Transcript
Thank you. So actually having seen on an earlier version of the program that I was following Dr. Bederson and knowing, you know, all of the fantastic work that's being done at Mount Sinai with augmented reality and heads of visual display and so forth, I actually decided to build off of that guessing that this is what your talk would be and kind of take it to the next level and show you, you know, kind of simplified a little bit, what we can do with the technologies that we have in the operating room now.
So I think that what you just showed us truly is tomorrow's, you know, operating it's today for you, but for the rest of us, I think it's something that we will come to be using, but also clearly requires a lot of technology which is a large financial investment and also integrating many, many different technologies that aren't built to integrate. We don't have all of those technologies at Northwestern, but we are lucky enough to have the broad spectrum of Brainlab products. And so I wanted to share with you a little bit about how we're using different aspects of the Brainlab imaging and intraoperative portfolio to improve our skull base surgery.
You know, visualization during surgery really is a number of different things. It's using image-guided navigation to help us localize our lesions, to help orient us when we're looking at small openings that may be disorienting with anatomy that is not entirely clear and can be obscured by tumor. It can actually help us in approach selection, both preoperatively and intraoperatively when we're deciding exactly how much bony exposure is necessary to get at our lesion. And it helps us assess the progress as we're going through surgery to figure out how much extent of resection we have and how much we have left to do, which can often be difficult when looking down a narrow corridor and only seeing a portion of the tumor.
It allows us to integrate information. I think we just saw that as a very good example, and bringing in different imaging modalities from different systems and then incorporating them all into one intraoperative visualization. And theoretically, it should help us minimize our exposure and create smaller surgeries that may reduce pain and discomfort for the patient, and also reduce time by making us faster and more efficient.
So, you know, how invasive should we be with skull base tumors? I think that's been a deep theme of this entire meeting, and I would say that you can go to both directions and their indications in both ways. Sometimes it's important to be maximalistic and truly go for a gross total resection in order to achieve a surgical cure or to at least substantially cite or reduce to have a better long-term outcome. At other times, we wanna be minimalists. With benign disease, particularly small lesions, we don't wanna do very, very large approaches when a smaller, minimally invasive approach would be equally well for achieving our goal. And intraoperative imaging can help us choose which one is correct. And also facilitate that in the most efficient way.
So, you know, a few pieces of equipment that most of you probably have in your operating rooms, you probably have some frameless stereotactic navigation system, you know. Traditionally in the past, we just used that as GPS as localization, you put a pointer in and see where you are spatially on your preoperative scans. But now actual preoperative image identification. We heard that, you know, some of this is done automatically through auto segmentation algorithms. Some of it is done manually through manually painting the tumor. But by predefining objects that are gonna be of interest during surgery is actually quite helpful either through the standard frameless stereotactic navigation display, because it allows you to highlight the structures that you're most interested in. And when you place your pointer in there, you actually get a better idea of where am I relative to the tumor and the tumor brain stem interface. And if you're using heads-up display, it's absolutely necessary.
There's augmented reality in the use of the microscope. And there's a few different ways in which we can make use of that. One is the heads-up display that was just discussed quite a bit. The other reason to integrate your microscope with your system is actually so that you just don't have to raise your head up out of the field to look at the navigation.
So I think we're probably all used to operating, putting the navigated pointer in, and then having to look up and around our microscope to the navigation screen in order to see where the pointer tip is. But now with some of the new microscope integration tools, you can actually get in your heads-up display a projection of your orthogonal views with your tracking, so that you never have to come out of your field of view and break your concentration in order to see how your navigation is working out.
And then lastly, the integration of intraoperative imaging. We are fortunate enough to have an arrow inoperative CT. Some people even have a intraoperative MRI, which has quite a number of uses. And so if you can incorporate that with your navigation, that's fantastic. If you don't have this though, you're not completely out of luck because using image fusion, you can actually obtain preoperative CTs and MRIs and use image fusion to make the most of multimodality imaging. And I'll talk a little bit about how to use that.
So I wanna talk about being minimally invasive and using your tools in the operating room to actually help facilitate that. And I wanna do it by way of example of a case. So here's a patient of mine actually fairly recent in the last couple months who showed up with headaches and some personality changes and confusion from this olfactory groove meningioma that was causing a fair bit of frontal edema. And, you know, you look at this, it's not a very big lesion and there are a number of different ways to approach this. Certainly, if you've been paying attention, you know, over the last day or so, there have been many talks about endonasal endoscopic approaches, and you absolutely could approach this endonasally transcribiform.
