10.14639/0392-100X-N0779
Objective. The interest in surgical routes to the internal auditory canal (IAC) through the external auditory canal for vestibular schwannoma removal has been recently raised by the endoscopic approaches to the lateral skull base. The aim of the study was to reappraise the transmeatal microsurgical approach (TMMa) to the labyrinth and IAC, first described 50 years ago.
Methods. A retrospective series of 8 consecutive patients treated for intralabyrinthine and intrameatal schwannomas through TMMa is presented. Main outcome measures consisted of surgical indications, postoperative complications, facial nerve status, bed mobilisation time, hospitalisation time and tumour&nbsp;recurrence rate.
Results. Surgical indications for TMMa were tumour growth (62.5%) and disabling vertigo (37.5%) in the present series. Complete tumour removal with no complications and postoperative normal facial nerve function was obtained in all cases. Bed mobilisation occurred after a median of 3 postoperative days (IQR 2.2-3.0) and discharge after a median of 5.6 days (IQR 4.7-7.0). After a median follow-up of 13 months (IQR 7.5-27.5), no tumour recurrence was observed. Conclusions. TMMa indications are limited to schwannomas of the labyrinth and IAC, which dropped out from observation protocols due to unmanageable symptoms or growth. Despite the narrow mini-invasive surgical corridor, the TMMa was a safe an effective microsurgical technique in terms of tumour removal and postoperative course.
application/xml
1827-675X
779
5
en
Alessandro Martini
https://creativecommons.org/licenses/by-nc-nd/4.0
ACTA Otorhinolaryngologica Italica
Internal Auditory Canal
Transmeatal microsurgery for intralabyrinthine and intrameatal schwannomas: a reappraisal
Text.Serial.Journal
https://www.actaitalica.it/
40
Otology
2020-12-03
2020-04-03
2020-12-04
2020-12-04
390-395
1
Alessandro Martini
2020/12/03
10.14639/0392-100X-N0779
390
Otolaryngology Section, Department of Neuroscience DNS, Padova University, Padova, Italy
1827-675X
5
Internal Auditory Canal
en
395
Transmeatal microsurgery for intralabyrinthine and intrameatal schwannomas: a reappraisal
https://www.actaitalica.it/article/download/779/468
40
ACTA OTORHINOLARYNGOLOGICA ITALICA 2020;40:390-395; doi: 10.14639/0392-100X-N0779




Otology


Transmeatal microsurgery for intralabyrinthine
and intrameatal schwannomas: a reappraisal
Approccio transmeatale microchirurgico nei neurinomi intralabirintici e intrameatali:
rivalutazione di una tecnica
Antonio Mazzoni1*, Elisabetta Zanoletti1*, Diego Cazzador1,2, Leonardo Calvanese1, Domenico d’Avella3, Alessandro Martini1
1
  Otolaryngology Section, Department of Neuroscience DNS, Padova University, Padova, Italy; 2 Section of Human Anatomy, Department of
Neuroscience DNS, Padova University, Padova, Italy; 3 Academic Neurosurgery, Department of Neuroscience DNS, Padova University, Padova, Italy
*
  A. Mazzoni and E. Zanoletti should be considered joint first authors.


