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Malignant Peripheral Nerve Sheath Tumor: Venous Infarction-When to Stop

January 28, 2016


Knowing when to stop in surgery can affect the outcome quite significantly. This video describes an example where I should have stopped earlier and have not proceeded with further tumor resection. It also describes techniques for the exposure, including Retromastoid Craniotomy. This is a 32 year old female who presented with imbalance and double vision and was diagnosed with a heterogeneously enhancing mass within the anterior aspect of the brain stem encasing the basilar artery. You can also appreciate the, location of the mass in relationship to the ventral aspect of the brain stem on the T2 axial image. Shunt went at left sided, retro mastoid, craniotomy, A curvilinear muscle flap was reflected inferiorly. As described in our previous videos, you can see the mastoid groove. Nuchal line most likely located here. The junction of the mastoid groove and the nuchal line, would be a good location to start the burr hole at. The initial burr hole is expanded towards the dural venous sinuses. Lumbar puncture was performed at the beginning of this procedure and approximately 35 CCF CSF was drained. You can see the dura is relatively relaxed. You can see the junction of the transfers in sigmoid sinuses. After mobilization of the dura from inner aspect of the calvarium. The craniotomy is performed. The first cut is away from the dural venous sinuses. In this case the sigmoid sinus. A generous one is elevated due to the ventral location of the tumor. I advanced the drill all the way to the poster aspect of the sigmoid sinus and then turn the drill 180 degrees, remove the foot plate and complete the final arm of the craniotomy. Just medial posterior to the sigmoid sinus. Avoid drilling directly on this sigmoid sinus, as this sinus can be quite adherent to the inner table of the dura. Next an M3 bit is used to perform a partial mastoidectomy, so that the sigmoid sinus is unroofed. This maneuver allows mobilization of the sigmoid sinus after dural opening. The air cells are thoroughly waxed, and they do rise in size parallel to the dural venous sinuses. Sleeve of dura is left at the edges of the venous sinuses. Two or three retention sutures mobilize the sigmoid sinus, as much as possible, so that the journey around the cerebellum, towards the CP angle, is possible with less cerebellar retraction. Piece of is cloth is cut to the shape of the Cottonoid. This rubber dam allows the cottonoid to slide around the cerebellum and avoids the friction and potential cortical injury from the rough surface of the cottonoid. Petrous tentorial junction is a good initial landmark. Some of the arachnoid bands here are being mobilized from the lower cranial nerves first. You can see the tentorium, Petrous bone tumor, which is medial to the cranial nerves complicating our resection strategy. All the arachnoid bands are thoroughly dissected. This is one of my older videos, where I used the fixed retraction more liberally. First the tumor is debulked thoroughly. Ring curettes are also useful, to work around the edges. Next the capsule is being mobilized from the fifth cranial nerve. You can see the tumor is quite adherent unfortunately at the level of its capsule to their neurovascular structures. Here's the fourth nerve that is being mobilized gently. I continue to debulk and dissect the capsule away from the neurovascular structures, as much as possible. A more aggressive de-bulking would be prudent to avoid traction on the neurovascular structures. The fifth cranial nerve is more accommodating than any of the other cranial nerves in the posterior fossa, and I'm gently mobilizing it to resect additional tumor. Obviously the seventh and eighth cranial nerves are not as forgiving, and therefore I have to be mindful of that during my resection. Now I'm going to use my next organ window, between the seventh and eighth cranial nerves and the lower cranial nerves, can see the tumors quite adherent to the pia of the brainstem. I continued to remain persistent and dissect the capsule. Hoping that in this young patient I can achieve a more aggressive resection. Additional attempts at de-bulking the tumor were made. Here's the tumor at the level of the lower cranial nerves. Capsule appears less adherent. Their brainstem auditory vocal responses were monitored during this case. I felt that I have done as much de-bulking as possible and now it's time to finally determine if there is any chance that dissecting of the capsule away from the brain stem. The pathology of this tumor was consistent with a malignant nerve sheath tumor. You can see the pia is violated. It would've been best if I had stopped at this time and have not gone further. Further dissection again reveals additional violation and transgression of the pia. I shrink the part of the tumor that's been mobilized. Continue to work on the anterior edge of the tumor, mobilizing it into the resection cavity and working across, towards the contralateral side. I was able to deliver more tumor fragments. I was very encouraged that these maneuvers would provide an opportunity for more aggressive resection, but as you can see again, the capsule is quite invading the pia of the anterior brain stem. Sharp dissection seemed to accomplish more. Nonetheless, the capsule is quite attached. Piecemeal removal continued, around the area ventral to the brain stem. No clear plane is possible. Some of the perforators appear to be adherent to the capsule of the tumor as well, and at this time I felt further resection would be too risky. Post operative MRI demonstrated subtotal resection of the mass, adequate decompression of the brainstem was accomplished however you can see evidence of a small venous infarction in the brain stem related to my overaggressive manipulation of the tumor capsule. This patient unfortunately suffered from mild-hemiparesis and swallowing difficulties after surgery. However these symptoms resolved within about three months after surgery and she made an excellent recovery. However they important learning point in this video is, avoidance of pial transgression when operating on the brain stem, if their tumor capsule is very adherent, it's best to leave more of a sheet of the tumor over the brain stem and not attempt transgression into the parenchyma of the brain stem. This patient subsequently underwent proton therapy. Thank you.

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