It has a nice plane of surrounding parenchyma around it and isn't in contact with the vessels, but this patient has normal smell. So if you do go transcribiform for something that's basically covering both sides of the cribriform, you're going to make her anosmic. And that's a discussion, you know, that we had with the patient and was not something she was terribly interested in.
So what are our other options for dealing with this? So there's a traditional, you know, open bifrontal craniotomy, but we wanna be minimally invasive in this era. That didn't seem like a good idea. I mentioned that you could do an endonasal endoscopic transcribiform approach. But alternatively, you could do something transcranial through a super orbital keyhole. Now, this approach is really all above the orbital rim, right? So this is just a low frontal craniotomy through a small super orbital incision.
You can modify this a little bit and do a cranial orbital keyhole by using the same technique as you would for a one-piece cranial orbital craniotomy, and actually extending your craniotomy down to include the orbital rim. And that gives you a little bit more visualization, but also takes a little bit more effort and increases the chances of getting into the frontal sinus and the possibility of a leak.
So how do you decide which one of these two approaches, if you are gonna use a cranial approach is appropriate? Well, that's where imaging intraoperatively can really help out. So you've seen that we can project tumor through the heads-up display on the microscope. And so the standard incision for our super orbital approach is an eyebrow incision here. We can see where the tumor is relative to this. And an important point that was made in the earlier augmented reality session earlier today, is that when you're looking at this, parallax comes into view very importantly.
So it depends on which way you have the microscope angled towards the lesion. The lesion is actually gonna shift when you're looking at the surface of the skin and the lesion is quite deep in there. So as we look here, very superficially, you know, this doesn't really look like it's in the midline, right? We know that the tumor is actually quite midline over the cribriform plate, but we're looking at a slight angle with the microscope and we see where this ends up. So we can make our incision because it's not gonna change. You know, we can do both potential bony approaches through the same incision, but when we open up and we actually do get a look at the orbit here, we see that this tumor seems to be going pretty low. And if you stuck with a standard super orbital craniotomy, which is gonna end above the orbital rim, it's gonna be pretty hard to reach medial and low, to get all the way down to the base.
And so that suggests to us that doing a cranial orbital approach is gonna give us a better visualization here. And also it seems that if we do go down and the limitation of this usually is the superior orbital notch where the nerve is coming through, it looks like from the angulation that we have here, that we're gonna be able to see most of the tumor and only have a little bit past the margin that we're gonna have to reach out laterally to. And again, we can continue this heads up display. As we do the craniotomy, we have our little one-piece cranial orbital craniotomy here, and now we see clearly we're gonna be able to fold the dura down over the orbital contents, pull them down a little bit and get all the way to the base of this tumor.
And here, you know, you can navigate using the integrated navigation off of the microscope. So you can actually see the projection of your angle that you're looking at with the microscope projected here. It's a little bit hard to see with the blue line, but what it shows you clearly is, as you move the microscope around, you're going to be able to get all the way down to the base anteriorly on this, which you know, is hard when you're coming from the sort of front lateral approach to get all the way to the front of the cribriform to get the most anterior portion of this tumor. But this allows you to know that this is gonna work out before you're done with all of your bony opening, and decide to actually open the dura and proceed.
And so with this, we're able then to remove the tumor, the tumor comes out in whole. And for some of the people in here who like endoscopic surgery, like my friend, Dr. Lee you know, whether I use this approach versus an endoscopic approach, this patient was able to keep her sense of smell here. And I'll point out that this is heard or two-week postoperative visit, right after we've removed her sutures. This was left-sided, although you can barely tell there, you know, the pain associated with this minimally invasive cranial orbital approach is very, very limited. I actually find it's less than when we have to go in endonasally and raise up a nasal septal flap.
There's no issues with endonasal crusting and so forth that that are then gonna need debridement later. And the risk of CSF leak into the sinuses, of course, is non-existent here unless we penetrated through during the drilling of the cribriform. So I feel like this is really an effective way to treat anterior skull-based tumors in a minimally invasive way that, you know, I think endonasal endoscopic approaches are great also. But as a transcranial approach, this really is minimally invasive and achieves the same task.