SUMMARY
Objective. The interest in surgical routes to the internal auditory canal (IAC) through the exter-
nal auditory canal for vestibular schwannoma removal has been recently raised by the endoscop-
ic approaches to the lateral skull base. The aim of the study was to reappraise the transmeatal
microsurgical approach (TMMa) to the labyrinth and IAC, first described 50 years ago.
Methods. A retrospective series of 8 consecutive patients treated for intralabyrinthine and
intrameatal schwannomas through TMMa is presented. Main outcome measures consisted
of surgical indications, postoperative complications, facial nerve status, bed mobilisation
time, hospitalisation time and tumour recurrence rate.
Results. Surgical indications for TMMa were tumour growth (62.5%) and disabling vertigo
(37.5%) in the present series. Complete tumour removal with no complications and postoperative
normal facial nerve function was obtained in all cases. Bed mobilisation occurred after a median        Received: April 3, 2020
of 3 postoperative days (IQR 2.2-3.0) and discharge after a median of 5.6 days (IQR 4.7-7.0).           Accepted: May 18, 2020
After a median follow-up of 13 months (IQR 7.5-27.5), no tumour recurrence was observed.
Conclusions. TMMa indications are limited to schwannomas of the labyrinth and IAC,                      Correspondence
which dropped out from observation protocols due to unmanageable symptoms or growth.                    Diego Cazzador
Despite the narrow mini-invasive surgical corridor, the TMMa was a safe an effective mi-                Otorhinolaryngology Unit, University of Padova,
crosurgical technique in terms of tumour removal and postoperative course.                              via Giustiniani 2, 35128 Padova, Italy
                                                                                                        Tel. +39 049 821 8778. Fax +39 049 821 1994
KEY WORDS: microsurgery, vestibular schwannoma, endaural approach, transmeatal                          E-mail: diego.cazzador@unipd.it
approach, internal auditory canal
                                                                                                        Funding
RIASSUNTO                                                                                               None.
Obiettivo. L’interesse per i corridoi chirurgici dal condotto uditivo esterno al condotto uditivo
interno (CUI) nel trattamento del neurinoma è incrementato negli ultimi anni grazie alla divulga-       Conflict of interest
zione di approcci endoscopici al basecranio laterale. Lo studio si prefigge di rivalutare l’approccio   The Authors declare no conflict of interest.
microscopico transmeatale (TMMa) al labirinto e al CUI, descritto in origine circa 50 anni fa.
Metodi. Otto pazienti sottoposti a TMMa per exeresi di neurinomi intralabirintici o intra-                How to cite this article: Mazzoni A, Zano-
meatali sono stati inclusi nello studio. Indicazione chirurgica a TMMa, complicanze posto-                letti E, Cazzador D, et al. Transmeatal micro-
peratorie, funzionalità del nervo facciale, tempo di mobilizzazione dal letto e di degenza,               surgery for intralabyrinthine and intrameatal
tasso di recidiva sono state le principali misure di outcome analizzate.                                  schwannomas: a reappraisal. Acta Otorhi-
Risultati. Crescita tumorale (62,5%) e vertigini incoercibili (37,5%) hanno rappresentato                 nolaryngol Ital 2020;40:390-395. https://doi.
l’indicazione chirurgica più frequente. In tutti i pazienti il tumore è stato rimosso in toto,            org/10.14639/0392-100X-N0779
in assenza di complicanze postoperatorie. La mobilizzazione dal letto è avvenuta dopo 3
                                                                                                        © Società Italiana di Otorinolaringoiatria
giorni (IQR 2,2-3,0), la dimissione dopo 5,6 giorni (IQR 4,7-7,0). All’ultimo follow-up                 e Chirurgia Cervico-Facciale
(mediana 13 mesi, IQR 7,5-27,5) non sono state registrate recidive.
Conclusioni. L’indicazione al TMMa è limitata agli schwannomi intralabirintici e/o estesi
                                                                                                                       OPEN ACCESS
al CUI, che escono dal protocollo di osservazione a causa di sintomi invalidanti o cresci-
ta. Nonostante l’accesso chirurgico mini-invasivo offra uno spazio limitato di manovra, il              This is an open access article distributed in accordance with
                                                                                                        the CC-BY-NC-ND (Creative Commons Attribution-Non-
TMMa si è dimostrato una opzione di trattamento microchirurgico sicura ed efficace in                   Commercial-NoDerivatives 4.0 International) license. The
termini di rimozione tumorale e decorso postoperatorio.                                                 article can be used by giving appropriate credit and mentio-
                                                                                                        ning the license, but only for non-commercial purposes and
PAROLE CHIAVE: microchirurgia, schwannoma vestibolare, approccio endocanalare,                          only in the original version. For further information: https://
approccio transmeatale, condotto uditivo interno                                                        creativecommons.org/licenses/by-nc-nd/4.0/deed.en




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                                                                                                  Transmeatal microsurgery for vestibular schwannoma




