Full text of DOI:10.1097/00005537-200209000-00021

The Laryngoscope
Lippincott Williams & Wilkins, Inc., Philadelphia
©
2002 The American Laryngological,
Rhinological and Otological Society, Inc.
Tympanometric Findings in Patients With
Enlarged Vestibular Aqueducts
Eisuke Sato, MD; Tsutomu Nakashima, MD; David J. Lilly, PhD; Stephen A. Fausti, PhD;
Hiromi Ueda, MD; Hayato Misawa, MD; Yasue Uchida, MD; Atsushi Furuhashi, MD;
Kiyomitsu Asahi, MA; Shinji Naganawa, MD
Objectives: The purpose of this study was to study
systematically some relationships between the reso-
nance frequency of the middle-ear transmission sys-
tem and the volume of the endolymphatic duct and
sac in patients with an enlarged vestibular aqueduct
Enlarged vestibular aqueduct, resonance frequency,
multifrequency tympanometry.
Laryngoscope, 112:1642–1646, 2002
INTRODUCTION
(EVA). Study Design: Prospective study. Methods:
The vestibular aqueduct (VA) is a bony canal within
the otic capsule. It extends from the medial wall of the
vestibule to the posterior surface of the petrous pyramids.
The endolymphatic duct traverses this canal. In 1978,
Thirteen patients (24 ears) with EVA, 17 subjects (29
ears) with normal hearing, and 17 patients (21 ears)
with sensorineural hearing loss without EVA served
as experimental subjects. Standard pure-tone audi-
ometry, standard clinical tympanometry (using a
1
Valvassori and Clemis published the first radiographic
2
26-Hz probe tone), and multifrequency tympanom-
study that focused on pathologic enlargement of the VA in
humans. They identified 50 enlarged vestibular aqueducts
in a group of 3700 consecutive patients who had been
referred for polytomography of the inner ear. Although
complete otologic and audiologic data were not available
for all 50 patients, Valvassori and Clemis concluded that
an enlarged VA (EVA) is usually “associated with a con-
genital or a possibly early acquired HL that may be purely
sensorineural, or may be mixed in nature.” Subsequent
research has supported the work of Valvassori and Clemis
and the relationship between EVA and hearing loss that
etry were performed on each ear. Magnetic resonance
imaging was used to determine the area of the co-
chlear modiolus and the volume of the endolymphatic
duct and sac. Results: The audiometric configurations
for most patients sloped downward from the low to
the high frequencies. A significant air–bone gap was
computed at each of these test frequencies. Multifre-
quency tympanometry yielded resonance frequencies
for the patients with EVA that was significantly lower
than those measured for the control subjects. In gen-
eral, for patients with EVA, the resonance frequency
of the middle ear system decreased as the volume of
the endolymphatic duct and sac increased. This in-
verse relation was significant (correlation coefficient
2–6
typically is progressive and bilateral.
The air-
conduction audiometric configuration usually slopes
downward from the low frequencies to the high frequen-
cies. A conductive component to the hearing loss has been
؍
؊0.483, P ؍ .0157). However, there was no correla-
tion between resonance frequency and the degree of
cochlea modiolar deficiency. Conclusions: Clinically,
our findings suggest that EVA probably should be
included in the differential diagnosis for a patient
who presents with a moderate to severe mixed hear-
ing loss, a normal tympanogram at 226 Hz, and a res-
onance frequency that is abnormally low. Key Words:
7
reported in most cases of EVA.
Tympanometry obtained with a single low-frequency
probe tone provides useful diagnostic information for pa-
tients with disorders of the tympanum, for patients with
disorders that affect the tympanic membrane, and for
8
patients with eustachian tube dysfunction. Govaerts et
6
al. used standard tympanometry (with a probe-tone fre-
quency of 226 Hz) to investigate the cause of the conduc-
tive component in 6 patients with EVA. A normal (type A)
pattern was generated for all patients. Multifrequency
tympanometry is a more sensitive method for evaluating
lesions that affect the ossicular chain and for detecting
Presented at the 10th Annual Meeting of Otology Japan,
Hamamatsu, Japan, October 19, 2000.
From the Department of Otorhinolaryngology (E.S., T.N., H.U., H.M.,
Y.U., A.F., K.A.), Nagoya University School of Medicine, Nagoya, Japan; VA
National Center for Rehabilitative Auditory Research, Department of Vet-
erans Affairs Medical Center (D.J.L., S.A.F.), Portland, Oregon, U.S.A.; and
the Department of Radiology (S.N.), Nagoya University School of Medicine,
Nagoya, Japan.
