Large Acoustic: Techniques
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Let's use this video to further describe the techniques for Resection of Large Acoustic Neuromas. This is a 62-year old male who presented with progressive gait difficulty and hearing loss. And on MRI evaluation was diagnosed with a relatively large vestibular schwannoma. There was also some mild hydrocephalus present. This patient's preoperative facial function was relatively poor. And despite my careful search, the nerve could not be found or salvaged during the surgery. You can see also some evidence of mild edema within the lateral aspect of the brain stem and middle cerebellar peduncle. A right-sided retromastoid craniotomy was completed based on regular anatomical landmarks. A lumbar puncture was also conducted and about 35 cc of CSF was removed. Here's the sigmoid sinus, transverse sigmoid junction. The dura was incised parallel to the dural venous sinuses. Additional release incisions within the dura were used to expand the operative corridor. CSF was released over the lower cranial nerves. You can see the lower pore of the tumor, the lower cranial nerves identified early. All the arachnoid bands were widely dissected so that the tumor can be generously exposed. Early identification of neurovascular structures keeps them out of harms way. The tumor was relatively soft and could be mobilized and the lower cranial nerves were dissected. The capsule was very carefully mapped at 0.1 milliamps. No motor activity within the facial nerve was apparent. Here's a branch of PICA. The tumor was debulked and then the capsule was further mobilized inferiorly. Further mapping along the lower portal of the tumor was non conclusive. The tumor was devascularized along the posterior aspect of the IEC. This was a relatively vascular tumor. Aggressive debulking is a key factor in advancing the efficiency of the operation. Tumor decompression now allows dissection of the superior petrosal sinus and a trigeminal nerve from the superior pole of the tumor. Aggressive mapping was also performed in this area as some of the larger tumors carry the facial nerve over their superior pole. Debulking continues within the heart of the tumor so that the tumor can be dissected away from the PICA at its lower pole and also can be rolled from the medial to lateral direction. The sixth nerve was apparent a moment ago. Here's the tumor removal more medially. This part of tumor removal is especially important for mobilization of the tumor away from the brainstem. Now I moved back to the superior pole of the tumor. The root entry zone of the trigeminal nerve is found. Again their facial nerve is not apparent despite an increase in our stimulation parameters. The trigeminal nerve is mobilized away. Sometimes I found the facial nerve to be hiding just underneath the trigeminal nerve. But in this case the facial nerve could not be stimulated even next to the trigeminal nerve. Here is further mapping of the nerve over the part of the tumor getting closer to the area of the porous. Trigeminal nerve is being further dissected and released from the tumor capsule. Next, the capsule is removed to create additional working space for the next phase of the operation which will involve mobilization of the capsule in the medial to lateral direction. Here you can see that maneuver where the tumor is mobilized toward the porous. Careful debulking and generous debulking is quite effective for mobilization the capsule efficiently. Piece of cottonoid can be used to protect the part of the brain stem where peal invasion by the tumor is possible based on preoperative presence of edema on imaging. You can see this maneuver of using the fine forceps to grab the arachnoid bands over the pia and mobilizing the pia away from the capsule of the tumor. Now that some of the tumor capsule is delivered laterally the tumor is further debulked and the capsule is further mobilized in the lateral direction. You can use of the fine forceps to grab the arachnoid bands and untethered intervascular structures is quite effective. Now more of the tumor is debulked along its anterior and medial poles so that the capsule can be reflected away from the pia of the brain stem effectively. Here's along the more inferior pole of tumor. Capsule again is continuously reflected anteriorly in steps. Here's the root entry zone of the trigeminal nerve. Some of the arachnoid bands of the Pia are again gently reflected off of the tumor capsule. Invasion of the pia can significantly increase the risk of the operation and should be avoided as much as possible. You can see how a very thinned out capsule the tumor is very amenable to mobilization without significant resistance. The cycle repeats itself again, in other words, after the tumor capsule has partly mobilized away from the brain stem, the tumor is resected partially and debulked further. And again, the pia is reflected away and peeled off the tumor capsule. Now the inferior pole is mobilized away from the brain stem as safely as possible the arachnoid bands are protected. I continue to use mapping to find the route of the facial nerve. 0.2 milliamps was used. Nonetheless facial function was not found. Here's the use of cotton patties to preserve the dissection planes. As I move from one plane toward the other aggressive coagulation over the brain stem is avoided and cottonoid patties and gentle tamponade are used for hemostasis while the dissection is diverted to a different location. And later I returned to the initial part of the dissection planes after the bleeding has spontaneously being controlled. Here are some of the arachnoid bands that are being reflected off of the tumor capsule. We have removed a very reasonable portion of the tumor. You can see the sixth cranial nerve. This is essentially a medial acoustic neuroma. Now that the tumor is primarily reflected off of the middle cerebellar peduncle, I continue to debulk the tumor further. The facial nerve was not found within any of these bands. These are some of the arachnoid bands that led to adherence of the trigeminal nerve on the superior pole of the tumor. The nerve is being mobilized further and the tumor capsule is being reflected toward the porous. The last pieces of the tumor near the area of the porous are being removed. Here's the sixth nerve entering the Dorello's canal, which is also slightly adherent to the pull of the tumor. Here's the trigeminal nerve. Further inspection reveals no evidence of the intact nerve. I continue to remove the portion of the tumor at the area of the porous. The nerve did not appear to accompany the trigeminal nerve. I do believe that poor facial function in this patient compromised our ability to be able to monitor the nerve intraoperatively and find its route. Here's our final resection cavity. Postoperative CT scan demonstrates no other complicating features. Thank you.
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