Introduction                                                                thine in 59, middle cranial fossa in 26, retrosigmoid in 64,
                                                                            the two latter with hearing preservation intent. The TMM
The straight line encompassing external auditory canal,                     technique was added to the treatment options since 2015,
tympanum, labyrinth and internal auditory canal (IAC) is                    with the goal of assessing its potential in itself and in re-
the anatomical premise for the transmeatal approach to the                  lation to the well documented endoscopic technique 14 -16 ,
above mentioned sites. The transmeatal route to the laby-                   as well as defining a mini-invasive surgical corridor to the
rinth was used for draining suppurative labyrinthitis and for               labyrinth and IAC.
labyrinthectomy in vertigo 1-3, and was proposed in 1970
as a microsurgical technique for schwannomas of the IAC,
sectioning the vestibular or cochlear nerve or exploration-                 Methods
graft of facial nerve 4. In 1976, Bochenek 5 introduced a                   Ethical considerations
modification in the approach. The few reports on the                        The procedures hereby described were in accordance with
transmeatal approach to acoustic schwannoma are reported                    the ethical standards of the University and the Declaration
in Table I 4,6-13.                                                          of Helsinki. Written informed consent was obtained from
The endoscopic surgery of the middle ear recently evolved                   all patients prior to participation.
into the transcanal endoscopic approach to labyrinth and
IAC for schwannoma with good outcomes 14-16.                                Participants
It is universally acknowledged that the endoscope al-                       From 2012 to 2019, 142 patients were diagnosed with in-
lows excellent visualisation of structures and hidden sites                 tralabyrinthine schwannoma (ILS) or intrameatal vestibular
“around the corner”. The endoscopic transcanal approach                     schwannoma. Ninety-seven patients were sent to observation,
nevertheless has some drawbacks: 1) the need to create                      45 were submitted to surgical excision. Twenty-one cases
space at the expense of the tympanic bone for placing both                  (46.5%) were operated on with hearing preservation intent,
instruments and endoscope; 2) the one-hand surgical tech-                   16 (35.5%) with translabyrinthine approach, eight patients
nique; 3) the 2D view.                                                      (18.0%) with ILS and/or intrameatal vestibular schwannoma
The transmeatal microsurgical approach (TMMa) was reap-                     were operated on via TMMa. The present report focuses on
praised as an effect of modern imaging and increase in early-               this latter group composed of five ILSs, two intralabyrinthine-
diagnosed small vestibular schwannomas. It underwent rapid                  intrameatal tumours and one pure intrameatal tumour.
development given the promising experiences of the transca-
nal endoscopic approaches and the expertise gained over the                 Preoperative assessment
years with conventional microscopic approaches.                             Hearing was evaluated with pure tone and vocal audiometry
Our small series of TMMa is part of a long-lasting ex-                      as pure tone average (PTA) at frequencies 500, 1000, 2000
perience in the microsurgical management of vestibular                      and 4000 Hz and word recognition score (WRS) classified ac-
schwannoma. Between 1972 and 2019, 2048 cases were                          cording to the American Academy Otolaryngology-Head and
treated with different microsurgical approaches. Pure were                  Neck Surgery (AAO-HNS) classification 17. Diagnosis was
                                                                            obtained with contrast enhanced magnetic resonance imag-
operated on with conventional approaches, translabyrin-
                                                                            ing (MRI) (Fig. 1). High resolution computed tomography

Table I. Literature on transmeatal microsurgical approach for schwannomas
of the labyrinth and/or internal auditory canal.
 Author                           Year of publication   Number of cases
    Alvarez De Cozar et al. 4                    1970             1
    Karlan et al. 6                              1972             1
    Wanamaker et al. 7                           1972             1
    Antoli Candela et al. 8                      1975             5†
    Weimuller et al. 9                           1975             1
    DeLozier et al. 10                           1979             6
    Jiang et al. 11                              2011             2
    Zhu et al. 12                                2012             1
    Mazzoni et al. 13                            2017             1‡
†
    The case reported in Alvarez de Cozar et al. 4 is included.             Figure 1. Contrast enhanced T1-weighted MRI of an intrameatal tumour, left
‡
    Included in the present series.                                         side. The facial quadrant of the fundus is free from tumour.



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A. Mazzoni, E. Zanoletti et al.




