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Surgical Management of Pineal Region Tumors

Jeffrey Bruce

September 29, 2020

Transcript

- Good evening, ladies and gentlemen. Thank you for joining us for another session of the virtual operating room from The Neurosurgical Atlas. As you might be able to guess, my name is not Aaron Cohen. He will be joining us later on in the lecture. I'm Luke, the man who normally is just pushing buttons behind the curtain. Our guest this evening is Dr. Jeffrey Bruce from Columbia University who will be speaking on the topic of surgical management of pineal region tumors. So without further ado, I'll turn it over to him.

- Great. Thank you. Thanks Luke. Well, it's a pleasure to be here today. I'd like to thank Dr. Aaron Cohen-Gadol for inviting me here. And I'm impressed by the number of international people we have on board here. This is still, these webinars are still a little funny when you're giving these lectures, 'cause you know you don't have much feedback and, you know, I'm not generally very funny to begin with and I think I'm even less funny on a webinar on a Zoom camera. So, I am happy to be here today talking about my favorite topic. I love pineal region surgery. You know, the anatomy is beautiful and the surgery is challenging, and yet the patients generally do very well. So I'm happy to share with you some of my operative nuances today. You know, historically, if you look at pineal surgery, I was fortunate to train under Dr. Bennett Stein who really rediscovered the approaches to the pineal region once the operating microscope came into vogue in the early 1970s. So I was really the beneficiary of that and have been able to build a very nice pineal practice as a result of that. Now, historically patients with pineal tumors did not do well with surgery. The early surgical results, even as much as a hundred years ago, Walter Dandy and others tried pineal surgery with very poor results. And so, as a result, patients were just shunted, for their hydrocephalus, and then blindly given a full course of radiation. And now we're much more sophisticated. The surgical options are much more refined and the current emphasis is really on establishing at a minimum, a histological diagnosis so that you can optimally manage these patients. Now, in the past, patients were given this so-called radiation test dose. And a lot of this had to do with the early Japanese neurosurgeons and the high prevalence of germ cell tumors in that group. Many of the patients respond very well to radiation. So patients were radiated and if the tumor responded, they were given a full course of radiation. And of course, what we've come to understand is that there's a lot of long-term effects from high dose radiation. We're mostly familiar with radiation with patients who have glioblastoma. Those patients generally don't live very long and don't live long enough to get all of this serious complications of pineal radiation. But patients with relatively low grade or benign pineal tumors, even those with malignant pineal tumors, they can live for decades. And so they get some of these really bad side effects from radiation, such as radionecrosis or hypothalamic dysfunction, or even de novo tumor growth. So current emphasis these days is really on keeping in mind the diverse histological considerations. So there's probably no area of the brain that has a more diverse group of tumors that occur there. And these tumors are divided essentially into four different groups, either pineal cell, germ cell, glial cell, or a big number of miscellaneous tumors. And in addition to these different tumor types, there's a lot of heterogeneity and diversity within each tumor type. You have tumors that are in each category, pineal, germ cell, that are either malignant, some are benign, or some are an intermediate grade. You can even have mixed cell types, particularly among germ cell tumors. You can have multiple different germ cell types within the tumor. And then you can encounter a lot of non-neoplastic pathology, vascular malformations, inflammatory infectious diseases, or even benign cysts. So establishing a histological diagnosis is really the fundamental initial principle with pineal tumors. I want to just make a parenthetical comment about pineal cysts. As you may know, about 3 or 4% of the population has pineal cysts. And if we took a hundred people off the street, three or four of them have a pineal cyst. Therefore, if we take a hundred people with headaches, three or four of them will have a pineal cyst. If you take a hundred people who are a little bit crazy, three or four of them are gonna have pineal cysts. So attributing these neurological symptoms to a pineal cyst is usually misleading. And so we don't really operate on pineal cysts unless there's clear evidence of radiographic progression or unless there's some degree of hydrocephalus, at least compromise of the aqueduct. Now, getting back to the histology here, one of the reasons why it's important to be aggressive with surgical biopsy and surgical approaches is that despite the advances we've made in radiology, radiographic variations are not really reliable for predicting