So now let's switch over to being maximally invasive. So sometimes going small is not the goal, we actually wanna go big. And the place that that is probably most important is when we're talking about meningiomas associated with hyperostosis because we know that the hyperostosis contributes to the mass effect and the symptoms that the patients have. The hyperosteotic bone is infiltrated by meningothelial tumor cells. And we are not really achieving a Simpson grade one gross total resection with a low risk of recurrence, unless we remove this bone in addition to the soft tissue component of the tumor. And so complete resection, including the bone, is the goal. But when you do that, you have to make sure that you get everything out.
You know, the tumor is what's...or the hyperostosis bone when we're talking about these lateral sphenoid wing lesions, is what's responsible both for the visual consequences, because it puts pressure on the globe and even on the optic nerve, within the optic canal, and it's associated with the cosmetic deformity and the proptosis, which we're trying to also treat for the patient.
If you do get a complete resection, you're able to remove all that bone. Of course, reconstruction is necessary. I'm not gonna go in that today, but I tend to use a combination of med poor products for that. But what's really important about intraoperative imaging and the reason why I feel that all these tools are important rather than just doing this by look and feel is that you, you know, we really need to ensure a complete resection of the affected bone.
Navigating off MRI alone, in this case, is insufficient. Although you can see very, very thickened bone on MRI, it's very hard to tell at the margin where that meets normal bone, what's slightly hyperostotic, and what's not MRI is just not the ideal modality. And if you're trying to do it, it by look and feel alone, I would say that's even less reliable because different areas of bone are gonna have different thickness. Something may thin out just because you're getting back along this sphenoid wing. And you may think that you're through the hyperostosis, but in fact, your scan would argue differently.
And so the best way to do this is to integrate CT imaging, which is much better for the bone with MR which is good for your soft tissue. If you're lucky enough to have a intraoperative CT scan, you can actually obtain that image intraoperatively, and it'll assist you with registration as well. But if not, you can just get a preoperative thin-cut CT and fuse that to your MRI. And what you end up getting here is imaging that looks at both the soft tissue component, as well as the bony hyperostotic component.
Now, you know, we've talked about the importance of painting the target using these smart brush tools in order to identify it and highlight it on your scans, and that's very important even for the hyperostotic bone. So we're used to identifying the soft tissue component of the bone by creating it as an object in the navigation. But we can also create an object out of the hyperostotic bone, and you can somewhat automate this by windowing and on the bone and using thresholding to actually just highlight all of the bone off the CT, and then creating a region of interest, narrowing that down, and then using the smart brush to kind of erase the normal areas of bone around it. So this is actually a very rapid process. And then you can end up fusing these images and create either 2D or 3D fusions of it so you can really get a sense of the anatomy of the soft tissue component along with the hyperostotic bone component.
And then we go into the actual resection itself. So Brainlab has a number of different elements, and there is this element adaptive hybrid surgery, which is meant to look at extensive resection and then do radiation planning as you're resecting a tumor.
But one of the components of that is something called the intraoperative structure update. And basically, that's like a real-time eraser for your objects. It allows you to put your navigated wand into the field and navigate through the areas where you've resected tumor or hyperostotic bone. And it effectively deletes that from the scan and shows you what's left in terms of tumor that you haven't resected. And what you end up getting is, you know, a changing tumor object with changing dimensions as you go through and do this iteratively. But it can be very useful to look at the extent of your bony resection.
So when you start by identifying that hyperostotic bone, and then you go through there, as you're resecting, it can show you where you're left with hyperostosis, where you've actually drilled it away and so you know how much bone is left. And if we look here at a postoperative CT scan fused with the preoperative navigated CT scan, you can see that it matches pretty well. You know, we targeted this area for removal and we were able to remove that, and it showed us that we still had a remnant here that we actually ended up leaving and you can see that that remnant is still there. That's deep along the medial posterior apex of the orbit where we decided to leave that in order to not violate into the sinus.
So, you know, a few people have said today throughout the earlier augmented reality session, and you've heard this from Dr. Bederson earlier that the quality of your is only as good as the quality of your registration. If your registration is off, your navigation is off and all of these tools become basically ineffective for you. And so it's very important for us to get very highly accurate registration. This is true in other areas. And I think it's probably absolutely most important when you're doing anything that involves stereotactic guidance such as implantation of probes, stereotactic, biopsies, and so forth. We're being a little bit off on the navigation and inserting something deep into the brain can set you way, way off because of the angular distortion. And so having a way to get very, very highly accurate registration is very important.
