David M. Frim, MD, PhD, narrates his surgical procedures for the treatment of epilepsy - the placement of subdural electrode arrays and cortical topectomy.
[MUSIC PLAYING] DAVID FRIM: My name is David Frim. I'm a neurosurgeon at the University of Chicago. Today I'd like to discuss with you and review a video about the subdural implantation of electrodes on the brain for the diagnosis and subsequent treatment of epilepsy. Our evaluation included a variety of tests done by our neuro-medical colleagues. They included EEG examination of her scalp, as well as a variety of other pre-operative tests. These tests localized the area that was producing her epilepsy to what appeared to be possibly the temporal lobe or some area close by. In the first procedure, which we'll be watching in a moment, we're doing an operation to open the cranial vault and to place electrodes similar to those used in the scalp EEG directly onto the surface of the brain to try and localize in a millimeter to millimeter way, the location of the seizure focus. In the second operation that followed approximately one week later, we'll be able to see how we reopened the first operative bed, and then used the location of the electrodes to pinpoint on the brain surface where the epilepsy was coming from, and then to remove those parts of the brain that we felt would most likely leave the patient without any seizure-generating tissue. Why don't we begin watching the video right now? As you can see, we've positioned the patient, and now we're incising the skin in a way that will allow optimal healing but also give us the best view and the best working space around the various areas where we think the epileptic focus might be. The patient is asleep. And she's positioned on her back, with a roll under her shoulder that allows us to easily turn her head so that it is, in a sense, sideways but parallel to the floor. This allows the anesthesiologist access to her airway and other items that are very important to them. Moving along the operation-- we have turned back a flap of skin and muscle. As you can see now, the incision is curvilinear, and it's based on the anterior skull base between the frontal and temporal insertion of the zygoma. This then gives us exposure over the bones over the temporal lobe, over the anterior and interior part of the frontal lobe, and then more posteriorly, over the parietal bone covering the parietal lobe. Here we're outlining our craniotomy flap, the bone that we're going to remove and that will give us access to the dura, which is the overlying tissue on top of the brain itself. There's a number of things that we're considering as we look around our bony exposure, having to do with where we're going to enter through the bone, what's the most efficient and safe way to cut the bone edges so that they'll heal optimally but also give us adequate access to the brain surface. We tend to outline our bone cuts as you see. And we try to be very precise in our planning, so that it allows us to be just as precise in the execution of most of what we do. Currently, we're outlining near the skull base. And we'll be bringing the drill onto the field momentarily to make our holes. Once the holes through the bone are completed then we can connect them with a specific drill bit that we call the craniotome that allows a very specific and precise cut of the cranial bone. You see the bone is opened delicately with these various drill holes. There's always some danger, when doing this, of injury to the brain surface underneath. Though certainly the modern equipment that we have obviates that considerably. As you can see now, we're taking the what we call the bone dust, which is the material that the drill went through to get to the dural surface. And the average adult, perhaps their bone thickness, towards the upper part of the exposure, might be up to a centimeter. As we go more towards the skull base and the bone over the temporal lobe, it's much thinner, and can be just a few millimeters thick in the bone underneath the zygoma. Before we can use the drill bit that cuts the bone and removes it as a plate, we generally have to strip away the dural connections under the bone to the underside of the bone that allows our drill then to slide easily over the dura, cutting the bone. Here's the drill, as you can see, usually passing through the bone of the cranial vault, connecting the small holes that we've made to allow the bone to be removed in a large plate that we oftentimes call a bone flap. And then replaced again at the end of the operation to heal in a cosmetically-pleasing fashion up to the second operation. There is some bleeding that occurs during this phase of the operation, though a lot of the fluid that you see coming off the field is the irrigation that keeps the drill and the bone itself cooled during the procedure so that the bone won't be injured by the heating of the drill. Once we've completed the circuit of the bone cuts, we gently life the bone up. There can be some residual bone connections, particularly in the sphenoid ridge as it comes up towards the frontal and parietal bones. And oftentimes, that last connection will need to be broken before the bone can be lifted off, as you see here. What we can see now in the field is, to the left, the inferior part of the frontal lobe, and to the right, the superior part of the temporal lobe. We spent some time achieving hemostasis, because one of our goals is to have as little blood as possible get into the subdural space and cause its own irritation of the brain surface, which potentially could lead to seizures that would not be the seizures that the patient has been having previously. Once we're satisfied with that hemostasis, then we'd be able to proceed with opening the dura. We generally obliterate the epidural space along the edge of the bone cut with a variety of materials, some gelatin foam or oxidized cellulose, to try and promote blood clotting. And others are physical, where we [INAUDIBLE] bleeding by lifting the dura with the retention stage that you're now seeing put in to obliterate the epidural