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Vestibular neurectomy via middle fossa approach
was performed in one patient to control intractable ver-
tigo, even after successful ablation of vestibular function
on a caloric test (canal paresis: 89%) with five rounds of
intratympanic gentamicin injections. The hearing of the
52-year-old woman after ITG was still acceptable (36.25
dB of pure tone average, with 82% for speech discrimi-
nation in the audiometry taken on a day prior to the
surgery). After surgery, complete control of vertigo (class
A) was achieved and hearing threshold was 35 dB after
surgery. However, the hearing was progressively wors-
ened to 55 dB after 1 year 6 months postoperatively,
which was comparable with the worst hearing (53.75
dB) during 6 months prior to the surgery.
Hearing Outcomes
Overall, there was no significant change in hearing
thresholds with the mean pure tone average 59.7 dB
prior to ITG and 63.2 dB after ITG (
P
5
0.343, Student’s
t-test). In total, 80 (84.2%) patients showed less than 10
dB change in hearing after ITG; hearing was improved
more than 10 dB even after ITG in six (6.3%) patients;
and three of them improved by more than 20 dB. Five of
the six patients with hearing improvement achieved suc-
cessful ablation of vestibular function on bithermal
caloric test, and all of them did not show hearing fluctu-
ation thereafter. In contrast, a patient with initially
impaired vestibular reflex showed fluctuation of hearing
with temporary hearing improvement at the point of
assessment according to the 1995 AAO–HNS guideline.
Two of the six patients experienced hearing aggravation
in the proximity of the ITG, with the worsening of ver-
tigo including the patient with hearing fluctuation. A
total of eight (8.4%) patients experienced more than a 10
dB worsening of hearing levels. Four of the eight
patients received more than three rounds of ITG; and
2.6 injections were applied, on average, in the eight
patients. However, a careful review of the data revealed
that most hearing loss took place after one (4 patients)
or two (2 patients) injection(s), and only two patients
experienced hearing loss after three injections. We com-
pared the results of hearing changes with the success of
ablation and the preoperative vestibular status, but nei-
ther showed a statistically significant difference
(
P
5
1.00 and 0.54, respectively, Fischer’s exact test).
Bilateral Progression of Menie`re’s Disease After
ITG
Two patients progressed to bilateral Menie`re’s dis-
ease after ITG. Both of them developed vertigo with
aggravation of hearing on the other side. The hearing
levels of the injected side were already worse than 60 dB
HL prior to ITG and were not aggravated after injection
in both patients. Physical examination and the caloric
test revealed apparently successful ablation of vestibular
function on the injected side. One patient developed con-
tralateral Menie`re’s disease at 2 years after ITG, and
the other patient developed it at 5 years after ITG.
DISCUSSION
Previously, the effectiveness of ITG was commonly
highlighted, with little discussion of its limitation.
7–12
The reason for failure is important because there could
be some substantial limitation to drug passage through
the round window membrane. In previous studies, mark-
edly limited permeability or impermeability was
reported in approximately 20% of cases.
16
In another
study that directly visualized the passage of gadolinium
injected into the tympanic cavity into the inner ear, 13%
showed poor drug passage through the round window
membrane, with 5% of cases showing no permeability.
17
This is very similar to our failure rate for ITG.
The tympanum was inspected for any possible ana-
tomical barrier around the oval window and/or the
round window membrane that might limit the access of
gentamicin. However, no obvious barrier such as muco-
sal folds, mucosal thickening, or bone chips was evident,
except a prominent bony overhang over the round win-
dow in two patients. Such a prominent bony overhang
could be a possible reason for the failure of ITG, accord-
ing to a previous report,
14
because vestibular function
was attenuated substantially and recurrent vertigo
attacks were controlled after ETG in a patient. However,
the reasons for the failure, especially in the two cases
who needed additional labyrinthectomy, remain unclear.
The permeability of the round window membrane is
determined by several factors, such as the thickness of
the membrane, the size of the particles, concentration,
liposolubility, and electrical charge.
18
Considering that
most of the listed variables were almost identical
TABLE III.
Summary of Patients Undergoing Labyrinthectomies and Vestibular Neurectomies.
Pt
CP Before ITG
CP After ITG
CP After ETG
Class*
Dx
Comments
1
75%
–
No ETG
A
MD
Labyrinthectomy
1
STP
†
2
77%
83% (3 inj
‡
)
No ETG
A
EH
Labyrinthectomy
(intralabyrinthine schwannoma)
3
15%
28% (3 inj
‡
)
32%
A
EH
Labyrinthectomy
4
4%
31% (3 inj
‡
)
29%
A
MD
Labyrinthectomy
5
44%
89% (4 inj
‡
)
No ETG
A
MD
Vestibular neurectomy
*Functional classification according to the 1995 American Academy of Otolaryngology–Head and Neck Surgery guideline.
†
Surgery to control chronic otitis media.
‡
Number of intratympanic injections of gentamicin.
CP
5
canal paresis on bithermal caloric test; Dx
5
diagnosis; EH
5
secondary endolymphatic hydrops; ETG
5
exploratory tympanotomy and gentamicin
application; ITG
5
intratympanic gentamicin injection; MD
5
definite Menie` re’s disease; Pt
5
patient; STP
5
subtotal petrosectomy.
Laryngoscope 125: April 2015
Rah et al.: Intractable Menie` re’s Disease
51