And I deal with this very often because I also do a lot of laser ablation and there, you know, we place a probe in the operating room, and then we transfer the patient to the MRI scanner, and that probe's gotta be placed perfectly centrally within the tumor in order to be able to get the heat distribution to reach all boundaries of the tumor. We do a lot of pre-planning and plan trajectory. But if your navigation registration is off, you're not gonna hit your target.
And so when we do these lit cases, we've actually gone to registering patients using intraoperative CT, even though it's not useful for us for actual navigation purposes. So here's a case of a patient I did a couple of weeks ago. She's got a metastasis in the occipital lobe that's been treated with radiosurgery a few times, continues to progress. We suspected that this was actually radiation necrosis. She's having seizures coming from this area because of extensive edema. And she's very, very poorly functional at this point because she's got advanced cancer. She's not doing very well. We could easily take this out with a craniotomy, but we want to take a more minimally invasive approach.
And so lit is perfect for her, but this is on the back of her head, which means we're positioning her lateral with her head turned down, and we've got to position our laser probe in the perfect center of this lesion. And so we have to have very accurate registration, what we use in this case is the arrow. Which you'll notice, if you've seen an arrow, is that it has these reflective markers over the surface of the scanner. And what that does is these are similar to the reflective spheres on your navigated instruments. It allows the camera to see this and recognize what air the machine is in space. And it knows the configuration of the imaging centrally.
And if you have a reference frame attached to the patient there, it can calculate the distance between the central point of the scanner itself and the reference array on the patient so that when you construct a CT scan off of this in time, it knows the distance from every voxel to the reference array. And so it is a perfect registration and that registration can then be fused CT to MR so that you can navigate off of an MRI with submillimetric accuracy.
And so we use that for these cases and you can see this is an intraoperative MRI imaging. We positioned the probe perfectly centered, where we wanted, and ablated this lesion. And so, you know, basically, in summary, inoperative image-guided navigation can be integrated with things like augmented reality, real-time intraoperative imaging to enhance the quality of your skull base imaging, both to plan minimally invasive approaches and to assess your extent of residual when you're trying to be maximally receptive for the tumor.
But image guidance is only as good as its registration. And so I would say that automated registration techniques, whether it's through the use of intraoperative CT or any kind of future technology that's emerging is critically necessary to be accurate with what we do. So I thank you very much for your time and...
So I think that what you just showed us truly is tomorrow's, you know, operating it's today for you, but for the rest of us, I think it's something that we will come to be using, but also clearly requires a lot of technology which is a large financial investment and also integrating many, many different technologies that aren't built to integrate. We don't have all of those technologies at Northwestern, but we are lucky enough to have the broad spectrum of Brainlab products. And so I wanted to share with you a little bit about how we're using different aspects of the Brainlab imaging and intraoperative portfolio to improve our skull base surgery.
You know, visualization during surgery really is a number of different things. It's using image-guided navigation to help us localize our lesions, to help orient us when we're looking at small openings that may be disorienting with anatomy that is not entirely clear and can be obscured by tumor. It can actually help us in approach selection, both preoperatively and intraoperatively when we're deciding exactly how much bony exposure is necessary to get at our lesion. And it helps us assess the progress as we're going through surgery to figure out how much extent of resection we have and how much we have left to do, which can often be difficult when looking down a narrow corridor and only seeing a portion of the tumor.
It allows us to integrate information. I think we just saw that as a very good example, and bringing in different imaging modalities from different systems and then incorporating them all into one intraoperative visualization. And theoretically, it should help us minimize our exposure and create smaller surgeries that may reduce pain and discomfort for the patient, and also reduce time by making us faster and more efficient.
So, you know, how invasive should we be with skull base tumors? I think that's been a deep theme of this entire meeting, and I would say that you can go to both directions and their indications in both ways. Sometimes it's important to be maximalistic and truly go for a gross total resection in order to achieve a surgical cure or to at least substantially cite or reduce to have a better long-term outcome. At other times, we wanna be minimalists. With benign disease, particularly small lesions, we don't wanna do very, very large approaches when a smaller, minimally invasive approach would be equally well for achieving our goal. And intraoperative imaging can help us choose which one is correct. And also facilitate that in the most efficient way.
