10.14639/0392-100X-N2367
Objective. Vestibular schwannoma surgery leads to acute unilateral vestibular loss. In some patients, however, the process of post-operatively initiated central compensation proceeds more rapidly than in others. This study aimed to evaluate post-operative vestibular function and correlate it with morphological findings of MRI scans. Methods. The study included 29 patients who underwent surgery for vestibular schwannoma. Vestibular function was analysed post-operatively by video head impulse test (vHIT). Subjective symptoms were evaluated using validated questionnaires. All patients underwent MRI 3 months post-operatively, and the presence of the facial and vestibulocochlear nerves in the internal auditory canal was assessed. Results. The vestibulo-ocular reflex gain measured by the vHIT correlated positively with audiological findings. Subjective perception of vestibular disorder did not correlate with objectively measured vestibular impairment or with MRI findings. Conclusions. After the resection of vestibular schwannoma, some patients may still have preserved vestibular function as measured by vHIT. The preserved function does not correlate with subjective symptoms. Patients with partially deteriorated vestibular function showed lower sensitivity to combined stimuli.
text/xml
1827-675X
2367
en
Zdeněk Čada
http://creativecommons.org/licenses/by-nc-nd/4.0
ACTA Otorhinolaryngologica Italica
vestibular function
Does vestibular function correlate with objective MRI findings after vestibular schwannoma surgery?
Text.Serial.Journal
https://www.actaitalica.it/
43
Vestibology
2023-05-16
2022-11-03
2023-05-19
2023-05-19
212-220
1
Zdeněk Čada
2023/05/16
10.14639/0392-100X-N2367
212
Department of Otorhinolaryngology and Head and Neck Surgery, 2nd Faculty of Medicine, Charles University and Motol University Hospital, Prague, Czech Republic
1827-675X
vestibular function
en
220
Does vestibular function correlate with objective MRI findings after vestibular schwannoma surgery?
https://www.actaitalica.it/article/download/2367/991
43
ACTA OTORHINOLARYNGOLOGICA ITALICA 2023;43:212-220; doi: 10.14639/0392-100X-N2367




Vestibology


Does vestibular function correlate with objective MRI
findings after vestibular schwannoma surgery?
Dopo chirurgia del neurinoma vestibolare la funzione vestibolare correla
con dati oggettivi estratti dalla risonanza magnetica?
Zuzana Balatková1, Markéta Bonaventurová1, Rudolf Černý2, Jiří Lisý3, Silvie Brennerová1, Vladimír Koucký1,
Veronika Bandúrová1,Veronika Svobodová1, Zdeněk Fík1, Martin Komarc4, Eva Mrázková5, Klára Kučerová6,
Pavel Hermann7, Zdeněk Čada7
1
  Department of Otorhinolaryngology and Head and Neck Surgery, 1st Faculty of Medicine, Charles University and Motol University
Hospital, Post-graduate Medical School, Prague, Czech Republic; 2 Department of Neurology, 2nd Faculty of Medicine, Charles
University and Motol University Hospital, Post-graduate Medical School, Prague, Czech Republic; 3 Department of Radiology, Na
Homolce Hospital, Prague, Czech Republic; 4 Department of Anthropomotorics and Methodology, Faculty of Physical Education
and Sport, Charles University, Prague, Czech Republic; 5 Department of Otorhinolaryngology and Head and Neck Surgery, Havířov
Hospital, Czech Republic; 6 Department of Rehabilitation and Sports Medicine, 2nd Faculty of Medicine, Charles University and
Motol University Hospital, Prague, Czech Republic; 7 Department of Otorhinolaryngology and Head and Neck Surgery, 2nd Faculty of
Medicine, Charles University and Motol University Hospital, Prague, Czech Republic