8–13
subtle anomalies of the peripheral auditory system.
This technique allows one to measure the resonance fre-
Editor’s Note: This Manuscript was accepted for publication March
5, 2002.
quency (f ) of the entire middle ear transmission system.
0
2
Resonance occurs at the frequency where the stiffness and
the mass elements of the ear are in balance. If the stiffness
element of the ear increases, the resonance frequency is
Send Correspondence to Eisuke Sato, MD, Department of Otorhino-
laryngology, Nagoya University School of Medicine, 65, Tsurumai-cho,
Showa-ku, Nagoya 466-8550, Japan.
Laryngoscope 112: September 2002
Sato et al.: Enlarged Vestibular Aqueducts
1
642

higher than normal. Conversely, if the mass element of
the ear increases (or if the stiffness decreases), the reso-
14
nance frequency is lower than normal. We have reported
that f0 in patients with EVA is lower than in normal
individuals. However, there is no pathologic evidence in
15
the middle ear of patients with EVA. The complex acous-
tic immittance at the lateral surface of the tympanic mem-
brane and the resonance frequency of the middle ear are
determined by the mass and the stiffness of the middle ear
transmission system, by the volume and the pressure of
air in the tympanic cavities, by the tonus of the middle ear
muscles, and by the mechanical immittance of the cochlea.
If enlargement of the VA produces an enlargement of the
endolymphatic duct and sac and if this, in turn, increases
the volume of endolymphatic fluids and reduces its imped-
ance, then patients with EVA should have a resonance
frequency that is lower than normal.
The purpose of this study was to examine some rela-
tionships between resonance frequency and the volume of
the endolymphatic duct and sac in patients with EVA and
between the resonance frequency and deficiency in the
cochlea modiolar.
Fig. 1. Heavily T2-weighted transverse magnetic resonance image
in a 29-year-old man with an enlarged endolymphatic duct and sac
(arrow). Inset shows cochlear modiolus of the right ear (arrowhead).
MATERIALS AND METHODS
Thirteen patients (24 ears) with EVA (5 males and 8 fe-
males; age range ϭ 6–36 y; mean age ϭ 20 y) were included in
this study. These patients were referred to our tertiary care
center by other physicians. Twelve patients had bilateral enlarge-
ment of the VA and 1 patient had unilateral enlargement. One
ear was excluded from this study because of a perforation of the
tympanic membrane. The control group consisted of two groups:
A and B. Group A included studies n 29 ears with normal hearing
for pure tones (17 subjects; 11 males and 6 females; age range ϭ
duct and sac was multiplied by the thickness of the section (0.8
mm) to compute the total volume. This method has been de-
17
scribed in detail previously. An endolymphatic duct and sac is
considered enlarged when the diameter at the midpoint between
the common crus and the external aperture is greater than 1.5
16
mm on thin-section MR images.
RESULTS
6
–34 y; mean age ϭ 23 y). Group B included studies n 21 ears
with sensorineural hearing loss without enlargement of the VA
17 subjects; 10 males and 7 females; age range ϭ 8–30 y; mean
Figure 2 depicts the mean air-conduction and bone-
conduction thresholds for the 13 patients (24 ears) with
EVA. Vertical lines through each mean datum point de-
fine Ϯ 1 SD. Table I summarizes the air–bone gap data at
three frequencies for the patients with EVA. If a patient
did not respond to the maximum output of the bone vibra-
tor at a given frequency, their data were excluded for this
frequency. The audiometric configurations for most pa-
tients sloped downward from the low frequencies to the
high frequencies. Consequently, hearing by bone conduc-
tion in the middle and in the high frequencies often could
not be measured. The mean air–bone gap at 250 Hz was
greater than at 500 Hz and 1000 Hz. These differences
were significant (Fisher’s Protected Least Significant Dif-
ference test, P Ͻ.01 at 500 Hz and P Ͻ.001 at 1000 Hz).
Standard tympanometry (using a 226-Hz probe tone)
produced a normal (type A) pattern for all patients with
EVA and for all control subjects. In contrast, multifre-
quency tympanometry produced results for the patients
with EVA that differed from the results produced by both
control groups.