So, you know, a few pieces of equipment that most of you probably have in your operating rooms, you probably have some frameless stereotactic navigation system, you know. Traditionally in the past, we just used that as GPS as localization, you put a pointer in and see where you are spatially on your preoperative scans. But now actual preoperative image identification. We heard that, you know, some of this is done automatically through auto segmentation algorithms. Some of it is done manually through manually painting the tumor. But by predefining objects that are gonna be of interest during surgery is actually quite helpful either through the standard frameless stereotactic navigation display, because it allows you to highlight the structures that you're most interested in. And when you place your pointer in there, you actually get a better idea of where am I relative to the tumor and the tumor brain stem interface. And if you're using heads-up display, it's absolutely necessary.
There's augmented reality in the use of the microscope. And there's a few different ways in which we can make use of that. One is the heads-up display that was just discussed quite a bit. The other reason to integrate your microscope with your system is actually so that you just don't have to raise your head up out of the field to look at the navigation.
So I think we're probably all used to operating, putting the navigated pointer in, and then having to look up and around our microscope to the navigation screen in order to see where the pointer tip is. But now with some of the new microscope integration tools, you can actually get in your heads-up display a projection of your orthogonal views with your tracking, so that you never have to come out of your field of view and break your concentration in order to see how your navigation is working out.
And then lastly, the integration of intraoperative imaging. We are fortunate enough to have an arrow inoperative CT. Some people even have a intraoperative MRI, which has quite a number of uses. And so if you can incorporate that with your navigation, that's fantastic. If you don't have this though, you're not completely out of luck because using image fusion, you can actually obtain preoperative CTs and MRIs and use image fusion to make the most of multimodality imaging. And I'll talk a little bit about how to use that.
So I wanna talk about being minimally invasive and using your tools in the operating room to actually help facilitate that. And I wanna do it by way of example of a case. So here's a patient of mine actually fairly recent in the last couple months who showed up with headaches and some personality changes and confusion from this olfactory groove meningioma that was causing a fair bit of frontal edema. And, you know, you look at this, it's not a very big lesion and there are a number of different ways to approach this. Certainly, if you've been paying attention, you know, over the last day or so, there have been many talks about endonasal endoscopic approaches, and you absolutely could approach this endonasally transcribiform.
It has a nice plane of surrounding parenchyma around it and isn't in contact with the vessels, but this patient has normal smell. So if you do go transcribiform for something that's basically covering both sides of the cribriform, you're going to make her anosmic. And that's a discussion, you know, that we had with the patient and was not something she was terribly interested in.
So what are our other options for dealing with this? So there's a traditional, you know, open bifrontal craniotomy, but we wanna be minimally invasive in this era. That didn't seem like a good idea. I mentioned that you could do an endonasal endoscopic transcribiform approach. But alternatively, you could do something transcranial through a super orbital keyhole. Now, this approach is really all above the orbital rim, right? So this is just a low frontal craniotomy through a small super orbital incision.
You can modify this a little bit and do a cranial orbital keyhole by using the same technique as you would for a one-piece cranial orbital craniotomy, and actually extending your craniotomy down to include the orbital rim. And that gives you a little bit more visualization, but also takes a little bit more effort and increases the chances of getting into the frontal sinus and the possibility of a leak.
So how do you decide which one of these two approaches, if you are gonna use a cranial approach is appropriate? Well, that's where imaging intraoperatively can really help out. So you've seen that we can project tumor through the heads-up display on the microscope. And so the standard incision for our super orbital approach is an eyebrow incision here. We can see where the tumor is relative to this. And an important point that was made in the earlier augmented reality session earlier today, is that when you're looking at this, parallax comes into view very importantly.
So it depends on which way you have the microscope angled towards the lesion. The lesion is actually gonna shift when you're looking at the surface of the skin and the lesion is quite deep in there. So as we look here, very superficially, you know, this doesn't really look like it's in the midline, right? We know that the tumor is actually quite midline over the cribriform plate, but we're looking at a slight angle with the microscope and we see where this ends up. So we can make our incision because it's not gonna change. You know, we can do both potential bony approaches through the same incision, but when we open up and we actually do get a look at the orbit here, we see that this tumor seems to be going pretty low. And if you stuck with a standard super orbital craniotomy, which is gonna end above the orbital rim, it's gonna be pretty hard to reach medial and low, to get all the way down to the base.
