MVD for Hemifacial Spasm: Craniotomy and Vascular Decompression
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Microvascular decompression surgery for hemifacial spasm is technically more challenging than the one for trigeminal neuralgia. A detailed understanding of cerebrovascular anatomy around the lower cranial nerves is pertinent for success in this operation. This video reviews all the details regarding the craniotomy, as well as details of intradural dissection and microvascular decompression for right-sided hemifacial spasm. This is a 42 year old female who presented with long-standing history of right-sided hemifacial spasms and on high resolution T2 axial sequences of the MRI demonstrated a vascular loop close to the lower cranial nerves on the right side. Here you can see the lower cut, which shows the vascular loop at the root exit zone of the facial nerve. That is most likely this structure at the tip of the arrow. And furthermore, the higher cut demonstrates, again, the cranial nerve seven and eight entering the internal auditory meatus. Just like the MVD for trigeminal neuralgia, I use a curvilinear incision. I do not monitor brainstem auditory evoked potentials for microvascular decompression surgery for trigeminal neuralgia. However, I do monitor brainstem auditory evoked potentials during MVD for hemifacial spasm. I believe the risk of hearing loss due to the intradural work we do around the eighth cranial nerve is significant, and therefore, monitoring hearing is almost part of standard care for this operation. The incision for hemifacial spasm surgery is somewhat smaller than the one for trigeminal neuralgia. You can see the inion here, the root of zygoma there. A line connecting the two identifies the transverse sinus. This is the marking for the mastoid tip. And this is the mastoid groove. The location where the vertical line from the mastoid groove joins the initial horizontal line is the junction of transverse and sigmoid sinuses. It is unnecessary to expose the junction of the dural sinuses for hemifacial spasm, since most of the work is done along the lower cranial nerves in order to expose the root exit zone of the seventh cranial nerve. As you can see, the curvilinear incision moves the myocutaneous flap out of the working zone or the surgeon, and it provides a lower working distance toward the lower cranial nerves. Here's the initial skin incision that has been completed. Again, the mastoid groove and the burr hole started somewhere around here, below the junction of the transverse and sigmoid sinuses more superiorly. Essentially, the burr hole is placed right above the mastoid groove. The air cells are entered early during the operation, as we would like to place the burr hole as lateral as possible, just over the edge of the sigmoid sinus. The initial burr hole exposes the dural. We would like to stay away initially from the sigmoid sinus. The lower puncture that was performed at the beginning of the operation provides us with a very relaxed dural, which makes the bone work relatively easy and safer. We've continue to thin out and shell out the bone over the sigmoid sinus. And Kerrison rongeurs are then used to remove the bone over the sigmoid sinus. The roof of the sinus is carefully dissected away from inner surface of the skull bone. You can see the edge of the sigmoid sinus. That is very apparent at this time. We like to expose at least half of the width of the sigmoid sinus. You can see the transverse sinus is not apparent here. The dural is opened in a curvilinear fashion, parallel to the sigmoid sinus and the floor of their posterior fossa. Here's the elevation of the sigmoid sinus with our retraction sutures. You can see the dural of the petrous bone early on. The cerebellum is retracted superomedially, and the lower cranial nerves are identified. We stay away from the seventh and eighth cranial nerve early during the operation. A meningeal artery is often present, which can be coagulated and cut. Microscissors are used to mobilize the arachnoid membranes. And here is the lower cranial nerves. After the lower cranial nerves are found, we continue our dissection more superiorly. Here is the choroid plexus, you can see the seven and eighth cranial nerves. And here's the root exit zone of the seventh cranial nerve. And here's the vascular loop that is compressing the root exit zone of the facial nerve. You can see the area of the discoloration and the impression dysvascular loop has made on the root exit zone of the facial nerve. Again, this is the cranial nerve eight, cranial nerve seven. The vascular loop is being mobilized. You can see, we completely focus our attention underneath the nerve. There is no retraction parallel to either cranial nerve seven or eight. Here's another view of the compression. Shredded pieces of Teflon are used to mobilize the artery away from the area of the vascular conflict. In a stepwise fashion, we place small pieces of shredded Teflon to model the implant to the area of the compression, to prevent any risk of delayed displacement of the implant. Both the root exit zone of the facial nerve and the brainstem has to be thoroughly decompressed. So you can see, additional pieces of Teflon have been placed to decompress the artery away from the brainstem. And here's again, the area of the decompression that we reviewed a moment ago. You can see the root exit zone of the facial nerve is more inferior than the one for root entry zone of cranial nerve eight. Mouth switch allows surgeon to continue to remain in focus while using dynamic retraction and working with both hands in order to accomplish microsurgery. So now that initial decompression has been performed, again, you can see the area of the vascular conflict that convincingly demonstrates that the pathology has been found and addressed. Additional pieces of Teflon have been placed. A moment ago, you saw the papaverine soaked gelfoam that was placed over the other arteries around the seven and eighth cranial nerves to avoid vasospasm. And the final product reveals padding over the root exit zone of the facial nerve, as well as over the area of the brainstem. This assured no further contact between the vascular loop and the surrounding nervous structures. The closure is performed, as you can see, using interrupted 3-0 non-absorbable sutures. I do not persist to have a watertight closure if the intradural work was performed in a bloodless fashion, as CSF pressures are relatively normal in these patients. However, mastoid air cells have to be very thoroughly waxed and either cranioplasty, or the craniotomy bone flap will be replaced at the end of the procedure, thank you.
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