SUMMARY
Objective. Vestibular schwannoma surgery leads to acute unilateral vestibular loss. In some
patients, however, the process of post-operatively initiated central compensation proceeds
more rapidly than in others. This study aimed to evaluate post-operative vestibular function
and correlate it with morphological findings of MRI scans.
Methods. The study included 29 patients who underwent surgery for vestibular schwanno-
ma. Vestibular function was analysed post-operatively by video head impulse test (vHIT).
Subjective symptoms were evaluated using validated questionnaires. All patients underwent
MRI 3 months post-operatively, and the presence of the facial and vestibulocochlear nerves
in the internal auditory canal was assessed.                                                    Received: November 3, 2022
Results. The vestibulo-ocular reflex gain measured by the vHIT correlated positively with       Accepted: January 15, 2023
audiological findings. Subjective perception of vestibular disorder did not correlate with
objectively measured vestibular impairment or with MRI findings.                                Correspondence
Conclusions. After the resection of vestibular schwannoma, some patients may still have         Rudolf Černý
preserved vestibular function as measured by vHIT. The preserved function does not cor-         Department of Neurology, Motol University Hospi-
relate with subjective symptoms. Patients with partially deteriorated vestibular function       tal, V Úvalu 84, 150 06, Praha, Czech Republic
showed lower sensitivity to combined stimuli.                                                   Tel. +42 0224436802. Fax +42 0224436820
                                                                                                E-mail: Rudolf.Cerny@lfmotol.cuni.cz
KEY WORDS: vestibular schwannoma, video head impulse test, magnetic resonance
imaging, unilateral vestibular lesion, vestibular function
                                                                                                  How to cite this article: Balatková Z, Bonaven-
                                                                                                  turová M, Černý R, et al. Does vestibular func-
RIASSUNTO                                                                                         tion correlate with objective MRI findings after
Obiettivo. La chirurgia dello schwannoma vestibolare causa un deficit vestibolare unila-          vestibular schwannoma surgery? Acta Otorhi-
terale acuto. Tuttavia, in alcuni pazienti il processo di compenso centrale post-operatorio       nolaryngol Ital 2023;43:212-220. https://doi.
progredisce più rapidamente rispetto ad altri. Il presente studio è finalizzato a valutare la     org/10.14639/0392-100X-N2367
funzione vestibolare post-operatoria e correlarla con i dati morfologici della risonanza
magnetica.                                                                                      © Società Italiana di Otorinolaringoiatria
Metodi. Lo studio analizza 29 pazienti sottoposti a chirurgia per schwannoma vestibolare.       e Chirurgia Cervico-Facciale
La funzione vestibolare è stata analizzata nel post-operatorio con il “video head impulse
test” (vHIT). I sintomi soggettivi sono stati indagati mediante questionari validati. Tutti i                  OPEN ACCESS
pazienti sono stati sottoposti a risonanza magnetica 3 mesi dopo l’intervento, e su questo      This is an open access article distributed in accordance with
esame è stata determinata la presenza dei nervi facciale e vestibolo-cocleare nel canale        the CC-BY-NC-ND (Creative Commons Attribution-Non-
uditivo interno.                                                                                Commercial-NoDerivatives 4.0 International) license. The
                                                                                                article can be used by giving appropriate credit and mentio-
Risultati. Il riflesso vestibolo-oculare misurato con il vHIT correla positivamente con i       ning the license, but only for non-commercial purposes and
dati audiologici. La percezione soggettiva dei sintomi vestibolari non correla né con i dati    only in the original version. For further information: https://
oggettivi di deficit vestibolare né con le immagini della risonanza magnetica.                  creativecommons.org/licenses/by-nc-nd/4.0/deed.en




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                                                                             Vestibular function and MRI findings after vestibular schwannoma surgery




Conclusioni. Dopo la resezione di uno schwannoma vestibolare i pazienti possono ancora preservare la funzione vestibolare, come è stato mi-
surato con il vHIT. L’entità della funzione preservata non correla con i sintomi soggettivi. I pazienti con una funzione vestibolare parzialmente
deteriorata mostrano una minor sensibilità agli stimoli combinati.
PAROLE CHIAVE: schwannoma vestibolare, video head impulse test, risonanza magnetica, deficit vestibolare unilaterale, funzione vestibolare



