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Grand Rounds-Resection of Spinal Cord Hemangioblastoma

Paul McCormick

July 10, 2011

Transcript

- Hello and welcome, ladies and gentlemen, we're pleased to have with us Dr. Paul McCormick, our WNS president from Columbia University. Our discussion will focus on micro surgical resection of spinal cord hemangioblastomas. Paul, thank you for your time, and we look forward to your expert discussion.

- Thanks, Aaron. It's really a delight for me to be here. This is really a fantastic format to present this type of information. I'm very pleased to join you this morning.

- Thank you, our agenda would be first to have your do set of slides and go over a detailed surgical video of yours. After which I'm gonna go ahead and discuss two other surgical videos. And have you comment on the nuances of techniques. So please go ahead with your discussion. And thank you.

- So good morning. Thank you, Aaron. Welcome, everybody to this presentation of operative Grand Rounds. And the topic of this morning's presentation is on intramedullary spinal cord hemangioblastomas. And intramedullary spinal cord hemangioblastomas count for about somewhere between 10 and maybe five to 10% of intramedullary tumors. Most of them occur as solitary or sporadic occurrences about one quarter of them occur in a combination with Von Hippel Lindau. The vast majority of these arise from the pia these are not so much intramedullary tumors as much as they are just imaginary tumors, and that they have a surface presentation characterized by a sunset orange appearance, which is very characteristic for hemangioblastomas. And then a differentiating amount of a tumor then invalidates into the into the spinal cord itself. And as you can see in the upper right of the screen, there's a fair amount of intramedullary tumor at that area that extends into the spinal cord. Now, these are very heterogeneous tumors in terms of their presentation and how we have to treat them both in terms of their size and their location. They're often associated with the nerve roots, particularly the the dorsal roots, because they often have a dorsal or dorsal lateral, originate from them. They can be variable in terms of their vascularity, they often present with a significant amount of intramedullary edema, or even a cyst associated with them. And most importantly, is that there's a variable degree of proportion to tumor that has a surface presentation, versus a number of the tumors that have a large amount of tumor within the spinal cord itself. So these very superficial tumors, as you'll see, I call them snow cones. Whereas the tumors which have a small surface presentation, but a lot of tumor imaginating, into the spinal cord, and more iceberg type tumors. And you'll see that they create different challenges and there's different strategy of in terms of their removal. Here's a case of what we call a snow cone type of a tumor. We see in the upper left, there is a very superficial dorsal presentation, you see a very bright homogeneously enhancing mass in the dorsal aspect of the spinal cord. In the upper right, you see the surface presentation, where you see a tuft of vessels, if you will, and a characteristic sunset orange appearance of a tumor that's right in the dorsal midline. And then you'll see the tumor specimen in the lower left it's been removed and the tumor resection bed on the lower right hand part of the screen. Again, these tumors can be fairly small in terms of their presentation, as you can see, in this case, with the dorsal lateral tumor with very homogeneous enhancement, but you see this patient has Cerebral Wailea and even celebral bowlby and extends all the way up into the brainstem here, so these patients can often have symptoms out of proportion to the size of their tumor, and often the localizing symptoms are falsely localizing and these patients can have upper extremity symptoms or even more brainstem symptoms when their tumor is down in the thoracic area as it was in this case. These tumors can be very intimidating in terms of the vascularity here you see a tumor which is extremely vascular, and this is the interoperative picture right in the lower screen and you can see just barely that sunset orange appearance, just lateral to that top two vessels. So you can see can be very intimidating in terms of its appearance, because of this vascularity of these tumors. Here's another lesion which is actually quite large. It has a surface presentation, as you can see in the lower part of the screen, but it occupies almost the entire cross sectional area of the spinal cord. This is a very challenging tumor to take out. And one very different than the first case that I showed you, which had a very superficial presentation. And again, here's a patient, he had Von Hippel Lindau disease whose spinal cord is literally studded with these pia based lesions. Now, with Von Hippel Lindau disease, I look at the individual tumors as symptoms, whereas Von Hippel Lindau is their disease. So these are patients that you're giving them palliative treatments, symptomatic treatment of what might be a symptomatic lesion. And so this is a situation where we'll treat the patient, not the MRI. And so we will typically follow these patients over time and monitor the growth of these tumors, both in terms of the size of the lesion, but also the extent of edema or cystic formation and when they do get symptomatic, then that's the time to intervene. Remember, this is a lifetime disease that these patients have and you want to manage them over a long period of time, and only expose them to the risk of surgery when they have symptomatic lesions. And this is a fundamentally different strategy than patients who have solitary and sporadically occurring hemangioblastomas. Here's another case where there was a patient also had Von Hippel Lindau and had numerous tumors affecting the lower conus in the upper spinal area. But you can see a very characteristic sunset orange appearance of a superficially based hemangioblastomas, which is usually pretty typical in these patients. So there's a number of general principles of management for intramedullary tumors in general and specifically also for hemangioblastomas. My practice almost all these are approached with patients in a prone position I will use may fail to headpins for lesions above T6, the arms are usually put it aside and patted for lesions above the T6 but below T6, I'll generally put the arms up. Always use atrial line, I do use somatosensory evoked potentials and motorboat potentials, we can talk about their utility for intramural intramedullary tumors a little bit later during the discussion, I will use perioperative steroids. I think it's critical that you have adequate bone epidural exposure, I don't think it's a good idea to hinder your intradural work by trying to limit the amount of exposure through bone removal or drill opening, I think it's important to try to work orthogonally to the margins of the tumor and to the surface of the spinal cord whenever possible. And if stability is an issue, if you have to resect a preset joint or even do a little bit more of a bilateral approach, then stabilization should obviously be considered. Another consideration is that since you're doing these patients in a prone position is you're violating a fundamental surgical principle in that your operative exposure is really at the lowest part of your field. And so gravity does not work to your advantage. So it's extremely important to have very good hemostasis of the bone of the epidural space of the muscle before you open the dura otherwise you are you're tortured by this leakage of blood into your otherwise pristine surgical field and that can hinder your your safe achievement of the surgical objective. So general principles are somewhat different with hemangioblastomas as I said, nearly all of them right over 95% will have a surface presentation and presentation and gracefully most of these patients and tumors obviously will have a dorsal or dorsal lateral presentation. It's rare that we are presented with a ventral intramedullary tumor. They create different problems for exposure, and certainly the small sure, ventral lesions are often more appropriately approached through a ventral exposure but for the purpose of this conversation and presentation, we'll talk mainly about the dorsal and dorsal lateral tumors. And so, the key here is to identify the tumor and then to get adequate exposure over the rostral caudal medial lateral margins as you see here. This is a case of a very superficial left tumor in the dorsal midline of the spinal cord the upper cervical level which we had seen earlier and the general principle the fundamental principle is to understand that these tumors hemangioblastomas that was the spinal cord arise from the pia they are pia-based lesions and so that the key here to resection is to detach is to circumferentially detach the tumor pia which is which is sunset orange from the surrounding interface with a normal pia which is a very glistening longitudinally oriented white layer that's very robust is very different in the spinal cord than it is at the brain. And so by circumferentially, detaching the tumor pia from the surrounding one pia that devascularized is the tumor. And that really detaches the tumor from the surrounding spinal cord. The remainder of the dissection is actually fairly straightforward. So this is the key is the initial circumferential detachment of tumor pia, which is sunset orange, with a very distinct and obvious margin with the normal pia which is a glistening white. And that's the fundamental key and strategy in the removal these tumors. Now, the problem and the challenge in some of these, what I call iceberg tumors is that you have a very small surface presentation with a very large intramedullary imagination underneath this. And so a circumferential detachment by itself is not gonna give you adequate exposure of the intramuscular extension of the tumor, as you'll see in this case. And so this is a situation where, after doing the circumferential detachment, you'll have to extend both rostral and caudal, the initial pia opening into what I call P, or polar, polarmylotenemies that extend from the rostral on the caudal tip of your circumferential margin and this gives you the exposure into the spinal cord, so that you can gain access to the information a component of it and remove the rest of the tumor. So I'll stop here, and if it's okay, and take any of the questions that you might have here before we proceed with the intramedullary video case that we're gonna show here.

