unfortunately, no postoperative we just put some fat graft in there especially, with the U-shaped flap, this prevents it, it's a nice deep area and you should not have a high flow leak. You can get infection. I try to avoid when possible extra dissection of the joints, either the occipitocervical joint or C1-2 joint. Obviously the joint itself is more prone to infection. And in addition, when we leave soft tissue there, as long as we can oppose it with the defect, we can avoid infection. Another reason, to avoid fat, unless you really need it. We did have one death eight days after surgery. This was very, very early in the series and a patient who due to age was sort of a last ditch effort, but this was a patient over 90 that was treated very early on at our institution. So I do think Endoscopic Endonasal Approach can be used essentially for all of these cases, as I mentioned, we've not done a transoral approach since we first described this in 2005. Perioperative dysphagia is extraordinarily common. And it's related to preoperative dysfunction, something that should be evaluated very closely by ENT colleagues and also effected by occipitocervical fixation. This does minimize however, the approach, the postoperative difficulties that we can get and avoids altogether velopalatal insufficiency. I want to go through some cases now to discuss, you know what type of treatments should you use in many of these cases? Here's a patient who has severe quadriparesis and dysphagia with what they're presenting. And you can certainly see why there's significant extension of C2 up above here and just notice the occipital, the C1 joint involvement. And so, you know what's, a question here really, what is this diagnosis? Not all of these are the same. You can't just call odontoid disease and apply the same treatment, because they're all dramatically different. Well, this particular case we see basilar invagination. So the dens is dramatically invaginating above the base of the skull. The C1 lateral mass is essentially completely collapsed. Here's the occipital joint essentially now articulating the C2 because of complete collapse of C1. And there's also a simulation of C1 through the degenerative process. So this patient, are these treatment options? What are our choices here? While trying to reduce this completely clamp C1, I don't think is an option whether you do it closed or open. This is a completely degenerated joint, and you're gonna leave a space there. I think the simplest thing in this situation is simply to do some sort of a ventral decompression with posterior fixation. And of course, you'd know my views on endonasal versus transoral. Another quite important question always is, do we include the occiput in the fixation? In this particular case, the decision for that I think is largely based on the complete collapse of C1. You have to at least fuse to C1 and if it doesn't exist, you have no choice but to cross that up to the occiput. And so that's what we did here. You can see we resected the clivus here for much of it, because of the degree of basilar invagination, to even get to the tip of the dens, we had to resect the clivus, which did have some platybasia with it and did perform an occipitocervical fixation in order to make sure that we had adequate fixation across that joint. Here's perhaps a little more controversial. This is an older man was presenting with progressive myelopathy. And you can see here has this to, you know, we have this tissue here at the front and the question is, you know what is this? Well, this is a C1-2 pannus. it's just a degenerative or in this case actually ironically turned out to be Pseudogout pannus. So what are our treatment options for this? Well, here I think are, probably what are considered the standard. There's not necessarily a wrong answer in this situation. The standard dogma would say, this patient simply needs a posterior decompression and fixation and if you do that, the pannus will disappear and the patient will do well. I think there are some questions about this. I think the length of time it takes for the pannus to dissipate is unclear. And also how often does the pannus dissipate? There's aren't large series or great data on this. I do think in a situation like this, if you don't fuse a patient like this, you're asking for trouble, because inherently there is some instability of the joint that's leading to the pannus. This is an overt instability. But this patient underwent actually a C1-2 decompression at an outside facility. This was done to try to relieve symptoms, but the patient actually progressed relatively quickly after that. Here you can see, now they haven't done anything to relieve the pannus and they haven't done a fixation. I do think that probably with a fixation, this patient would have at least stabilized and slowly improved with their symptoms. So now what do we do? Well, you could certainly just do a C1-2 fixation. This patient has gotten progressively symptomatic to the point that he's actually not able to walk. And here you can see other options include doing the odontoid or doing a transoral and trying to decide whether or not to fuse along with that. Would you include the occiput in this? Again, I think this is like many of them, C1-2 disease. The interesting question is if I just do that fixation, what is the chance of this improving? Well, the chance is really very good. So this is obviously what is the standard dogma to treat this, is that you should do a C1-2 decompression and fixation. And then the pannus will resolve. The question I always have about this is how long does it take for that pannus to resolve? How quickly are the symptoms from the patient improves and what are