histology. So you can see here are three different types of tumors that look pretty similar radiographically, yet they're very different histologically, and they all have different implications for treatment. You know, ependymomas are treated different than a pineocytoma, which are treated different than a germinoma. So really, can't go by how you think they look on the MRI scan. You really need tissue. And also, as part of the initial workup, you want to rule out germ cell tumor. So a small percentage of tumors, particularly in young males, are malignant germ cell tumors. And so, you wanna make sure, in every pineal patient that you've measured beta HCG and alpha fetoprotein in the serum, or in the CSF, if you're doing a spinal tap. And patients with positive germ cell markers, by definition, have a malignant germ cell tumor, and they don't require a tissue diagnosis. You would treat them with radiation and chemotherapy. They're fairly aggressive tumors. And many times after radiation and chemotherapy, there may be some residual tumor remaining. And in that case, we do recommend surgery, because invariably, those are benign elements of a germ cell tumor that have not responded to radiation and chemotherapy. And so, your surgery is clearly indicated for them. But in patients otherwise with positive germ cell markers, you don't need to get a tissue diagnosis. So I'm gonna speak very briefly about comparing open resection to endoscopic surgery. The benefits of open resection, or first of all, to get a definitive diagnosis, you avoid sampling error problems that occur with when you're just doing simple biopsies or with limited endoscopic approach. Most, nearly all, benign tumors can be cured with surgery. So for the 40 or 50% of benign tumors that occur in the pineal region, surgery is going to be curative. Many non-benign tumors, that is low-grade tumors that technically are not benign, such as intermediate-grade pineal cell tumors or some intermediate-grade glial tumors, or a pet line such as ependymomas, many cases, surgery alone can be curative for them as well. And malignant tumors can benefit from debulkings. And in many cases you can get a pretty radical resection, even of a malignant tumor. And, as I'll show you later on, the operative risks are acceptable. And by removing the tumor, you eliminate some of the problems that are needed to control hydrocephalus in this group of patients. So simply doing a biopsy and then treating with radiation can be acceptable in some cases. But I think, in general, when we speak of pineal tumors, open resection is best. Endoscopic considerations. Endoscopy has become more popular as more endoscopic surgeons are trained. And I think this can be a very valid approach for certain selected cases, particularly cysts, where you can puncture them and decompress them and then remove the capsule. But you still have to be concerned with sampling error if you're not getting, if you're not able to do an aggressive resection, or bleeding risks, when you biopsy these tumors within a ventricular surface, there's no tissue to really tamponade the bleeding. So even minor bleeds can become problematic. One of the advantages of that, it can be combined with an endoscopic third ventriculostomy, although generally require a separate burr hole because you don't have the right trajectory to do both through one single burr hole. Let me talk a little bit about the anatomy. One of the things that I like about pineal surgery is that when you look at the pineal gland, you can see that it's essentially a, like an extra axial structure, and therefore tumors that grow within the pineal gland can actually grow within the pineal capsule. And then they're easily separable from the surrounding structures. Anatomically, we can see that the, within the pineal region, we have the superior colliculus here, the quadrigeminal plate. We have the third ventricle here, all contained around the midbrain. And then you have the deep venous system, the internal cerebral veins here, and the vein of Galen here, and then the straight sinus. You can see the corpus callosum here as well. And when we look at this in close-up, you can once again see where the pineal gland is and see that your approaches, whether they're approaches from the supracerebellar approach or whether they're approaches coming from the occipital or parietal approach, bringing you nicely into the pineal region, because the pineal region is at the center of the head, so you're at the furthest distance from a surface. So you need to be familiar with the anatomy and with these long distances of approaches. So this is a sagittal view. If we look at this view from the top where the, where we've, this is from Dr. Rodin's book, but with the fornices having been removed and reflected back here, we see that this is the roof of the third ventricle. You see the internal cerebral veins here, and the velum interpositum, which contains the other vascular structures. When we go forward and we separate the internal cerebral veins, we can see these are essentially choroidal vessels here. And if they're in the midline, they're just going to the corpus callosum and they can often supply blood