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Large Acoustic Neuroma: Maximizing the Efficiency of Technique and Facial Function

July 15, 2019

The drilling of the internal auditory canal and corresponding tumor resection was performed by Dr. Rick Nelson (Indiana University Department of Otolaryngology Head & Neck Surgery.)

Transcript

This is a nice video describing the technical pearls for resection of large acoustic neuromas and more specifically removing these large complex lesions under two hours via again, improving the efficiency of technical maneuvers. This is a 33 year old male who presented with left sided hearing loss and gait imbalance. MRI evaluation revealed a very large acoustic neuroma on right side with minimal amount of edema in the right middle cerebral pineal gland, cerebellum. This true size of this acoustic neuroma was about four centimeters. I like placing the patient in the lateral position as this keeps the neck in a more physiologic position and posture and avoids neck pain post-operatively. I also like to use a curvilinear incision as situated here you can see the inline located here to transfer sinus, sigmoid sinus. This curvilinear incision mobilizes the myocutaneous flap inferiorly and I like a curvilinear or linear incision, will minimize the risk of the muscles to be bulked up under the retractor and increase the working distance of the surgeon. Let's go ahead and complete the craniotomy. Here's the sigmoid sinus, mastoid air cells, transverse sinus. Obviously this is a retro-sigmoid approach. I use a rubber dam to go around the cerebellum. Here is the 11th cranial nerve. CSF is released. I'll go ahead now open the arachnoid adhesions in this case there were numerous adhesions and you can see the superior patrocul vein has been coagulated. The arachnoid bands are opened and we'll go ahead and de-dress the tumor. Stimulation is used over the posterior capsule of the tumor. One of the maneuvers that I'm a very big fan of is removing a very small amount of cerebellum. The thin cap of cerebellum over the lateral aspect of the tumor. This maneuver has many advantages that improves the efficiency of tumor resection. Number one, removal of small cap of cerebellum will prevent additional retro-retraction on the rest of the cerebellum as the cerebellum is being mobilized and minimizes cerebella swelling during the surgery. In addition, it provides a significant amount of additional exposure along the medial capsule of the tumor. Therefore, allowing very thorough visualization of the posterior capsule of the tumor and improving the efficiency of tumor resection. Here, the tumor capsule posteriorly has been cut and the number one most important factor after adequate exposure of the capsule is aggressive de-bulking of the tumor in order to improve the efficiency of tumor resection. Again, I spend significant amount of time de-bulking the tumor. Here are the lower cranial nerves at the tip of my arrow. Now that the tumor has been significantly de-bulked I can efficiently mobilize the inferior capsule of the tumor, find the brain stem. As we know the origin or the exits of another facial nerve would be just slightly above the exits on one of the ninth nerve. So I follow the ninth nerve. Here is the sixth nerve at a depth, and I'll be able to find the exits on of the facial nerve at some point in this area. The inferior capsule of the tumor was thoroughly coagulated, and then will also be cut. As you can see, because of very nice exposure of the tumor I'm able to coagulate the large portion of the capsule and make good progress very quickly. Here again, looking for the facial nerve along the inferior pole of the tumor, just following the route of the ninth nerve toward the brain stem. I don't see any evidence of the nerve at 0.1 mil amp of stimulation. Now I'm looking around the superior pole of the tumor. Here's the tentorium, and I'll perform a similar maneuver in order to stimulate, coagulate and cut large portion of the capsule. This additional cuts superiorly and inferiorly, as you can see dramatically improves the visualization within the nucleus of the tumor and helps me again de-bulk the tumor very aggressively. Hemostasis is obviously critical. We wanna make sure that the operative field is clean. So surgical planes are recognized. Here is mobilizing an inferior medial pole of the tumor. I'll go ahead and mobilize the inferior pole of the tumor. Here we can see the origin of the facial nerve identified very early on during the operation, essentially within 30 minutes of starting intradural dissection. This very early identification is so paramount in terms of improving the efficiency operation, because the moment the exit zone of the nerve at the brain stem is identified so early, the rest of the operation is extremely facilitated because I'm now more comfortable where the route of the nerve is and can be more efficient in coagulating the rest of the capsule. A mirror cell cut wide was placed at the route exit zone of the nerve at the brain stem for orientation. Now I'm working along the superior pole of the tumor and mobilizing the cerebellum. Again, you can see the maneuver of grabbing the arachnoid membranes and pushing the nervous tissue away from the capsule of the tumor. This is a very efficient technique that allows mobilization of the