space along the edge of the bone and keep any blood from accumulating in the space between the bone and the dura. The dura itself can be quite vascular. As you see, our bipolar cautery device is busy at work cauterizing the vessels that are on the surface of the dura. And the maneuver that you're now watching, small holes are drilled in the bone edge that allow the stitches placed along the edge of our craniotomy to be brought through to the native bone, lifting up the dura and obliterating the epidural space, so that there can be no bleeding that accumulates in that area. As you can see, the surface of the dura stays moist. This allows it to be then re-stretched back over the brain during the closure. When this portion of the operation is completed, we're now preparing to open the dura to be able to look directly at the surface of the brain. Our philosophy in this portion of the operation is actually to open the dura as little as possible so that it remains intact, and then to slide the electrode arrays underneath the dura, so that the dura then works as a, in a sense, pressure envelope, holding the electrodes up against the surface of the brain. We now placed hemostatic cottonoid paddies over the surface of the dura that we're not going to open. And then here, in that sharp fashion, we open through the dura and make a long straight incision, a type of slit, that then will allow us to pass the electrodes on the surface of the brain and slide them over that. There's always some risk in doing that maneuver, because we can't see exactly what the tip of the electrode arrays are encountering. Here you see us trying to open the dura with some precision that allows it to be closed more easily. And also, it reduces the blood loss from the dura, which as I've mentioned, can be very vascular. The dura's prepared for closure in many ways because underneath the cottonoid paddies are hemostatic agents applied to the surface of the dura that's not going to be opened. That will promote blood clotting on that surface to reduce blood loss after the craniotomy is closed. Here we use a special kind of scissor to cut the dura that tends to move the dura up away from the brain as it's cut, and also has a guard on its tip, so that the dura can't be cut when it's too close to a bone, thereby making eventual dural closure more difficult. As you can see, there is some pressure of the brain on the other side of the dura. And here you can see the entire durotomy open, going from relatively high up on the frontal lobe over the veins of the sylvian fissure, which are visible about 2/3 of the way down towards the right, which is the feet of the patient, and then over the temporal lobe. That thin strip with the white dots on it is a electrode array that's the width of one electrode and eight electrodes long. That's being slid forward towards the patient's face, and is in fact going around the temporal fossa, so its tip has now curved around the temporal tip and is medial. We'll end up placing several of these, what I call, one-by-eight electrode strips, that go around the front of the temporal lobe and underneath the temporal lobe, here for the posterior part of the temporal lobe, versus finding a strip that is eight electrodes long and two electrodes wide. And this will delineate the most posterior part of our zone of potential epileptogenic activity, so that we'll be able to localize between the electrode arrays any epilepsy-generating tissue. This is a much larger electrode array. It's six electrodes wide and eight electrodes long. This array is designed and was custom-cut to its size to be able to cover most of the parietal tissue, going as far back as the anterior part of the occipital lobe. As you see, the array's slid somewhat blindly underneath the dural edge. But in this patient, there do not seem to be any significant adhesions between the brain surface and the dura. And the array is allowed to slide more or less freely throughout its length, covering all that area and allowing us very precise localization of any seizure activity that would be generated from that cortical surface. Sometimes we do reach areas where there are adhesions. We may need to change our angle of delivery of the electrode. In this case, we're trying to mobilize the two-by-eight electrode array, which seems to be blocking the electrode from sliding to its full length, after which we'll replace the two-by-eight electrode. There you see the two-by-eight electrode now, able to fit back where it had originally placed, but now rather than underneath, it's actually on top of the larger electrode. We went ahead and performed the same thing using a smaller electrode array on the frontal lobe, and then completed our what one could consider a blanket-type covering of the frontal lobe, the parietal lobe, and then the temporal lobe. And though we've not shown it, there is four-- there are four white electrode leads that are coming from anterior to posterior. So in our view here, from the upper left to the lower right, and those are the electrodes that come from the frontal array that was placed. Now we just have our slit to close, and we close it as watertight a fashion as possible, with the electrodes tied into the exit sites. At this point, it's my practice to cover the dural surface with a layer of this oxidized cellulose that promotes blood clotting on the surface of the dura. After that's been fashioned to sit as comfortably as possible on the exposed dura, I cover that over with a sheet of the gelatin foam, which also promotes clotting. The bone flap is then brought into place. As you see, it's being replaced with a series of small plates with holes on either end the allow the bone plate to be held in place. For this first operation, we tend to put the bone in place in a somewhat lax fashion so that if there's brain swelling or any small amount of bleeding, the bone can actually become mobile and provide additional space. The electrodes are then tunnelled through the skin, as you see, through a angiocatheter, which allows the electrodes then to be tightly covered by the skin to reduce