- Thank you, Paul, I think we cannot stress enough what we just mentioned about the issue of still location of these lesions and the fact that the key component is to de vascularized these lesions from their periphery, and before you do anything else, because if you don't have enough control over the bleeding aspect of it and you don't devasculize early on, you're going to have a lot of bleeding that planes are not clear and you could enter into the deep for the spinal cord because of inadequate visualization, and that could be very harmful. So I just would like to echo what you're very well meant.

- Okay, so the this is a video case here that I think illustrates a number of the principles that I've discussed in the previous slides. This guy this is a patient young man came from Greece 29 year old man, excellent health otherwise, who noted, had a numbness in both hands and weakness in his legs worse on the right than the left and his radiographic evaluation, including the MRI shows what I mentioned earlier, he has fairly extensive a string though amyelia that extends up into the upper cervical component of the spinal cord, even though the tumor is located down at about the T11, T12 level. So here is a case with a patient presenting with fast localizing signs of the syrinx extending all the way up into the cervical spine. And it's important here and underscores the importance of imaging the entire spinal cord, sometimes the entire neural axis in patients who had a string of amyelia as was done in this case. And so here on a more focused view, you can see the intramedullary component is a tumor, little unusual and that the tumor is not homogeneously enhancing, but it enhances very brightly. There's a surface presentation that you can see both on the MRI the axial on the upper left in the sagittal on the right side and and you'll see kind of a before and after surgical picture where you can see in the lower left the very intimidating feeding vessels and draining veins, and that little knob in of the characteristic sunset orange parents which virtually guarantees the diagnosis of hemangioblastomas. And now my man right side, you'll see at the end of the dissection, the tumors been detached from the surrounding spinal cord and its ready to be removed. But there's a lot of key steps that occur in between obviously, and we're going to go over those now with the video. So I like to kind of characterize the removal of these tumors into a number of different stages. And the first stage is really the initial exposure. That's you've done your bone work, you've opened the dura, you've identified the tumor and now you want to begin to prepare the tumor for resection. And what you'll see in the first part of the of the video is the initial arachnoid dissection. Then some characterization of the tumor surface in the feeding vessels as Aaron has talked about, which is a critical component of this tumor to manage the bleeding and to avoid the bleeding and to identify the attachment of the tumor to the surrounding spinal cord. You'll see in this case that this dissection of the nerve root early on nerve almost always has to be resected in this and then we'll identify the tumor peel margin whether it were the sunset orange appearance of the tumor pia interfaces very distinctly with the surrounding normal pia and that's the key to the removal of these of these lesions. So here is the the initial opening, the door has been opened and tented ladder with suture. Now opening the arachnoid over the tumor surface, you can see this characteristic sunset orange appearance of the superficial hemangioblastomas. Just don't bring the arachnoid over it. Mobilizing some of the feeding vessels, I notice is a very large tumor that extends into the spinal cord beginning to cauterize the tumor surface to begin to work, preferably to find out where it interfaces with a normal pia. This is the dorsal root right here that really goes right through the tumor. And you can see we're just mobilizing some of the fibers and fascicles of the dorsal root off of the tumor surface. Obviously this never will have to be cauterized and resected divided. Here's some feeding vessels at the margin of the tumor and because they are they're overlying the tumor spinal cord interface there cauterized divided so that I can see the interface between the tumor pia and the normal glistening white normal pia. These are the lateral margins of the tumor that's being mobilized. And here now I'm beginning to identify where the tumor surface meets the pia and you'll see there's a very robust peel membrane in the spinal cord and it requires sharp dissection either with a knife as here or with scissors. Here again, I'm using a neuro probe to develop