February 09, 2016
Here are the tenets for resection of a medium size acoustic neuroma via the retromastoid approach. This is a 35 year-old male who presented with decreased hearing and tinnitus on the left side. MRI evaluation revealed a relatively heterogeneously enhancing acoustic neuroma with infiltration of the IAC. Patient underwent a left sided retromastoid craniotomy. The sigmoid sinus was somewhat unroofed and the mastoid air cells were generously waxed. The dura was opened along the dural venous sinuses, and the cerebellum was gently retracted to expose the posterior capsule of the tumor. Mapping was used to exclude the location of the facial nerve along the posterior aspect of the tumor. Aggressive debulking is critical for efficient removal and mobilization of the tumor capsule. I use rongeurs to emulsify the tumor and evacuate the center of the mass. Next, the capsule of the tumor is rolled laterally and removed piecemeal. Again, I continue to roll the capsule laterally and the cerebrovascular structures are gently dissected from the tumor capsule. Here are some of the fine vessels adherent to the inferior pole of the tumor, lower cranial nerves are readily adherent to this pole of the tumor and are readily mobilizable. Mapping continues along the lower part of the capsule. Here's a more demagnified view of the operation. Now that more of the capsule has been isolated, the tumor can be more aggressively debulked. Here's the trigeminal nerve along the superior pole of the tumor, here is the tentorium. Sharp dissection is used as much as possible. For this tumor, the trigeminal nerve was readily mobilized away. Again, mapping continues along the superior pole of the tumor. Ring curettes may be used to further debulk the tumor. Part of the capsule superiorly is also disconnected. Now that the center of the tumor is more enucleated, I can more readily mobilize the capsule away from the brainstem. Sharp dissection is quite useful for disconnecting the capsule from the middle cerebellar peduncle. I make sure I stay within the correct epi-peeled dissection planes. As I get close to the root exciton of the facial nerve, I continue to use mapping. The vestibulocochlear nerves are disconnected, especially if the hearing is non-functional preoperatively. Here's the portion of the middle cerebellar peduncle that's adherent to the tumor capsule. The probe is used to exclude the presence of the facial nerve. Stimulation is applied at .1 milliamps. Only very small fragment of the tumor is left now. I like to use the fine forceps to gently separate the arachnoid bands away from the tumor capsule. We're now getting quite close to the root exciton of the facial nerve. Again, micro-scissors are used to disconnect the arachnoid bands and the peeled surfaces are left intact. The dissection can be quite tedious, but it's sure worth the time to avoid any peel injury. You can see now a more demagnified view of the operative corridor. Further debulking continues as well as mapping. I'm convinced that the nerve is essentially directly anterior along the capsule of the tumor. Let's go ahead and roll the tumor more anteriorly. I suspect the location of the nerve is just about here. Here's the root exciton of the nerve away from the brainstem. The nerve is quite attenuated. Stimulation continues at .05 milliamps. Overstimulation of the nerve can lead to post-operative facial paresis as well. Now I cover the operative field with a piece of Gelfoam and my ENT colleagues conduct intracanalicular portion of the surgery. The dura over the IAC is stripped away and drilling allows 270 degree skeletonization of the IAC. Ample amount of irrigation is used to avoid thermal injury to the nerves. As I get close to the intracanalicular contents, a diamond bur is employed. Here's the skeletonization of the IAC. Thin shell of bone is removed. Here you can see the tumor within the canal. Here's the debulking of the tumor within the canal. After tumor debulking, the facial nerve can be found via stimulation mapping. The air cells are then heavily waxed. I believe in radical subtotal removal of the tumor while preserving relatively normal facial function. I attempt gross total removal of the mass when possible. However, if portion of the tumor is very adherent to the nerve at the area of the porus, I will leave a very small piece of the tumor to avoid post-operative facial weakness. Here you can see very small residual tumor left behind at the level of the porus. This piece was adherent to the nerve. The nerve is anatomically intact. The nerve was easily stimulated at .05 milliamps. Post-operative CT-scan revealed adequate resection of the tumor without any complicating features and this patient recovered from his surgery with normal facial function. Thank you.
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