the likelihood that any cerebral spinal fluid would leak around the tubes and out. The skin is then brought back together, and both the muscular layers of the temporalis muscle, the layer of the galea and the layer of the skin, are closed in a relatively meticulous fashion to prevent cerebral spinal fluid leakage. This is the look of the situation. After a week has gone by, the patient's brought back to the operating room. As you can see here, we've recorded her seizures, and I found that the seizures seem to be emanating from two areas. One, a small area in her parietal region, and then on the medial part of her temporal lobe. The patient is positioned again. In the first operation, she is placed on a headrest without any rigid fixation of her head. In this operation, because we're planning to resect brain, we'll need to have the head and the bony structures held very tightly. The head is placed in a pin headrest, where a small pin is penetrated through the skin and they're attached to a clamp, which provides significant pressure on those pin devices to hold the head rigidly throughout the entire operation. As you saw, we remove the electrodes by cutting them during the first step of our prep. And then, as you see now, you open the skin mostly by cutting the stitches that were placed a week before, and avoiding the electrode wires so as not to dislodge any of the arrays that are on the brain's surface. They're still a risk for a significant amount of bleeding whenever we open the skin of the scalp, and there's certainly a variety of accepted ways to try and minimize that. Though it might be that we would expect the opening of the second operation to be much quicker, as we've already made the various cuts, oftentimes it takes us as long or longer, because the tissues are somewhat delicate from the previous trauma. And we need to have the same visualization as we had before. Here we're modifying our original opening, as the parietal electrode array localized a seizure-generating area that was behind the initial opening of the bone that we had planned. Because of the way we placed our incisions, we have the flexibility now to make additional radial incisions that allow us access more posteriorly, so that we can get access to a seizure focus that is out of our initial field that was exposed by our first bone removal. But as you see, we're able to enlarge that quite easily. Here now we're beginning to unscrew the-- both screws that had been placed and be able to remove the previous bone flap that we had fashioned to place our electrode arrays. Once that is done, we'll need to assess the relationship of the old bone hole with the area of the more posterior parietal seizure focus, and then make a plan for enlarging that by removing additional bone. As you can see by the drawing on the bone, we're using an anatomic drawing of the bone surface as well as the brain surface. We're able to correlate that and produce this map on the bony surface for how we can cut the bone and remove an additional swath of it, and be able to have access to that second area where the seizure focus in the parietal lobe is located. This again is the maneuver to gently separate the undersurface of the bone from the surface of the dura to allow our drill to smoothly move under the bone and remove that entire bone flap that's outlined by the purple drawing that we've placed on its surface. You can see off to the right side, the electrode arrays that had been placed before and their various wires exiting from the single, long slit that we had made in the dura. Underneath there, it's been dissected, is where that large six-by-eight electrode array was placed over the parietal lobe. And one could imagine how the intact dura has held that quite tightly up against the brain surface, which improves our electrical transmission from the brain to the electrodes themselves. The same drill is used. Because there's already a large opening in the bone, we don't need to drill anymore bone holes to guide us. And that motion was just outlining the area where we felt we would find the epileptic zone. This area of bone, which is superior in the field, is a part of the calvaria that is the most thick. As the drill traverses around the curve of the new piece of bone that we're moving, the bone will get thinner and the drill will be able to move in a bit more smooth fashion. As you can see, there are these four hands in the field, so I think this sort of work is done best with capable assistance in a team fashion. Important, as is being done here, to make sure all those connections between the dura the other side of the bone are broken, to our very smooth and safe use of the drill. The new bone is now removed. I can see the surface of the dura that was not exposed at the previous surgery. And we can begin to perform hemostasis on that surface in preparation for widening of the opening that we have of the dura, to give us access to all the areas of the brain surface that we're going to use in our goal of removing the areas that are producing the epileptic discharges. This again is placing the oxidized cellulose, which is a hemostatic agent, over the surface of the dura to reduce bleeding. And now we're planning our dural opening so that we can have good access to the surface of the brain. And yet, already in our minds, have a plan for how we're going to reconstruct the dura so that it will be watertight and viable for good healing. This again this is the same activity that we performed the week before on the first bony opening, where we placed a variety of hemostatic agents to reduce the bleeding on the surface of the brain. Here as we open the dura by cutting perpendicular to the initial slit going posteriorly, we see a small amount of blood that's oozing from underneath the electrode array. That blood is all clotted and poses no danger. Important at this point to make sure that the electrode array stays exactly where it had been placed so that we can find the epileptic focus, based entirely on our cortical surface electrical mapping. We could correlate the electrodes as we visualize