Download Reliability of High-Resolution CT Scan in Diagnosis of

Otology & Neurotology
30:1152Y1159 Ó 2009, Otology & Neurotology, Inc.
Reliability of High-Resolution CT Scan
in Diagnosis of Otosclerosis
*Sebastien Lagleyre, *Tommaso Sorrentino, *Marie-Noelle Calmels,
*Young-Je Shin, †Bernard Escudé, *Olivier Deguine, and *Bernard Fraysse
*Department of Otology-Neurotology and Skull Base Surgery, Purpan University Hospital; and ÞDepartment
of Neuroradiology, Clinique Pasteur, Toulouse, France
Objective: To assess the reliability of high-resolution computed tomographic scan (HRCT scan) for the diagnosis of otosclerosis and to determine its usefulness to predict hearing
deterioration and surgical difficulties.
Study Design: Prospective study.
Setting: Tertiary reference center.
Patients: Two hundred nine ears (200 patients) presenting progressive conductive hearing loss with normal tympanic membrane, abnormal stapedial reflex, and scheduled for stapes
surgery. The mean age was 47.3 years.
Intervention: All patients underwent HRCT scan before surgery (slice thickness of 0.6 to 1 mm). Stapedotomy was performed in 99% of cases.
Main Outcome Measures: High-resolution computed tomographic scan results were categorized as positive, doubtful, or
negative. We classified a CT scan as positive for otosclerosis
when a hypodense focus was seen around the otic capsule.
Preoperative and postoperative air- and bone-conduction
thresholds were collected.
Results: Of 209 HRCT scans, 84.2% were classified positive,
8.6% doubtful, and 7.2% negative. In all patients with positive
CT scan, otosclerosis was confirmed in surgery. Among 15
negative cases, we found 4 minor malformations and 1 fracture
of the stapes. Footplate incidents (mobilized, floating, or fractured footplate; 5.3%) occurred significantly more frequently
when an HRCT scan was negative or doubtful ( p = 0.05).
Mean preoperative air-bone gap was 27.7 dB (standard deviation, 10). Mean postoperative air-bone gap was within 10 dB in
65% and within 20 dB in 92% of cases. Greater than 10 dB
deterioration of bone-conduction thresholds occurred in 2% of
cases. Mean preoperative and postoperative bone-conduction
thresholds were significantly lower in cases of round window
obliteration, pericochlear, or internal auditory canal hypodensities ( p G 0.005 and p G 0.0001, respectively).
Conclusion: In our series, the sensitivity of HRCT scan to
otosclerosis was 95.1%. Hypodense otosclerotic foci were
mostly localized at the anterior part of footplate. Negative or
doubtful cases were associated with the highest incidence of
stapes footplate complications. Foci involving otic capsule,
internal auditory canal, or round window led to a significantly higher risk of sensorineural hearing loss. Key Words:
CT scanVFloating stapes footplateVMobile footplateV
OtosclerosisVStapedotomy.
Otol Neurotol 30:1152Y1159, 2009.
Stapes surgery remains the established treatment for
otosclerosis. Stapedotomy is usually a safe procedure,
performed under local anesthesia with minimal complications. Developments in otologic surgery are aimed to
minimize the risk of failure.
Since its introduction into otology, the computed
tomographic (CT) scan has been shown to be an useful
instrument for diagnosis of otosclerosis (1,2). Many studies found a reliability of more than 90% in the diagnosis
of otosclerosis (1,3). The reliability was only limited in
cases of isolated otosclerotic foci (4Y6) or by superficial
foci too small to be visualized on the CT scan (1,3).
The main goal of this study was to specify the reliability of high-resolution CT scans (HRCT scans) in the
diagnosis of otosclerosis based on comparing radiologic
and surgical findings. Results are compared with those of
previous studies (3,7) conducted in the same department
with lower-resolution CT scans. In addition, we discuss
the role of preoperative CT scans in preventing intraoperative incidents and their importance in localizing hypodensities for hearing prognosis.
Address correspondence and reprint requests to Sebastien Lagleyre, M.D.,
Service d’ORL et Otoneurologie, CHU Purpan, Place du Docteur Baylac,
31059 Toulouse Cedex, France; E-mail: [email protected]
Additional Information: This work was presented in part at the 2nd
International Symposium of the Politzer Society on Otolosclerosis and
Stapes Surgery, May 8Y10, 2008, Biarritz, France.