Introduction                                                              Vestibular function and hearing tests
                                                                          All patients were examined clinically before and after sur-
Vestibular schwannoma constitutes 80-90% of all cerebel-
                                                                          gery. vHIT (ICS Impulse, Otometrics, Denmark) was used
lopontine angle tumours 1. It often presents with hearing
                                                                          to determine the post-operative function of each semicir-
impairment, tinnitus, dizziness, or vertigo. Large tumours as
                                                                          cular canal. vHIT was performed between the 7th and 10th
well as smaller but growing or symptomatic tumours are in-
                                                                          post-operative day. Two patients were excluded since they
dicated for surgical resection 2. Vertigo is a dominant symp-
                                                                          did not undergo the examination in this period. The gain of
tom after vestibular schwannoma resection. Compensation
                                                                          the vestibulo-ocular reflex (VOR gain) for each semicircu-
of the post-operative vestibular disorder is a multifactorial
                                                                          lar canal was calculated as the ratio of the areas under the
process 3. Age, tumour size and comorbidities are the factors
                                                                          eye velocity curve and the head velocity curve from the
that influence the compensation process. Other factors that
                                                                          start to the end of the head impulse 11. The pattern of sac-
affect vestibular compensation, such as mental state, inclina-
                                                                          cades was studied, and the saccades were divided into scat-
tion to anxiety and depressive states, are also being studied 4-6.
                                                                          tered and clustered patterns; the clustered pattern was sub-
Subjective symptoms and mental state are usually measured
                                                                          divided into covert and overt saccades 12. Pure tone average
with validated questionnaires. As the tumour originates from
                                                                          (PTA) was counted from hearing levels in dB at 0.5, 1, 2
the vestibular portion of the vestibulocochlear nerve, tumour
                                                                          and 4 kHz pre-operatively and post-operatively (3 months
resection results in the disruption of the vestibular nerve.
                                                                          after the surgery). MRI findings of the vestibulocochlear
Transection of the vestibular nerve can be partial or radical.
                                                                          nerve were correlated with the function of the semicircular
Several objective tests are available to measure residual ves-
                                                                          canal of each side (operated and intact one). All patients
tibular function, such as the caloric test, video head impulse
                                                                          completed two questionnaires before surgery and 3 months
test (vHIT), rotational test and vestibular evoked myogenic
                                                                          after surgery to evaluate vertigo symptoms and their im-
potential (VEMP) test 7. In the present study, vHIT was used
to objectively measure vestibular function. vHIT has recent-              pact on quality of life based on subjective perception. The
ly become a popular test to determine vestibular function 8,9.            first was the Dizziness Handicap Inventory (DHI) question-
It uses high-frequency impulse stimulation corresponding to               naire. This questionnaire consists of 25 items, and the score
natural head movements, instead of non-physiological low                  ranges from 0 to +100. The higher the score, the more se-
frequency stimulation used in the caloric test. Both methods              vere the handicap it corresponds to 13.
are complementary to each other and examine slightly differ-              The second questionnaire 5,6 (Tab. I) was developed by neu-
ent phenomena. Even though all patients with radical resec-               rotologists from the Department of Otorhinolaryngology
tion of vestibular schwannoma undergo concurrent vestibu-                 and Head and Neck Surgery of the 1st Faculty of Medi-
lar neurectomy, an unusually high vHIT gain was observed                  cine, Charles University in Prague, Faculty Hospital Motol.
in some of these patients as reported in a previous study 10.             Scores for each question range from 1 to 4. A higher score
Therefore, in the present study, we aimed to describe chang-              corresponds to more severe handicap.
es in vestibular function in more detail and correlate them
with morphological changes in the internal auditory canal                 MRI
(IAC) observed on post-operative MRI scans.                               The post-operative evaluation of the possible presence of
                                                                          residual nerve structures within the IAC was performed
                                                                          on an MRI machine (1.5 T Magnetom Avanto, Siemens,
Methods                                                                   Erlangen, Germany) using a 3D-T2 space sequence (voxel
                                                                          size: 0.6 × 0.6 × 0.6 mm). The original dataset obtained in
Patients                                                                  the transversal plane and multiplanar reconstruction (MPR)
The study included 29 patients with unilateral vestibular                 in the oblique sagittal plane perpendicular to the long axis
schwannoma, aged 25-69 years, who had undergone sur-                      of the IAC were evaluated for the presence of the facial
gery through a retrosigmoid approach for tumour resection.                nerve (in the anterior upper quadrant), cochlear nerve (in
Complete surgical removal of the tumour was achieved in                   the anterior lower quadrat), superior vestibular nerve (in
all patients (Fig. 1).                                                    the posterior upper quadrant) and inferior vestibular nerve



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Z. Balatková et al.




Figure 1. Overview of patient characteristics.

Table I. A 9-question questionnaire used by neurotologists from the Department of Otorhinolaryngology and Head and Neck Surgery of the 1st Faculty of Medi-
cine, Charles University and Faculty Hospital Motol, Prague.
 1. Do you have instability with/or does faster rotational motion bother you (e.g., rotating head from side to side when crossing the road)?
 2. Do you have instability with/or does walking on uneven surfaces bother you (e.g., walking up the stairs/walk in the snow)?
 3. Do you have instability with/or does quickly changing position bother you (e.g., lying on a bed/getting up/recumbent)?
 4. Do you have instability with/or does walking in darkness/twilight bother you?
 5. Do you have instability with/or does reading while driving bother you (the ability to keep eyes fixed when walking)?
 6. Do you have instability with/or does shopping in a supermarket bother you (rapid changes in products on the shelves)?
 7. Do you have instability with/or does a greater amount of auditory and visual sensations bother you (e.g., shopping malls)?
 8. Do you have instability with/or does a longer reading time bother you?
 9. Do you have instability with/or does watching TV bother you?



(in the posterior lower quadrant). MRI findings were not                        gain in the horizontal canal as measured by the vHIT on
evaluated in two patients who underwent post-operative                          the operated side: 1st group: ≤ 0.40; 2nd group: 0.41 to
MRI scans at a different hospital, where special sequences                      0.69; 3rd group: > 0.70. The between-group differences
for reconstruction of the IAC were missing.                                     (both pre-operative and post-operative) were then exam-
                                                                                ined using Kruskal-Wallis one-way analysis of variance
Statistical analysis                                                            (ANOVA), followed by post hoc comparison with Mann-
Statistical analyses were performed using SPSS version                          Whitney U test. The within-group differences of repeated
25 (SPSS Inc., Chicago, IL, USA). For processing de-                            measurements (e.g., pre-operative vs post-operative values)
scriptive data, we used standard measures of central ten-                       were analysed by a Friedman test (an alternative to repeat-
dency (e.g., mean and median), dispersion (e.g., variance,                      ed-measures ANOVA), followed by a series of Wilcoxon
standard deviation and percentiles) and data shape sta-                         signed-rank tests. Given the relatively small sample size for
tistics (kurtosis and skewness). The research sample was                        both between- and within-group comparisons, we used the
divided into three subgroups based on the values of VOR                         Monte Carlo resampling procedure with n = 10,000 sam-



214
                                                                                            Vestibular function and MRI findings after vestibular schwannoma surgery




ples, which compensate for tied values and do not depend                                 canals on the operated side, which corresponds with acute
on asymptotic approximations for p-values 14. The level of                               peripheral vestibular loss after vestibular neurectomy. Al-
statistical significance was set at α = 0.05. Pearson’s cor-                             though the surgeon reported the complete resection of the
relation coefficient was used to determine bivariate associa-                            vestibular nerve in all patients from this group, the radiolo-
tions between the variables.                                                             gist described the presence of a portion of the vestibular
                                                                                         nerve on MRI in four patients. Even after declared ves-
Results                                                                                  tibular neurectomy the gain higher than 0.7 was observed
                                                                                         in group 3. Similar results were reported in a previous
Responses to the questionnaires and objective findings                                   study 10. According to the surgeon, complete resection was
were evaluated. Changes in subjective perception of bal-                                 achieved in five patients, and in one patient the resection
ance disorder were evaluated through responses to the ques-                              was incomplete and the vestibular nerves were preserved.
tionnaires, and statistical analysis was used to compare the                             None of the branches of the vestibular nerve were discern-
survey results with vHIT results. All patients were tested                               ible on MRI in one patient in this group. Figure 1 shows
clinically before the surgery. None of the patients had posi-                            the detailed results of MRI. An example of MRI finding
tive head impulse test, so we assume that the gain of vHIT                               in the IAC with all nerves preserved is shown in Figure 2.
would be normal (0.7-1.1) in the study population 15. vHIT                               Figure 3 shows a case with only the facial nerve preserved.
was performed between the 7th and 10th post-operative day                                Group 2 patients had a borderline VOR gain between 0.41
and showed interesting results. Patients were divided into                               and 0.69 (Fig. 4). Of the 10 patients in this group, the su-
three groups according to the value of VOR gain in the hor-                              perior vestibular nerve was preserved in two patients, and
izontal canal on the operated side (Fig. 1). The first group                             complete resection was achieved in the remaining patients
had VOR gain less than 0.4 (n = 9), the second group had                                 according to the surgeon. The superior vestibular nerve
partially deteriorated vestibular function with VOR gain be-                             was observed on MRI in three patients, while the inferior
tween 0.41 and 0.69 (n = 10), and the third group had VOR                                vestibular nerve was observed in one patient. This group
gain higher than 0.7 (n = 6). In most patients in group 1, a                             showed different functional characteristics than the other
VOR gain of less than 0.4 was observed in all semicircular                               two groups. Comparison between VOR gain of semicircu-




