This lecture will be on surgery for deep and brain stem cavernous malformations. The lessons from this talk are derived from a microsurgical experience that spans almost 23 years now. And I've done over 900 cavernous malformations in the brain, 261 in the brain stem, and 64 spinal cord cavernous malformations. So hopefully, with all of those cases, I've learned a few things which I think will find a value. One of the things I'd like to introduce is some taxonomy. And I like to think of surgery for deep cavernous malformations or cavernous malformations in general as having these key corridors to go through. The first category is the trans-gyral and trans-sulcal approaches. Next is the trans-sylvian approach. The third is the inner hemispheric fissure. Fourth is through the ventricular system. Fifth is through or along the tentorium. Sixth, through the petrous bone. And finally, lastly, through the foramen magnum. So these are the seven different corridors that we typically utilize for these cavernous malformations. When I think about the surgical approaches for the brain stem and deep lesions, these are some of the big workhorses. From orbitis diagomatic all the way down to suboccipital. This talk is really just a tour through the various approaches. One of the things that's really important is to look at where the lesion comes to the surface. And that really defines which surgical approach you're going to select. These are some of the various surfaces shown in different colors for midbrain, pontine, and medullary lesions. You can see the different approaches that expose these surfaces. This is a slide that summarizes the various brain stem safe entry zones. And lesions that aren't exactly on the peel surface but are within a few millimeters of these safe entry zones can also be accessed through these various approaches. This table summarizes the surgical approaches used for a published series of mine for brain stem cavernous malformations. And you can see that there really is a limited number. And for midbrain, it's either from above using a transcolosal transcoroidal approach, or from in front using an orbitis diagomatic approach, or from behind using a supracerebellar infratentorial approach. For pontine lesions, it's either an extended retrosigmoid or a translabyrinthine from the side, or a more anterior approach through the Kawasii triangle. For medullary lesions, we have the suboccipital transventricular approach, which is the main workhorse. We have the suboccipital telovilar approach, far lateral, and then far lateral retrosigmoid. So in all, less than a dozen different approaches, subtle variations of these, but I'm going to take you through these. First is the midbrain cavernous malformation. And this is a lesion when it comes to the surface anteriorly that is nicely approached with an anterior transsylvian approach. So this is very much like an approach to a basilar apex aneurysm. On the images to the left, you can see the head position, supine with the head turned, the standard orbitis diagomatic osteotomy cuts with dural opening there to widen that sylvian fissure corridor. And then after splitting the sylvian fissure, you see the dissection down into the carotid cistern, back into the interpeduncular cistern, following the post-decommunicating artery, and getting to the midbrain. Here's a case example. Here you can see the MR images showing the lesion in the midbrain. The operative craniotomy transsylvian approach takes you all the way down to the cerebral peduncle. This sequence of the video is just the dissection of the sylvian fissure, splitting the frontal and temporal lobes apart and parting these arteries to one side or the other. The dissection now is down at the level of the optic nerve, and I'm elevating the olfactory track off the optic nerve. This is the dissection into the interoptic triangle around the region of the acom. And this is down lateral to the third nerve. Here I'm opening membrane of liloquist. And as we get through the membrane of liloquist, you can see the course of the third nerve all the way back into the interpeduncular fossa. So underneath the third nerve, you can see the superior cerebellar artery. And as we open up that arachnoid over the midbrain, we can see this bulging cavernous malformation that's right on the peel surface, and we just get right into the substance of the malformation. So one of the first steps is to just get inside, evacuate any of the liquid blood, and by removing those contents of the caverns, we can create this nice working space internally. You'll notice this lighted sucker in my right hand, which is also very useful down these deep corridors. It shines light into the resection cavity and allows us to see better the lesion. So as you go inside, you'll see portions that are cavernous malformation and other portions that are hematoma. And they're all intermixed. Sometimes a little traction on the lesion capsule allows you to develop that plane. And you can see how as you shift the vector of force, you can kind of move it from side to side and help to develop those dissection planes. You can see how this is really quite stuck, and it's important to keep delicately applying pressure, working those planes, and this malformation starts to release itself, and it comes out piecemeal. You can see a few of these perforating arteries that are overlying the malformation. Those are swept to the side. Gives you better access now to the deeper portions of the malformation. Here I'm using this angled round knife to help dissect