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Ventral Brainstem Epidermoid

June 08, 2015


Let's discuss resection of challenging large ventral brainstem epidermoid cysts. This is the case of a 28-year-old female who presented with progressive gait imbalance related to brainstem compression by the epidermoid cyst along the ventral aspect of the brainstem. You can see the craniocaudal extension of the tumor all the way to the area of the subchaismatic space. Diffusion weighted images demonstrate the classic findings of hyperintense lesion, which is consistent with an epidermoid cyst. Most colleagues approach this tumor via a posterior petrosal approach to be able to reach the contralateral aspect of the brainstem on the other side of the basilar artery. However, I believe the extended retromastoid approach is as effective for gross total removal of the lesion. However, certain intraoperative tricks are necessary to do so via the retromastoid approach. And I'm going to review these tricks. Here's a right-sided classic horseshoe incision for a retromastoid craniotomy. You can see the extent of bony removal here. The bone over the sigmoid sinus is resected. Here's the transverse sinus. Retention sutures are used to immobilize the sigmoid sinus as much as possible outside our working zone. Next, I use a piece of rubber dam to go around the cerebellum. This maneuver protects the cerebellum. Here's the superior petrosal sinus. You can see the tumor. All the arachnoid bands are widely opened. You can see the seven and eighth cranial nerves. Any of the adhesions between the capsule of the tumor and the nerves are sharply disconnected. I work between the septations of the tumor to remove the contents of the tumor. Here again, working between the cranial nerves, the part of the tumor that is lodged into the midbrain. You can see by using a very lateral to medial operative trajectory, the tumor can be carefully removed along the interior aspect of the midbrain. I work on both sides of the seven and eighth cranial nerves to remove the tumor. The fifth cranial nerve is much more forgiving and flexible in terms of manipulation versus the seven and eighth cranial nerves. Therefore, I gently mobilize the fifth cranial nerve using dynamic retraction to remove the tumor. Brainstem auditory evoked responses are monitored during the procedure. Now here's the critical part of the operation, the trick that I talked about at the beginning of the video. I use the space between the fifth and the seventh and eighth cranial nerves and go ventral to the brainstem. You can see the ventral dura, the clival dura there, and use dynamic retraction on the basilar artery to go around the artery and then use the capsule of the tumor as a handle to deliver tumor into my resection cavity and mobilize that part of the tumor that is lodged in into the contralateral aspect of the brainstem. Here is the operative corridor, it's relatively narrow. I mobilize the fifth nerve more than the seven and eighth cranial nerves. I follow the capsule of the tumor, as you can see, here's the basilar artery. I use my suction to gently compress the artery only intermittently and for a short period of time. And then I use the capsule of the tumor, as you see here, to deliver the contralateral piece of the tumor that is not readily visible due to my operative blind spot. All the perforators are carefully protected. Here again, you can see the maneuver of just reaching beyond the basilar artery, moving the capsule over the pia of the brainstem, and then delivering that tumor anteriorly, so it's now visible and therefore removable. Here you can see, again, another example and demonstration of this technique. The pearls of the tumor are relatively easily removable via the suction device. And therefore, I do not believe a petrosal approach is necessary in this case. Again, you can preserve the capsule of the tumor. In fact, you have to preserve it to be able to avoid losing the sight of the exact, plan out the section for gross total removal of the mass. Here's the final adhesions of the tumor capsule and the post-operative MRI scan in this patient demonstrated complete removal of the mass without any complicating features and the post-operative diffusion imaging scans also further verified a complete removal of the mass without any residual. And this patient recovered from her surgery uneventfully. Thank you.

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