Name:
Dorsal displacement of the facial nerve in vestibular schwannoma surgery
Description:
Dorsal displacement of the facial nerve in vestibular schwannoma surgery
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Duration:
T00H09M13S
Embed URL:
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Upload Date:
2021-10-27T00:00:00.0000000
Transcript:
Language: EN.
Segment:0 .
[MUSIC PLAYING]
GUSTAVO JUNG: This is Dr. Gustavo Jung, and I will demonstrate the microsurgical resection of the vestibular schwannoma with the facial nerve dorsally displaced and the technique to identify the course of the patient there during surgery. This 57-year-old male discovered a vestibular schwannoma during a diagnostic workup for right-sided tinnitus. It was classified as T3b according to the Hannover classification and stage III according to Koos classification.
GUSTAVO JUNG: The patient had a AAOHNS hearing class B and a House-Brackmann grade I facial nerve function. The T1 postgadolinium MRI demonstrated a CP angle mass compressing the brainstem with distinction to the most lateral part of the internal auditory canal. The tumor was predominantly solid, and the CSF cleft sign was not visible between the tumor and the brainstem.
GUSTAVO JUNG: The CISS MRI did not raise any suspicion on the facial nerve's position, and DTI-based fiber tracking was not acquired in this case. The patient was positioned supine with the head turned approximately 60 degrees to the left side. The right shoulder was elevated with a cushion to facilitate their head turning. Facial nerve monitoring and brainstem auditory evoked response were used.
GUSTAVO JUNG: A straight skin incision 4 cm behind the pinna is designed, and the retrosigmoid craniotomy is elevated in my standard fashion. The dura is incised in a C-shape fashion, and a perpendicular cut is made toward the sigmoid transverse junction to increase the view angle of the petrous surface. The dura is elevated with 4-0 Prolene sutures. The inferior surface of the cerebellum is gently retracted, and the cerebellum medullary cistern is opened to brain relaxation.
GUSTAVO JUNG: The microscope is turned toward the tentorial surface of the cerebellum, inspecting for cerebellar bridging veins and Dandy’s vein. A small bridge vein is coagulated around the jugular foramen and cut. The arachnoid main brain is adhering to the dorsal surface of the tumor. To avoid the injury to the nerves or the tumor capsule, the arachnoid's released from the lower cranial nerves.
GUSTAVO JUNG: At this place, it is not tightly adherent to the tumor capsule. The arachnoid layer becomes visible at the dorsal surface of the VS. A narrowed stricture is visible on the dorsal surface of the tumor, and the EMG activity of the facial nerve is recorded. A further dissection of the arachnoid around the lower cranial nerves is necessary to expose the brainstem.
GUSTAVO JUNG: A progressive 1.0- and 2.0-mA stimulus is used, and only a mild response is observed. The brainstem is inspected, and the facial nerve is visualized running dorsally to the tumor capsule. Be sure your vestibular nerve and the proximal portion of the facial nerve are identified. Some mild EMG response is also evoked during the stimulation of the upper pole of the tumor, making unpredictable the precise course of the facial nerve.
GUSTAVO JUNG: To better delineate the trajectory of the facial nerve, the distal portion of the FN is exposed inside the IAC. A dural flap is harvested and kept attached over the jugular foramen. We start drilling the IAC with a large cutting bore, creating a safe cavity to prevent the drill's light. The smaller cutting bores are used until the eggshell bone is left over the IAC.
GUSTAVO JUNG: Diamond drills are used to expose the tumor inside the IAC and enlarge the bony cavity sufficiently to access the lateral portion of the tumor. The dura inside the IAC is incised with microscissors, and the inferior vestibular nerve is dissected away from the tumor. The tumor within the IAC is dissected with a blunt hook dissector and removed. The facial nerve is identified, and stimulation of the upper and lower portions of the cisternal meatal region identify the facial nerve running dorsal inferiorly.
GUSTAVO JUNG: After identifying the facial nerve running dorsal inferiorly, intracapsular tumor debulking is done. And the attention is kept to the upper pole of the tumor. The arachnoid is firstly dissected in the upper pole of the tumor, coming from the meatus up to the facial nerve at the brainstem. The inferior portion of the tumor is dissected from lateral to medial, and additional debulking is done.
GUSTAVO JUNG: A decrease in the amplitude of waves III and V in the AED is recorded, and papaverine solution is instilled until waves recovered. The cochlear nerve is identified anterior to the inferior vestibular nerve and the facial nerve. Bimanual dissection with a tumor forceps in nondominant hand and a blunt hook dissector in the dominant hand, the facial nerve is dissected from the tumor capsule all the way to the IAC.
GUSTAVO JUNG: Preservation of the facial nerve function is confirmed with proximal and distal electrical stimulation with 1.0 mA. The vascularized dural flap is rotated into the IAC covering the nerves. A 0.5-mm hook dissector is used to inspect the walls of the IAC for the presence of open mastoid cells. The cells are occluded with a small piece of muscle, and the IAC is completely occluded with a larger piece of muscle, Surgicel, and fibrin glue.
GUSTAVO JUNG: It deteriorates close in a watertight fashion with 4-0 Prolene sutures. And the mastoid cells are closed with bone loss. The bone flaps were positioned and fixed with titanium plates, Postoperative MRI did not show any residual lesion, and the facial nerve is well visualized in the CISS MRI. The patient remained 1 day in the ICU and was discharged home on the postoperative day 4. The patient remained stable with a House-Brackmann grade III facial palsy that recovered to grade I 4 months after surgery with physiotherapy.
GUSTAVO JUNG: Hearing decreased to AAOHNS class C. In summary, vestibular schwannoma are challenging lesions, regardless of the position of the fascial nerve. Dorsal displacement of the facial nerve is rare and accounts for less than 3% of the cases. DTI-based fiber tracking can help to identify the facial nerve course preoperatively, but its accuracy is intermediate when the nerves run dorsally.
GUSTAVO JUNG: Starting arachnoid dissection at the lower pole of the tumor around the tubular foramen where it is looser helps to release the arachnoid from the dorsal surface of the tumor. This strategy, associated with the newer monitoring, may avoid the injury to the tumor capsule and dorsally displaced nerves. In those cases, our strategy is to first identify the nerve at the brainstem and then open the IAC to dissect the facial nerve within the IAC.
GUSTAVO JUNG: The nerve is usually very adherent to the tumor capsule at the meatal's entrance. The electric stimulation of the cisternal-meatal transition of the facial nerve will help in its identification and dissection. Thank you.
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