 TR: 1200/ TE: 266; slice thickness: 0.6 mm without gap; voxel size: 0.6 × 0.6 × 0.6 mm; FOV: 200 × 100; Pat factor: 2.

Figure 2. MRI scan of the internal auditory canal on the operated side. Facial (empty arrow), cochlear nerve (full arrow), superior vestibular nerve (empty arrowhead),
inferior vestibular nerve (full arrowhead), still preserved within internal auditory canal, have blurry contours corresponding with post-operative changes: 3D T2/space.



                                                                                                                                                                  215
Z. Balatková et al.




 TR: 1200/ TE: 266; slice thickness: 0.6 mm without gap; voxel size: 0.6 × 0.6 × 0.6 mm; FOV: 200 × 100; Pat factor: 2.

Figure 3. MRI scan of the internal auditory canal on the operated side. Usual configuration of the nerves inside the right-sided internal auditory canal is observed. Of note
is the absence of the vestibulocochlear nerve and deformation of the facial nerve (arrow) within the post-operatively changed left-sided internal auditory canal: 3D T2/space.


                                                                                         lar canals on the operated and healthy sides is shown in
                                                                                         Figure 4. Subgroups were classified according to VOR gain
                                                                                         of the horizontal canal on the operated side. The values for
                                                                                         vertical canals were similar to those for the horizontal canal
                                                                                         for each subgroup. The lateral semicircular canal is com-
                                                                                         monly examined because the measurement is less affected
                                                                                         by artefacts as compared to that for the vertical canals.
                                                                                         Comparison of the three groups using other observed varia-
                                                                                         bles revealed that post-operative hearing (Pure Tone Average,
                                                                                         PTA) differed among the patients, which was similar to the
                                                                                         difference in VOR gain in the horizontal canal on the operated
                                                                                         side as measured by the vHIT. Patients with the highest post-
                                                                                         operative gain also showed better post-operative PTA. Hear-
                                                                                         ing level was post-operatively good in one patient (26 dB),
                                                                                         two patients had serviceable hearing and the remaining pa-
                                                                                         tients had non-serviceable hearing according to the Gardner-
                                                                                         Robertson scale. Post-operative PTA correlated significantly
                                                                                         with tumour grade (p = 0.001) and size (p = 0.049) (Fig. 5).
                                                                                         Statistical analysis was performed to observe the correla-
                                                                                         tion between the DHI result, VOR gain and post-operative
                                                                                         morphological findings on MRI scans. Our findings suggest
                                                                                         that the post-operative result of the DHI is not influenced
                                                                                         by the presence of any specific nerve or combination of
                                                                                         preserved nerves. The presence of the inferior or superior
                                                                                         vestibular nerve on MRI or higher VOR gain measured by
                                                                                         the vHIT in the post-operative stage did not predict a better
Figure 4. Post-operative vHIT results. Values of VOR gain in the anterior (A),
lateral (H) and posterior (P) semicircular canals measured by the vHIT post-             result in the DHI. However, the DHI result had a positive
operatively on the operated and healthy sides.                                           correlation with better PTA level.



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                                                                                              Vestibular function and MRI findings after vestibular schwannoma surgery




 X-axis: Time 1 – before the surgery, Time 2 – 3 months after the surgery; Y-axis: 0-100 – hearing level measured in decibels.

Figure 5. Change in pure tone average before and after the operation. The study group was divided in three subgroups (1, 2 and 3) according to the value of
VOR gain in the horizontal canal measured by the vHIT on the operated side.