supply to the tumor. But generally you can take these tumors that are in, take these vessels that are in the midline, 'cause they're just supplying the tumor. Vessels that are off laterally, I think you have to be more careful of, because those are often supplying parts of the thalamus or even midbrain. Operative approaches. So the operative approaches to the pineal region, which is basically the posterior third ventricle, you have the infratentorial supracerebellar approach, which is sort of the classic approach coming from the midline. You have the occipital transtentorial approach, which brings you at a more superior approach. Then you have the posterior transcallosal, which comes really through the corpus callosum. I've done some transcallosal approaches in the past, but I rarely do them anymore, as I think almost every pineal tumor can be removed through an either occipital transtentorial or an infratentorial supracerebellar approach. So when it comes to the choice of approaches, I think it depends on the surgeon's experience, but also on the anatomical location of the tumor. So I think if you're a surgeon that wants to get involved with pineal surgery, it's to your benefit to learn all of the different approaches and to be facile with them. The supratentorial approaches are generally preferred for tumors that are very large, or that extend very far up supratentorially or laterally to the ventricular atrium, or those that have a significant caudal extension. The infratentorial approaches, such as the supracerebellar approaches, are generally preferred for midline tumors or tumors that are rising ventral to the deep venous system, or that extend further ventrally into the third ventricle, because you have the sort of straight trajectory to get to them. I'm gonna start by talking about the occipital transtentorial approach, which to me is a versatile, supratentorial approach. And it's very useful for tumors like you see here, because you're essentially coming from a trajectory, like this, and you are going to access the tumor right in its central geometric center. And as long as the tumor doesn't extend too far anteriorly, you'll be able to reach that part of the tumor very easily with your surgical approach. And so, one other caveat is the inferior portion of the tumor down here can be very difficult from an infratentorial approach. And so, that's another reason why we prefer the occipital transtentorial approach. And with the occipital transtentorial approach, you get a very broad exposure, you get a good view of the quadrigeminal plate, and I prefer the lateral position, but you can do this position prone. So I think from a surgeon point of view, the lateral position is very nice because you can remain seated for it. The disadvantage is that you're going to encounter the venous system overlying the tumor, such as the, to a degree, the precentral cerebellar vein, and to some degree, the vein of Galen. You do require a little bit of occipital retraction, which you have to be careful, because that can give you some temporary visual field defects. And you often have to sacrifice at least one bridging vein between the hemisphere and the sagittal sinus. And finally, it may be difficult to resect tumors that are projecting very anteriorly. So if you have a really big tumor up here, this approach makes it difficult to remove that part of the tumor. So you may be better with an infratentorial approach in that instance. Here is the setup that I like to use. I like a lateral approach. I like to be able to tilt the head downward, so that once the dura's open, just by gravity, the hemisphere drops away from the falx. And generally this can be retractorless surgery. You don't really need a retractor. And the nice thing about the lateral position is that the surgeon's hands are working in a horizontal plane. So it's a very comfortable position, even if you have a long surgery. Here is what the view looks like once you've done your parietal occipital craniotomy. You're looking at the sagittal sinus here. You have a bridging vein that's gonna have to be cauterized and divided, but then you're looking at the interhemispheric fissure and with some gentle retraction and some hyperventilation, you get a nice look down the corridor into this interhemispheric fissure. Now, here's what this looks like once you've got the brain retracted out of the way. Here is the straight sinus. Here is the tentorium, and you're going to make a cut along here, just parallel to the sagittal, to the straight sinus. Here's the falx up here. And once you make this cut, you'll be looking at the quadrigeminal plate and the tumor. Here, you can see on the diagram, here's your cut, and this correlates with the cut made over here on the operative photo. Now, here's the view once you've opened the tentorium. So here's the cut edge of the tentorium. And here is the tumor. Here's some of the overlying bridging veins overlying the quadrigeminal region, the precentral cerebellar vein. And here's your cerebellum over here. So you see have a very nice view of the tumor. There's a retractor here, which is just there to enable the photograph. But generally, I like to avoid these retractors. Here is the view looking in. Here's the tumor bed after the tumor is removed. Here is the cut edge of the tentorium. And again, you see that nice view. Okay, here is a short video. Okay, we're looking at the cut along the tentorium. And I like to cauterize the tentorium. You gotta be careful not to make this too close to the straight sinus, as the edges will bleed. You can carefully use a Bovie. Here's the tumor. We're going to cauterize and then open the capsule of the tumor, and then internally debulk it. And once the tumor is internally debulked, then we can peel it from the surrounding structures, such as the deep venous system, the cerebellum and the quadrigeminal plate. Here you can see a nice, again, a nice capsule. You can cauterize the capsule to toughen it up and facilitate your dissection. And even malignant tumors, you can try and look for that plane. The plane may be less developed, but if you look for it, it's there and it's sort of a pseudo plane in some cases. But under the microscope, you can see the difference between the tumor and the surrounding structures. And here you can see a nice view right into the third ventricle, after the tumor has been completely removed. And sometimes I'll use mirrors to look down the aqueduct, or to look towards the anterior portion of the third ventricle and make sure there are no tumor specimens remaining. Okay, next slide. Here's your postop scan. You can see the deep venous system is intact, the tumor is gone here, and you see a nice quadrigeminal plate is intact, and the cerebellum is intact. And this was a nice pineal cell tumor, low grade, and so, it had a nice capsule, it's much easier to get a complete resection with those. Okay, let me talk now about the infratentorial supracerebellar approach. And this is the sort of a classic approach that most of you are familiar with. This approach is directly in the midline. So you have a nice anatomical relationship between the trajectory and the tumor itself. And if you do this correctly, you're coming right down the geometric center of the tumor, which enables you to get tumors that extend pretty far anteriorly into the third ventricle. Going this way, you avoid any of the deep venous system. And I like to do this in the sitting position because gravity assists with the exposure, it allows the cerebellum to drop down, and you have a nice view of the dorsal surface of the tumor. Now, many people don't like the sitting position. Anesthesiologists don't like it if they're not familiar with it. But I think in this day and age, everybody is more or less familiar with it. And it's a very safe approach. You obviously have to be aware of air emboli and make sure that there are no holes in the sinus or holes in blood vessels that can entrain the air, and you obviously need to have an end-tidal PCO2 marker, so that you know if there's air getting in. But generally, in this day and age, sitting position is not a problem for most anesthesiologists. You do have to sacrifice the midline bridging veins between the cerebellum and the tentorium, and as well as the precentral cerebellar vein. And in some cases, that can be a problem if you get the venous infarcts. Here is the setup for the sitting position. Now, the infratentorial supracerebellar approach is a very difficult position, it is a very difficult surgery to do if you don't have the proper position. It can be torture for you if you don't have things set up correctly. And that means having the head flexed and the trunk flexed, so that the tentorium is approximately parallel to the floor. So if you don't have the head flexed here, and if you don't have the trunk flexed here, you're not gonna get that degree of head position that you need to be able to look through your microscope in a, you know, parallel, down the edge of the tentorium. And if you don't have this right from the beginning, it's very difficult to do this operation successfully. Here is the view, the opening. I like to bring the craniotomy just above the straight, just above the transverse sinus, and then open the dura in a U-shaped fashion and reflect it upwards, so that you're looking at the dorsal surface of the cerebellum. There are invariably some bridging veins in the midline. But by bringing the craniotomy above the transverse sinus and flapping the dura upwards, you protect the sinus and you provide the direct trajectory to the pineal region. Here's a closeup. Again, you can see those bridging veins. Those bridging veins have to be cauterized and divided. You have to be careful. If you tear them, they bleed terribly from the tentorial, from a hole in the tentorium, which can be very difficult to control. And you're best off just being careful and cauterizing and dividing it right, just above the surface of the cerebellum. Here is the view, once you've divided those veins and are coming along the surface of the cerebellum. So this retractor is on the cerebellum. And here you see the tumor. Precentral cerebellar vein, which you're going to cauterize and divide. Here's the superior colliculus. And you can see the thalamus is going to be over here and the deep venous system, the basal veins of Rosenthal are coming in from this direction on either side. But that's the view you have, and it's a very nice view of the tumor, it gives you all of the exposure you need to remove the tumor. Here is the view after you've taken the precentral cerebellar vein. You have a nice view of the entire tumor. Again, quadrigeminal plate down here. And I like to, before I even debulk the tumor, I like to really find the plane, the interface between the tumor and the quadrigeminal plate, and then between the tumor and the lateral thalamus. And finally, along the velum interpositum above. Here is the view after the tumor's removed, nice view into the third ventricle. And again, quadrigeminal plate here, and nice view into the third ventricle. And there's your postop scan. Okay, here's a video of the approach. We've got the tumor exposed. Again, the first thing I like to do is establish that plane and try and do it in an arachnoid plane, almost like you're taking out an angioma. And there can be some, there can be a small number of bridging vessels, you cauterize and divide them. And again, by exploiting that plane, you can come completely around the tumor, and then to the tumor connections along the velum interpositum. That's where the vessels are coming from. You cauterize and divide that and separate that from the velum interpositum. Once you do that, your tumor is essentially free. And, in many cases, you can remove these on block. And there, you can see the nice view into the third ventricle with the aqueduct down here, and I'll often use a mirror to be able to look down the aqueduct and again, look, make sure there's no tumor remaining. Okay, back to the slides. Okay, here... So that's the infratentorial approach. These two, the occipital transtentorial and the infratentorial approach are the two main approaches. And up till this point, probably most, about 80% of the surgeries that I did, I did from an infratentorial supracerebellar approach. And these were all midline approaches. What can happen though, is something I wanna show you here. This is one of the limitations of the infratentorial supracerebellar approach. Here you can see, this is a hemorrhagic tumor. This patient presented acutely with a hemorrhagic tumor that caused acute hydrocephalus. And we simply did a supratentorial, I mean, infratentorial supracerebellar approach. Here you can see the exposure. Here's the tumor. We took the precentral cerebellar vein, we had a nice view of the tumor. And you see, after the tumor's resected, the brain looks completely well relaxed. The thalamus, the third ventricle structures are all intact. And this patient initially woke up great, she was fine for the first couple of hours, awake and talking, and about two hours later, became sleepy, complained of headache and began a very quick spiral downhill. And when we did the scan, we see this huge venous infarct. And the venous infarct was not only in the cerebellum, because that would not be much of a problem, we could just resect some cerebellum and provide some space for the swelling, but the infarct extended into the brainstem. And essentially, this is, resulted in what essentially was a fatal outcome for this patient, because the venous infarct, once it extended into the brainstem, was fatal. So what that told us is that 1%, and we've seen this twice in 200 patients, that 1% of patients cannot tolerate taking the deep, taking the precentral cerebellar vein and any midline bridging veins. And so, that 1% mortality may be acceptable in a large series of pineal tumors, but it really made us think about the approach and see if there was some other way we could really get around this. And that led us to rediscover the lateral supracerebellar approach. And so, a number of surgeons have described this. And by coming laterally, rather than midline, you can use a smaller craniotomy and you avoid the bridging veins that are in the midline. And so, you essentially have a direct corridor to the pineal region without taking any major veins. There may be one or two small bridging veins that have to be taken, but essentially you're avoiding those midline brains. So the craniotomy is much smaller. You can see, I'd like it to extend above the transverse sinus, and a fairly small craniotomy there, but that's all you need. And by coming through a lateral approach, you again, here, you're coming laterally here. Here's a more midline approach. You avoid all of these bridging veins and you still see the deep venous system here, but your approach is right along this line, right into the pineal region. And so, what this does is it allows you, as I said, to avoid any of the deep venous system. So here's craniotomy here. Here's the approach that you see anatomically, and here's what you see in the operative microscope. So the operative field is a little bit smaller, but you don't really need much room. Even if, for a big tumor, you're gonna be working in different quadrants, and you can still remove even a large tumor with this lateral approach. And the principles are the same. You open the tumor, you internally debulk it, and then you try to develop the plane around the outside of the tumor. Here is after the tumor's remove again, looking into the