And so that suggests to us that doing a cranial orbital approach is gonna give us a better visualization here. And also it seems that if we do go down and the limitation of this usually is the superior orbital notch where the nerve is coming through, it looks like from the angulation that we have here, that we're gonna be able to see most of the tumor and only have a little bit past the margin that we're gonna have to reach out laterally to. And again, we can continue this heads up display. As we do the craniotomy, we have our little one-piece cranial orbital craniotomy here, and now we see clearly we're gonna be able to fold the dura down over the orbital contents, pull them down a little bit and get all the way to the base of this tumor.
And here, you know, you can navigate using the integrated navigation off of the microscope. So you can actually see the projection of your angle that you're looking at with the microscope projected here. It's a little bit hard to see with the blue line, but what it shows you clearly is, as you move the microscope around, you're going to be able to get all the way down to the base anteriorly on this, which you know, is hard when you're coming from the sort of front lateral approach to get all the way to the front of the cribriform to get the most anterior portion of this tumor. But this allows you to know that this is gonna work out before you're done with all of your bony opening, and decide to actually open the dura and proceed.
And so with this, we're able then to remove the tumor, the tumor comes out in whole. And for some of the people in here who like endoscopic surgery, like my friend, Dr. Lee you know, whether I use this approach versus an endoscopic approach, this patient was able to keep her sense of smell here. And I'll point out that this is heard or two-week postoperative visit, right after we've removed her sutures. This was left-sided, although you can barely tell there, you know, the pain associated with this minimally invasive cranial orbital approach is very, very limited. I actually find it's less than when we have to go in endonasally and raise up a nasal septal flap.
There's no issues with endonasal crusting and so forth that that are then gonna need debridement later. And the risk of CSF leak into the sinuses, of course, is non-existent here unless we penetrated through during the drilling of the cribriform. So I feel like this is really an effective way to treat anterior skull-based tumors in a minimally invasive way that, you know, I think endonasal endoscopic approaches are great also. But as a transcranial approach, this really is minimally invasive and achieves the same task.
So now let's switch over to being maximally invasive. So sometimes going small is not the goal, we actually wanna go big. And the place that that is probably most important is when we're talking about meningiomas associated with hyperostosis because we know that the hyperostosis contributes to the mass effect and the symptoms that the patients have. The hyperosteotic bone is infiltrated by meningothelial tumor cells. And we are not really achieving a Simpson grade one gross total resection with a low risk of recurrence, unless we remove this bone in addition to the soft tissue component of the tumor. And so complete resection, including the bone, is the goal. But when you do that, you have to make sure that you get everything out.
You know, the tumor is what's...or the hyperostosis bone when we're talking about these lateral sphenoid wing lesions, is what's responsible both for the visual consequences, because it puts pressure on the globe and even on the optic nerve, within the optic canal, and it's associated with the cosmetic deformity and the proptosis, which we're trying to also treat for the patient.
If you do get a complete resection, you're able to remove all that bone. Of course, reconstruction is necessary. I'm not gonna go in that today, but I tend to use a combination of med poor products for that. But what's really important about intraoperative imaging and the reason why I feel that all these tools are important rather than just doing this by look and feel is that you, you know, we really need to ensure a complete resection of the affected bone.
Navigating off MRI alone, in this case, is insufficient. Although you can see very, very thickened bone on MRI, it's very hard to tell at the margin where that meets normal bone, what's slightly hyperostotic, and what's not MRI is just not the ideal modality. And if you're trying to do it, it by look and feel alone, I would say that's even less reliable because different areas of bone are gonna have different thickness. Something may thin out just because you're getting back along this sphenoid wing. And you may think that you're through the hyperostosis, but in fact, your scan would argue differently.
And so the best way to do this is to integrate CT imaging, which is much better for the bone with MR which is good for your soft tissue. If you're lucky enough to have a intraoperative CT scan, you can actually obtain that image intraoperatively, and it'll assist you with registration as well. But if not, you can just get a preoperative thin-cut CT and fuse that to your MRI. And what you end up getting here is imaging that looks at both the soft tissue component, as well as the bony hyperostotic component.
Now, you know, we've talked about the importance of painting the target using these smart brush tools in order to identify it and highlight it on your scans, and that's very important even for the hyperostotic bone. So we're used to identifying the soft tissue component of the bone by creating it as an object in the navigation. But we can also create an object out of the hyperostotic bone, and you can somewhat automate this by windowing and on the bone and using thresholding to actually just highlight all of the bone off the CT, and then creating a region of interest, narrowing that down, and then using the smart brush to kind of erase the normal areas of bone around it. So this is actually a very rapid process. And then you can end up fusing these images and create either 2D or 3D fusions of it so you can really get a sense of the anatomy of the soft tissue component along with the hyperostotic bone component.