that plane. And now you see this is the key to the procedure is to detach the normal white glistening pia, from the sunset orange tumor pia and here again you see the nerve hook going right underneath that peel plane here. And sharp dissection is required because of the size of the tumor more arachnoid just being open so that I can identify the margin of the tumor and its interface with a normal spinal cord and also mobilize some of the vessels. And here's a pea attraction suture I use six apparently provide some nice traction on the lateral aspect of the core, so that I can provide counter traction and dissect out the intramedullary tumor components. There's more tumor attachment here there's a feeding vessel that crosses over this margin. So this has to be cauterized and divided. And again, you just circumferentially in a very careful fashion work around the circumferential margin of the tumor where it interfaces with the glistening white pia and then you go ahead and cauterize the feeding vessels that cross over and obscure that margin and go ahead and divide this with cautery. Here you can see the nerve of developing that plane or circumferentially around the tumor. And now using attraction and counter attraction technique you begin to mobilize the intramedullary tumor components fibers attachments, and some feeding vessels are cauterize and divided and the tumor is very large. So I'm doing a polarmyelotomy first at the rostral end of the tumor as you see here. And now working down at the caudal end you need to identify both polar ends of the tumor. You'll notice that I don't have enough exposure quarterly so all it stands I'll do a conus some of the superficial vessels and I'm extending the initial circumferential myelotomy quarterly a few millimeters so that I can gain more access to the intramedullary space. Placing another pia traction suture to give me some gentle traction on the part of the spinal cord as you can see here, you can clip these lateral into the dura hang them onto a small mosquito. But now you can see the tumor beginning to deliver itself because I've circumferentially detach this peel attachment right here. I still can't see the rostral tumor margin. So I'm gonna go ahead and extend the polarmyelotomy a few millimeters more as you'll see here I'm using the micro scissors here so that I can get and I can get around and work orthogonal to the roster, follow the tumor and replace one more peel traction suture rostrally. Again, you'll see that calcium with just a little bit gain a little bit more access and a little bit more mobilization. Now what you can see is you begin to see some of the CSF now coming out of the rostral tumor cyst, you can see it now coming out. There you go right there. And that tells me that I've cut on on the polar aspect polar margin of the tumor. And we're just actually help you because it's done a lot of dissection for you. And we need to also do that quarterly to get around to the polar margin, the inferior polar margin of the tumor. And once we do that we can begin to mobilize intramedullary tumor component. One of the problems with these tumors they're so vascular, and you often can't use cautery on the surface. But when you do use a use cautery to low setting using irrigating cautery, and here again, we're just developing the intramedullary tumor component, gentle traction, counter traction, uses the inferior portion, I'm now pulling out of the tumor itself, pulling on the tumor surface right here, again, getting some traction. And you'll see that the intramedullary tumor dissection is actually fairly straightforward because there's not many feeding vessels or fibrous attachments, or few ones you do have you come around them and you cauterize the bottom. And then you here's the last feeding or draining vein right here that I've left till the very end. And just circumferentially working around, and now the tumor has been completely resected. And you can see this detached peel attachment all the way around, that allows me to deliver this tumor out of the intramedullary aspect of the spinal cord. So I think that's the end of the of the video. But you see here, despite the very large size of this tumor, despite the extreme vascularity of tumor, if you just employ certain straightforward principles on a case by case basis in terms of identifying the tumor surface, following it peripherally to the margin of the tumor cauterizing and dividing the feeding vessels that obscure that tumor, spinal cord interface, and then detaching that provides you the strategy that allows you to safely remove these tumors in the vast majority of cases. So I'll end there with the video and we can then proceed with the discussion component of this Aaron.

- Thank you, I think you have a few more slides if you'd like to review them. If not, I think you went through them very thoroughly during your video. What would you like to do or you want to just go head through my cases?

- I will go through your cases because I think these last slides really reiterate the stages of how you go about identifying, mobilizing and resuckling these tumors. And so I think we get into your component of this presentation.

- Thank you. These are the disclosures, which we should have presented the beginning of the discussion, none of which we didn't appear with the contents today. I would like to mention a paper that really I refer to very much about nuances of technique for management of spinal cord hemangioblastomas. And that's a very nice article you published, I think a few years ago on the topic in the Red journal. So I would like to attract the attention of our viewers if they would like to read more about these nuances. I would like to present a couple of cases, Paul and get your expert opinion and how you would do it differently. A 46 year old male with a one year history of progressive left upper extremity and somebody numbness and in detail exam actually, he really had only mild numbness to pinprick on the left lower extremity. MRI evaluation of the entire neuro axis was positive for the following sequences. And as you can see here, there is a nodule. I'm gonna go ahead and activate my own arrow as well. You will see a nodule right along the posterior aspect of lower part of the brainstem and medulla oblongata, where it has caused a sizable cyst. And as you very eloquently mentioned, these cysts can be causing a lot of symptoms, despite their size because of the large cyst often associated with them. More imaging reveals a nodule again on the almost midline aspect of the medulla oblongata and a large cystic component causing the displaying of the brainstem. Let's go ahead and review this surgical video if you don't mind, Paul, and here is the video of the exposure of this case as you can see through a C1 laminectomy and also the lower portion of the forum and magnum has been slightly removed with care scissor on jurors. Here I'm sort of showing the anatomy of the pica vessels moving superiorly and again, just as you mentioned coagulating the peel vessels, devascularizing the lesion is the key to go and then after that just using sharp dissection this case is more midline and posteriorily located maybe be less challenging than the keys you mentioned. But I'll let you go ahead and comment more on this video, please.

- Well, yeah, and so this is a superficial lesion, what I call a snow cone lesion. And what you're doing right now is circumferentially, detaching the attachment of the tumor, the pia from the surrounding lesion itself, you're going a little bit deeper now to develop the intramedullary component. But that's that's the key is to devascularized, the superficial component of the tumor. And then circumferentially in a very systematic fashion working around the margins of the tumor at the pia level where the tumor pia is interfacing with the normal pia. And this is just a systematic, you're just working progressively from the rostral component of the tumor on one side, and then the other side developing, it can't bring it out of the spinal cord. Obviously, internal decompression is not an option here because the vascularity of these tumors. And so you really are forced in the vast majority of cases to remove these on block. And you'll see that the intramedullary tuber component is actually fairly straightforward once you've done what you're doing here, and that is circumferentially, detaching the tumor from the surrounding peel attachment. And it's coming off very nicely here. And with a very little in the way of disruption or even manipulation of the spinal cord in the lower brainstem tissue.

- Thank you and I think one point that I should mention clearly is at the beginning of this surgery, or the micro dissection part of it, we did go as you can see all the way around and cauterize the peel feeders. As you can see, sometimes it can bleed and the surgeon has to be patient, and take his time in terms of using very fine bipolar two cautery to achieve hemostasis. But again, the key part is even though I went deep, as you can see, without going along the inferior aspects of the pull of the tumor, those features were very much coagulated at the beginning. And again, the key component is coagulated peel vessels early and then stick with microsurgical techniques or expose the polar, do some polar myelotomy in order to clearly expose the tumor and unnecessarily forced herself upon pulling the tumor from below and above and putting unnecessary traction on the spinal cord. And as you can see, this is the last stage of my resection trying to deliver the tumor. Go ahead Paul, please.

- Yeah, so as I said, once you kind of circumferentially come around, you'll find that the tumor just delivers itself right out of the spinal cord. These are very well circumscribed lesions, they have a nicely developed capsule, they're very vascular, but they provide a very clean plain between the tumor surface and the surrounding spinal cord. And the key as you mentioned is that circumferential devascularization and detachment at the peel interface where these tumors arise from.

