Surgical approaches to vestibular schwannomas (VS) are widely known and extensively recorded. For the first time, an exclusive endoscopic approach to the internal acoustic canal (IAC) was described and used to safely remove a cochlear schwannoma involving IAC in March 2012. The aim of this article was to summarize indications and technique to treat intracanalicular VS by transcanal/transpromontorial endoscopic approach. Because management of intracanalicular VSs is complex and strongly debated, this kind of therapeutic option in the appropriate and selected cases could modify classic concepts of the management of this pathology.
Key points
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Transcanal/transpromontorial endoscopic approach is an effective surgical technique for small intracanalicular acoustic neuroma removal.
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The surgical approach must follow strict landmarks to identify and preserve facial nerve.
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Although there is no possibility for hearing preservation, facial nerve results are encouraging.
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Transcanal/transpromontorial endoscopic approach can be an alternative to wait and scan policy or radiosurgery in this kind of pathology.
Introduction
Fully endoscopic surgery is a surgical standard of care in minimally invasive neurosurgery of the anterior skull base. The successful implementation of the endoscope in pituitary surgery has allowed many surgeons to adopt the benefits of endoscopy such as panoramic view, brilliant illumination, and faster postoperative recovery. Endoscope use in other areas of the brain, such as the cerebellopontine angle (CPA) and the internal acoustic canal (IAC), however, has been limited.
At present, endoscopy in CPA surgery is primarily used as an adjunct to conventional microscopic surgical techniques, so called endoscope-assisted microsurgery (EAM) for removal of acoustic neuromas (ANs). The first introduction of the endoscopic technique in IAC surgery has been in combination with the retrosigmoid approach after removal of the CPA extension of the tumor.
The intracanalicular extension would be removed under endoscopic control, trying to avoid extensive drilling of the posterior aspect of the petrous bone. More recently, a keyhole retrosigmoid approach has been proposed for surgical removal of ANs.
EAM in CPA has been an excellent start for the use of the endoscope in the posterior fossa and the advances in the application of endoscopy in the surgical treatment of middle ear cholesteatoma with the natural evolution of the otologic/endoscopic techniques allowed the use of the endoscopes in lateral skull base surgery.
By studying and understanding the endoscopic anatomy and procedures, approaches of the middle ear have been gradually completed until endoscopic anatomy of the labyrinth and IAC were thoroughly known. Recently, a progression from EAM to a fully appropriate endoscopic technique in the internal auditory canal (IAC) surgery has been recorded and applied clinically for removal of AN in the IAC.
Retrosigmoid, transmastoid-translabyrinthine, and middle cranial fossa approaches are the most popular surgical approaches to treat pathology extending into the IAC, such as ANs.
All these approaches are characterized by the fact that they are indirect approaches to the inner ear and require wide external incisions and a variable degree of temporal bone removal to access the IAC and CPA.
Hence, the technique outlined in this publication provides a safe and effective step-by-step way to perform CPA surgery using a fully endoscopic transcanal technique for the resection of ANs, as it has superior visualization of the neurovascular relationship allowing for successful resection of ANs.
Introduction
Fully endoscopic surgery is a surgical standard of care in minimally invasive neurosurgery of the anterior skull base. The successful implementation of the endoscope in pituitary surgery has allowed many surgeons to adopt the benefits of endoscopy such as panoramic view, brilliant illumination, and faster postoperative recovery. Endoscope use in other areas of the brain, such as the cerebellopontine angle (CPA) and the internal acoustic canal (IAC), however, has been limited.
At present, endoscopy in CPA surgery is primarily used as an adjunct to conventional microscopic surgical techniques, so called endoscope-assisted microsurgery (EAM) for removal of acoustic neuromas (ANs). The first introduction of the endoscopic technique in IAC surgery has been in combination with the retrosigmoid approach after removal of the CPA extension of the tumor.
The intracanalicular extension would be removed under endoscopic control, trying to avoid extensive drilling of the posterior aspect of the petrous bone. More recently, a keyhole retrosigmoid approach has been proposed for surgical removal of ANs.
EAM in CPA has been an excellent start for the use of the endoscope in the posterior fossa and the advances in the application of endoscopy in the surgical treatment of middle ear cholesteatoma with the natural evolution of the otologic/endoscopic techniques allowed the use of the endoscopes in lateral skull base surgery.
By studying and understanding the endoscopic anatomy and procedures, approaches of the middle ear have been gradually completed until endoscopic anatomy of the labyrinth and IAC were thoroughly known. Recently, a progression from EAM to a fully appropriate endoscopic technique in the internal auditory canal (IAC) surgery has been recorded and applied clinically for removal of AN in the IAC.
