Name:
Removal of Koos IV acoustic neuroma and auditory brainstem implant in NF2 patient
Description:
Removal of Koos IV acoustic neuroma and auditory brainstem implant in NF2 patient
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Duration:
T00H10M24S
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Upload Date:
2021-10-27T00:00:00.0000000
Transcript:
Language: EN.
Segment:0 .
[MUSIC PLAYING]
SPEAKER: In this video, we will present the removal of Koos grade IV acoustic neuroma, followed by auditory brainstem implant in an NF2 patient. The 16-year-old girl affected by NF2 had already been operated in our department of complete removal of a left CP angel transition meningioma. Here you can see the pre- and postoperative MRI with bilateral Koos grade I neuromas, followed by minor surgery for CSS circulation troubles. In 2020, she was operated on for subtotal removal of left acoustic neuroma.
SPEAKER: But in the following 2 years, despite bevacizumab therapy, regrowth of the left residual and rapid volume increase of the right neuroma with severe hearing loss was observed. Neurological examination at admission showed profound hearing loss in the right ear and deafness in the left ear, gait instability, positive Romberg, left facial nerve palsy, and nystagmus in all directions. Preoperative MRI showed a large right acoustic neuroma, significant regrowth of the left tumor, and several other small enhancing tumors compatible with the neurofibromatosis 2.
SPEAKER: Right retrosigmoid approach for tumor removal and auditory brainstem implant was decided. Retrosigmoid approach allows good microsurgical control of the whole tumor mass from the lower bound to the upper bound. For the intracanalicular component, removal of the posterior wall of the internal acoustic canal would be necessary, with good control of the most hidden part of the tumor. Left lateral positioning-- three-pins head frame under IOM and magnetic navigation, incision was large and then started the retrosigmoid approach in order to allow partial mastoidectomy and cochleostomy and provide place for subcutaneous implant.
SPEAKER: Here, the ENT is performing the partial mastoidectomy in order to identify the cochlea, perform the cochleostomy, and implant a test cochlear electrode to detect residual hearing. In case residual hearing is present after the neuroma resection, cochlear implant instead of brainstem implant could be indicated. Here we are implanting the cochlear electrode inside the cochleostomy.
SPEAKER: After fixation of the cochlear electrode, we then start with a standard retrosigmoid approach. After retraction of the cerebellum, we opened the cistern in order to release the CSF and facilitate further cerebellar retraction. Large opening of the arachnoid allows to expose the tumor very nicely, and the mild retraction of the cerebellum allows significant exposure of the tumor.
SPEAKER: After coagulation of the outer part of the tumor, we can incise the outer capsule and perform a biopsy and extensive surgical debulking with the ultrasonic aspirator. Significant debulking is necessary in order to allow further dissection of the tumor from the cerebellum. As you can see, it is not necessary to remove a cerebellar parenchyma.
SPEAKER: As proposed by some author, it is always possible to perform a slow and careful dissection of the tumor from the cerebellum, progress with ultrasonic aspirator with a significant progressive debulking, and expose progressively the outer part of the tumor. Here, in the upper part of the tumor volume, we are trying to identify the facial nerve in order to protect it during the further phases of dissection.
SPEAKER: And here we can see the facial nerve. And we can isolate him and continue with the debulking and the removal of the tumor safely without risk to damage the facial nerve during these phases. This phase of identification is mandatory in order to try to save the facial nerve. Although in such a large tumor and especially NF2 patient, it is always very difficult to protect and respect the facial nerve that, as you can see, is extremely squeezed by the tumor compression.
SPEAKER: But we try to keep the integrity of the facial nerve throughout the surgery, dissecting it slowly from the outer capsule of the acoustic neuroma. The bleeding is usually relatively easy to control, even in the dissection of the outer capsule. And we can continue the dissection of the facial nerve throughout the circumference of the upper and posterior pole of the tumor. Then, we continue by isolation of the lower part of the tumor, trying to identify the lower cranial nerves and trying to identify the brainstem.
SPEAKER: Continued alternance of debulking and dissection is necessary until finally we can find and identify clearly the lower part of the tumor after the significant debulking that has been performed with the ultrasonic aspirator. Here, we can see very nicely the lower plan of dissection that allows visualization of the brainstem surface and lower cranial nerves. Here is the brainstem visible, and we continue then with further ultrasonic aspirator internal debulking.
SPEAKER: We identify the lower cranial nerves below the lower pole of the tumor-- respecting them, of course-- and we continue the progressive dissection of the outer capsule from the lower part of the brainstem. Then, we continue with the complete isolation and identification of the adhesions between the tumors and the brainstem. And we can limit, finally, the residual tumor to the intracanalicular part and to the part that is bulging from the internal acoustic meatus inside the cistern.
SPEAKER: At this point, we decompress and we debulk the part that is bulging from the internal acoustic meatus. So we open the posterior wall of the internal acoustic meatus in order to expose the tumor part that is inside the internal acoustic meatus in order to try to perform the removal as complete as possible in this phase. Due to the loss of any auditory response in the cochlear nerve, we perform the largest possible removal without any attempt to preserve the residual eighth nerve fibers.
SPEAKER: Here, the transducer is located under the skin, and we decide for the auditory brainstem implant. And we look for the foramen of Luschka that is easily identified in the lower part of the surgical field and identifiable by the presence of the choroid plexus. Then, we take the electrode that is inserted into the surgical field, and we look for the best possible location of the electrode.
SPEAKER: The electrode itself is composed of 12 microelectrodes that must be placed in the closest possible contact with the cochlear nuclei in the brainstem, inside the foramen of Luschka. Positioning of the electrode in close contact with the auditory nuclei of the brainstem may require some dissection of the foramen of Luschka to obtain the best possible anatomical contact between the implant pedal and the cochlear nuclear region.
SPEAKER: Here, you can see the position of the 12 electrodes and of the 13th reference electrode that is in the middle of the electrode itself. After a first placement inside the foramen of Luschka, we realized that the placement is not ideal because of the presence of the choroid plexus that does not allow the complete unfolding of the support of the electrode. Intraoperative stimulation shows that only four electrodes can have response, so the electrode must be repositioned.
SPEAKER: The shape of the Luschka foramen is adapted, and the orientation of the electrode needs to be modified. And we found that with a simple angle more upward directed allows the introduction of a few millimeters more of the electrode, well inside the Luschka foramen. At this point, intraoperative monitoring shows that nine electrodes are in good position with a good response. So we leave the electrode as it is in its final position.
SPEAKER: Postoperative MRI shows good placement of the electrode and a nice removal of the tumor. And postoperative CT scan shows that the electrode is in good position inside the foramen of Luschka. The patient presented postoperative right facial nerve palsy, House-Brackmann score IV. One month after surgery, the auditory brainstem implant has been successfully switched on. The last audiogram, 2 months after surgery, disclosed already a significant improvement of the right hearing threshold levels, 40 dB.
SPEAKER: In conclusion, bilateral acoustic neuromas associated with type 2 neurofibromatosis remain one of the most challenging forms of acoustic neuromas. Bevacizumab can delay progression, but it is not a definitive solution. Surgery needs to be timely in the attempt to save residual hearing. In advanced cases with profound hearing loss, auditory brainstem implant at the time of neuroma removal is a feasible option to restore some hearing capacity.
SPEAKER: