Download Correlations between CT scan findings and hearing

Acta Oto-Laryngologica, 2011; 131: 351–357
ORIGINAL ARTICLE
Correlations between CT scan findings and hearing thresholds
in otosclerosis
MATHIEU MARX1, SEBASTIEN LAGLEYRE1, BERNARD ESCUDÉ2, JULIE DEMESLAY1,
TARIK ELHADI1, OLIVIER DEGUINE1 & BERNARD FRAYSSE1
1
Department of Otology-Neurotology and Skull Base Surgery, Purpan University Hospital, Toulouse and 2Department of
Neuroradiology, Clinique Pasteur, Toulouse, France
Abstract
Conclusion: High-resolution computed tomography (CT) scan may reveal an isolated fenestral form of otosclerosis, and an
extensive form, which involves multiple foci around the otic capsule. Pre- and postoperative hearing thresholds are poorer in
patients with extensive otosclerosis and their chance of overclosure is reduced by 90%. Objectives: To evaluate the
relationship between CT scan extension of otosclerotic foci and hearing thresholds in the operated ear, before and after
stapedotomy. Methods: A preoperative CT scan was performed in 200 patients suspected of having otosclerosis. CT scan
findings were categorized as negative, isolated fenestral otosclerosis, and extensive otosclerosis. Preoperative and 2 months
postoperative air-conduction (AC) and bone-conduction (BC) thresholds were collected. Results: In the operated ear,
150 CT scans (75%) revealed an isolated fenestral otosclerosis; 35 (17.5%) were classified as extensive otosclerosis. Mean
preoperative BC was significantly poorer in extensive otosclerosis (30.3 dB) than in isolated fenestral otosclerosis (24.6 dB).
Mean postoperative BC remained lower in extensive otosclerosis (30.3 dB) than in isolated fenestral otosclerosis (21.2 dB).
An overclosure greater than 10 dB was found in 20% of isolated fenestral otoscleroses and in 2.85% of extensive otoscleroses
(chi-square: 5.5; p = 0.02).
Keywords: Bone conduction, cochlear endosteum, otosclerosis
Introduction
Otosclerosis is typically defined as a primary dystrophy affecting the otic capsule bone and represents a
common etiology of conductive hearing loss. It may
sometimes display a sensorineural pattern, although
its involvement in such a hearing loss entity remains
controversial. For instance, in Schuknecht’s temporal
bone studies [1–3], sensorineural hearing loss was
generally due to different pathologies but not to
otosclerosis. Only rare cases of severe sensorineural
hearing loss may be related to extensive otosclerotic
foci involving the endosteum of more than one
cochlear spiral turn. However, according to some
authors [4], the impact of endosteal lesions on hearing
thresholds appears to be more common and may
manifest in more limited foci cases.
High-resolution computed tomography (HRCT)
scan can be used as an additional diagnostic tool
for otosclerosis when clinical symptoms are not indicative enough. In most cases, it reveals a hypodensity in
the anterior part of the footplate [5]. Nevertheless,
several other anatomic locations may coexist, such
as pericochlear, cochlear endosteum, and internal
auditory canal wall.
The first aim of our study was to evaluate the
relationship between otosclerotic foci extension on
CT scan and pure tone audiometry (PTA) thresholds.
Our second aim was to assess hearing progression
characteristics in the operated ear and in the
Correspondence: Mathieu Marx MD, Department of Otology-Neurotology and Skull Base Surgery, Purpan University Hospital, Place du Docteur Baylac,
31059 Toulouse, France. Tel: +33 5 61 77 22 11. Fax: +33 5 61 7721 49. E-mail: [email protected]
(Received 6 September 2010; accepted 14 November 2010)
ISSN 0001-6489 print/ISSN 1651-2251 online 2011 Informa Healthcare
DOI: 10.3109/00016489.2010.549841
352
M. Marx et al.
nonoperated one, considering audiometric and CT
scan findings.
Material and methods
This was a retrospective study, performed in a tertiary
referral center between 2004 and 2006. All patients
suspected of having otosclerosis and scheduled for a
surgical middle ear exploration were included. Suspicion of otosclerosis was based upon conductive or
mixed hearing loss with normal tympanic membrane
and abnormal stapedial reflex in at least one ear. In all,
200 patients matching the inclusion criteria were
found in the database. Clinical, audiological, and
radiological data were collected. Surgical data were
also gathered.