- Thank you Paul, and as you can see, at the end this cystic cavity to was shown just to assure that this has also been decompressed. Let's go ahead and show one more case. 20 year old male with Von Hippel Lindau disease and progressive paraparesis. At this patient had a known a diagnosis and had a servo lesion previously removed. Again, many lesions and we do not necessarily do surveillance imaging on these patients unless they become symptomatic. For one of these lesions, we do not remove lesions prophylactically on these patients, because you can't cure them, they're going to continue to for more lesions. So you only treat the symptomatic ones. And so my question for you at this juncture is Paul, do you do surveillance imaging on your Von Hippel Lindau patients if they don't have any symptoms?

- Not really. I mean, I think if they're in some sort of a experimental protocol or they're being followed by the genetics department, but from my standpoint, I agree with you, if you're not going to do anything on the basis of the imaging, then there's no point in really doing routine surveillance. Obviously, if the patient develops some symptoms or or might have some symptoms, it obviously it would be important to to get some MRIs. But I think routinely the answer is no not unless they have symptoms and as I mentioned before, Von Hippel Lindau tumor is the symptom. Von Hippel Lindau is their disease.

- Thank you. So this patient had therapists on exam. And as you can see, again, it's very impressive settings that you mentioned previously and a more laterally located nodule or hemangioblastomas. And in this case, if I may show that surgical video here in a second. So here is the video, Paul. And if I may ask you if this is too much of laminectomy in terms of exposing the lesion and the dura exposure.

- Well, you probably don't need as much a bone removal or even dura opening at the rostral caudal margins. But I think that's a minor issue. I mean, obviously, you want to have adequate exposure, which you certainly have here, particularly laterally. And even if that means removing a little bit of the medial aspect of the set joint, that's important. And here, again, you're in a very nice dissection, a very clear cut margin, between the tumor and the spinal cord, the feeding vessels that cross over this are systematically being divided after they've been cauterized, and you're using some gentle traction on the tumor to develop it and bring it out of the spinal cord. Sometimes there can be a dominant draining vessel at either end. And often I'll leave that intact and have that be the last component of the tumor, so that you don't get into a kind of a hyperemia or increased venous pressure within the spinal cord. But usually these these vessels are just as they cross over the surface cauterized divided and nice traction on the tumor surface developing out a plane between the tumor and the intermediary component a small vessels and feeding attachments or systematically cauterize the body and as you're doing here, again, working systematically around the margin the peel margin of the spinal cord, which is really the key to remove all these tumors that is fundamentally different than the other intramedullary tumor such as the astrocytoma and ependymoma.

- Thank you. And I think these are the later stages of their resection, as you can see where the last attachments are being severe. And here it is that final product of the tumor being sort of rolled out and hemostasis obtained.

- And that's typically what you see.

- Here is the resection.

- And this is a very well defined margin, where normal pia interface is distinctly with a pia of the tumor. And this is the key this dissection, the circumferential dissection. In this case, you didn't need to do very much in the way of any polar myelotomy or rostrally or cautery. But some cases you do have have to do that as well. But there's a very nice selection of a case that shows the principles of removal.

- Thank you. I thought we can conclude this session with some of more common questions people have and get your expert opinion Paul, do you regular do a preoperative angiogram and embolization on these tumors?

- I do not. I find that the MRI is usually pretty diagnostic in these circumstances, and an angiogram is not helpful from a diagnostic perspective. In terms of the globalization, most of these feeding vessels are superficial and really feed the tumor from the peel aspect of it. And since that is a usually dorsal or dorsal lateral, you usually can identify those vessels very early on into surgery. And you can manage them, you can isolate them, cauterize and divide them and so I just not felt the need for embolization preoperatively. Sometimes the liquid adhesives that are used can be problematic in terms of mobilizing those vessels cauterized and dividing them. So I've just not found it very important for that. What about you Aaron?

