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Posterior Petrosectomy: Nuances of Osteotomy

September 17, 2018

Transcript

- This is another video describing the methodologies for completion of a combined anterior and posterior petrosectomy for a large and complex petroclival meningioma. This is a 30 year old female, who presented with gait and balance and partial third nerve palsy, very large petroclival meningioma was diagnosed, as we'll see in a moment, and she underwent a petrosectomy approach. Patient is positioned under our prelim table in a supine position. You can see the incision extending from the root to zygoma, all the way up, curving backwards, just behind the edge of the mastoid bone. The pin sites are illustrated. This is one positioning, where the single pin has to be placed on the forehead of the patient. Facial monitoring, as well as the motor evoked and so much sensory evoke potentials, are also used. For the petrosectomy approaches for large meningiomas, I stage the operation. This is during the second stage of the operation, next day. The patient's head position is slightly different, where the head of the patient is tilted toward the floor, so that an inferior to superior trajectory is evident for resection of the tumor. Here's the tumor for which a petrosectomy approach was utilized. You can see the edema within the brain stem, which is quite an ominous sign, which means that the tumor has invaded the resection is not possible. In another image demonstrating the invasion of the foramina of the cranial nerves, angiogram demonstrating the encasement of the arteries, and its displacement. Here is the incision, completed in layers. The temporalis muscle and fascia are dissected first. The skull flapper is reflected all the way in fairly. One has to be careful not to violate the external auditory canal, or enter the ear. Suboccipital muscles over the mastoid tip are exposed. Multiple fish hooks are used for maximal and aggressive mobilization of the skull flap. Next, the fascia and the temporalis muscle are cut. Can see the incision within the fascia in this area, in order to mobilize the temporalis muscle inferiorly and the suboccipital muscles toward the feet. Again, one has to be careful not to enter the ear. Lunday section is useful during the later stages of this dissection. Ruta zygoma is also exposed. Here's the dissection of the suboccipital muscles. The mastoid tip is generously exposed. Here's the emissary vein. There can be quite brisk bleeding. From in soak Gelfoam is used to plug the bleeding point. Here's the air of the mastoid bone. Some of the sutures are quite evident. I'll go ahead and expose the tip of the mastoid, for anatomical orientation and the next step of the operation, which would be a mastoidectomy. Here's the mastoid, the mastoid groove. Can see the entire mastoid is uncovered. Here's the tip of the mastoid. I prefer to complete the mastoidectomy first, rather than the craniotomy. This maneuver allows exposure and safe uncovering of the venous sinuses and the dura. It is important to know, that the lumbar drain was placed at the beginning of the procedure and approximately 40 CC of CSF was removed gradually, up to this point so that the dura and the venous sinuses are decompressed and can be easily dissected away from the inner surface of the skull. Here, you can see the bone over the Troutmann's triangle. Here is the sigmoid sinus. Thin shells of bone are mobilized over the venous sinuses to protect their walls. We continue drilling, so that the pure sigmoid dura, is also uncovered. And see the root of zygoma there at the tip of my arrow. We continue dissecting the dura of the suboccipital area. This form of on roofing the sinus appears to be safer than performing the craniotomy first. There will be two bone flaps, one over the middle fossa and the temporal lobe and another in the suboccipital area. Can see the toggling of the drill in order to dissect the dura away from the inner aspect of the skull bone. And here's the transverse sinus. Seeing my sinus, transverse sinus, presigmoid dura, dura over the temporal lobe. Here's now completing the second bone flap, or the suboccipital dura. I avoid going over the wall of the sigmoid sinus as much as possible on this. The dura is freely dissected, and the roof of the sinus is freely dissected, away from the skull bone. Here is some bleeding from the emissary vein and simple coagulation of the vein controls the bleeding very effectively. This should not be confused with a tear of the sigmoid sinus wall. Transverse sinus, turning into the sigmoid sinus, the dura over the presigmoid dura, here's the floor of the middle fossa. Our ENT guy, Kolicks, proceed with skeletonization of the semicircular canals. Please refer to the corresponding atlas chapter for description of the mastoidectomy and of the semicircular canals. In this case, since the patient's hearing was very much affected, preservation of this semicircular canals or the cochlea was not of significance. We can be aggressive regarding bony removal over the presigmoid dura. The facial nerve is not a skeletonized and a sheet of bone are left over the nerve. Furthermore, this posterior petrosectomy is extending more anteriorly over the middle fossa to also complete a partial anterior petrosectomy, therefore further mobilizing the bone over the dura. This allows a more direct approach toward the tumor and a shorter working distance toward the tumor capsule. Here's removing the tumor over the internal auditory canal. Here's the tumor infiltrating the internal auditory canal. And we're removing as much bone as possible over the petrous apex in order to remove any hurdles toward reaching the tumor, since that hearing is not of a concern in this patient. The edge of the bone over the middle fossa, is also drilled away, flush with the floor of the middle fossa. And here's the portion of the operation, where the petrous' apex is drilled away. Part of the anterior petrosectomy approach. Reasonable bony removal is complete, so that the presigmoid dura is very much uncovered and the facial nerve can be stimulated through the dura, identifying again the approximate location of the nerve in relation, to the block of the tumor, that has invaded the IAC. Let's go ahead and open the dura. I start first with the posture fossa dura, dissecting the tumor and incising it anterior to the sigmoid sinus and parallel to it. The superior petrosal sinus along the edge of the tentorium is preserved. This is the second incision or the temporal lobe, parallel to the middle fossa floor. The vein of Labbé has to be carefully protected. You can see here is a branch of it, entering the transverse sinus. There's another vein here. It's a large one, therefore has to be protected. Appears that its insertion points, should not be affecting our approach. Here's the superior petrosal sinus again, and again the current cutting of the dura extends all the way to the superior petrosal sinus. Here is the tentorium, apparent here and we'll use wet clips to isolate the superior petrosal sinus and transect it. Here's one wet clip, we need a second one and then we'll cut between the wet clips. Here's the cutting of the tentorium. There's already tumor apparent just below the tentorium. One has to stay somewhat parallel to the posterior petrous Ridge. In cutting the tentorium from posterior to anterior direction, tentorium appears to be very vascular in this case, due to hyper vascularity of the tumor. Here's the meningioma above and below the tentorium. One has to be careful about the fourth cranial nerve, that's located just medial to the edge of the tentorium, here. A fixed retractor holds the temporal lobe. We're almost getting to the edge of the tentorium here. Can see how the tumor has been indented by the edge of the tentorium. Here's the completion of the transection of the tentorium. You can see the tumor below and above. Creating groove within the tumor. Here's the trigeminal nerve, which is the center of the attention in this approach, tumor medial to it. Again, this approach is a good approach for tumors that are very firm, not easily suckable, very large and originating medial to the trigeminal nerve. These are the true petroclival meningiomas. Here is the seventh and eighth complex, trigeminal nerve entering the tumor capsule. Thank you.

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