third ventricle there. Here is a short video. Again, the craniotomy, you're looking at the cerebellum here, the pineal, that's the tumor way at the bottom there, you have one small bridging vein here, which you can cauterize and divide, and that's the only bridging vein that gets in your way. You can see we're not even using the retractor. The brain is coming away. And again, a smaller operative field. It's a little bit more confining, but you can see, you can dissect the tumor and then open the capsule, internally debulk the tumor. Most of these tumors are very soft. It lends itself to an internal debulking. And once you've done that, then you simply work the outer plane, the outer capsule of the tumor. And you may have to do this piecemeal in some cases, but ultimately you have a nice view into the third ventricle. And as I say, even large tumors can be removed that way. You can see the CSF there from the third ventricle. Removing your cottonoid and... Back to the slides, please. So here are results. I'm sorry, the numbers are a little bit off on this. This is an old slide, but we've done a little over 200 pineal surgeries and we have either a gross total resection or a radical subtotal resection. By radical subtotal resection, that means you've removed all visible tumor. Radiographically, the tumor is removed, but microscopically, if it's an invasive tumor, there may be some microscopic tumor. But we're able to achieve this in over 90% of benign tumors and nearly two thirds of malignant tumors. Overall, you can get a gross total or radical subtotal resection in about 78% of patients. Here in our series, operative-related deaths, we actually have two deaths. One was from the venous infarct that I showed you, and another was from a pulmonary embolus. We had two patients with major morbidity. One was another venous infarct and others were vascular related. Yeah, it's not unusual to have some transient major morbidity. Whenever you have a big tumor in the midbrain, it may require an extended ICU course. Patients are then prone to pneumonias and all of the other morbidity that occurs with extended neuro ICU stay. And in our series, we saw this in about 8% of patients. Although many patients did recover quite well. And if we look overall at benign tumors, which account for about 42% of all pineal tumors, 100% of them have ten-year tumor-free survival following complete resection. And nearly all of these benign tumors can be completely resected with a microsurgical approach. Even among malignant tumors, you can have excellent long-term survival. And many of these are germ cell tumors, of course, that respond well to radiation, but from a surgical point of view, the point being that two-thirds of patients, you're able to achieve a radiographic resection. And even if they're gonna get radiation chemotherapy afterwards, you've put them in the best position possible. So, as we summarize here, if I can just point out some of the operative nuances that we've discussed here, that the surgical approach options are based on the location of the tumor. Is it anteriorly in the third ventricle? Is it more posterior? Or does it extend more inferiorly into the quadrigeminal plate? So depending on the anatomical location, you can choose your operative approach. And to some degree, the surgeon experience. Although, again, if you're going to do a number of these tumors, you're best off being facile with all of the approaches. And I think as the videos illustrated, the idea is to look for the tumor capsule and the brain interface for, certainly for benign tumors, but even many malignant tumors, a capsule is nicely defined. And if you look for it, it's there. And it's what allows these tumors to be safely removed and completely removed. And it may be that you have to do some tumor debulking. Again, it's sort of like the meningiomas, convexity meningioma. You debulk the tumor, then you peel them away from the surrounding structures. It's the same concept. I like to avoid retractors, whether it's in the occipital transtentorial approach, avoiding retractors on the hemisphere or any of the infratentorial approaches, avoiding the cerebellar retraction, patients do much better. Respect the vascular structures. You saw the anatomy early on. Arteries and veins are all important. You take them at your own peril. And as the one caveat I showed you that a venous infarct is an unpredictable, there there's no preoperative studies you can do to predict who's gonna be in this 1% of patients, but the complication can be devastating. So you can avoid that 1% complication with an occipital transtentorial or a lateral supracerebellar approach. Although, this may be difficult if you have tumors extending into the third ventricle. If you have a really large tumor, you may simply have to accept the risk of the midline approach and just hope that they're not in that 1%. So to summarize, pineal tumors, a histological diagnosis is mandatory because there's so many different types of tumors that occur in this location and optimizing the treatment strategy and the outcome relies on accurate histological diagnosis. Aggressive surgical approaches result in excellent long-term survival, greater