MATERIALS AND METHODS
The only way to be certain of the diagnosis of otosclerosis
is to find specific features of otosclerosis during surgery, as
1152
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RELIABILITY OF HRCT SCAN IN OTOSCLEROSIS
FIG. 1. Computed tomography, axial cut, showing fenestral otosclerosis characterized by a hypodensity immediately adjacent to
the anterior margin of the oval window, including the anterior
branch of the stapes. This CT scan was considered positive.
defined as the presence of macroscopic otosclerotic foci on the
oval window with stapedial fixation. Therefore, we conducted
an open prospective study, including patients with Btypical[
and Bnontypical[ clinical forms of otosclerosis who were
scheduled for surgery. A Btypical[ clinical form of otosclerosis
was defined by the presence of a bilateral conductive hearing
loss, a normal tympanic membrane, and the absence of stapedial reflex and a family history of otosclerosis. We considered
patients had bilateral conductive hearing loss when air-bone
gap (ABG) was more than 10 dB in both ears and evidence
of family history when a previous surgery for otosclerosis had
occurred in the family. Patients with Bnontypical[ clinical form
of otosclerosis presented a conductive hearing loss with normal
FIG. 2. Computed tomography, axial cut, showing absence of
hypodensity or thickening of the stapes footplate. This CT scan
was considered negative.
1153
tympanic membrane and abnormal (biphasic or absent) stapedial reflex in at least 1 ear.
Between September 2004 and September 2006, we collected
data on 209 ears (200 patients), including demographic, radiologic, audiologic, and surgical data.
Before surgery, all patients underwent HRCT scan with helical acquisition in axial and coronal planes. High-resolution CT
scans were performed in 25 different radiology departments.
Reconstructed slices were of thickness 0.6 mm from 19 departments to 1 mm from 6 departments. One hundred twenty-one
examinations (57.9 %) were obtained with a slice thickness
of 0.6 mm.
For each case, the result of the CT scan was confirmed by an
experienced neuroradiologist. Computed tomographic scan
results with respect to the presence of otosclerosis were classified as positive, negative, or doubtful: positive when hypodense
foci were seen around the otic capsule (Fig. 1); negative in the
absence of any hypodensity or other temporal bone finding,
including tympanosclerosis, ossicular malformation or fixation,
modiulus anomalies, and superior semicircular canal dehiscence (Fig. 2); and doubtful in cases of minimal hypodense
foci such as an isolated thickening of the anterior part of
the footplate or a triangular widening of the anterior branch
of the stapes (Fig. 3).
Different sites of otosclerosis were classified according to
Veillon et al. (2): anterior fenestral hypodensity (AFH; Ib, II),
isolated thickening of the footplate hypodensity (Ia), hypodensity extended to the endosteum (III) or to the vestibule (IVb),
pericochlear hypodensity (PH; IVa), internal auditory canal
hypodensity (IACH; IVa), and ossification of the oval window
or of the round window.
The decision to perform a surgical middle ear exploration
was based upon the history of the pathology, clinical reports,
and the needs of the patient in terms of hearing. During surgery,
performed under local anesthesia by a classical tympanomeatal
approach, the mobility of the ossicular chain was tested, and the
presence of an otosclerosis focus was determined by observation. Positive surgical diagnosis of otosclerosis was confirmed
FIG. 3. Computed tomography, axial cut, showing an isolated
thickening of the anterior part of the footplate or a triangular
widening of the anterior branch of the stapes. This CT scan
was considered doubtful.
Otology & Neurotology, Vol. 30, No. 8, 2009
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1154
S. LAGLEYRE ET AL.
TABLE 1. Details of locations of otosclerotic hypodensities
across all CT scans (several locations could be
encountered in the same ear)
Location of otosclerotic hypodensities
(classification of Veillon)
n (% of all
CT scans)
Isolated or associated AFH (Ib, II)
Isolated AFH
Isolated thickening of the footplate hypodensity (Ia)
Hypodensity extended to the endosteum (III)
Isolated or associated PH (IVa)
Isolated PH
IACH (IVa)
Ossification of the round window (IVa)
Stage A (normal window)
Stage B (edge hypodensity with normal round
window membrane)
Stage C (round window obliteration)
Stage D (basal turn ossification of the cochlea)
Hypodensity extended to the vestibule (IVb)
No hypodensities
185 (88.5)
143 (68.4)
4 (1.9)
5 (2.4)
20 (9.6)
2 (1)
17 (8.1)
6 (2.9)
V
4 (1.9)
2 (1)
0 (0)
0
15 (7.2)
AFH indicates anterior fenestral hypodensity; PH, pericochlear
hypodensity; IACH, internal auditory canal hypodensity.
by the presence of macroscopic otosclerotic foci on the oval
window with stapedial fixation. In the case of an absence of
these signs, other diagnoses were considered.