the chances of it not resolving? Well, I think the chances are low of it not resolving. This was one of the larger series and it's only four patients. This same group had another study with five patients and one of their patients did die out of the five, but this one, they had one patient who didn't resolve the pannus. So another piece of this is that I think part of this dogma comes from the morbidity of a transoral approach. There is no other location in the spine where if we have a ventral compression of the spinal cord, or we don't do the most rapidly decompressive procedure possible and do a ventral approach whenever possible. So ventral approaches are used routinely throughout the spine, as long as the morbidity is not too great. And I think using an endonasal quarter, somewhat shifts us when it comes to pannus. Still, if there's not a dramatic pannus or dramatic symptoms, I still think a simple fixation from a posterior approach is a simpler approach and we should avoid it. But I do think an endonasal odontoid can provide a instant decompression of the patient. The occiput is not needed as part of this fixation. So here we can see if we can play the video. This is that patient. And we'll do us a small portion of a posterior septectomy. This is just the inferior septum. The good thing about this is we're staying below the level of our flap. So here's this portion of the septum, but here's the clivus, so our flap is everything above it, is our flat pedicle. So flat pedicle is preserved. Just a small posterior septectomy. Here's that maxillary crest I talked about. That has got to be drilled down. Very important subtlety of this. You can drill that flesh all the way with the hard palate. But if you look at the hard palate, it comes up dramatically in a peak here. And if you don't drill this down, then your instruments can't reach as low as possible. Here's that little inverted U-shaped or RP, rhinopharyngeal flap that we do. You always have to be careful about where's the location of your parapharyngeal carotid arteries when we do this. And so we always check that with navigation, but they're usually hiding behind the Eustachian tube. You can see the Eustachian tube there and now we've dissected down and here you can see the, we can see down to the bottom of the foramen magnum. We can even drill out the inferior clivus. Just to gain a little more access to the tip of the dens, which is slightly invaginated in this case. And now I try to not remove all of the anterior archs of C1. So here's a little bit of the bottom of the arch of C1 left. And the reason is that creates a little more stability by leaving the ring of C1 intact. So here we see the condyle, there we see that lateral mass and I can remove the soft tissue between the C1-2 joint, and start to expose the dens. You can see how widely I've drilled all the way out, even up to the lateral mass. And up to the condyle in order to make sure I can get all the way around the odontoid, you get a nice wide decompression. Now here's our tip of the dens. Here you can see the apical ligament. We want to make sure to drill this down flush with the ligaments. And the last thing I want to do is disconnect the down at the neck of the dens and have a free floating tip of the dens, which can be very challenging to try to remove. So we eggshell this, you can drill it right up to the ligament if you feel comfortable with it and we're dissecting away the posterior table of the dens itself and then drilling right back. Here's the last bit of the periosteum being removed, so removing the rest of the cruciate ligaments here. And there's the transverse ligament, of course, runs from one tubercle to the other on C1. And once that's removed, the transverse ligament, we can then start to remove the pannus. Now, the pannus is a little bit of the tricky part. You have to have a good sense for how much you need to remove. And what we're looking for is either a sign of the tectorial membrane or periosteum that's deep to it. Remember there are two layers of dura here that blend right at the foramen magnum, or we're looking for wide pulsatility again. So you can see a lot of the transverse segments actually degenerated. And there's a large amount of degenerative pannus here. By removing this, really provides of course, instantaneous decompression of the cervicomedullary junction. Of course, the fixation will stop the active process that leads to this and it will stop some of the micro motion that causes the damage from this. But I find that patients in this situation gets such a rapid decompression when you remove the pannus that especially when they're progressing, that they may do better in this situation. Obviously, something that needs to be studied, and this has to be done with low morbidity, but removing this pannus, removing the ventral compression in my opinion, has to provide a more rapid decompression for these patients. You can see the amount of pannus that we're removing here. And now finally starting to resect a little bit of the tectorial membrane to make sure that I have a complete decompression. Again, the tectorial membrane does often not have to be removed in this situation, because it has some involvement of the pannus, some sort of peeling it down until I can see the periosteum. We don't ever want to or need to see the meningeal layer of dura, definitely not necessary. But when there's a pannus it becomes a little more challenging in here, we call in this dura, but I think this is really periosteal layer of dura. And this is that inverted U-shape flap being flipped up. We hold it in place and place some Tisseal over it. Here you can see I'm pressing it in with a suction to hold it back into place. And