Retrosigmoid, transmastoid-translabyrinthine, and middle cranial fossa approaches are the most popular surgical approaches to treat pathology extending into the IAC, such as ANs.
All these approaches are characterized by the fact that they are indirect approaches to the inner ear and require wide external incisions and a variable degree of temporal bone removal to access the IAC and CPA.
Hence, the technique outlined in this publication provides a safe and effective step-by-step way to perform CPA surgery using a fully endoscopic transcanal technique for the resection of ANs, as it has superior visualization of the neurovascular relationship allowing for successful resection of ANs.
Transcanal transpromontorial endoscopic approach to the internal auditory canal
The transcanal transpromontorial endoscopic approach (TTEA) representing the first fully endoscopic approach for the acoustic neuroma, the external auditory canal (EAC) is used as a natural surgical corridor to reach the fundus of the IAC; passing through the cochlea and the vestibule, exposing the whole IAC from the external auditory canal ( Fig. 1 ). From an anatomic point of view, this approach allows work on the medial wall of the tympanic cavity and lateral skull base dissecting the whole IAC from the fundus to the porus, avoiding cerebellum, middle and posterior fossa manipulation, reducing the mobility related to the standard procedures (middle cranial fossa, translabyrinthine, and retrosigmoid approaches). However, because cochlea removal is mandatory to have access to the IAC, the sacrifice of hearing function is required ( Fig. 2 ).
Indications
We considered indications for this surgical route:
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Acoustic neuroma limited to the IAC growing or symptomatic with hearing loss (type D hearing according to American Academy of Otolaryngology – Head and Neck Surgery [AAO-HNS] classification).
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Cochlear schwannoma with or without IAC involvement.
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Residual acoustic neuroma into the IAC after previous surgery.
Surgical Technique
During surgery, 0° rigid endoscopes (Karl Storz, Tuttlingen, Germany) are used, 15 cm in length and 3 mm or 4 mm in diameter. An AIDA 3-chip high-resolution monitor and camera (Karl Storz) are used.
The patient is in a supine position, the head gently rotated in the contralateral side, and facial nerve monitoring is used (nerve integrity monitor).
A circumferential incision of the skin of the EAC is made with a round knife using the 0° endoscopic view, between the cartilaginous and bony portions of the EAC; the skin is elevated with the eardrum circumferentially detaching the annulus from the bony ring, and the flap, pedicled on the umbus, is transposed laterally and then detached from the malleus using a microscissors. The skin of the EAC with the eardrum is so removal exposing the tympanic cavity and the bony portion of the EAC ( Fig. 3 A).
To gain optimal surgical access to the entire medial wall of the tympanic cavity, the EAC is drilled ( Fig. 3 B) detecting anteriorly the temporomandibular joint, posteriorly the mastoid segment of the facial nerve; the bony annulus is also drilled circumferentially exposing the hypotympanum, protympanum, retrotympanum, and attic spaces. After this procedure, good control of the whole tympanic cavity is achieved, and the ossicular chain and promontory region are easily exposed endoscopically ( Fig. 3 C).
The ossicular chain removal is a crucial procedure so as to have good access to the medial whole of the tympanic cavity; the incus and the malleus are removed, maintaining the integrity of the stapes ( Fig. 3 D). The tympanic segment of the facial nerve is so exposed from the second genu until the geniculate ganglion, located between the cog and the cochleariform process.
The stapes is then removed entering into the vestibule, exposing the saccule ( Fig. 4 A, B). The vestibule with the spherical recess in the saccular fossa are endoscopically detected, as the spherical recess is the end of the inferior vestibular nerve, representing an important landmark for the localization of the fundus of the IAC. The tegmen of the round window niche is removed carefully, exposing the membrane of the round window.
Using a Piezosurgery instrument (Mectron, Carasco/Genova, Italy), the promontory with lateral aspect of the otic capsule is removed at the cochlear level, identifying the basal, middle, and upper turn of the cochlea ( Fig. 4 C). After the exposition of the cochlear turns, the bony wall between the cochlea and the spherical recess is removed carefully, entering in the fundus of the IAC ( Fig. 4 D).
A dissection of the IAC is then progressively made, following the dura of the IAC from the fundus until the porus, exposing the AN ( Fig. 5 A). During this step, the bony tissue of the lateral skull is removed progressively between the IAC and the surrounding anatomic structures, exposing circumferentially the IAC. Respectively, the bony tissue between the IAC and the internal carotid artery anteriorly, the IAC and the mastoid portion of the facial nerve posteriorly, the IAC and the jugular bulb inferiorly, and the IAC and the tympanic segment of the facial nerve superiorly is removed, permitting a wide access to the IAC. The bony tissue of the otic capsule is removed from lateral to medial wall exposing the dura of the medial surface of the temporal bone, representing the deepest limit of the dissection.