nervous tissue away from the tumor wall and minimizing the manipulation of the nervous tissue. A piece of mirror cell cottonoid is also placed along the superior pole of the tumor where the trigeminal nerve was identified. Now we're ready to mobilize the tumor laterally away from the cerebellum and the brain stem since I have identified most of my important neurovascular structures. You can see that this procedure can be conducted extremely quickly and now most of the capsule is mobilized laterally. We're just about 40 minutes through the tumor resection. And as you can see, almost more than two third of the tumor has been removed and most of the neurovascular structures have been identified. Now that the tumor has been further de-bulked, I go ahead and further mobilize the inferior pole and also dissect the capsule away from the brain stem. Here you can see the mirror cell cottonoid, which again, identifies the location of the route exit zone of the nerve. Since the exit zone of the nerve was identified early on I can be more efficient in mobilizing the capsule away from the brain stem without worrying about injuring the facial nerve. I'll go ahead and stimulate the capsule as I get closer to the facial nerve, as you can see here, to make sure that the nerve does not have any unusual paths around the posterior capsule of the tumor. Here you can see the inferior pole of the tumor. The facial nerve is being identified as it exits here, and we'll go ahead and carefully mobilize the tumor away from the brain stem and the facial nerve in order to preserve function. Here you can see the use of mouth switch, which is also critical in improving the efficiency of the operation. As the mouth switch allows me to focus my image through the microscope without the use of my hands while I continue efficient dissection. Here again, using that arachnoid teasing technique via the fine bipolar forceps where the arachnoid bands are mobilized away from the tumor capsule. Sharp dissection is also used to mobilize the tumor away from the brain stem and naturally protect the peel membranes of the brain stem at all times. Now that most of the capsule is mobilized away from the brain stem I'll go ahead and de-bulk the tumor that has been dissected away from the peel membranes. Ultrasonic aspirator is very useful. Let's go ahead and continue dissection of the brain stem. Obviously, this tumor is relatively large and significant amount of dissection is required. Again, one more time, that arachnoid teasing technique, where you can mobilize the peel membrane away from the tumor capsule. Go ahead and now mobilize the superior pole of the tumor. Again, stimulating the capsule making sure that the nerve is not necessarily going over the superior pole. Obviously this case will be a very small chance, but we wanna exclude that small chance and maximize the probability of preservation of function for the facial nerve. Now we're getting very medial and almost around to the anterior capsule of the tumor. Here you can see a peak of the anterior capsule. I'll go ahead and coagulate the capsule to mobilize it and keep it stay away from the brain stem. Small amount of tumor within the cisterns is now left. We'll go ahead and work around the inferior capsule, preserve all the vessels over the brain stem and use the stimulator to dissect and find the pathway of the facial nerve. Obviously, the facial nerve in this case is going around the posterior capsule toward the IAC here. This is a classic location of the nerve along the anterior capsule of the tumor. Here again, dissection of the capsule very much almost to the anterior aspect of the capsule of the tumor. I'll go ahead and use the stimulator again. We know the nerve is somewhere here protecting the small vessels on the brainstem peel. Further tumor de-bulking continues. So I have a working space to mobilize the tumor away from the brain stem. And teasing away the arachnoid bands of the brain stem away from the tumor capsule and the fine adherent strands are coagulated and sharply cut. I expect the facial nerve to be somewhere here. Here you can see the origin of the nerve. Here's the brainstem, here's the inferior and superior borders of the nerve. As you can see most of the dissection is occurring on the tumor capsule and a nerve is left intact. You can see the width of the facial nerve, use of high magnification, also irrigation to clear the operative field rather than use the suction tip directly on the nerve to cause injury. We'll go ahead and dissect more of the intracisternal portion of the nerve along the anterior capsule. You can see that the tumor is really very small at this point and so aggressively de-bulked that I can really easily mobilize it toward the IAC. Here is removing the final pieces of the tumor close to the area of the porous and the suction keeps the tumor away from the nerve. So I have a sense of orientation of where the nerve is as I de-bulk the tumor. Here again, that arachnoid dissection technique, mobilizing the nerve and the brain stem. Here you can see the route of the facial nerve along the anterior aspect of the tumor. Very important finding. You can see the nerve is being easily stimulated along its entire path at less than 0.05 milli amps. Go ahead and now de-bulk the tumor in expectation of dissecting the IAC. You can see the sixth