In positively diagnosed cases of otosclerosis, stapedotomy
was performed using an argon laser, followed by a skeeter
microdrill. Anatomic difficulties or complications encountered
during surgery were noted.
Pure-tone 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.
Hearing tests were realized according to the Committee on
Hearing and Equilibrium (8). The preoperative and postoperative ABG and ABG closure (ABGC) were calculated from airand bone-conduction thresholds. The sensorineural hearing
level (SNHL) was estimated by averaging the bone-conduction
levels for frequencies 1, 2, and 4 kHz. The preoperative to
postoperative change in SNHL was the measure of surgically
induced sensorineural hearing loss. Positive values reflected
improvements in bone-conduction levels, referred to as overclosure, whereas negative values indicated surgically induced
high-frequency sensorineural hearing loss. The change in
SNHL was stratified as worse, 910 dB; unchanged, T10 dB;
and improved, 910 dB.
Statistical analyses were performed using the W2 test and
Fischer’s exact test. The significance threshold was 0.05.
surgery. Therefore, the Btypical[ form of otosclerosis
was rare in our sample.
Radiologic Results: Operated and Opposite Ears
Operated Ear
Of 209 CT scans, 176 were positive (84.2%), 18 were
doubtful (8.6%), and 15 were negative (7.2%).
Across all CT scans (Table 1), otosclerotic hypodensities were classified as anterior fenestral hypodensities
in 88.5%, pericochlear in 9.6%, and internal auditory
canal in 8.1% of the cases (Fig. 4). Hypodensities
involved the round window in 6 ears (2.9%), and for 2
of these, it was obliterated.
For positive CT scans, anterior fenestral (isolated or
associated) was the most frequent location (96.6% of
cases). Other positions of hypodensities for positive CT
scans were pericochlear in 12.5%, internal auditory canal
in 9.6%, and involving the round window in 3.4%.
Among doubtful cases, a triangular widening of the
anterior branch of the stapes was found in 83.3% of
ears. Other associated diagnoses were suspected in 3
patients (2 cases of ossicular chain malformation and 1
case of malleus fixation).
Computed tomographic scans results were positive
bilaterally for 135 cases (64.6%). Of the 200 patients
included, only 9 patients (4.5%) were operated bilaterally
during the period of study (mean preoperative ABG: first
side, 31.4 dB [SD, 13.9]; second side, 26.5 dB [SD, 7.3];
mean delay, 12 mo). Here, of the 126 unoperated opposite ears, ABG was less than 10 dB in 50% of cases.
Opposite Ear
Concerning the opposite ear, we defined 3 groups
from pure-tone audiogram: normal hearing, pure sensorineural hearing loss, and conductive hearing loss.
RESULTS
For the 209 ears (200 patients), the mean age was 47.3
(range, 17Y77) years, with a male-female ratio of 2.21.
Mean preoperative ABG was 27.7 dB (standard deviation [SD], 10). The stapedial reflex was absent in 47.5%
of cases, and we found a biphasic reflex in 51% of cases.
Of the 200 patients, 120 (60%) presented a unilateral
conductive hearing loss. Among the 80 patients with
bilateral hearing loss, only 15 (7.5%) presented the
Btypical[ clinical form of otosclerosis. The remaining
65 patients (32.5%) with bilateral conductive hearing
loss did not exhibit all the typical features of otosclerosis
such as absent stapedial reflex and/or family history of
FIG. 4. Computed tomography, axial cut, showing an internal
auditory canal hypodensity on the internal auditory meatus associated with a large anterior fenestral hypodensity.
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RELIABILITY OF HRCT SCAN IN OTOSCLEROSIS
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TABLE 3. Details of intraoperative variations and incidents
(several problems could be encountered in the same ear)
Intraoperative problems
Incidents
Stapes footplate incidents: mobilized,
floating, and fractured footplates
Vertigo
Variations
Narrow oval window niche, including
overhanging facial nerve
Facial nerve dehiscence
Incus malformation
Obliterated footplate
Persistent stapedial artery
Other
FIG. 5.
Comparison of surgical and radiological findings.