(HRCT) was indicated for surgical planning and immediate                             usually 2 mm but on the anterior wall, where it remains
postoperative evaluation (Fig. 2d). Facial nerve status was                          intact.
evaluated with the House-Brackmann (HB) grading system 18.                           3. Vestibulo-cochleostomy. This is sufficient for intrameatal
Indications to TMMa included ILS and intrameatal vestib-                             tumour, it is a step for the exposure of IAC. After foot-
ular schwannomas, hearing class D according to the AAO-                              plate removal, the promontory is drilled between the oval
HNS, unmanageable vertigo and/or tumour growth at serial                             and round window (Fig. 2a), and further anteriorly to open
imaging. Hearing preservation or rehabilitation were not                             the cochlea basal and second turns, the access to vestibule
considered.                                                                          is enlarged. The medial wall shows the whitish dot of the
                                                                                     saccular nerve entry. For ILSs, the vestibulocochleostomy
Surgical technique                                                                   is extended to the sites occupied by tumour itself. In tu-
The patient is lying supine with the head turned to the op-                          mours of the vestibule only, it is not necessary to drill out
posite side; surgery is performed with general endotracheal                          the cochlea. After carefully drilling the bone between the
anaesthesia and continuous facial nerve monitoring.                                  upper margin of the oval window and the Fallopius, and
1. After the endoaural incision, the tympano-malleo-meatal                           redirecting cranially the scope, the dot of the superior ves-
flap is harvested with circumferential (from 10 to 2 o’clock)                        tibular nerve entry comes under view. The latter dot is the
and longitudinal incisions. Malleus neck and tensor tym-                             landmark leading to the superior vestibular nerve to facial
pani tendon are sectioned. The complex of skin-drum-mal-                             nerve and Fallopius entry (Fig. 2b).
leus handle is raised against the anterior wall of the canal.                        4. Exposure of IAC. The medial wall is thinned out with drill-
If the anterior wall is to be drilled, the flap is raised further                    ing first around the saccule dot, thereon the utricular dot (Fig.
up and placed against the cartilaginous wall.                                        2b), being here cautious as the facial nerve lies just deep to
2. Enlarging the ear canal. The outer ear canal is enlarged                          the superior vestibular nerve. The crista trasversalis, emerging
by drilling of its bony walls as much as required by the                             in the drilled bed, is a landmark leading the bone removal to
anatomy of the canal and by the access either to labyrinth                           completely open the fundus. Following the full exposure of
or IAC, the latter requiring a larger access. The walls are                          the fundus, the facial nerve entering the labyrinthine portion
not removed in full thickness, as they need to accommo-                              of the Fallopius can be appreciated (Fig. 2c). The canal can
date the repositioned tympanomeatal flap at the end of the                           be exposed up to the porus by drilling first along the floor and
procedure. The bony tympanic annulus is removed for                                  thereon extending to the complete posterior wall.
                                                                                     5. Tumour removal. After opening the dura, displacing the
                                                                                     tumour gives way to a moderate outflow of CSF. The main
                                                                                     step here is to follow the interface between the tumour and
                                                                                     the facial nerve at the fundus and Fallopius orifice, thereon
                                                                                     proximally. The CSF pressure let the tumour herniate and
                                                                                     favours grasping it with suction or instruments, allowing its
                                                                                     piecemeal or en-bloc removal (Fig. 3). The cochlear nerve lies
                                                                                     at the inferior-anterior wall of the canal. The flattened facial
                                                                                     nerve is seen lying almost vertically at the anterior or antero-
A                                         B                                          superior wall held by arachnoid at the porus and floating on,
                                                                                     and pushed outward by the CSF (Fig. 4a, b). A piece of fat
                                                                                     is placed to seal the IAC and labyrinth; the Eustachian tube
                                                                                     is closed with muscle and fat obliterates the tympanum. The
                                                                                     drum is repositioned, and the external auditory canal is packed.
                                                                                     CSF leak was to be ruled out at day 5th, facial nerve func-
                                                                                     tion was evaluated at day 1st and day 5th, then at one, 6 and
                                                                                     12 months after surgery. Vertigo, dizziness, imbalance, pain
C                                         D
                                                                                     or other symptoms were recorded. Contrast enhanced MRI
Figure 2. Transmeatal microsurgical approach, intraoperative pictures:               was planned at one month, then 1-3-5-10 years.
A) round window (arrow) and oval window (arrowhead) after removal of os-
sicles; B) medial wall of vestibule with the whitish foramina of saccular (arrow)
and utricular nerves (arrowhead); C) the tumour is visible in the internal audi-     Results
tory canal (arrow), the facial nerve exits from the Fallopius (arrowhead). D) Left
side, postoperative coronal CT scan showing the surgical corridor from the           Patient characteristics are summarised in Table II. At presen-
external to the internal auditory canal.                                             tation, severe to profound hearing loss was the most reported