- No, I have never embolized any of these. In all honesty, I think if you pay special attention to peel cauterization of the vessels early on, you'll be able to manage the vascularization very well. Also, there is a risk with embolize these lesions, the feeders are very small. And if you really push your interventional radiologist to try to put something in there, they may at times, place the patient at risk. So I totally agree with you that embolisation work for these tumors are really very, extremely rarely, if at all indicated. Extended laminectomy. One point well I wanted to mention is you really don't have to expose over the good portion of this cyst or the syrinx, you really need to get a good exposure, maybe one level above or below the sunset looking appearance or the term you very well used of the nodule itself. Do you have any other thoughts regarding that, Paul?

- Yeah, I agree with that. I think that I like to be able to work orthogonal to the cause of the tumor, I don't like to work at it at an angle, but I like to look at him at a 90 degree. And so for me, I think removal of enough bone did allow me to have exposure, both in terms of not only the bone, but also the dura opening and also the myelotomy so that I can work at 90 degrees. And orthogonally to the power aspect of the tumor is really all you need. So you're right, you do not need to expose the polar cysts to any significant degree.

- Thank you. And then then three, trans sectioning and spinal cord mobilization is really an art and you're very well suited through your video. It really helps on laterally local lesions, if you just remove a little bit more facet most of these lesions on the thoracic spine anyways, so you're allowed to remove more facet with our need for stabilization. So be generous on the facetectomy side of the lesion. And then using traction sutures really almost can remove any laterally or often extra laterally located lesions without significant risk to the spinal cord, don't you think?

- Yeah, I completely agree with that. And a number of these lesions, as you showed in your last case can have a lateral extension. And sometimes just dissecting, identifying the dentate ligaments and sectioning them, where they attach to the dura can be very helpful in getting that last millimeter to have exposure for safe removal.

- Thank you. For X ray loci lesions, I guess if they're exactly right in the midline, there is no lateral extension and corpectomy would be indicated. But these really are extremely rare and doing a thoracic or pectoral to remove it. And for lateral loci lesions. I just have not heard of it. Although I've heard of it in the upper thoracic spine. What are your thoughts about the very end located lesions Paul?

- So we just had a paper that came out in July of this year, in journal Neurosurgery Spine, we have a series of 35 I think anteriorly located lesions some of them within the spinal cord, and your points are good one if the spinal cord is not significantly enlarged. If the tumor is fairly small and does not rotate the spinal cord, it's very difficult to get appropriate exposure via posterior or even posterior lateral exposure. We have used minimally invasive techniques for some smiles from intramedullary lesions, which has been helpful kind of going through in a electroplural fashion. But if you have that options here, then corpectomy either electropular or transthoracic corpectomy has to be considered in the thoracic region, and certainly an anterior cervical up in the in the cervical spine or retroperitoneal, down in the lumbar spine. Gratefully, that's pretty rare. But we gain up to 70, not only with exposure ventually, but also with reconstruction of the dura and also the spine that really allows us to do it with increasing facility.

- Thank you. It's very interesting topic, spinal cord monitoring for intramedullary lesions, you have written much about that. And your experience with resection or intramedullary tumors in general, would also give us some, so hopefully idea about what to do. Let's say you're trying to remove a hemangioblastoma, you have a little bit of change in your spinal cord function and monitoring. What are you going to do differently anyways, at that point, I mean, you may increase the blood pressure you may be remove your traction sutures, but if you're not doing any of any traction on the spinal cord, how does that change the management? Would you please tell us more about that?