In the opposite ears of 200 patients, we found 120
(60%) with no conductive component, defined as ABG
less than or equal to 10 dB (mean AC, 23.6 dB [SD,
16.8]; mean BC, 16 dB [SD, 12.1]). Among these 120
ears, 69 ears presented normal hearing (34.5%), defined
as ABG less than or equal to 10dB and mean AC less
than 20 dB (mean AC, 18.7 dB [SD, 18.6]; mean BC, 8.4
dB [SD, 4.1]). The remaining 51 ears presented a pure
sensorineural hearing loss (25.5%; mean AC, 30.2 dB
[SD, 11.2]; mean BC, 26.3 dB [SD, 11.8]).
In the 69 opposite ears with normal hearing, we found
32 positive (46.5%), 27 negative (39%), and 10 doubtful
CT scans (14.5%). The position of the hypodensities in
these normal-hearing opposite ears on positive CT scans
was anterior fenestral in 87%, pericochlear in 12%,
around the internal auditory canal in 15%, and involving
the round window in 6%.
In the 51 opposite ears with pure sensorineural hearing
loss, we found 35 positive (68%), 11 negative (22%), and
TABLE 2.
n
% of surgeries
11
5.3
1
0.5
7
3.3
6
3
2
1
6
2.9
1.4
0.9
0.5
3.4
5 doubtful CT scans (10%). The position of the hypodensities in these opposite ears on positive CT scans
was anterior fenestral in 94%, pericochlear in 20%,
around the internal auditory canal in 20%, and involving
the round window in 6%.
Finally, in the 80 opposite ears with conductive hearing loss (mean AC, 34.4 dB [SD, 16.9]; mean BC, 21.8
dB [SD, 16]), CT scan was positive in 81%, negative in
11%, and doubtful in 8%. The position of the hypodensities in these opposite ears on positive CT scans was
anterior fenestral in 100%, pericochlear in 17%, around
the internal auditory canal in 15%, and involving the
round window in 3%.
In conclusion, for unoperated normal-hearing opposite ears, the CT scan indicated the presence of otosclerotic hypodensities in 46% of cases, with a greater
proportion of hypodensities with endosteal extension
than in operated ears. Opposite ears with pure sensorineural hearing loss had the greatest proportion of hypodensities with endosteal extension compared with
normal-hearing opposite ears, bilateral conductive hearing loss ears, and operated ears.
Comparison of Surgical and Radiologic Findings
The results of comparing surgical and radiologic findings are presented in Figure 5.
All ears with positive CT scan results had a positive
diagnosis of otosclerosis during surgery.
Among 18 ears with doubtful hypodensity, during surgery, we found 17 with otosclerotic foci (94.4%) and in
1 a minor malformation of the anterior branch of the
stapes.
Comparison of surgical and radiological findings
Positive and doubtful scans
Negative scans
Total
TABLE 4.
Positive surgical
otosclerosis
Other
diagnosis
Total
193
10
203
1
5
6
194
15
209
Ten surgical otosclerotic foci were missed on the CT scan (i.e.,
sensitivity of 95.1%), and 1 minor malformation was confused with a
radiologic hypodensity (i.e., specificity of 99.5%).
Stapes footplate
complications
Positive scan (176)
Doubtful scan (18)
Negative scan (15)
Total (209)
Stapes footplate complications and
radiologic diagnosis
Mobilized and
floating footplate
4
3
0
7
Fracture Incidence, %
2
0
2
4
Z
3.4
16.7^ p = 0.05
13.3
5.3
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S. LAGLEYRE ET AL.
21.2
34
31.3
27.2
20.5
23
(10.9)
(21.2)
(19.4)
(12.6)
(12.3)
(13.5)
+2.8
+1.7
+0.1
+1.4
+3
+2.6
dBHL
dBHL
dBHL
dBHL
dBHL
dBHL
(9)
(4.9)
(9.2)
(5.2)
(4.8)
(8.6)
27.5 (10)
32 (10.7)
32 (10.8)
31 (8.8)
23.2 (6.5)
27.7 (10)
9.6
9.2
9.3
12.7
12
10
(7.1)
(6)
(8)
(16.1)
(6.5)
(7.4)
17.9
22.8
22.7
18.3
11.3
17.4
(10.9)
(10.2)
(10.1)
(12.4)
(7.4)
(10.6)
Among 15 negative CT scans, we found 4 minor malformations of the ossicular chain and 1 fracture of the
stapes. The remaining 10 cases (66.6%) were positively
diagnosed as otosclerosis during surgery and were defined
as Binfraradiologic[ forms (i.e., a patient with negative
CT scan presenting a positive surgical otosclerosis).
In summary, the preoperative sensitivity of HRCT
scan in the diagnosis of otosclerosis was 95.1%, and its
specificity was 99.5% (Table 2).