the Tisseal glue will hold it in place until it takes on its own. And that avoids dead space in that area and has very nice healing. Onto the next slide, please. And here we see again, no occiput necessary because of further disease lower down at C2-3 a posterior decompression who had been done previously. And so that we extend this down to C4 because of that, but you can see here a little bit of a ring of C1 left, and you can see this is actually immediately postop complete decompression. I think this has to have potential value for the patient just to remind you what it looked like immediately pre-op. Here's another case, this is a patient, a younger patient presenting with paresthesias and imbalance. And you can see this kind of a little bit different of a scenario. What's our diagnosis here? Look, you can see here how flat the clivus here, now kick back the dens. So this was platybasia and a retroflexed dens. A little different diagnosis here. What are our treatment options? Here's a whole list of them. I think any of these are probably options, but again, try to observe whenever possible, especially in the younger patient. Because many of these if not now, in the future will require fixation. This patient after several years, three years in fact had symptom progression. Important thing to notice here. If you look now the condyle joint is not normal, which certainly may be a problem down the road, but there is a condyle joint, there's not assimilation, but it is not a nice round joint as we would like to see. So what are our options here? Again, a C1-2 fixation will not relieve the retroflex dens or some degree of basilar invagination, but might be an option. I think a Chiari decompression is probably not a great idea. So it will allow progression in the future. And then what we ended up doing in this case was an endonasal odontoid with a C1-3 fixation. Again, avoided the condyle, even though it's somewhat flat, may have problems in the future for this young person. Avoiding condyle, or rather avoiding occipital fixation is important. Here's a more severe case are very similar. You'll notice in here, what's our diagnosis? Well, there's an additional thing going on here. And this is a Chiari plus syndrome. So a dramatic Chiari, a platybasia, and retroflexed dens. And I'd say, well, this is obviously a different scenario. And so you have to do something from posterior as well, some sort of posterior decompression, or try to do traction in this case. Well, if this patient was your child, and so did undergo a Chiari. And unfortunately, what happens in many of these cases is that after the Chiari, they then progress over time because you've removed the posterior band and the anterior or the ventral compression, the retroflexed dens worsens. So Chiari's not a wrong answer in this situation. It does delay the fixation, but it will lead to progression. It's important that patients understand this. Well, what about traction and fixation? Well, there's no real malalignment here. This is the fixed alignment of the patient, the condyle doing so okay, right here. The C1-2 joint shows no subluxation. So traction has nothing to really undo here. So I think you're really stuck with doing an endonasal odontoid, it's exactly what we did. We minimize the posterior fixation and here you can see on the immediate postop, there's already good decompression in that soft tissue. That soft tissue will only improve with pulsations over time. Here's a woman, again, young woman presenting with purely Chiari symptoms. You could of course, do a Chiari decompression in this situation. That's certainly an option. This is a Chiari, this is platybasia and a retroflexed dens. Very similar to the last, a little bit older patient. Again, a normal C1-2 joint, and a normal condyle. Important things to always look at to understand if there's subluxation or if there's a flattened condyle or assimilation. Here again are our options, everything from a Chiari decompression with fixation, I don't think is a crazy idea, but you're really not addressing the issue, which is the ventral component. And so here we can see progression over time. We observed it, and eventually progressed again, young patient. So now we have to move on to, I think the right thing to do here is a ventral decompression. And you'll notice just by doing a ventral decompression in C1-2 fixation, I haven't touched the occiput. I haven't done anything to it from anterior or from posterior, I haven't done a Chiari decompression. And this provides enough room that the Chiari itself lifts up. The vector here is ventral. This is not posterior disease. This is not too small of a posterior fossa for the tonsils. This is merely a ventral trajectory. So treating the actual disease is important here. Here's a another case. This is again, a relatively young patient with quadriparesis and pretty severe dysphagia. Looks very similar to those last cases, there's of course no Chiari. But look at this portion here, look at the C1-2 joint. There is assimilation of the condyle. So there is no occiput, the C1 joint and there is actually subluxation of C1 and C2. So this is basilar invagination caused by C1-2 subluxation. This is surprisingly common and often missed. This was something that was pointed out to me by my good friend, Raturi Goel when he criticized us doing a ventral approach for this and he's absolutely correct. Now, I don't think this fits for every patient, but when they have the subluxation using this Goel Technique where you place entirely from posterior, you have to do a very wide exposure. So we can see the vertebral arteries, but from posterior type C1-2 screws, this was of course done by my spine colleagues and I can't