that medial plane between gliotic tissue and the capsule. You can see that that medial portion of the capsule is very adherent to the cerebral peduncle, but it finally gives here and now it comes out as a nice final piece. And then it's important to go back into the capsule to make sure that all of the remnants have been removed to inspect that gliotic capsule 360 degrees circumferentially. And here's a good overview showing the P1 segment, the thalamal perforators. There's a nice view of the contralateral P1 segment with its thalamal perforator, mammillary bodies there, and the overview of the sylveon fissure. So you can see that transsylveon exposure offers a very nice route down to the midbrain, and our postoperative imaging shows a complete resection. This next approach is the transcolosal transcoroidal fissure approach to midbrain cavernous malformations. These illustrations show some of the anatomy more for an AVM than for cavernous malformation, but the approach is the same. The view is into the lateral ventricle, and the way that one gets down further into the third ventricle and ultimately to the midbrain is to open the coroidal fissure. The illustration on the right shows that incision along the tinea fornis, which is between the fornix and the attachment of the choroid plexus. As you go through that layer, which is an arachnoidal layer, it gets you into the third ventricle, and as you go through the third ventricle all the way to the floor, it'll take you to the top of the midbrain. We have an operative video showing this. This is the transcolosal portion, resecting some of the corpus colosum down to that ependymal layer, and now we've got a beautiful view inside the ventricle with the foramen of Monroe seen here, the fornix wrapping into the foramen of Monroe, and this tuft of choroid plexus running just on top of the septal vein. As the choroid gets cauterized, you can see the coroidal fissure coming into view. It's that arachnoidal layer that's adjacent to the vein. As that layer is dissected, you can see the foramen of Monroe widening and opening into the third ventricle, and at the very bottom or floor of the third ventricle, you can see the cavernous malformation. You can see how this transcolosal, transcoroidal fissure approach gives you a beautiful top-down view of the lesion. And I'm using my cautery to shrink the lesion, to pull it away from the adjacent tissue, and to develop this dissection plane. You can see a very nice clean gliotic margin right there. I'm using the cautery only on the lesion side, and using that cautery to shrink the pathology into the center. You can see how that malformation pulls away from the gliotic plane. That's our plane of separation, and you can see those little caverns just pop and evacuate with each bit of cautery. The lesion comes out through the enlarged foramen of Monroe, and now we've got a beautiful view looking down onto the top of the basilar apex and down the basilar trunk. This next approach is the supracerabellar infratentorial approach. For the midbrain, you can see that this can be a paramedian, or midline, or a lateral supracerabellar approach. The anatomy illustrations show the lateral approach right along the transverse sigmoid junction. So for this exposure, you can see that the trochlear nerve is one of the key landmarks in the field. You can see the superior cerebellar artery is also one of the key landmarks in the field, and these had some orientation along the way. Here is our next video. You can see the lesion sitting on the left posterolateral midbrain. This is that supracerabellar plane. So the cerebellum is nicely retracting to the left. You can see the tentorium to the right. And as we deepen our dissection, we get all the way down into the ambient cistern and quadrageminal cistern. Now as we get medially, you can see the fourth cranial nerve in that layer of arachnoid. As that arachnoid is opened, you can see that we've gotten into the ambient cistern. The midbrain comes into view. You can see some of the branches of the superior cerebellar artery. And as we widen our exposure, we get all the way back to the quadrageminal cistern. ... Here's the fourth nerve coming up from the collicular plate and coursing into the tentorium. And our cavernous malformation is gonna be located right in this area. We use our stealth to confirm the underlying location. And then once we've confirmed its location, you can see the hemocytin stain and our incision is gonna be just beneath the trochlear nerve. You can see that even though that lesion appeared right at the PL surface on the MR imaging, there's a millimeter or two of normal tissue that overlies it. But with a small opening, we get right down to the lesion itself. And once again, you can see these angled round knives that are very nice for developing those dissection planes, those separation planes between lesion and midbrain. And that combination of sharp dissection with a little bit of traction is what helps to separate this. There's a piece of the lesion coming out, and as we get to the bottom, you can see a more normal-appearing gliotic plane on the deep side, nice preservation of the fourth nerve. Here's her postoperative MRI, shows a complete removal of the lesion. This next approach is what I call the contralateral supracerebellar transcentorial approach, and you can see that for lesions in the posterolateral thalamus, if you were just to go straight midline, you only get so far laterally, whereas if you come from the contralateral side and angle across, it