During surgery, we found 51 (17.7%) variations or
incidents (Table 3).
Anatomic variations were narrow oval window niche
and overhanging facial nerve (3.3%), facial nerve dehiscence (2.9%), incus malformation (1.4%), obliterated
footplate (0.9%), and persistent stapedial artery (0.5%).
No associated malleus fixations were found.
The main surgical incident concerned the stapes footplate (5.3%). The risk of a mobilized, floating, or fractured footplate was significantly more frequent ( p =0.05)
in cases of doubtful (16.7%) or negative (13.3%) CT
scans than in positive ones (3.4%; Table 4). It was possible that in doubtful or negative CT scans, the superficial otosclerotic foci made the stapes less immobile,
and that this increased the risk of footplate fragility.
(15)
(24.2)
(22.8)
(20)
(8.1)
(16.6)
20.3
25.4
23.6
19.8
14
20.1
dBHL
dBHL
dBHL
dBHL
dBHL
dBHL
(14.1)
(11.3)
(13.5)
(16.2)
(7.9)
(13.5)
24
35.7
31.4
28.6
22.7
25.5
(11.8)
(20.9)
(19.1)
(11.8)
(14)
(13.7)
Hearing Results and the Position of Hypodensities
For the 209 ears, mean postoperative ABG was 10 dB
(SD, 7.4). Mean postoperative ABG was within 10 dB in
65% and within 20 dB in 92% of cases. Sensorineural
hearing level improved by more than 10 dB in 13.4% of
cases and was greater than 10 dB worse in 1.9%. No
patient had a dead ear postoperatively. Hearing results
before and 2 months after stapedotomy are classified in
Table 5 according to hypodensity location.
For the 36 ears with endosteal involvement (pericochlear, internal auditory canal, or round window hypodensities), mean preoperative and postoperative BC
thresholds were significantly lower than the 143 ears
Hearing results between patients with and
without endosteal involvement
29
40.6
37.7
36.7
31.2
31.2
TABLE 6.
n
143
22
17
6
15
209
Hypodensity location
Isolated anterior fenestral
Pericochlear
Internal auditory canal
Round window
No location
All
dBHL indicates decibel hearing level.
dBHL
49.4 (14.9)
66 (25.7)
61.5 (25.2)
56.4 (14.4)
44.2 (12.6)
51.3 (17)
Mean
postoperative
BC (SD)
Mean
preoperative
BC (SD)
Mean AC
improvement
(SD)
Mean
postoperative
AC (SD)
Mean
preoperative
AC (SD)
TABLE 5.
Hearing results versus hypodensity location
Mean change
SNHL (SD)
Mean
preoperative
ABG (SD)
Mean
postoperative
ABG (SD)
Mean
ABGC (SD)
1156
Mean preoperative AC (SD)
Mean postoperative AC (SD)
Mean AC improvement (SD)
Mean preoperative BC (SD)
Mean postoperative BC (SD)
Mean change SNHL (SD)
Mean preoperative ABG (SD)
Mean postoperative ABG (SD)
Mean ABGC (SD)
SNHL percentage of ears
Improved 910 dB
No change (T10 dB)
Worse 910 dB
Group 1
(n=36)
Group 2
(n=143)
Statistical
significance
61.2 (23.4)
39.2 (23.7)
22.1 (12.9)
31.4 (19)
30.9 (19.5)
+0.5 (6.9)
31.7 (10.5)
10.9 (8.8)
20.8 (10.3)
49.4 (14.9)
29 (15)
20.3 (14.1)
24 (11.8)
21.2 (10.9)
+2.8 (9)
27.5 (10)
9.6 (7.1)
17.9 (10.9)
p G 0.0001
p G 0.005
ns
p G 0.005
p G 0.0001
p = 0.1
p G 0.005
NS
p G 0.05
5.6
88.8
5.6
14.7
83.9
1.4
Z
NS
Group 1, patients with endosteal involvement (pericochlear, internal
auditory canal, and round window hypodensities); Group 2, patients
without endosteal involvement (isolated anterior fenestral hypodensity).
dBHL indicates decibel hearing level; ABG, Air-bone gap; ABGC,
Air-bone gap closure; SNHL, sensorineural hearing level.
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RELIABILITY OF HRCT SCAN IN OTOSCLEROSIS
without endosteal involvement (isolated AFH; p G 0.005
and p G 0.0001, respectively; Table 6). Comparing the
group with endosteal extension (pericochlear, internal
auditory canal, and round window hypodensities) and
the group without endosteal involvement (isolated anterior fenestral hypodensities), a significant difference was
found in the overclosure; +0.5 versus +2.8 dB. The percentages for SNHL worse than 10 dB were 5.6% and
1.4%, respectively.