The study group showed a significant difference in re-                                     used for closure). To the best of our knowledge, the present
sponse to question seven of the questionnaire used in our                                  study is the first to investigate the correlation between MRI
department, which evaluates the response to multisensorial                                 findings of patients with vestibular schwannoma and their
stimuli (combined audio-visual stimuli). While patients in                                 vHIT results post-operatively.
groups 1 and 3 showed deterioration in their response to                                   Normal or only a mild decrease in VOR gain measured by
multisensorial stimuli post-operatively, mild improvement                                  the vHIT post-operatively was observed in many patients.
was observed in patients in group 2 compared to their pre-                                 This finding corresponds to preserved vestibular function
operative status (Fig. 6).                                                                 post-operatively. However, our study shows that this pres-
                                                                                           ervation of vestibular function contrasted with MRI find-
Discussion                                                                                 ings in some patients in whom complete resection of the
                                                                                           vestibular nerve was performed. In group 3 patients with
During resection of vestibular schwannoma through the
retrosigmoid suboccipital approach, the surgeon’s aim is to                                high VOR gain, only facial and cochlear nerves were pre-
preserve the nerves in the internal auditory meatus. It is                                 served in two patients, while in group 2, the nerves were
usually impossible to preserve the vestibular portion of the                               preserved in six of 10 patients. A non-zero VOR gain was,
vestibulocochlear nerve as the tumour originates from one                                  however, noted in complete unilateral peripheral vestibu-
of the vestibular nerve branches. This approach enables to                                 lar loss. These non-zero values in complete unilateral pe-
preserve the cochlear portion of the vestibulocochlear nerve                               ripheral loss are due to the contralateral disinhibition path-
and thus to preserve hearing. The presence of an anatomi-                                  way 16,17, but the values of gain are subnormal. In our study,
cally uninterrupted nerve can be post-operatively evaluated                                we observed patients with borderline and normal gain,
with MRI multiplanar reconstruction in a plane perpendic-                                  which is in contrast with the finding of unidentified vestibu-
ular to the internal acoustic meatus. The radiologist must be                              lar nerve on MRI. Based on this finding, it can be hypothe-
informed about the approach used for dural closure in the                                  sised that some vestibular nerve fibres may be conducted in
region of the IAC (if a muscle or an artificial material was                               the cochlear nerve, or the vestibular pathway might be par-



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Z. Balatková et al.




 X-axis: Time 1 – before the surgery, Time 2 – 3 months after the surgery; Y-axis: score of the answer (1-4), the lower the score, the better result.

Figure 6. Response to question 7: Do you have instability with/or does a greater amount of auditory and visual sensations bother you (e.g., shopping malls)? The
graph shows the mean value of PTA in each subgroup before and after the operation. The study group was divided in three subgroups (1, 2 and 3) according to the
value of VOR gain in the horizontal canal measured by the vHIT on the operated side. The graph shows the mean value for each subgroup before and after the operation.


tially dominated by the cochlear nerve. These fibres might                                    sion of vestibular, visual and proprioceptor inputs results in
be responsible for the preservation of vestibular function 18.                                sensorial reweighting differentiated according to the final
Another explanation of this phenomenon is that the vHIT                                       vestibular deficit 21.
itself is not sensitive enough to detect impaired function of                                 Our data also did not show any correlation with MRI find-
individual semicircular canals. Even in a non-functioning                                     ings. Objectively measured vestibular hypofunction did not
semicircular canal, residual VOR gain can be measured 19.                                     correspond to MRI findings. It may be also because MRI
Comparison of subjective symptoms evaluated by the ques-                                      is not sensitive enough to display slight changes in the in-
tionnaires showed no significant correlation with possibly                                    ternal auditory canal. A higher level of visual dependency
preserved nerves or combination of nerves in the IAC. No                                      is often observed during the compensation process in these
significant difference was observed in response to ques-                                      patients. The process of compensation of a vestibular le-
tionnaires between patients with resected and those with                                      sion is probably more complicated, and is affected centrally
intact vestibular nerve including its branches. According to                                  by other brainstem centres 22. According to some previous
a previous study, instability or dizziness perceived subjec-                                  studies, it seems that responsiveness to mental status may
tively by a patient does not seem to correlate with objective                                 affect the compensation process 5,23. The overall result of
findings measured by vHIT 20. This shows that multimodal                                      compensation may be affected by anxiety, insufficient cop-
sensory loading is particularly demanding for patients with                                   ing behaviour, or adaptation disorder. The precise mecha-
vestibular peripheral loss. Patients with partial preservation                                nisms need to be studied further.
of the VOR response were found to compensate this handi-                                      Theoretical framework for the change in the sensitivity
cap on follow-up examination, but not those with VOR loss                                     to various sensory inputs is laid by the sensory weighting
or good VOR response. This finding is not easy to explain;                                    model. Multiple estimates of head and eye movements in
moreover, it corresponds neither to the DHI nor to other                                      space are calculated by central nervous system using in-
similar questions (e.g., question 6) of our questionnaire re-                                 ternal models of sensory and physical relationships. Multi-
sults. We therefore hypothesise that the central sensory fu-                                  ple sensory inputs are complemented with internal models