And then we go into the actual resection itself. So Brainlab has a number of different elements, and there is this element adaptive hybrid surgery, which is meant to look at extensive resection and then do radiation planning as you're resecting a tumor.
But one of the components of that is something called the intraoperative structure update. And basically, that's like a real-time eraser for your objects. It allows you to put your navigated wand into the field and navigate through the areas where you've resected tumor or hyperostotic bone. And it effectively deletes that from the scan and shows you what's left in terms of tumor that you haven't resected. And what you end up getting is, you know, a changing tumor object with changing dimensions as you go through and do this iteratively. But it can be very useful to look at the extent of your bony resection.
So when you start by identifying that hyperostotic bone, and then you go through there, as you're resecting, it can show you where you're left with hyperostosis, where you've actually drilled it away and so you know how much bone is left. And if we look here at a postoperative CT scan fused with the preoperative navigated CT scan, you can see that it matches pretty well. You know, we targeted this area for removal and we were able to remove that, and it showed us that we still had a remnant here that we actually ended up leaving and you can see that that remnant is still there. That's deep along the medial posterior apex of the orbit where we decided to leave that in order to not violate into the sinus.
So, you know, a few people have said today throughout the earlier augmented reality session, and you've heard this from Dr. Bederson earlier that the quality of your is only as good as the quality of your registration. If your registration is off, your navigation is off and all of these tools become basically ineffective for you. And so it's very important for us to get very highly accurate registration. This is true in other areas. And I think it's probably absolutely most important when you're doing anything that involves stereotactic guidance such as implantation of probes, stereotactic, biopsies, and so forth. We're being a little bit off on the navigation and inserting something deep into the brain can set you way, way off because of the angular distortion. And so having a way to get very, very highly accurate registration is very important.
And I deal with this very often because I also do a lot of laser ablation and there, you know, we place a probe in the operating room, and then we transfer the patient to the MRI scanner, and that probe's gotta be placed perfectly centrally within the tumor in order to be able to get the heat distribution to reach all boundaries of the tumor. We do a lot of pre-planning and plan trajectory. But if your navigation registration is off, you're not gonna hit your target.
And so when we do these lit cases, we've actually gone to registering patients using intraoperative CT, even though it's not useful for us for actual navigation purposes. So here's a case of a patient I did a couple of weeks ago. She's got a metastasis in the occipital lobe that's been treated with radiosurgery a few times, continues to progress. We suspected that this was actually radiation necrosis. She's having seizures coming from this area because of extensive edema. And she's very, very poorly functional at this point because she's got advanced cancer. She's not doing very well. We could easily take this out with a craniotomy, but we want to take a more minimally invasive approach.
And so lit is perfect for her, but this is on the back of her head, which means we're positioning her lateral with her head turned down, and we've got to position our laser probe in the perfect center of this lesion. And so we have to have very accurate registration, what we use in this case is the arrow. Which you'll notice, if you've seen an arrow, is that it has these reflective markers over the surface of the scanner. And what that does is these are similar to the reflective spheres on your navigated instruments. It allows the camera to see this and recognize what air the machine is in space. And it knows the configuration of the imaging centrally.
And if you have a reference frame attached to the patient there, it can calculate the distance between the central point of the scanner itself and the reference array on the patient so that when you construct a CT scan off of this in time, it knows the distance from every voxel to the reference array. And so it is a perfect registration and that registration can then be fused CT to MR so that you can navigate off of an MRI with submillimetric accuracy.
And so we use that for these cases and you can see this is an intraoperative MRI imaging. We positioned the probe perfectly centered, where we wanted, and ablated this lesion. And so, you know, basically, in summary, inoperative image-guided navigation can be integrated with things like augmented reality, real-time intraoperative imaging to enhance the quality of your skull base imaging, both to plan minimally invasive approaches and to assess your extent of residual when you're trying to be maximally receptive for the tumor.
But image guidance is only as good as its registration. And so I would say that automated registration techniques, whether it's through the use of intraoperative CT or any kind of future technology that's emerging is critically necessary to be accurate with what we do. So I thank you very much for your time and...