In cases of a completely obliterating focus in the round
window (2 ears), we found a worsening of hearing results
compared with the group without endosteal involvement,
with a mean change SNHL of -4.2 versus +2.8 dB and
with a mean ABGC of 7.5 versus 17.9 dB, respectively.
Therefore, we think that there is a risk of a worsening
of hearing in patients with endosteal involvement of
otosclerosis.
DISCUSSION
Sensitivity of the CT Scan in Diagnosis
of Otosclerosis
In 1993, Valvassori (1) reported that otoslerotic hypodensities must be 1 mm or more in diameter to be visible
1157
in CT slices. Therefore, infraradiologic forms of otosclerosis were thought to be due to superficial otosclerotic foci, too small to be seen on CT scan. According to
Thiers et al. (4), developments in CT imaging will produce images of higher resolution. Better collimation and
decreased pixel size will improve the sensitivity of CT
scans in the diagnosis of otosclerosis.
In previous retrospective studies (3,7), performed
between 1996 and 1999 on 437 cases, CT scans had a
sensitivity of 91.3%. Slice thickness of the machine was
1 mm. In our present series with better resolution, sensitivity was improved to 95.1%. The sensitivity of HRCT
scan in otosclerosis diagnoses followed an improvement
in resolution. Future reductions in slice thickness should
further reduce the frequency of infraradiologic forms.
Naumann et al. (9) reported that the detection rate of
hypodense foci increased by 11% (from 74 to 85%)
when computer-aided analysis was used instead of simple manual reading. Despite this improvement, 2 of
their patients without any radiologic findings showed
at surgery otosclerotic foci around the anterior oval
window. Infraradiologic forms may be due to inactive
lesions of otosclerosis. The same density of these foci
to the surrounding bone left them undetected (4,6). This
FIG. 6. A, Computed tomography, axial cut, showing a normal round window. This image is classified as Stage A. B, Computed
tomography, axial cut, showing an edge hypodensity on the round window niche with normal round window membrane. This image is
classified as Stage B. C, Computed tomography, axial cut, showing a round window obliteration. This image is classified as Stage C. D,
Computed tomography, axial cut, showing basal turn ossification of the cochlea with pericochlear and round window hypodensities. This
image is classified as Stage D.
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1158
S. LAGLEYRE ET AL.
hypothesis can only be confirmed with a histopathologic
sample from these patients. However, inactive isolated
forms of otosclerosis were rare in histologic reports.
Shucknecht (10) considered it common to find inactive
and active regions in otosclerotic foci. For Mafee et al.
(11), the CT scan is likely normal in cases of otosclerotic foci less than 2 to 3 mm or in the case of a simple
fibrous fixation of the footplate. Finally, infraradiologic
forms could be considered like isolated and superficial
otosclerotic lesions in the antefenestram fissula region.
Schuknecht and Barber (12) localized histologic foci at
the fissula antefenestram in 95.9% of cases. Among positive CT scans of our series, AFH was the main localization in 96.6% of cases. Thus, the anterior part of the oval
window is the most important site to investigate in radiologic diagnosis of otosclerosis especially in doubtful and
normal CT scans.
The Use of the CT Scan in Foreseeing the Risk of
Stapes Footplate Problems
After a positive result from CT scan, it would be useful to foresee possible problems that may be encountered
at surgery. Each surgeon should be aware of the risk of
stapes footplate problems before surgery and should
inform the patient. However, we think that in light of
this information at the preoperative stage, one may
reconsider surgery as a function of the surgeon’s experience. In our series, we encountered footplate incidents in
5.3% of cases. Ayache et al. (13) observed an incidence
of 5.8% of floating footplate, associated with narrow
oval window niche in half of cases. Lippy et al. (14)
reported an incidence of 1.2%, but the authors analyzed
only nonremoving floating footplate. In our series, this
situation occurred in only 1 case (0.5%).
In our study, incidents involving the stapes footplate
were significantly more frequent when the CT scan was
doubtful or negative. In a previous study, Shin et al. (3)
found the same results with a significant risk ( p = 0.04)
of complication of the stapes footplate in cases of infraradiologic forms. Infraradiologic forms correspond to
superficial histopathologic otosclerotic foci usually associated with reduced stapes fixation and a higher risk of
fragile footplate. Thus, in cases of negative or doubtful
HRCT scan otosclerosis, could not be excluded, but the
surgeon is alerted to the higher risk of encountering a
stapes footplate problem.