- That's very situationally based. And so it depends on the specific circumstances that you're having these alterations, I mean, sometimes over the period of the case, you'll begin to lose some of your amplitude with an increase duration of your somatosensory evoked potentials, that's actually fairly common. And if you're not doing anything specific that you think is responsible for that, I mean, you do just what you said is you make sure that the blood pressure is okay, you might alter the pressure on some of your retraction sutures, which might happen, if you get a diminishment of your motor response, you might stop the dissection for a period of time. But it depends on the circumstances within which it's occurring. So I mean, it's clear that monitoring correlates with post operative deficit, what's not so clear is how it can help you prevent it. Obviously, in situation where you're applying a force, or there's a blood pressure alteration, they're very important and and you need to pay attention to them. But again, it depends on the situation. And I've not find them all that helpful for the resection of these tumors, because they don't really change what you do in the vast majority of cases.

- So you don't necessarily recommend using what's called core monitoring and every case of a hamartoblastoma?

- Well, I think I use them as just as a matter of routine, whether they're useful is another story altogether. I think they're one level of protection, a safety net, if you will, but they're not infallible, and I don't really depend on the neurophysiologist to decide the extent or the method of my resection, that is information that we get, sometimes it can be helpful. And so I'd rather have it and not needed to need and not have it. So most of the time, I'll use it. It's just I found it not very useful on a case by case basis.

- Thank you. Do you find any reason for large hamartoblastoma to do piecemeal resection versus enbloc? Obviously, you don't want to get in the middle of the tumor and the bleeding and all the problems that comes with it. But for large ones, have you ever thought about, piecemeal versus enbloc?

- I have and again, I think it depends on the circumstance. Sometimes the vascularization of these tumors is more, it's segment like and there can be like a dorsal segment, a lateral segment. And I've heard and I've seen instances where some internal decompression is done, just when the sheer size of the tumor might be too large. But that's pretty rare. You can use the laser maybe the cavitron. I know at our field at NIH has talked about some subtitler or internal decompression very large tumors, I found that rarely necessary, because again, these tumors are extremely vascular and cutting into the tumor, as you need to do for an internal decompression really causes more trouble than it solves in the vast majority of cases. Occasionally might be helpful as Dr. Oldfield has showed, but most cases you remove the tumor on block.

- Thank you. Also, if you have very large feeder to some of those intimidating hemangioblastomas that you showed in your presentation that you have operated on previously, you may use a temporary clip just to see if there is a change in spinal cord function before you take it is that correct?

- I have used that much more commonly with with ABMS, obviously, but every now and again you get a tumor that has a very prominent vessel to it. And those are cases where you may wanna put a temporary clip and just watch it for 20 minutes. And again, that's a situation where the presence of interoperative monitoring can be very helpful.

- And we talked about the follow for one people in our patients. Before we conclude that Paul, are there any other pearls that you would like to share with our viewers from your experience?

- I think we touched base on most of them and not not only in terms of identification of these tumors, but how you manage them in terms of recommending surgery. For patients who have sporadic lesions. The patient has absolutely no symptoms. I tend to follow them over time you're not going to make a perfect patient better, you will often make them worse. But once they do develop symptoms, even minor symptoms in a patient with a sporadic solitary lesion I usually recommend surgery in those cases because once neurologic function begins to become impaired, you usually can't get that back. So I think that's an important issue. On the other side of Von Hippel Lindau, you want to manage these patients, you want to expose them to the least risk as possible over their lifetime. And those are patients that will allow to become symptomatic, before we would recommend surgery. Once surgery is done, I think the key components are adequate exposure, kind of conceptualizing what the surgical strategies are what the different tips that we've talked about what the sequencing of the surgery is, and doing it in a very systematic, progressive fashion and that you can give actualize these tumors, detach them from their threatening spinal cord and deliver them in a very safe and reliable manner out of the spinal cord. They become run by a very straightforward lesion to remove just following these fairly straightforward and simple principles.

- Thank you, Paul. I think those pearls are definitely key for success. I want to thank you very much for being with us this morning and helping our viewers taking better care of patients. Thank you again and thanks to our viewers for being with us.

- Thanks, pleasure.

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