In our institution, HRCT scan is systematically
performed in the preoperative assessment in cases
of mixed or conductive hearing loss with normal
tympanic membrane. Therefore, an institutional
review board was not required. Axial and coronal
cuts were obtained with 0.6 mm slice thickness in
121 patients (60.5%) and 1 mm in the remaining
79 cases (39.5%).
CT scans were analyzed by a single neuroradiologist. Three categories of CT scan results were defined
based on the site and the extension of otosclerotic
lesions. (1) Negative CT scan: absence of otosclerotic
foci or any other middle and/or inner ear abnormalities (including tympanosclerosis, ossicular chain fixation, superior canal dehiscence, modiolus dysplasia,
and enlarged vestibular acqueduct). (2) Isolated
fenestral otosclerosis, i.e. either foci limited to the
oval window area, such as anterior fenestral hypodensity (Figure 1) and/or complete thickening of the
footplate; or doubtful small lesions, such as isolated
partial thickening of the anterior part of the footplate
or triangular enlargement of the anterior crus of the
stapes. (3) Extensive otosclerosis with one or several
hypodensities involving the pericochlea, the internal
auditory canal, and/or the round window (Figure 2).
Fenestral lesions extended to the cochlear endosteum
or to the vestibule were also included in this category.
CT scan sensitivity and specificity were evaluated
by comparing CT scan results to the surgical findings.
Positive surgical diagnosis of otosclerosis was confirmed by the presence of macroscopic otosclerotic
foci on the oval window, with stapes fixation. In
confirmed otosclerosis cases, stapedotomy was
performed using argon laser and skeeter microdrill.
Air-conduction (AC) and bone-conduction (BC)
thresholds were measured in all patients the day
before surgery and 2 months later in the same
double-walled soundproof room. Audiometric data
were collected and compared as recommended by the
Figure 1. CT, axial cut, showing an isolated fenestral otosclerosis,
characterized by a hypodensity immediately adjacent to the anterior
margin of the oval window, including the anterior branch of the
stapes.
guidelines published in 1995 by the Committee on
Hearing and Equilibrium of the American Academy
of Otolaryngology-Head and Neck Surgery (AAOHNS) [6]. Thus, AC and BC thresholds were averaged on 0.5, 1, 2, and 3 kHz frequencies. Air–bone
gap (ABG) was calculated using same time AC and
BC measurements. Sensorineural hearing level
(SNHL) was estimated by averaging the BC thresholds in 1, 2, and 4 kHz frequencies. A positive change
in postoperative SNHL was referred as an overclosure
and a negative change was considered as a surgically
induced hearing loss.
Figure 2. CT, axial cut, showing an internal auditory canal hypodensity on the internal auditory meatus associated with a large
anterior fenestral hypodensity.
CT findings and hearing thresholds in otosclerosis
The second aim of this study was to evaluate
hearing evolution in the nonoperated ears, particularly those with normal hearing. Three years of
follow-up (mean 46 months, SD 8.7) was available
for 77 patients (39.5%), including 37 patients with
initially normal hearing in the opposite ear. The
number of patients in this subgroup was adapted
for running comparative analyses. Surgical events
such as revision surgery or contralateral stapedotomy
were reported. Pure tone audiometry was performed
and results were compared to those collected
preoperatively.
Statistical analysis was performed using Statview
software. Nonparametric and classic bivariate tests
were used according to the distribution features.
These tests included one-way analysis of variance
(ANOVA) to compare the values of a continuous
variable between categories and the Mann-Whitney
U test. The threshold of significance was 0.05.
Results
Operated ear
Description (Table I). The mean age was 47.3 years,
ranging from 17 to 77 years. The sex ratio was 2.44.
The mean BC threshold was 25.4 dB (SD = 13.42)
and mean preoperative ABG was 27.8 dB (SD = 10).
Concerning CT scan findings, 15 CT scans (7.2%)
did not show any temporal bone abnormality and
were classified as negative; an isolated fenestral otosclerosis was found in 150 cases and 35 patients had
extensive otosclerosis.
Among the 150 CT scans (75%) showing isolated
fenestral otosclerosis, 4 had thickened footplate, 9 had
both anterior hypodensity and thickening of the
footplate, and 137 had isolated anterior fenestral
hypodensities. In the last subgroup, 18 (8.6%) cases
353
appeared as a triangular widening of the anterior crus
(15) or as a minor malformation of the stapes (3) and
were thus defined as doubtful.
Thirty-five CT scans (17.5%) revealed extensive
otosclerosis. Lesions were multifocal in 32 cases,
affecting the pericochlea in 17 cases, the internal
auditory canal wall in 15 cases, the round window
in 6 cases, and the cochlear endosteum in 7 cases.
Two isolated pericochlear foci and one isolated internal auditory canal focus were also identified. For the
six cases with round window lesions, four involved
the round window niche edge with a normal
round window membrane and two were completely
obliterating it.
CT scan findings and surgical diagnosis. Otosclerosis
was confirmed during surgery in all ears with positive
CT scan findings. The 18 ears with doubtful hypodensity revealed 17 positive diagnoses of otosclerosis
during surgery and 1 minor malformation of the
stapes. Among the 15 negative CT scans, we found
10 false-negative cases diagnosed as otosclerosis during surgery, 4 minor malformations of the ossicular
chain, and 1 fracture of the stapes. Seven of the falsenegative CT scans were obtained with 1 mm thickness
slices and three with 0.6 mm thickness slices. Sensitivity of HRCT in the diagnosis of otosclerosis in this
series was 95% and specificity was 99.1%.
Relationship between CT scan findings and audiometric
data (Figure 3). Extension of otosclerotic lesions was
found to have an effect on preoperative PTA. In fact,
PTA thresholds were significantly poorer in cases of
extensive otosclerosis. Mean preoperative AC and BC
were respectively 44.2 dB (SD 12.61) and 22.6 dB
(SD 14.01) in patients with negative CT scans,
49.9 dB (SD 14.68) and 24.6 dB (SD 11.83) in
Table I. Patients’demographic and audiometric data according to the CT scan findings.
Parameter
Negative CT scan
Isolated fenestral
otosclerosis
Extensive
otosclerosis
No. of patients
15
150
35
Mean age, years (SD)
51.2 (8,4)
47 (10.4)
46.8 (10.9)
Side
10R, 5L
81R, 69L
19R, 16L
Mean preoperative BC (SD)
22.6 dB (14)
24.6 dB (12.1)
30.3 dB (18.1)
Mean preoperative AC (SD)
44.2 dB (12.6)
49.9 dB (14.9)
59.9 dB (22.4)
Mean preoperative ABG (SD)
23.2 dB (6.93)
27.3 (9.91)
31.7 (10.46)
Mean postoperative BC (SD)
20.4 dB (12.31)
21.2 dB (11.08)
30.3 dB (19.46)
Mean postoperative AC (SD)
31.2 dB (8.08)
29 dB (14.64)
39.2 dB (23.72)
Mean overclosure (SD)
2.9 dB (4.81)
3 dB (9.14)
0.5 dB (6.88)
SD, standard deviation; R, right ear; L, left ear.
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M. Marx et al.
90
90
80
80
70
60
*p = 0.02
50
NS
40
30
20
10
Mean post op BC (dBHL)
B 100
Mean pre op BC (dBHL)
A 100
70
60
*p = 0.016
50
NS
40
30
20
10
0
0
Negative CT
Isolated fenestral
otosclerosis
Extensive
otosclerosis
Negative CT
Isolated fenestral
otosclerosis
Extensive
otosclerosis
Figure 3. Mean preoperative bone conduction BC (A) and postoperative BC (B) in the operated ear for patients with negative CT scans,
isolated fenestral otosclerosis, and extensive otosclerosis.
patients with isolated fenestral otosclerosis, and
59.9 dB (SD 22.44) and 30.3 dB (SD 18.12) in cases
of extensive otosclerosis. PTA thresholds were poorer
(ANOVA, p = 0.0012 for AC, p = 0.02 for BC) and the
ABG was significantly larger (ANOVA, p = 0.025) in
the group with extensive otosclerosis. BC thresholds
were within normal limits in 6 patients (40%) with
negative CT scans, 55 patients (36.6%) with isolated
fenestral otosclerosis, and 5 patients (14%) with
extensive otosclerosis.