(
age ϭ 15 y). The mean and standard deviation (SD) values for the
average hearing levels at three frequencies (500 Hz, 1 kHz, and 2
kHz) in group B were 71.0 Ϯ 32.2 dB. The hearing level was
matched to that of the patients with LVA syndrome (84.7 Ϯ 21.6
dB). The control subjects of both groups were also approximately
matched to the patients with EVA with respect to age. Otoscopic
examination for all ears proved normal.
Standard tympanometry (using a 226-Hz probe tone) and
multifrequency tympanometry were performed on each ear using
a middle ear analyzer (Grason-Stadler, Model GSI 33, Version 2).
Static acoustic admittance (at ϩ200 da Pa), tympanometric peak
pressure at 226 Hz, and resonance frequency were measured. The
same audiometer (Rion, Model AA-61BN) was used in the same
sound-insulated chamber for all pure-tone audiometry on all sub-
jects. Air–bone gaps were computed for each test frequency (250
Hz, 500 Hz, 1 kHz, 2 kHz, 4 kHz, and 8 kHz).
Magnetic resonance imaging (MRI; heavily T2-weighted
three-dimensional fast-spin-echo MRI) was used to determine the
area of the cochlear modiolus and the volume of the endolym-
phatic duct and sac for both ears of each experimental patient.
The VA itself is not visualized on MR images. Its contents, how-
The distributions of resonance frequencies (f ) for the
16
0
ever, are clear. Figure 1 depicts a transverse image of the right
petrous temporal bone in a 29-year-old male subject. The cochlear
modiolus is identified with an arrowhead. The distinct low-signal-
intensity area of the cochlear modiolus was outlined where it was
visualized at the maximum size, and the area was measured on
ears with EVA, for the ears in group A, and for the ears in
group B are shown in Figure 3. Resonance frequencies for
the patients with EVA ranged from 410 Hz to 1200 Hz,
whereas those for groups A and B ranged from 670 Hz to
1340 Hz and from 410 Hz to 1410 Hz, respectively. The
16
the console. The enlarged endolymphatic duct and sac is iden-
tified with an arrow. The sum of the areas of the endolymphatic
mean and SD values for f were 777.3 Ϯ 230.5 Hz in the
0
Laryngoscope 112: September 2002
Sato et al.: Enlarged Vestibular Aqueducts
1643

Fig. 3. Distribution of resonance frequencies for the ears with EVA,
for the ears in group A, and for the ears in group B.
with EVA, 1.03 Ϯ 4.89 da Pa in the ears of group A, and
Ϫ2.4 Ϯ 14.1 da Pa in the ears of group B, respectively. The
difference between these mean values is not significant
(
Mann-Whitney U test, P ϭ .5259 for group A and P ϭ
.
7587 for group B).
Fig. 2. Mean air-conduction (F) and bone-conduction (Ⅵ) thresh-
olds for 13 patients (24 ears) with EVA. Vertical lines through each
mean datum point define Ϯ 1 standard deviation. The arrow indi-
cates that the average hearing level is beyond the maximum output
at a given frequency.
The volume of the endolymphatic duct and sac for the
patients with EVA ranged from 55.5 ␮L to 709 ␮L. The
mean value was 368.2 ␮L with a SD of 204.4 ␮L. The
correlation between the resonance frequency and the vol-
ume of the endolymphatic duct and sac is shown in Figure
4
. In general, for these patients, the resonance frequency
ears with EVA, 956.2 Ϯ 200.2 Hz for the ears in group A,
and 944 Ϯ 247.7 Hz for the ears in group B. The value of
f0 in the patients with EVA was significantly lower than
both in group A and in group B (Mann-Whitney U test,
P ϭ .0064 for group A and P ϭ .0203 for group B). Values
(f0) of the middle ear system decreased as the volume of
the endolymphatic duct and sac increased. This inverse
relation was significant (correlation coefficient ϭ -0.483,
P ϭ .0157). The area of cochlea modiolus for the patients
2
2
with EVA ranged from 0.96 mm to 5.86 mm (mean Ϯ SD,
2
2
of less than 800 Hz for f in the ears with EVA were found
2.37 mm Ϯ 1.28 mm ). The correlation coefficient be-
tween the area of cochlea modiolus and resonant fre-
quency was 0.117 (P ϭ .5892).
0
in 14 of 24 ears, whereas values of more than 800 Hz in the
control groups were found in 39 of 50 ears. The sensitivity
and specificity of f for the diagnosis of EVA were 58.3%
and 78%, respectively.