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                                                                                Discussion
                                                                                The traditional approaches to the IAC and labyrinth, name-
                                                                                ly the microsurgical middle cranial fossa and translaby-
                                                                                rinthine with the extensions to the cochlea, are now faced
                                                                                by surgical corridors through the external auditory canal,
                                                                                i.e. the purely endoscopic transcanal and microsurgical
                                                                                transmeatal approaches. Although proposed in recent years
                                                                                with the exclusive use of the endoscope 14-16, a transcanal
                                                                                approach to the IAC was already described in 1970, when
                                                                                Alvarez De Cozar reported on the “… transvestibular ap-
                                                                                proach to the IAC, aiming at the surgery of the acoustic
                                                                                neuroma presents the following anatomical limits: anteri-
Figure 3. Intraoperative specimen of a 10-mm intrameatal tumour. The            orly, the carotid canal and Eustachian tube; posteriorly, the
proximal end is the round surface on the right pole of the tumour. Irregular
tumour borders are due to surgical manoeuvres.
                                                                                vertical Fallopius: inferiorly, the hypotympanum and the
                                                                                jugular bulb; superiorly, the tympanic portion of the facial
                                                                                nerve.” The authors added that “… The sacrifice of vesti-
                                                                                bule and cochlea provides a surgical field wide enough to
                                                                                remove an acoustic neuroma of one cm or less (…) and
                                                                                allows to drop the transtemporal approach as a route to ac-
                                                                                cess the IAC” 4. In 1975, the same group reported their ex-
                                                                                perience with the transvestibular approach to the IAC on
                                                                                178 otoneurological cases, including 5 vestibular schwan-
                                                                                nomas 8. At those times, the diagnosis of millimetric tu-
                                                                                mours was still to come, literature studies were sparse and
                                                                                mostly involved single case reports on intrameatal schwan-
A                                      B
                                                                                nomas removed through a transmeatal-transvestibular ap-
Figure 4. Intraoperative view at the end of the transmeatal microsurgical ap-   proach (Tab. I).
proach, after tumour removal. A) Endoscopic view with 0° endoscope; B) mi-      Currently, intrameatal tumours are frequently diagnosed
croscopic view. *: dura of the petrous posterior wall; arrow: entrance of the
facial nerve into the Fallopius canal; arrowhead: facial nerve.                 and intralabyrinthine lesions are not an exceptional finding
                                                                                anymore. In our series of patients who underwent surgery
                                                                                via the TMMa for the treatment of intrameatal and intral-
symptom (87.5%), followed by tinnitus (50.0%), vertigo                          abyrinthine schwannomas, the approach allowed direct ac-
(25.0%) and auricular fullness (12.5%). Prior to surgical re-                   cess to the labyrinth and the IAC fundus with complete tu-
moval, five patients had been enrolled in a wait and scan pol-                  mour removal in all cases. Surgical indications for TMMa
icy for a median of 61 months (IQR 31.5-136.0). During ob-                      included ILS or/and intrameatal vestibular schwannomas
servation, four of five patients (80%) showed tumour growth                     with AAO-HNS hearing class D, unmanageable vertigo, or
at serial MRIs. The only patient with serviceable hearing at                    tumour growth at serial imaging.
diagnosis went through progressive hearing loss to class D.                     The reappraisal of the TMMa at present might confer excel-
Indications for surgical treatment were tumour growth                           lent outcomes with minimum surgical morbidity, as well as
for five patients (62.5%) and disabling vertigo for three                       short hospital stay. TMMa allows to perform a straightfor-
(37.5%). There were no postoperative complications. Post-                       ward surgical corridor to the IAC. The two-hands dissec-
operative facial nerve status at day one and at last follow-up                  tion microsurgical technique involves improved ergonom-
was grade I HB for all the patients. None required post-                        ics, which is a fundamental requisite for adequate handling
operative ICU admission. One patient experienced vertigo                        of adherences tumour/facial nerve, as well as tumour/vas-
for few days. Patient mobilisation was performed after a                        cular loops 20. There is no inherent morbidity of the surgical
median time of 3 postoperative days (IQR 2.2-3.0). Patients                     access due to sacrifice of the external auditory canal.
were discharged after a median time of 5.6 days (IQR 4.7-                       As such, the technical highlights of TMMa included endo-
7.0). At last follow-up (median 13 months; IQR 7.5-27.5                         aural skin incision of the external auditory canal, tympa-
months), no tumour recurrence was observed. All patients                        no-malleo-meatal flap that fully opened the lumen of the
presented a well-healed tympanic membrane.                                      canal to view and instruments, and limited removal of the



