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MVD for Hemifacial Spasm: Nuances of Dissection

January 16, 2015

Transcript

This video reviews technical nuances for intradural microsurgical dissection for decompression of the facial nerve for hemifacial spasm. The previous videos reviewed some of the other nuances for the craniotomy, as well. This is a patient of mine who presented with right-sided hemifacial spasm and MRI of whom demonstrated a vascular loop along the facial nerve on the right side. You can see the internal auditory meatus, the seventh and eighth cranial nerves and evidence of a vascular loop at the root exit zone of the nerve. A curvilinear incision was completed. The myocutaneous flap was reflected inferior. This is the floor of the posterior fossa. The incision is below the junction of transverse sigmoid sinuses, and you can see the mastoid groove and to put the mastoid in the area, I'll go ahead and complete a burr hole just along the superior aspect of the mastoid groove. And the burr hole is expanded. Often, the craniotomy or ectomy needed is just slightly larger than a quarter coin. And an expanded burr hole is adequate to perform the procedure through. You can appreciate the width of the sigmoid sinus that's been exposed here. Removal of the thick mastoid bone here is important for the surgeon to be able to tack up the sigmoid sinus using the dural retention sutures to expand the operative corridor around the cerebellum. The fish hooks also expand the scalp flap mobilization more laterally. The dura is opened along the sigmoid sinus, as well as the floor of the posterior fossa. Two or three retention sutures are often more than adequate. The first landmark that is important is identification of dura over the petrous bone, where the petrous bone turns to become the floor of their posterior fossa. This turn around the petrous bone is a important landmark and where this is found, I go around the cerebellum to find the lower cranial nerves first. As we emphasized before, we follow the ninth cranial nerve pathway, in order to find the root exit zone of the seventh cranial nerve. The retinoid membranes over the ninth and tenth cranial nerves are opened generously. We do not initially plan to tackle the root exit zone of the facial nerve, as this would place undue traction parallel to the eighth cranial nerve. The retinoid membranes are sharply opened and again, the ninth cranial nerve is followed. You can see how the trajectory of view changes for the microscope. Often there is a meningeal branch or a meningeal artery that goes directly into the petrous dura, and as long as the trajectory and the route of the artery is clearly identified, it can be sacrificed and cut. You can see the third coracular membranes along the vascular loop that is most likely compressing the root exit zone of the facial nerve. We try to avoid manipulating the eighth cranial nerve as much as possible. We stay below the eighth cranial nerve. You can see now the root exit zone of the seventh cranial nerve here, the eighth cranial nerve here, the vascular loop that has been micro surgically mobilized away from the discoloration on the root exit zone of the facial nerve. No retractors are used. Here, a mobilization of the artery, and you can see the root exit zone of the facial nerve, just inferior to the root entry zone of the eighth cranial nerve. The discoloration is here, here is relatively impressive and it assures me that the pathology has been found and adequately mobilized. You can see the vascular loop falling back in place. Small pieces of shredded Teflon are placed between the vascular loop and the root exit zone of the nerve. Here's another piece to make sure both the nerve and the brainstem are adequately decompressed And the implant is pushed slightly more medially to assure that the entire vascular structure is mobilized. The labyrinthine artery that often joins the eighth cranial nerve is unlikely to be the cause of vascular conflict and should not be manipulated with. Here's the loop generously pushed away. We make sure that the vascular loop is completely dissected away, all the way to the anterior aspect of the brainstem. You can see a more demagnified view of the operative corridor. And a piece of muscle may be used to achieve a relatively watertight closure in these cases, if the dura has shrunken. The mastoid air cells are generously waxed and a cranioplasty is completed and the closure performed in standard manner. Thank you.

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