Table II provides a summary of correlation coeffi-
cients for the patients with EVA. More specifically, the
correlation coefficient between air–bone gap data and f0
0
Static acoustic admittance (Ytm) was measured and
expressed as an equivalent volume of air at 226 Hz. The
mean and SD values for Ytm were 0.56 Ϯ 0.25 mL for the
ears with LVA syndrome, 0.58 Ϯ 0.27 mL for the ears in
group A, and 0.63 Ϯ 0.30 mL for the ears in group B. The
difference between these mean values is not significant
(
Mann-Whitney U test, P ϭ .9359 for group A and P ϭ
.4193 for group B).
The mean and SD values for air pressure at the peak
of the tympanogram were Ϫ2.5 Ϯ 11.7 da Pa in the ears
TABLE I.
Means, Standard Deviations, and Ranges for Air–Bone Gaps at
250Hz, 500 Hz, and 1 kHz.
0
250 Hz (dB)
500 Hz (dB)
(n ϭ 22)
1 kHz (dB)
(n ϭ 20)
(
n ϭ 22)
Mean
34.3
10.4
5–45
25
19.5
10.1
0–35
Standard deviation
Range
11.2
0–50
Fig. 4. Graphic representation of correlation between the resonance
frequency and the volume of the endolymphatic duct and sac (r ϭ
Ϫ0.483). The line represents the best-fit regression line.
Laryngoscope 112: September 2002
Sato et al.: Enlarged Vestibular Aqueducts
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644

TABLE II.
Correlation Coefficients and Probability (p) Values Between Air–Bone Gap and Resonance
Frequency Values, Between Air–Bone Gap and Cochlea Modiolar Deficiency, and Between Air–
Bone Gap and Volume of the Endolymphatic Duct and Sac at 250 Hz, 500 Hz and 1 kHz.
250 Hz
500 Hz
1 kHz
Resonance frequency
Ϫ0.063 (P ϭ .7817)
Ϫ0.388 (P ϭ .0745)
Ϫ0.410 (P ϭ .0576)
Ϫ0.186 (P ϭ .4115)
Ϫ0.265 (P ϭ .2374)
Ϫ0.087 (P ϭ .7039)
Ϫ0.016 (P ϭ .9515)
Ϫ0.220 (P ϭ .9331)
Ϫ0.122 (P ϭ .6472)
Area of the cochlea modiolus
Volume of the endolymphatic
duct and sac
values, between air–bone gap data and the area of cochlea
modiolus, and between air–bone gap data and the volume
of the endolymphatic duct and sac are tabulated. Proba-
bility (P) values also are listed. Superficially, it appeared
that the air–bone gap at 250 Hz was larger for the pa-
tients with an increased volume of the endolymphatic duct
and sac but no significant correlation was found between
the air–bone gap and the volume of the endolymphatic
duct and sac at any frequency. Furthermore, no correla-
tion was found between the air–bone gap and frequency of
resonance and between the air–bone gap and the area of
cochlear modiolus.
volume of the endolymphatic duct and sac in the patients
with EVA varied from 55.5 ␮L to 709 ␮L. Thus, we can
assume that the volume of the endolymph was signifi-
cantly larger in patients with EVA than in those with
normal ears. Because the mechanical impedance at the
footplate of the stapes is inversely proportional to the
volume of fluid within the inner ear, an increase of the
volume of inner ear fluid may be responsible for the re-
duction in f0 that was measured during multifrequency
tympanometry.
Evidence for a second mechanism comes from re-
search in the area of hearing by bone conduction. Tonndorf
20
and Tabor investigated the compressional component of
bone conduction that was first described by Herzog and
DISCUSSION
21
The exact pathophysiology of the hearing loss that
accompanies EVA is unknown. It has been reported that
the size of the vestibular aqueduct or the size of the
endolymphatic duct and sac is not associated with the
Krainz. Their findings supported the notion that the
oval window and the round window are not the only re-
lease points for pressure within the cochlea. They used a
22
term proposed by Ranke et al., “the third window,” to
refer collectively to the vestibular aqueduct, to the co-
chlear aqueduct, and to other vascular and neural chan-
nels around the cochlea. Enlargement of the vestibular
aqueduct increases the size of this third (“window”)
pressure-release point of the cochlea, decreases the me-
chanical impedance of the inner ear, and thus reduces the
resonance frequency of the entire system.