emphasize enough how every single one of these cases should be done in concert with the right subspecialties and place a spacer right here. And the combination of that spacer and the screws allows a reduction of the C1-2 subluxation. We haven't done any decompression. The C1 ring is still intact, the odontoid is still here, we've merely reduced the C1-2 subluxation. Here you can see that spacer and we can see now the alignment of the C1-2 joint, and we have a perfect occipitocervical, craniovertebral junction now. Simply by understanding this is a different disease. It's a C1-2 subluxation. A couple of other different ones. There's a 46-year-old man presenting purely occipital headache. Look at the degree of this Chiari that's going on here, but there's obviously something else here as a mass anteriorly. Well, should we, you know, this really creates a little bit of a confusion. What's our diagnosis here? What's causing this Chiari, and what came first, the chicken or the egg? The Chiari or the mass? Look at the degree of Syringobulbia, Syringomyelia we see there. So this is a craniovertebral tumor and an induced Chiari. The Chiari is secondary to the tumor. You remove the tumor, you'll treat the Chiari. You don't have to do a Chiari decompression on this patient. In my opinion, I think the right answer here is to resect the tumor. Now, the question is, do I have to do a fixation? Well, we're not removing any joints. We're resecting the clivus and we're resecting all the way down to the tip of C1, but we're not resecting any joint here. We're not resecting the condyle joint, we're not resecting C1. So no fixation is necessary. And look, look what's happening with the Chiari? It's completely decompressed simply by doing the ventral decompression, the syringomyelia and syringobulbia is completely resolved. Here the wonderful resolution of the symptoms has avoided a fixation, but unfortunately, of course now has to deal with proton beam radiation after this Chordoma. Another one here, this is again, a little bit of an older patient presenting with occipital pain and imbalance, as well as, you know the headache that's involved with that. And we see this mass right here. A little different, you know there's a tumor what's going on here? What is the diagnosis? Here's looking at the bony imaging. Pretty good alignment. The joints are all normal here. So what's causing this mass here? Is this just another degenerative pannus? Well, it's similar but this is actually a synovial cyst. These are surprisingly common and the synovial cyst itself can be relatively symptomatic. Again, this can be treated with just a C1-2 fixation. I do think the fixation's necessary. You can do a laminectomy, try to resect the synovial cyst, but there's some pretty dramatic joint decompression here. Again, the argument for endonasal here is the fact that I can do an instant decompression. Here we see the postoperative MRI, complete resolution of that synovial cyst and instant decompression. There's no other situation where we wouldn't try to remove the cyst or the source of compression, except for with a C1-2 disease, because of the morbidity of prior ventral approaches. So in conclusion, I think odontoid disease is a really a myriad of pathologies and anatomic variations is very important to understand exactly what you're looking at. When you see these, they take a lot of study. You have to have MRI, you have to have CT scan to understand, make sure there's not actual tumor there. Understand are there anatomical abnormalities that are leading to this, but the vast majority is C1-2 pathology. It does not require an occipital fixation. You will dramatically impact more patients than you need if you always go to the occiput. The fusion arthrodesis rates are lower, if you involve the occiput and most of them simply don't need it. So avoid that occipital fixation when necessary. And certainly more controversial and philosophical perhaps is to consider Endonasal odontoid resection for severe ventral pannus compression. Again, this is far from necessary for the majority of patients with pannus compression, but if these patients had severe myelopathy, quadriparesis and that degree of the ventral compression, there's no other location in the spinal cord, certainly in the cervical spine that we wouldn't do a ventral decompression first. And so I think that same concept holds because of the decreased morbidity of an endonasal approach. Very important, odontoid disease in this case is best managed with a multidisciplinary team. All of these cases we discussed between the skull base and the spine team. I'm very fortunate to work with some super complex spine surgeons, Dr. David Okonkwo and David Kojo Hamilton, as well as Dr. Kanter, who does a lot of our minimal invasive surgery. And between them, in between our team, we discuss every single one of these cases with this kind of disease at the craniovertebral junction or basilar invagination to try to see can we get away with just a fixation, or can we do a Goel Technique, for example, with a spacer. And at between our team, we really think there is no, that we think that a ventral approach has an advantage. Then we'll do an Endonasal Approach, but this is done in a multidisciplinary fashion. In my opinion, the best way to have a collaborative decision made. This is just a quick plug for an upcoming book we have coming out. And again, I invite everyone to join the Skull Base Congress, which is an online educational website. Certainly, doesn't have some of the content that Aaron has, but I think all of these help us form an online community. Again, thanks Aaron for inviting me to speak and such a pleasure to be a part of the Neurosurgical Atlas.