Impact of the CT Scan on Audiometric Results
For Veillon et al. (2), pericochlear hypodensities may
correspond to an extension of the anterior foci of otosclerosis through the otic capsule or an independent
focus of the fissula antefenestram developed from the
cartilagenous residue. Generally, pericochlear hypodensities seem bigger than anterior fenestral lesions and are
easily detected on CT scans (15), contrary to internal
auditory canal hypodensities.
Shin et al. (7) found preoperative and postoperative bone conduction thresholds significantly lower
( p G 0.05) in patients with pericochlear foci on the CT
scan. This occurred especially when the endosteum was
involved. In our study, we found similar results with
mean preoperative and postoperative bone conduction
significantly lower ( p G 0.005 and p G 0.0001, respectively) in ears with endosteal involvement (pericochlear,
internal auditory canal, or round window hypodensities).
Otosclerosis may involve the round window niche.
Thiers et al. (4) recommended inspecting this area in primary stapes surgery. The radiologic and anatomic presence of round window foci varied between 3.2 (7) and
36.1% (16). For several authors, it was the second most
frequent anatomic site for otosclerosis (12,17). Round
window hypodensities were detected in 2.9% of cases in
our series. They were associated with pericochlear and
internal auditory canal hypodensities in 50% of cases.
Round window obliteration is classically considered as a
possible cause of surgical failure (18Y22). The incidence
of round window obliteration is generally less than 1%
(23Y25). According to Shin et al. (7), the risk of sensorineural hearing loss was significantly higher ( p G 0.05) in
cases of round window obliteration. However, in their
study, this obliteration was associated with a pericochlear
focus in 8 of 14 cases. Therefore, the degree of sensorineural hearing loss could not be interpreted as solely due
to the effect of round window obstruction. Wiet et al. (26)
considered that round window obliteration could induce a
hearing loss only if the round window niche is totally
obliterated.
To clarify otosclerotic involvement of the round window, we suggest adopting a new classification in 4 progressive stages (Fig. 6AYD). Stage A is defined as a
normal window, Stage B when hypodensity involves
the edge of the niche but the round window membrane
is normal, Stage C in case of round window obliteration,
and in Stage D, the basal turn of the cochlea is ossified.
In our series, we observed 2 cases of obliterated round
window niche (Stage C; 1%), both associated with postoperative high-frequency sensorineural hearing loss
(mean change, SNHL -4.2 dB). Following the suggestions of several authors (25,27) we did not drill the
round window area to avoid the increased risk of sensorineural hearing loss. From these results, we suggest that
for round window lesions classified as Stages C and D
from preoperative HRCT scans, patients should be informed of the possible risk of postoperative sensorineural
hearing loss.
CONCLUSION
The current study showed that for patients presenting
with conductive hearing loss, normal tympanic membrane, and abnormal stapedial reflex, the sensitivity of
preoperative HRCT scan in the diagnosis of otosclerosis
was 95.1%.
We found that the preoperative HRCT scan allowed us
to allow the positive diagnosis of otosclerosis in cases of
Bnontypical[ clinical form (Btypical[ defined as a bilateral conductive hearing loss associated with normal tympanic membrane, absent stapedial reflex, and a familial
Otology & Neurotology, Vol. 30, No. 8, 2009
Copyright @ 2009 Otology & Neurotology, Inc. Unauthorized reproduction of this article is prohibited.
RELIABILITY OF HRCT SCAN IN OTOSCLEROSIS
history of otosclerosis), foresee anatomic difficulties (i.e,
narrow oval window, facial dehiscence) and look for
other associated diagnoses (i.e, malleus fixation, ossicular malformation), identify a risk of mobilized stapes
footplate in cases of negative or doubtful images, and
inform patients of the possible risk of postoperative sensorineural hearing loss in cases of pericochlear, internal
auditory canal, or round window involvement.
The systematic use of HRCT scan before stapes surgery should be based on the experience of the surgeon
and on the socioeconomic context of each country, taking into account the great variability of CT scan costs.
Acknowledgments: The authors thank Vanina Bongard,
M.D. (Department of Epidemiology, Purpan Medicine Faculty,
Paul-Sabatier University, Toulouse, France) for statistical support and Chris James, M.D., for help.
10.
11.
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15.
16.
17.
REFERENCES
1. Valvassori GE. Imaging of otosclerosis. Otolaryngol Clin North
Am 1993;26:359Y71.
2. Veillon F, Stierle JL, Dussaix J, et al. [Otosclerosis imaging:
matching clinical and imaging data]. J Radiol 2006;87:1756Y64.