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A. Mazzoni, E. Zanoletti et al.




Table II. Clinical characteristics of patients underwent transmeatal microsurgical approach for schwannomas of the labyrinth and internal auditory canal.
 Patients Age Sex                Initial        Extension§        IAC              Decision for     Complications Hospitalisation              Follow-up
                              observation                     involvement            surgery                                (days)              (months)
 1              76        M              Y                IVC                   N                  Growth                      N                       3                       17
 2              59        F              Y                 IC                   N                  Growth                      N                       4                       35
 3              37        F              Y                 IV                   N                  Growth                      N                       5                       34
 4              48        F              Y               TLAB                   Y            Growth + symptoms                 N                       7                       21
 5              44        M              N                IVC                   N                Symptoms                      N                       5                        8
 6              48        F              Y                 IC                   N                Symptoms                    Vertigo                   9                        9
 7              38        M              N               TMOD                   Y                  Growth                      N                       7                        6
 8              76        F              N                IAC                   Y                Symptoms                      N                       5                        6
M: male; F: female; Y: yes; N: no; § according to the Modified Kennedy Classification 19; IVC: intravestibulocochlear; IC: intracochlear; IV; intravestibular; TLAB: translabyrinthine;
TMOD: transmodiolar; IAC: internal auditory canal.



tympanic annulus and tympanic bone, that allowed reposi-                                         vation. The goal is the removal of tumour with no surgical
tioning of the tympanic membrane. Unfavourable size and                                          morbidity, as it is postulated by the small benign lesion, as
shape of the canal conditioned its enlargement, but did not                                      well as by the results of the alternative, conventional op-
require its suture. The next steps of the approach involved                                      erations. Approaches through the external auditory canal
the drill out of promontory, cochlea, vestibule medial wall                                      are purported to having the advantage of a direct and quick
with the familiar landmarks of the saccule and utricle dots                                      route, which could appear to be progress over the conven-
leading to the vestibular nerves at the fundus, and the poste-                                   tional approaches. This theory seems to be supported by the
rior-inferior wall of the IAC. If compared to the traditional                                    initial experience and deserves further trial. Of the current
lateral approach, the small outflow of CSF is characteristic                                     endoscopic and microscopic approaches, the latter may be
of the transcanal/transmeatal approaches and may be due to                                       a step forward as effect of the microsurgical technique and
the short time of dural opening, and possibly to the arach-                                      safer handling of unexpected difficulties.
noid folds in the IAC. As a consequence of CSF sparing,
there are less brain collapse, less chances of pneumocepha-                                      Acknowledgements
lus and fast recovery.
Further considerations on TMMa concern the possibility of                                        The authors thank Frances Coburn for the English revision
hearing rehabilitation with cochlear implant. This requires                                      of the paper.
preserving the cochlear nerve and cochlea, or the full laby-
rinth 21 or carefully evaluating if the remains of the opened                                    References
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