17
degree of hearing loss in EVA. A recent MRI and com-
puted tomography study revealed that LVA syndrome is
16,18
often associated with cochlea modiolar deficiency.
correlation was found, however, between cochlea defi-
ciency and hearing level.
No
16
Regarding the air–bone gap observed in most cases of
EVA, the results from the present study suggest that
there is no significant relationship between the magnitude
of the air–bone gap and the volume of the endolymphatic
duct and sac. To date, no reports have described middle
ear or ossicular chain anomalies during operations for
inspection of the middle ear or during cochlea implant
surgery on patients with EVA. In some cases, however, a
profuse leakage of perilymphatic fluid has been ob-
Theories for hearing by bone conduction also may
help explain why we observed a significant air–bone gap
for our patients with EVA. At least four mechanisms are
responsible for hearing by bone conduction. In normal
ears, the magnitude and the phase of each mechanism
interact with frequency to yield “normal” bone-conduction
hearing and the bases for audiometric standards. If, how-
ever, the volume of the endolymphatic duct and sac is
abnormally large, then the relative contributions of: 1) the
6,15
served.
Intracochlear micromechanical alterations
may be considered as the cause of the air–bone gap in
EVA. However, there was no correlation between air–
bone gap and the degree of cochlea modiolar deficiency in
the present study.
2
3,24
ossicular–inertial mechanism
; 2) the cochlear–iner-
25
21
tial mechanism ; and 3) the compressional mechanism
are probably modified. This in turn could lead to an im-
provement in hearing by bone conduction and an air–bone
gap in the absence of middle ear or ossicular chain
anomalies.
We have reported that the resonance frequency (f ) in
0
the patients with EVA is low compared with the f mea-
0
7
sured for subjects with normal hearing. In the present
study, we have shown that the resonance frequency (in
hertz) and the volume of the endolymphatic duct and sac
As we have noted earlier, tympanometry with a sin-
gle low-frequency probe tone “can provide useful diagnos-
tic information for patients with disorders of the tympa-
num (effusion or abnormal air pressures within the
middle-ear cavity), for patients with disorders that affect
the tympanic membrane (atrophic scarring, retraction or
perforation) and for patients with Eustachian tube dys-
(
in microliters) are related inversely.
At least two mechanisms may be responsible for this
finding. The first mechanism involves the volume of en-
dolymph within the human inner ear. The total volume of
endolymph within the normal inner ear is approximately
8
3
4 ␮L, but there is no measurable amount of endolymph in
function.” Low-frequency, single-component tympanom-
etry, however, is relatively insensitive to lesions that af-
19
the normal endolymphatic sac. In the present study, the
Laryngoscope 112: September 2002
Sato et al.: Enlarged Vestibular Aqueducts
1645

fect the ossicular chain and, from the present study, to
lesions that involve enlargement of the endolymphatic
duct and sac.
Finally, when a patient presents with a moderate to
severe mixed hearing loss, the clinician typically will not
have computed tomography or MRI studies available.
Still, if the standard (226-Hz) tympanogram is normal,
and if the resonance frequency is abnormally low, then the
possibility of an enlarged vestibular aqueduct should be
included in the differential diagnosis.
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(
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1
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2
all patients with EVA and for the control subjects with
normal hearing. In contrast, multifrequency tympanom-
etry revealed that the resonance frequency for patients
with EVA is significantly lower than normal. These find-
ings provide support for our experimental hypothesis.
Namely, if enlargement of the VA produces an enlarge-
ment of the endolymphatic duct and sac and if this, in
turn, increases the volume of endolymphatic fluid and
reduces its impedance, then patients with EVA should
have a resonance frequency that is lower than normal.
Clinically, our findings suggest that EVA should probably
be included in the differential diagnosis for a patient who
presents with a moderate to severe mixed hearing loss, a
normal tympanogram at 226 Hz, and a resonance fre-
quency that is abnormally low.
1991;30:1–24.
1
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Acknowledgments
This work was supported by a Grant-in-Aid for Sci-
2
entific Research (B) (11470355) and by the Acute Pro-
1
1
found Deafness Committee of the Ministry of Health and
Welfare Japan. This work was also supported in part by a
grant to the National Center for Rehabilitative Auditory
Research (RCTR S97–0160), a Merit-Review Award from
the Department of Veterans Affairs Rehabilitation Re-
search and Development Service (C2225R), and by a grant
to Dr. Lilly from Japan Foundation for Aging and Health.
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