218
                                                                       Vestibular function and MRI findings after vestibular schwannoma surgery




to yield accurate estimate of gravity, head and eye move-          jective symptoms post-operatively. Vestibular function was
ments 24. In experiments on healthy volunteers, rapid, con-        preserved even in cases where none of the branches of the
text dependent, reweighting was observed between visual            vestibular nerve were identified by MRI of the IAC. MRI
and vestibular inputs 21. We hypothesise, that the above-          may not be sensitive enough to display fine post-operative
mentioned processes can explain increased weight of visu-          changes in the IAC. We hypothesise that some vestibular
al stimulation in our data.                                        fibres may pass through the cochlear nerve or are dispersed
During assessment of vestibular function, we examined              within the IAC and not discernible by MRI. Patients with
only the function of the semicircular canals by vHIT. Oto-         partially deteriorated vestibular function show lower visual
lithic function can be tested using the VEMP test; howev-          dependency to multisensory stimuli. Neither post-operative
er, this test was not included in our study. We measured           vHIT result nor post-operative MRI finding predict func-
the function of semicircular canals by vHIT only once in           tional vestibular performance status.
post-operative period, and this is a possible limitation of
the study. All patients in the study had a normal vHIT re-         Conflict of interest statement
sult pre-operatively, so we assume that pre-operative gain         The authors declare no conflict of interest.
would not be significantly alternated. According to the re-
sults in patients with vestibular schwannoma, we assume            Funding
that the VOR gain measured by vHIT does not change sig-            This work was supported by the Ministry of Health of the
nificantly when measured on 7th-10th post-operative day            Czech Republic (Grant No. NU20-08-00311) and GAUK
or 3 months post-operatively. The results of the present           No.192121.
study were compared with those of the study of Aw 7, in
which post-operative MRI findings were evaluated and the           Author contributions
preserved vestibular nerve observed on MRI was found to            ZČ, RČ: conceptualization; ZB: methodology; SB, VK,
lead to poor outcome after vestibular neurectomy. How-             VB, VS, PH, KK, ZF: investigation; MK: statistical analy-
ever, in our study, the nerve was affected pre-operatively         sis; JL: imaging methods analysis; ZB, MB: writing - origi-
by the growth of the tumour, which is in contrast with the         nal draft preparation; ZB, ZČ, RČ, EM: writing - review
condition of the pre-operative status of a healthy nerve and       and editing; ZČ: funding acquisition; ZČ: supervision.
impairment of the labyrinth in patients with Meniere’s dis-
ease in the study of Aw. This is the possible reason for the       Ethical consideration
difference in the results of these two studies.                    The study was approved by the Ethics Committee for Mul-
In agreement with a previous study, it was confirmed that pa-      ti-Centric Clinical Trials of the University Hospital Motol.
tients are more sensitive to optokinetic stimulation and other     (protocol number EK-297/20).
audio-visual stimulation post-operatively. Interestingly,          The research was conducted ethically, with all study pro-
group 2 patients with borderline gain between 0.41 and 0.69        cedures being performed in accordance with the require-
showed significantly lower sensitivity to combined audio-          ments of the World Medical Association’s Declaration of
visual stimuli than the remaining patients. Patients with nor-     Helsinki.
mal VOR gain and those with VOR lower than 0.4 showed a            Written informed consent was obtained from each partici-
deterioration in this parameter. Similar results were observed     pant/patient for study participation and data publication.
in a previous study where patients pretreated with gentamicin
were less sensitive to optokinetic stimulation 10. It seems that   References
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