Similarly, postoperative PTA results were found to
be correlated to the degree of otosclerosis extension.
Patients with negative CT scan (AC 31.2 dB, SD
8.08 and BC 20.4 dB, SD 12.31) or isolated fenestral
otosclerosis (AC 29 dB, SD 14.64 and BC, 21.2 dB,
SD 11.08) showed better thresholds than patients
with extensive otosclerosis (AC 39.2 dB, SD
23.72 and BC 30.3 dB, SD 19.46) (ANOVA,
p = 0.01 for AC, p = 0.012 for BC).
Regarding the SNHL, we considered clinically
significant changes of BC thresholds to highlight
the differences between groups. Among patients
with negative CT scans, there was no worsening of
BC more than 5 dB and one patient showed an
improvement above 10 dB.
A decrease of mean BC greater than 5 dB was more
frequently observed in patients with extensive otosclerosis (6 patients, i.e. 17.1%) than in patients with
negative or isolated fenestral otosclerosis (18 patients,
10.9%). Risk of worsening BC thresholds tended to
be higher in extensive otosclerosis, although this trend
did not reach statistical significance (chi-square = 3.8;
odds ratio = 2.8; CI 95% = 0.99–7.88; p = 0.054).
SNHL improvements greater than 10 dB were found
in 30 patients with isolated fenestral otosclerosis
(i.e. 20%), in only 1 patient with extensive otosclerosis (i.e. 2.85%). We measured the chance of getting
more than 10 dB SNHL improvement and found it to
be 90% lower in extensive foci than in isolated
fenestral focus (chi-square = 5.5; odds ratio = 0.11;
CI 95% = 0.01–0.84; p = 0.02).
The mean ABG closure was significantly different
between negative CT scans (11.3 dB, SD 7.4) and
positive CT scans for otosclerosis (ANOVA,
p = 0.02). ABG closure was found to have a tendency
to be better (p = 0.07) in extensive otosclerosis
(20.6 dB, SD 10.42) than in isolated fenestral otosclerosis (17.2 dB, SD 10.86).
Follow-up of the operated ear. Between 2004 and 2009,
4 of the 200 patients underwent a revision surgery for
the operated ear. The four revision procedures
revealed a lateralized piston. Three patients had an
extensive form of otosclerosis and one had an isolated
fenestral otosclerosis. Concerning the long-term
results, 77 of the 200 patients included in this study
completed a 3-year follow-up after surgery (mean
follow-up, 46 months, SD 8.7; n = 77). The comparative analyses that we conducted did not show any
statistical difference between groups, for any auditory
threshold (p > 0.05). Mean AC, BC, and ABG were
respectively 23.4 dB (SD 6.07), 14.6 dB (SD 6.29),
and 10.1 (SD 8.38) in patients with negative CT
scans. In patients with isolated fenestral otosclerosis
(n = 59), mean AC was 29.8 (SD 15.53), mean BC
was 25.1 dB (SD 14.61), and mean ABG was 5.9 dB
(SD 5.24). Concerning the group of patients with
extensive otosclerosis (n = 13), mean AC, BC, and
ABG were 33.3 dB (SD 20.49), 27 dB (SD 19.89)
and 6.3 dB (SD 4.06), respectively.
CT findings and hearing thresholds in otosclerosis
Nonoperated ear
Description. Concerning the 200 opposite ears, we
determined 2 groups from the initial PTA.
Group 1 had initially normal contralateral hearing
(AC £20 dB and ABG £10 dB) and included
68 patients. Mean threshold values were respectively:
12 dB (SD 4.87) for AC, 8.4 dB (SD 4.00) for BC,
and 3.7 dB (SD 2.71) for ABG. Among this group,
38 CT scans (55.9%) found 29 isolated fenestral
otoscleroses and 8 extensive otoscleroses (Table II).
Seven of the 29 fenestral otoscleroses presented as an
isolated widening of the anterior crus of the stapes and
were thus defined as doubtful. Extensive otosclerosis
was multifocal in six patients (two pericochlear foci,
two anterior fenestral foci, three foci localized to the
cochlear endosteum, six foci to the internal auditory
canal) and three patients with solely involvement of
the internal auditory canal. The other 30 CT scans
were described as negative (30, 44.1%).
Group 2 had initially abnormal hearing (AC >20 dB
and/or an ABG ‡10 dB) and included 132 patients.
Mean threshold values were respectively: 35.1 dB (SD
15.88) for AC, 23.1 dB (SD 14.36) for BC and
12.2 dB (SD 9.53) for ABG. In all, 80 patients had
conductive or mixed hearing loss, and 52 had pure
sensorineural hearing loss. A total of 111 CT scan
examinations (84.1%) showed 81 isolated fenestral
involvements and 31 extensive otosclerosis. The
extensive lesions were mainly multifocal (29 CT
scans) and involved pericochlea in 15 patients,
cochlear endosteum in 7 cases, and internal auditory
canal in 14 patients. Four patients had round window
foci, localized at the edge of the round window niche,
sparing the membrane. CT scan was found to be
negative in 20 patients (15.1%).
Comparing both groups, we found more negative
CT scans in group 1 than in group 2 (Mann-Whitney
U test, p < 0.001). Extensive otosclerosis ratio was
significantly higher in group 2 (23.5%) than in group
1 (11.7%) (Mann-Whitney U test, p = 0.002).
Relationship between location of otosclerotic hypodensities
and PTA results. Similarly to the operated ear, analysis
Table II. CT scan findings with respect to initial hearing status in
the nonoperated ear.
Parameter
Normal hearing
No. of patients
68
Isolated fenestral otosclerosis
29 (42.6%)
Extensive otosclerosis
CT scan negative
Hearing loss
132
81 (61.4)
9 (13.2%)
31 (23.5%)
30 (44.1%)
20 (15.9%)
355
of CT scans revealed a significant impact of otosclerosis extension on PTA results according to all the
nonoperated ears whether hearing level was normal or
not (groups 1 and 2). Actually, mean AC and BC
were significantly poorer in cases of extensive otosclerosis (36.6 dB and 27.2 dB) than in cases of isolated
fenestral otosclerosis (28.1 dB and 17.5 dB)
(ANOVA, p = 0.006 for AC; p = 0.001 for BC).
Patients with negative CT scans presented mean
AC and BC (18.7 dB and 12.8 dB) within normal
values. The mean ABG was lower in patients
with negative CT scans (5.9 dB, SD 5.22) than in
patients with fenestral (10.7 dB, SD 8.79) or extensive
otosclerosis (9.5 dB, SD 11.31).
The impact of foci extension was greater in group 2,
with mean AC and BC of respectively 29.8 dB (SD
8.48) and 20.7 dB (SD 10.64) in patients with negative CT scan, 33.8 dB (SD 13.51) and 20.8B (SD
10.29) in patients with isolated fenestral involvement,
and 42 dB (SD 22.67) and 31.1 dB (SD 21.53) in
patients with severe locations.
Progression of hearing in the nonoperated ear: relationship
with CT scan findings. In all, 77 of the 200 patients
included in this prospective study had a complete
3-year follow-up (mean follow-up 46 months, SD
8.72). Evolution of hearing in the nonoperated ear
was evaluated based on the comparison of 3-year PTA
data with initial audiograms. At 3 years, data were
available for 37 patients in group 1 and 40 patients in
group 2. A decrease in AC and BC was observed in
both groups (–4.4 and –6.6 dB, respectively). The
ABG remained stable at 3 years in group 1 compared
to the initial values (mean ABG evolution: –1 dB,
SD 6.40).
During the 3-year follow-up, stapedotomy in
opposite ears was performed in 12 patients in
group 2, whereas none of the patients in group 1 presented a hearing evolution justifying a contralateral
stapedotomy.
Mean interval between both stapedotomies was
22 months (SD 9.5) for patients who underwent
bilateral surgery. Before the second stapedotomy,
mean AC, BC, and ABG were respectively
48.25 dB (SD 3.61), 23.35 dB (SD 6.48), and
26.3 dB (SD 3.79). In group 2, patients who did
not undergo revision surgery revealed increased BC
and AC thresholds at 3 years, with a mean aggravation
of 8.8 dB (SD 15.92) and 5.3 dB (SD 8.57).
With regard to CT scan findings, the impact of foci
extension observed at inclusion was logically demonstrated at 3-year follow-up. Patients with extensive
otosclerosis showed poorer AC and BC thresholds
than patients with isolated fenestral lesions. Patients
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M. Marx et al.
with negative CT scan showed better AC and BC
thresholds than patients with positive findings. The
ABG was greater in patients with extensive otosclerosis (mean ABG 9.3 dB, SD 9.62) and isolated
fenestral otosclerosis (mean ABG 10.8, SD 9.41)
than in patients with negative CT scans (mean
ABG 3 dB, SD 3.10; ANOVA, p = 0.03). Nevertheless, worsening of AC, BC, and ABG was not related
to the location of the otosclerotic lesions: evolution of
these thresholds did not significantly differ from one
group to another.
Symmetry in CT findings
Finally, CT scans of both ears were analyzed in terms
of bilaterality of the lesions. For the 15 negative CT
scans in the operated ear, we found 13 contralateral
negative CT scans. The contralateral findings for
the 158 ears with isolated fenestral otosclerosis
were 108 contralateral fenestral otosclerotic foci
(68.35%), 14 extensive otosclerosis (8.8%), and
36 negative CT scans (22.8%). For the 35 operated
ears with extensive otosclerosis, we found 28 contralateral extensive lesions (77.5%), 5 isolated fenestral
otosclerosis, and 2 negative CT scans. Extensive
otosclerosis provided significantly more bilateral
positive findings than isolated fenestral otosclerosis
(chi-square = 5.28, p = 0.025).
Discussion
The relationship between the location of otosclerotic
foci and hearing thresholds has mainly been evaluated
in histological studies. As mentioned above, this topic
has generated several conflicting reports. Based upon
various temporal bone studies, Schuknecht and his
co-workers always stated that association between
otosclerosis and sensorineural hearing loss was rather
uncommon. For instance, Schuknecht and Barber [3]
studied 48 temporal bones with clinical otosclerosis
and did not observe any association between bone
conduction thresholds and the size of the lesion, the
activity of the lesion, the cochlear endosteum or the
round window involvement. In another study on
263 temporal bones of subjects with progressive
sensorineural hearing loss [1], 21 temporal bones
presented otosclerotic lesions with only 3 endosteal
involvements. Elonka and Applebaum [7] evaluated
this relationship in 29 temporal bones with clinical
otosclerosis and according to them, the strict correlation between endosteal involvement and bone conduction thresholds was poor. However, incidence of
sensorineural hearing loss was greater in the subgroup
of 15 temporal bones with severe otosclerotic extension affecting cochlear endosteum in 2 sites or more.
In contrast, Hueb et al. [4] showed a positive correlation in 37 temporal bones when the size of the
lesions, the activity, and the degree of cochlear endosteal involvement were compared to BC thresholds.
In the same way, Parahy and Linthicum [8] put in
evidence an association between cochlear endosteum
involvement and elevated BC thresholds. The sensorineural component in otosclerosis would be due to
spiral ligament hyalinization adjacent to the active
endosteal foci. In their study, the group with hyalinization of the spiral ligament presented a mean BC of
71.8 dB whereas mean BC in the group without
hyalinization was 33.6 dB. This hyalinization would
support a protein release, interfering with terminal
auditory nerve fibers. Histological studies provide an
incomparable description of otosclerotic lesions but
their validity in audiometric correlations seems limited by the delay between patients’ last audiogram and
patients’ death; CT studies may yield a better temporal matching for audio-radiological correlations.
A CT scan study by Shin et al. [9] compared patients
with isolated fenestral otosclerosis and patients with
pericochlear extension. The authors showed that BC
thresholds were poorer in a subgroup of patients with
endosteal involvement compared with BC in patients
with fenestral otosclerosis. Kawase et al. [10] evaluated the relationship between a determined cut-off
Hounfsield unit and PTA thresholds. They found a
significant correlation between the density in the
area anterior to the oval window and the hearing
thresholds (both AC and BC) on 500 and 1000 Hz.