than 70% 10-year survival in all comers, that's benign and malignant tumors. I think the surgical morbidity is acceptable with careful techniques. And I think in today's microsurgical world that the favorable surgical results were achievable with the state-of-the-art microsurgical techniques that are available to all of us today. And with that, I'd like to thank all of my residents and colleagues and crew. They're the ones that help us take care of these patients and do such a great job with the postoperative care. And we wouldn't be able to do these kinds of things without them. Fortunately, there're better ICU doctors and surgeons than they are softball players these days, but that's our woe, and hopefully that will get better too. So thank you for your attention. And if we're able to do questions, I'm happy to take that. Okay, I'm looking at the chat room here, and there's a question. "In the occipital transtentorial approach, how far do you incise the tentorium from the midline, so as to avoid venous bleeding and injuring the fourth nerve?" That's an excellent question. And I like to go as far from the straight sinus as reasonable, at least a centimeter or two, because if you make that cut too close to the straight sinus, you'll find that the leaves of the tentorium are still open, even though it looks like they're sealed. If you open into that, you're gonna get horrendous bleeding. So come as far laterally as you can, at least a centimeter or two. And the fourth vent, the fourth nerve is actually pretty far out of the way. It's actually pretty hard to see it. So I think if you're just retracting the hemisphere a little bit and seeing what you can get along the edge of the tentorium, you're gonna be fine. Okay. "What's the anterior limit on imaging at which point you'll say most likely a posterior approach will not be able to get a gross total resection?" Well, you know, it's an interesting question. I think I have been able to, with a midline, supracerebellar approach, get tumors all the way up to the foramen Monro. Now, you need extra long instruments. I have special instruments that I use. But I think as long as you have an instrument that can get far enough, I think you can take out any tumor in the anterior third ventricle. Obviously, if you don't have long instruments, or if you're a little reticent about getting that far anteriorly, you know, there are a number of anterior approaches, usually a transchoroidal approach will get you pretty far back into the third ventricle. Or you may have to do two separate approaches. Next question. "What criteria would you take into consideration when debulking a tumor versus removing the tumor at once?" I think, I like the, obviously the size of the tumor, if the tumor is really big, you're gonna have to debulk it. But as much as possible, I will work the interface between the tumor and the surrounding structures for as far as I can, until the bulk of the tumor gets in the way. And if you have a small tumor, generally, you can just move it on block. But at some point the bulk of the tumor just gets in your way. And that's really the deciding factor as to when you internally debulk the tumor. There's actually no real downside to it. One of the things you have to be careful with is that if you're debulking the tumor, you wanna make sure you don't go through the contralateral capsule, because once you've damaged the capsule in any direction, it makes it hard to continue that nice blunt dissection from the surrounding structures. Next question. "Is it possible to perform the supracerebellar infratentorial approach in the prone position?" I think it's really difficult. I think the trajectory that you need, it's nearly impossible to get the head flexed enough to do that. So I think if you're really against the supracerebellar, I mean, really against the sitting position, you might try a lateral approach. But I think prone, the angle is just too difficult. Hey Aaron, how are you? Good to see you.

- Jeff, same here. I wanna sincerely thank you for a great webinar. I'm sorry I was missing in action at the beginning. Obviously, you are world renowned on these very challenging brain tumors. So our audience is really, truly lucky to have you with us this evening. And I was watching part of the lecture and it was spectacular. I really appreciate the effort.

- Thank you. It's a pleasure to be here. This is really a great thing that you've set up, Aaron, and I'm delighted to be part of it.

- Thank you. I think-

- I think that might be all the questions, Aaron. Do you see anything else there?

- No, I think the lecture was superb. I really appreciate the time, and great learning experience. I think the recording will be available on the website, under the section of Grand Rounds on Wednesday, and that people who are not able to be here because of similar commitments they had this evening, unfortunately, will be able to use that. So with that, I wanna really thank you for your effort and giving us some incredible technical pearls. I wish everybody a great morning, evening, wherever you are.

- Thanks so much.

- Thank you.

- Bye everyone.

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