widens your lateral trajectory. That blue arrow tilts to the patient's right side with this kind of crossing trajectory. So it's a real nice way to get the full sweep of that trajectory. It's positioned in the sitting position with the head tucked forward, and you can see that contralateral trajectory as the blue arrow. This is a transcentorial approach because the tentorium becomes a limit that constricts the lateral reach of the surgical corridor. So in order to deal with that, an incision is made in the tentorial incisura, and that flap is pulled to the side, and that gives an additional amount of reach out laterally. The key anatomical features are the vein of Galen and the veins of that complex, which include the internal cerebral veins and the basal veins of Rosenthal, as well as the precentral cerebellar vein. You'll also see posterocerebral vessels in that cistern, and you can sometimes see the superior cerebellar arteries as well. Here's a case example. You can see this lesion is in the thalamus. It sticks upwards and really does not present any kind of peel surface. The contralateral supracerrebellar approach is nice for this. This first sequence here is getting down to the cisterna magnet to release CSF, and by releasing CSF, the cerebellum sags nicely. So you get some descent of the cerebellar tissue, and now we go over the top. So this stealth image shows the supracerrebellar trajectory, and as we go over the top, we get into the attic of the tentorial space. You can see the steep angles of the tentorium in this view, and now I'm working my way along the posterocerebral artery into that quadrageminal and ambient cistern, and I slowly and progressively work my way laterally. So the patient is in the sitting position, so this is the patient's left side, and I'm going to cut the tentorium on the left all the way to the incisura. By doing that, I can sweep the occipital lobe more laterally. That stealth image showed you the angle of the trajectory, and now with the little hiatus created through the tentorium, you can see that crossing contralateral exposure that gets you from one side to the other and really deeply into this incisural space. So here we are at the lesion. With a small incision, we can get through that thin layer of tissue. We come right upon the malformation itself. Once again, we evacuate whatever liquid component there is, we find the malformation tissue, and then we slowly work our dissection plane around it, removing it piecemeal if necessary. If it can come out as a single piece, that's ideal. It helps to ensure that all the lesion is removed. Here you can see we've got to debulk this, take it out in pieces. We make sure that we work inside the capsule as best we can, and once the capsule is reduced, we can then just focus on freeing it from its adhesion circumferentially, and then taking it out in a large piece. Here's a nice view of what the gliotic plane looks like. There's no evidence of any residual malformation. We just see normal thalamic tissue. You can see from stealth how it confirms our very lateral position. Here's an overview showing the supracerabellar approach, that crossing trajectory, and just how far laterally you can get. Here is the postoperative MRI imaging on this next slide, which shows the resection cavity, and it nicely stays away from the back portion of the internal capsule. This approach is also nice for medial occipital lobes, again, sitting position. The sitting position allows that cerebellar sag, and that contralateral approach allows you to really get a good angle across. You'll see how the arachnoid tethers the cerebellum, so it's important to take down these adhesions initially. As we do, we can get deeper down to the quadrageminal cistern. Here I'm opening up that arachnoid of the quadrageminal cistern. I can now see the venous anatomy, the veins of the galenic complex coming in. And you can see just a little bit of that medial occipital lobe sticking over the edge of the tentorium, running right along the basal vein. Here now is an incision in the medial part of the tentorium, and you can see the incision extends all the way medially to the incisor. This is a little trick I borrowed from my aneurysm technique, where we make an additional cut in the tentorium. We use an aneurysm clip. We pull that leaflet of the tentorium back, and we use that clip to hold the leaflet over. Now we've got a nice wide corridor. We can go back to the operative field, and you can see here is the posterior cerebral artery running back. I can nicely dissect that away from the malformation. And as I do, I have a clean shot at the medial occipital cavernous malformation. These are little perforators on the top and medial side, which I can visualize and dissect free. I can now turn my attention to the lesion itself. So here I'm pulling the top portion of the malformation downward, getting over the top of this separation plane. And here, the top part of the lesion is being swept free from its final adhesions. There's the posterocerebral artery, nicely protected along its course. You can see that hemocyterin stained margin. And now the malformation is free, we can roll it up and out. And even though this is quite deep, you can see how cleanly that comes free. Gravity is nicely holding the cerebellum down. We have a wide open corridor. And our postoperative MRI shows a clean resection cavity. This next case is an example of a spinal cord cavernous malformation. The other speakers will cover the pons and medulla. So I'm going to jump down to the