3. Shin YJ, Deguine O, Cognard C, et al. Reliability of CT scan in the
diagnosis of conductive hearing loss with normal tympanic membrane. Rev Laryngol Otol Rhinol (Bord) 2001;122:81Y4.
4. Thiers FA, Valvassori GE, Nadol JB Jr. Pathology case of the
month: otosclerosis of the cochlear capsule: correlation of computerized tomography and histopathology. Am J Otol 1999;20:93Y5.
5. Bonafe A. Imaging of conductive hearing loss. J Radiol 1999;80:
1772Y9.
6. Guneri EA, Ada E, Ceryan K, et al. High-resolution computed tomographic evaluation of the cochlear capsule in otosclerosis: relationship between densitometry and sensorineural hearing loss. Ann
Otol Rhinol Laryngol 1996;105:659Y64.
7. Shin YJ, Fraysse B, Deguine O, et al. Sensorineural hearing loss
and otosclerosis: a clinical and radiologic survey of 437 cases. Acta
Otolaryngol 2001;121:200Y4.
8. Committee on Hearing and Equilibrium guidelines for the evaluation of results of treatment of conductive hearing loss. American
Academy of OtolaryngologyYHead and Neck Surgery Foundation,
Inc. Otolaryngol Head Neck Surg 1995;113:186Y7.
9. Naumann IC, Porcellini B, Fisch U. Otosclerosis: incidence of
18.
19.
20.
21.
22.
23.
24.
25.
26.
27.
1159
positive findings on high-resolution computed tomography and
their correlation to audiological test data. Ann Otol Rhinol Laryngol
2005;114:709Y16.
Schuknecht HF. Disorders of Bone. Philadelphia, PA: Lea and
Febiger, 1993:365Y79.
Mafee MF, Henrikson GC, Deitch RL, et al. Use of CT in stapedial
otosclerosis. Radiology 1985;156:709Y14.
Schuknecht HF, Barber W. Histologic variants in otosclerosis. Laryngoscope 1985;95:1307Y17.
Ayache D, Sleiman J, Tchuente AN, et al. Variations and incidents
encountered during stapes surgery for otosclerosis. Ann Otolaryngol Chir Cervicofac 1999;116:8Y14.
Lippy WH, Fucci MJ, Schuring AG, et al. Prosthesis on a mobilized stapes footplate. Am J Otol 1996;17:713Y6.
Saunders JE, Derebery MJ, Lo WW. Magnetic resonance imaging
of cochlear otosclerosis. Ann Otol Rhinol Laryngol 1995;104:
826Y9.
Hueb MM, Goycoolea MV, Paparella MM, et al. Otosclerosis: the
University of Minnesota temporal bone collection. Otolaryngol
Head Neck Surg 1991;105:396Y405.
Guild SR. Histologic otosclerosis. Ann Otol Rhinol Laryngol
1944;53:246Y67.
Farrior J, Sutherland A. Revision stapes surgery. Laryngoscope
1991;101:1155Y61.
Cokkeser Y, Naguib M, Aristegui M, et al. Revision stapes surgery:
a critical evaluation. Otolaryngol Head Neck Surg 1994;111:
473Y7.
Hough JV, Dyer RK Jr. Stapedectomy. Causes of failure and revision surgery in otosclerosis. Otolaryngol Clin North Am 1993;26:
453Y70.
Somers T, Govaerts P, Marquet T, et al. Statistical analysis of
otosclerosis surgery performed by Jean Marquet. Ann Otol Rhinol
Laryngol 1994;103:945Y51.
Battista RA, Wiet RJ, Joy J. Revision stapedectomy. Otolaryngol
Clin North Am 2006;39:677Y97, v-vi.
Ginsberg IA, Hoffman SR, Stinziano GD, et al. StapedectomyVin
depth analysis of 2405 cases. Laryngoscope 1978;88:1999Y2016.
Gristwood RE, Venables WN. Otosclerotic obliteration of oval
window niche: an analysis of the results of surgery. J Laryngol
Otol 1975;89:1185Y217.
Shea JJ, Farrior JB. Stapedectomy and round window closure.
Laryngoscope 1987;97:10Y2.
Wiet RJ, Harvey SA, Bauer GP. Complications in stapes surgery.
Options for prevention and management. Otolaryngol Clin North
Am 1993;26:471Y90.
Causse JB, Causse JR, Wiet RJ, et al. Complications of stapedectomies. Am J Otol 1983;4:275Y80.
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