nerve inferior capsule, making sure that the nerve is protected now that the entire path of the nerve is identified. The rest of the operation can proceed very quickly. And the tumor is now shrunk away, de-bulked, as we'll start drilling the IAC very shortly. Keeping hemostasis is an important part of the operation. Here you can see the facial nerve very much intact in its arachnoids bands. The arachnoid sheath around the nerves should be protected as much as possible before I drill the IAC. I'll go ahead and place a mirror cell cottonoid on the nerve for orientation and preventing any bone dust to come in contact with the nerve. Go ahead and I drill the IAC as you can see here. Tumor is circumferentially exposed as much as possible. Here you can see stimulation mapping of the nerve along the entry aspect of the tumor within the IAC. Additional drilling is necessary until the extent of the tumor more laterally or its border is exposed. Here we'll go in and drill more around the lateral aspect of the tumor within the IAC. Now that the portion of the vestibular nerve without the tumor is identified, I'll go ahead and avoid the vestibular nerve and go ahead and roll the tumor more mediately toward the porous. Again the stimulation mapping continues at all times in order for me to be able to preserve the nerve and make sure that the dural adhesions are cut and not the nerve. During numerous dural adhesions at this juncture that may have to be cut as you can see here at the level of the porous, and one has to be able to carefully identify the tumor and the dural bands versus the facial nerve. And as this band was stimulated and was noted not to be part of the nerve, it was cut and the tumor was gradually mobilized more medially. Irrigation is used continuously. So the suction does not come in contact directly with the nerve. Here you can see dissecting the tumor away from the nerve rather than vice-versa. The manipulation of the nerve is kept to an absolute minimum. We're getting close to the area of the porous. Here is the IAC. You can see any of the arachnoid over the nerve is kept intact as much as possible. Again, some of the dural arachnoid bands along the inferior border of the nerve are cut. Here's the inferior border of the nerve as you can see here, and then I'll go ahead and continue to roll the tumor more medially. Here is the nerve, tumor, arachnoid bands that are adhering to the capsule of the tumor. Again, the tumor is being further de-bulked so we can mobilize it more efficiently while minimizing any traction on the nerve. Here you can see at the area of the porous where the tumor is more or most adherent to the nerve. And this is the critical part, one has to be very careful in order to preserve as much as function as possible. Here again cutting those adhesions to the tumor capsule. We'll go ahead and now find the nerve at the brain stem that was exposed before. Here you can see the route of a tumor toward the IAC, and now we'll go ahead and pull them both at the level of the brain stem and the porous in order to dissect the tumor away from the nerve. After this arachnoid band was stimulated it was noted to be silent. I went ahead and cut the band and again continued mobilizing the tumor away from the nerve. We're getting close to dissecting the tumor now completely. We're just about an hour and a half through our intradural dissection. Here you can see the nerve at the level of the brain stem coming up to the porous. Now we'll go ahead and dissect the tumor from the inferior border of the nerve. Here you can see the nerve outlines. Here's use of sharp dissection. Again, the nerve coming up and going into the porous. Here's the dissection of the tumor away from the nerve where it appears to be very adherent. And the suction does not come in contact with the nerve, ever. And most of the manipulation occurs on the tumor capsule rather than on the nerve capsule. We have a large adherent band here that we can go ahead and cut after stimulated. You can see that the larger bands are left behind until the last stages. When I know the exact route of the nerve. Now that the tumor capsule is mostly mobilized away the nerve is free, appears to be very healthy. Minimal amount of bleeding within the operative field. Tumor is removed, as you can see here. Here's the route of the nerve with its arachnoid band overlying it intact. No tumor left. Very healthy brain, and the nerve contains most of its neurovascular bundle. Here you can see viewing to the IAC and a relativity de-magnified view of the operative field. This patient awoke from surgery with very good facial function and recovered from the surgery very nicely. The three months MRI demonstrated complete resection of the tumor without complicating features. Again, this video demonstrates the techniques in efficient removal acoustic neuroma including adequate exposure. Minimal lateral sectional cerebellum, very aggressive de-bulking of the tumor, efficient mobilization of the capsule away from the neurovascular structures via use of the mouse switch. And again finding the facial nerve early on during the operation so that the surgeon can definitively remove the rest of the tumor and does not always worry about where the nerve is along the capsule. Thank you for your attention.

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