them, in real-time, to the map that's been constructed by the EEG, done over the past week . while the patient was in the epilepsy monitoring unit with all these electrodes connected to the monitoring machines. Here we have the entire field now open. You can see the array and all the electrodes over the brain's surface. And now here we begin to map out the area where the seizures that emanate from the parietal lobe are being generated. The cut string isolates the electrodes that are the ones over the cortex, that's generating the seizures. And that allows us then to remove the electrode array and still have that template showing us where those electrodes were. That circle bounded by the blue is when seizures are coming from. As you can see, that's where the electrodes have been, and we're able to realign that part of the electrode array over that area. Here we've cut the electrodes out from their initial full array and we've replaced them over the brain surface so that we can see the specifics that allows us to tailor the outline of our section. Bipolar cautery is then used to cauterize the surface of the pia of the brain. And then once that's performed in a relatively circular fashion around the edge of our exposure, I will cut the pia of the brain, and eventually dissect through the gray matter to the white matter underneath, removing the entire cortical covering of this area. You see that we've gone about halfway around our specimen. There's the slit to the left through the pia surface and the slit to the right at the bottom of the field. I tend to dissect around in such a fashion that we leave some of the blood vessels refusing the tissue, so that is what we usually handle until we get to the final few connections. And at that point we can then remove the tissue en bloc. As you see, there's four hands involved in this and the instruments generally are the suction devices-- a cautery device both for purposes of dissection as well as hemostasis and then the sharp micro scissors used to cut various vessels and tissues in a delicate but sharp fashion. As you can see, there's a bridge still left there of a vessel fusing the tissue, and the demarcation of our dissection will go down to the white matter below the specimen. Tissue is now almost completely separated from its pial connections, but we're still having to dissect into the superficial part of the white matter tracks below this tissue, to remove it without any potentially seizure-generating gray matter from the cortex left in that area of the brain. Here we now have severed one of the last connections. We can dissect underneath the specimen through the white matter, which one can see glistening, as we gently lift up and peel back the tissues. We try at all costs to avoid leaving any of the gray matter in that area, as it could still generate a seizure. As you see, the specimen is then gently being manipulated and finally lifted up and out of the area from whence it came. Hemostasis in this situation has to be meticulous and complete, as there is a very real risk of bleeding that can be significant. The techniques used are the ones that we have been using, both the bipolar electro-cautery as well as the oxidized cellulose, and sometimes small pledgets of the gelatin foam soaked in thrombin to aid in hemostasis. A very important area that needs to be covered with one of the hemostatic agents is the pial surface where it's cut, as there's certainly a significant number of small vessels in that area that can hemorrhage any time in the several hours after the operations is performed. Once this portion of the procedure is completed, and we're satisfied with the hemostasis in this particular patient, we then began our dissection of the temporal lobe. Our goal was both a lateral and medial temporal lobectomy. Here we're demonstrating our dissection through the middle temporal gyrus. And its posterior edge goes to the one-by-eight electrode array that you see flipped up towards the bottom part of the picture. That allows us a posterior margin for the lateral temporal section. The rest of the brain is covered with a what we call rubber dam, a sheet of silastic which keeps the brain moist throughout the rest of procedure. Then continue measuring distances between the areas of our section, as well as distances in this situation from the temporal to going posterial along the temporal floor, giving us an anatomical measurement for where the posterior edge of our resection should be. These measurements were also done on the preoperative CT and MRI scanner-- scanned images. And here we're able to correlate them with the exact in vivo anatomic relationships. We find in this situation that we're able to go as posterior as the vein of Labbe, which is oftentimes the anatomic landmark you use and left us a bit beyond five centimeters from the temporal tip in this particular patient. We then create a opening in the middle and inferior temporal gyri. And here we're dissecting through that opening, which will then turn anterior, to remove the middle and inferior temporal gyri all the way to the temporal tip, along the middle gyrus and then posteriorly to just in front of the vein of Labbe, but [INAUDIBLE] follow down to the temporal floor. This will then get us into the temporal horn of the lateral ventricle, which I believe are approaching at this point, which will mark the end of the dissection of the lateral tissues. The remainder of the procedure was then done with microscopic technique and microscopic elimination that can be presented in another video that will go into the specifics of micro neurosurgical resection of medial-temporal structures. The patient was then closed in a fashion that we demonstrated for the first operation and taken back to the intensive care unit. She woke up and was neurologically intact. And happily, her course over the next several days was relatively uneventful and the seizures that she'd been having several times a day seemed to dissipate. And when she left the hospital in good condition about five days later, she was without seizures for the first time in many years.
