Clip Ligation of Basilar Bifurcation Aneurysms
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This video reviews technical nuances for clip ligation of basilar bifurcation aneurysms, as well as explains the details for dissection around the interpeduncular cisterns. This is a 42-year-old female who presented with a severe headache and also was noted to have a lumbar puncture that whose results were questionable for evidence of subarachnoid hemorrhage. The CT angiogram demonstrated an approximately seven millimeter basilar bifurcation aneurysm with some irregularity around the dome of the aneurysm, and, as you can see, on the sagittal CT angiogram, the neck of the aneurysm is above the dorsum sellae, and there is available space to place a temporary clip and also to be able to dissect the aneurysm neck for clip ligation through a pterional approach. Since the morphology aneurysm is favorable, a craniotomy was designed for clip ligation of this aneurysm. The patient is also 42-years-old, and I felt that the durability of clip ligation would outweigh the risks and benefits of coil embolization in this case. The base of the aneurysm was also considered relatively broad in this case. Let's go ahead and review the technical nuances step-by-step. Left frontotemporal craniotomy was completed by one of my residents. You can see the roof of the orbit is relatively flat. It's a generous exposure of mainly the frontal lobe and the sylvian fissure. Before proceeding further, I usually check the work of my residents, in terms of the amount of bone work, so as they start dissecting the fissure, you can see the inside-to-outside technique is used. I'm going to reflect the dural and demonstrate the exposure. Here you can see the roof of the orbit is very flat. All the gyrations have been drilled away, and, also, in the case of aneurysms, where I want to approach the interpeduncular cisterns, the bone over the superior orbital fissure and the lesser sphenoid wing has been removed, so you can see that the superior orbital fissure is generously exposed and also a partial subtemporal craniotomy has been completed. Here you can see the exposure and how flat that trajectory is over the orbital roof. I'll go ahead and expose the sylvian fissure and sylvian cisterns, trying to save some of the bridging veins along the anterior aspect of the fissure. The arachnoid membranes are generously opened, you can see the optic nerve. Obviously, we're on the left side, opening the arachnoid membranes over the basal cisterns and optical carotid cisterns, more specifically. Dynamic retraction is used. You can see the carotid artery at the base of the skull. I use a round knife over the optic nerve to dissect the arachnoid membranes. I avoid the use of blunt dissectors in this area. All the arachnoid membranes are dissected sharply, if they are on the thicker side. This maneuver avoids undue traction on the nerves and the surrounding cerebrovascular structures. Fixed retraction is unnecessary, and the dynamic retraction actually facilitates more smooth dissection by exposing just the area where I want to see. Now that we have exposed the traditional optical carotid areas, I'll go ahead and stay retro carotid and try to find the membrane of liliequist and the dorsum sellae. We're just about there with opening of some of the more posterior parts of the arachnoid membranes of the basal cisterns. I customize my sylvian opening as we go along. In this case, you can see, the third nerve that's being released as it enters the edge of the tentorium. I customize the opening of the fissure as I start mobilizing the frontal lobe, and, if additional sylvian fissure dissection is necessary, I will go ahead and do that. Here's the membrane of liliequist that's being opened. It's quite thick and contains multiple layers. My suction is retracting the posterior communicating artery. The thalamic perforators originate from the more medial and superior aspect of the PCoA. Here, you can see, the trunk of the basal artery is quite evident after the membrane of liliequist is opened. Here, you can see a peak of the PCoA. The arachnoid layers of the liliequist are further opened sharply, and I want to gauge to see how much of the basilar bifurcation I'm able to expose, based on the current exposure. You can see the leash of the perforators from the posterior communicating artery. You can see the basilar artery. However, additional exposure is necessary for me to see more superiorly. Some of the perforating vessels are mobilized and encasing. Arachnoid membranes are opened. I'm trying to look both medial and lateral to the carotid artery to see what is the appropriate corridor for reaching the basil bifurcation. This is the optical carotid corridor. This is their retro carotid, or carotid ocularmotor triangle for reaching the basilar bifurcation. As you can see, exposure is still inadequate. You can see the posterior cerebral artery on the left side. Can see the third nerve there. Here is the posterior cerebral artery, however, the basilar bifurcation is somewhat more cranial. I'll go ahead and look medial to the carotid and exposure's inadequate. The superior carotid triangle is just above the A1, which is also will be inadequate in this case. Here's the PCoA again, under my suction, using dynamic retraction. I'm looking around the basilar trunk. So, I'll go ahead and expose more of the fissure, and the M1 is unroofed and dissected in the fissure. This marks the maximum amount of sylvian fissure opening that I can afford. I'll go ahead and mobilize some of the thalamoperforators off of the PCoA. Here's the third nerve, that also being untethered, so I can use dynamic retraction without placing any traction on the spinal cerebrovascular structures. Here is, again, the leash of perforating vessels that are being mobilized so I can work between them to reach the apex of the basilar artery. Here is the aneurysm that is now in view. You can see that I'm working between the perforators off of the PCoA. I'll go ahead and use sharp dissection to further mobilize the thalamogeniculate perforators posteriorly. Here is the dome of the aneurysm. Here is the blister off of the dome. Now I'm going to prepare for the next steps of aneurysm dissection. First, I use a piece of cotton with a paverin fluid in order to relieve the spasm from the posterior communicating artery perforators. I'll go ahead and place a temporary clip on the basilar trunk and now I can mobilize the aneurysm more forward and look behind the neck of the aneurysm, as you can see here, to make sure the pathway of the blades are completely clear from any perforating vessels. I'm going to use a fixed retraction, just briefly, to be able to see around the posterior wall of the neck. You can see I'm looking all the way across. There is no perforator that would be placed at risk using the clip blades. Here is the contralateral PCA or P1, so I can gauge the angle of my clip from one P1 toward the other. This is a contralateral ocularmotor nerve. I use a first tentative clip just to see how much I can see around the clip, and, unfortunately, I wasn't able to see as well as I wanted. I'll go ahead and place a temporary clip on the basilar artery again, and, this time, try to attempt to dissect more across the posterior neck of the aneurysm. This clip looks good, however, again, I'm just not comfortable with deploying it because I can't see the P1. I'll go ahead, now, and have a better angle with a microscope, and I can see the P1 on the other side and therefore deploy the clip. You can see the clip tip is just hugging the shoulder of the contralateral P1. The temporary clip was removed. You can appreciate the superiority of fluorescein fluorescence, in terms of gauging the occlusion of the aneurysm, which is located here, and patency of all the surrounding perforating vessels. The ICG is somewhat out of focus and the image is more granular, therefore, I have opted to use fluorescein angiography for cases where the aneurysm is very deep and additional viewing angles are necessary, under high magnification, to assure the aneurysm is completely excluded. Now that I'm satisfied with obliteration of the aneurysm, we'll go ahead and, just one final time, show the magnified view of our operative corridors, the optic nerve, carotid artery, and here's the basilar trunk, here's posterior clinoid. As you can appreciate, the brain is very much intact, due to use of dynamic retraction for the majority of part of the operation. The postoperative angiogram demonstrates a good clip ligation of the aneurysm without any complicating features. This patient recovered from her surgery without any new deficits, not even a third nerve palsy, and she has since returned to work. Thank you.
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