- Thank you so much, Paul. Really incredible work, pioneering, amazing skills, just beautiful to watch period. Just beautiful to watch. I really liked the techniques you described approaching eventual disease through eventual trajectories. Just make sense, it just a surgical principles that makes excellent sense. I wanted to go just as a last question, in depth more with the idea of, you know, basilar invagination with pannus with compression, fair amount of literature supports just a fusion from the back would allow the pannus to grow on its own versus decompressing in front and getting a more sort of timely decompression. Can you go in depth on that one a little bit more, because there's fair amount of literature these days that says, as long as you immobilize the craniocervical junction, the pannus will go away on its own.

- Yeah, I agree that, that is a concept that is appropriately entrenched in literature and understanding that, that improves is important. These are often very debilitated patients in the less surgery you can offer them the better. There's no question to this always adds length of time to the surgery, but the literature that I've been able to find is not very extensive and it is not very high quality evidence. The study I presented is, believe it or not the largest series I could find in the modern literature is five patients. So this is far from a widely reviewed concept or widely proved concept. The questions I have about that. And the only way I know to make that decision in a more educated fashion is to understand what's the time for relief of symptoms when you do that? And the degree of the relief of symptoms, because many of these patients, you know has such severe symptomatology that the sooner you can relieve them, the more likely they are to survive and have a better quality of life or even quantity of life. The other question I would have is how often does this fail? It's not universal, and that has to be weighed against the complications associated with a longer surgery by adding the three hours of endonasal odontoid resection. You've got to be able to do it in efficient fashion with a low complication rate. It'll never be zero complications because of potential for infection and CSF leak. But if you can avoid those, this is a very efficient surgery. And I think dramatically different from a transoral approach. The reason that, that dogma developed and the reason that concept has gained so much traction appropriately is because of the morbidity of a transoral approach is so much. I think it bears at least a re-exploration of the risk and benefit of doing a ventral decompression, given the lower risk of a transnasal decompression. Doesn't mean that's the right answer, but I think it would require a multicenter study. And I think at least there's a re-exploration of if and when you should do a ventral decompression.

- Very well said. What I was really looking forward to you're saying, which you said immediately is that really the dogma relates to the morbidity of a transoral approach. That is so entrenched in the surgeon's mind that unfortunately sometimes it prevents them from stepping out of the dogma and exploring more effective strategies, just like you mentioned in the Endonasal Approach. And I want to use that as a platform to really discuss the fact that dogma is such a big deal that really affects surgical innovation so deeply, that we got to think beyond what we trained in. You know I always hear people say, okay, I was trained to do this way, that's the only way I'm gonna do it. I think that's a big mistake. I think we should think beyond that. Surgery is a very evolving science. We always, you know come up with new strategies to solve old problems that are gonna be much more effective. I really do believe the endonasal odontoidectomy is extremely effective and relatively efficient. And so among all the complex skull base endonasal procedures we do, or you do, actually in fact this is a relatively straightforward one and can be mastered relatively quickly. So I think one has to keep that in mind. And again, remember that a ventral disease requires a ventral treatment. So with that in mind, I want to see if you have any other closing comments, Paul.

- I think the concept of dogma is a very interesting one. It plays an important role. I think the best thing we can do is understand dogma. Where does it come from? The vast majority of dogma is entrenched in very solid reasoning and years of experience. But you both learn from understanding dogma, you learn where it comes from and you also see its weak points when you do that. So I think you can't, I think you have to study dogma to learn from it. I've learned quite a bit by trying to, you know look at the papers and understand where did these concepts come from? Many of them are very important and you can't really understand when or where to use it if you don't know it. So I think like anything, the more you understand something, the better it is and the only way to change dogma is to understand it and decide when it should and shouldn't be changed also. So it's a very interesting topic and one that I probably talk about for quite a while. So anyway, thanks again for having me and I look forward to further questions.

- Yeah, we'll look forward to having you in next sessions as well. You know, Paul, I think dissecting the dogma is always the key. Sometimes surgeons are not open to that. That's the challenge. We've got to keep an open mind. We've got to dissect a dogma. We've got to see what's the reason behind something. We just, again, can't say I was taught this way, this is how I do it. We've got to have an open mind. That's just the best way to do it. That's the best patient care. So with that in mind, Paul, I can't thank you enough for being one of the very few recurrence speakers in our lecture series for very good reason, because you are truly innovative, you have obviously extreme expertise in complex skull base procedures. And I wanna thank you for all you have done for neurosurgery and specifically skull base surgery.

- Thank you very much, Aaron, very kind words, and always a pleasure and honor to be here.

- Thanks you.

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