spinal cord because I don't think this will be covered otherwise. This is a nice case example showing a cavernous malformation that occupies the center of the cervical spinal cord. For this one, it's a prone position, midline incision, two-level laminectomy. And in this particular case, what we try and do as we go to the operative video, we cut the dentate ligaments. This allows the spinal cord to float freely. And what you'll notice here as we inspect the surface of the cord is that the lesion is actually coming to the surface on the lateral and slightly medial aspect. So I've placed a proline stitch in the dentate ligament. I've lifted the spinal cord slightly. And you can see how that brings to the fore this point where the malformation works its way to the peel surface. You can see it's actually jutting through the peel layer. And by opening that incision in the pia, I can get my instruments in. I can define that dissection plane. And these cavernous malformations in the spinal cord often have a really nice gliotic plane. You can dissect the pathologic tissue. Here's a big pocket of liquefied blood that gets evacuated very easily. And as that comes out, we see even more clearly this separation plane between the malformation and the gliotic spinal cord. So this one has a particularly nice capsule, which you see here. There's some solidified blood internally, but this whole thing is going to roll nicely right out of the spinal cord. And I'm using a little sharp dissection here to free those last adhesions. You can see the mulberry-appearing malformation itself. And with a couple final cuts, the lesion becomes free. So this is a nice example of how inspecting for that point where the malformation comes to the spinal cord surface allows us to avoid a midline myelotomy or any other incision in the spinal cord tissue. Here I'm just doing my final inspection of the resection cavity, making sure there aren't small remnants left behind. And you can see here, there's a little remnant here that I've traced down and removed. And now you can see a nice clean gliotic margin there. I'll finish this talk with some thoughts about grading scale. We did look carefully at some of the variables that impact patient outcome. This is just a listing of those variables and the different values according to the level of the brainstem. We did come up with what we call the brainstem cavernous malformation grading scale. It has five different criterias, size, crossing the axial midpoint, associated developmental venous anomaly, age, and hemorrhage. And based upon the different categories here, you assign points. It's very analogous to the Spetzler-Martin grading system for AVMs. In fact, if you have a hard time remembering it, like I sometimes do, I like to think of it as the Spetzler-Martin and Lawton-Young systems rolled into one, where you've got a size element, you've got a vein element, you've got an eloquence element, which in this case is the crossing of the axial midpoint, you've got an age variable, and you've got a bleeding variable, and you put these together in order to assign points. And these, again, are predictors of surgical risk. And so this grading can actually help you when you're deciding whether or not to operate on a brainstem cavernous malformation, whether to do it or to manage it more conservatively. This grading system is really designed for lesions in the brainstem only. For other lesions in the cerebrum, it's much easier to make these decisions. It's really those in the brainstem where this might be of some value. These are graphs on this next slide showing my practice trends. You can see the numbers of cases plotted against the year, and it's a pretty steady rate of increase, ticked up a little bit recently, particularly with the high volume of brainstem cavernous malformations at the Barrow Neurological Institute. And this is just to let you see that this is a pretty healthy area of vascular neurosurgery where the volume is steady and, in fact, even growing, and it bodes well for continued good practice here. So to conclude, these are some closing thoughts. Since selection is the secret for good outcomes, as it is with many other vascular lesions, I look for candidates who have had a symptomatic hemorrhage and corresponding deficits. Lesions must surface on pia or ependyma because that allows you to get to that point and remove the lesion without having to violate brain tissue. The approach and the entry zone are critically important. You really have to select the approach very carefully and really look at that spot where you enter the brainstem to make sure that it's really right there at the surface. My resections are intracapsular as best I can, and I strive for an en bloc resection. If not possible, then I try to remove piecemeal working inside the capsule until the bitter end and then collapsing the capsule inward so that that can come out as an empty sac. As with these lesions, there's a fine line between a complete resection and surgical morbidity. If you push hard for a complete resection, you could injure adjacent brainstem tissue and get surgical morbidity that's new. On the other hand, if you're too hesitant, you can end up leaving remnant tissue and sparing neurologic morbidity but having other problems from recurrent hemorrhage in the future. So with that, I will close. I want to thank you for attending this virtual AANS session, and I hope this was educational for you. Thank you.

neurosurgeon

surgery

cavernous malformations

brain stem

taxonomy

surgical approaches