Our results emphasize the auditory consequences
of otosclerosis extension. AC and BC thresholds were
worse in cases of extensive otosclerotic foci. In fact,
BC thresholds were significantly higher when the
disease involved the pericochlea, the cochlear endosteum, the round window or the internal auditory canal
wall. Further, our findings regarding the SNHL indicate higher risk of aggravation and poorer chance of
improvement in extensive otosclerosis. Multifocality
of otosclerotic lesions should thus be considered as a
sign of severe prognosis in otosclerosis.
Otosclerosis is known as a bilateral osteodystrophy
but a significant amount of patients present only a
unilateral conductive or mixed hearing loss. In these
cases, the opposite ear should systematically be considered because hearing evolution and a subsequent
contralateral stapedotomy are recurrent questions
from patients. Our study found 68/200 patients
(34%) with strictly normal hearing in the nonoperated
ear. In this population, CT scans revealed a large
proportion of negative CT scans for the opposite ear
(44.1%), which significantly exceeded the rate of
negative CT scans when contralateral hearing was
abnormal (15.1%). Thirty-seven patients with normal
CT findings and hearing thresholds in otosclerosis
initial contralateral hearing were followed up for more
than 3 years and did not show any worsening in the
ABG (–1 dB, SD 6.02). In other words, no patient
with initial normal PTA thresholds decreased contralateral hearing enough to suggest a stapedotomy.
Some of these patients might be affected with strictly
unilateral otosclerosis but the follow-up duration was
undeniably short if we consider the slowly progressive
pattern of the disease.
Furthermore, the possible dissociation between
histological and clinical otosclerosis should not be
discarded. The study of temporal bones by Hueb
et al. [4] revealed a higher rate of bilateral histological
otosclerosis compared with bilateral clinical otosclerosis, confirmed by stapes fixation. They found bilateral otosclerotic foci in 75.6% of the cases while
45.8% of ears had clinical otosclerosis. In a CT
scan study, Vicente et al. [11] found bilateral hypodensities in 68.5% of patients with a surgical diagnosis
of otosclerosis. In Lee et al.’s series [12], 84% of
patients had bilateral foci but they did not report any
surgical confirmation. The present study reports bilateral positive findings in 77.5% of patients and emphasizes the role of foci extension. Bilateral otosclerosis
was more frequently found in the extensive form of
the disease, in which symmetry of lesions appeared
greater as well. Shin et al. [13] reported that extensive
and bilateral otosclerosis on CT scan was commonly
found in patients with a family history of otosclerosis.
Genetic factors would play a crucial role in extensive
otosclerosis, and may explain the homogenous association observed between clinical symptoms, poor
hearing thresholds, and radiological expression,
with multifocal and endosteal extended disease.
Conclusion
HRCT can detect various forms of otosclerosis, with
high sensitivity and specificity. We distinguished isolated fenestral otosclerosis from extensive forms,
which involved multiple foci such as pericochlea
and cochlear endosteum. In our series, patients
with extensive otosclerosis showed poorer preoperative and postoperative AC and BC thresholds. Further, their chance to improve their BC thresholds
postoperatively is significantly reduced, compared
with patients with an isolated form of otosclerosis.
Thus, CT scan may provide relevant information
regarding the prognosis for hearing in the operated
ear. Concerning the nonoperated ear, hearing thresholds are also related to CT scan findings but the initial
audiometric status remains a better predictive parameter. In our study, most patients with initial normal or
357
near-normal hearing in the opposite ear showed stable
hearing abilities 3 years later. Evolution of the hearing
thresholds in the nonoperated ear is a matter of
concern for many patients; long-term prospective
studies are needed to allow provision of appropriate
counseling.
Acknowledgments
The authors thank Kuzma Strelnikov for his contribution to statistical analyses, Chris James and Sara
Alshehri for their helpful comments.
Declaration of interest: The authors report no
conflicts of interest. The authors alone are responsible
for the content and writing of the paper.
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