10.14639/0392-100X-N0213
The Carhart notch (CN) is a depression in the bone-conduction audiogram of patients with clinical otosclerosis. The middle frequencies from 0.5 to 2 kHz, which correspond to the resonance frequency of the middle ear, can be substantially improved upon following successful stapes surgery. This retrospective audiometric database and chart review in a tertiary referral centre was performed with the aim of assessing whether the presence of a CN could be predictive of results after stapes surgery in otosclerosis, through improvement in bone conduction (BC) thresholds. Nine hundred and thirty-one cases of stapes surgery over a period of 25 years benefitted from audiological assessment before and 4 months after surgery. A CN was considered present when the BC threshold at the notch frequency (0.5, 1 or 2 kHz) exceeded the mean thresholds at higher and lower adjacent frequencies by at least 7.5 dB. BC threshold improvement was better at 2 kHz (+14.1 ± 12.5 dB vs +12 ± 13.2 dB) and lower at 4 kHz (+3.6 ± 13.5 dB vs +11 ± 14.7 dB) for the CN+ group compared to the CN- group. Moreover, sensorineural hearing loss was more frequent in the CN+ group than in the CN- group. These results indicate that a CN on preoperative audiogram should alert the clinician to lesser postoperative BC improvement at 4 kHz related to a preoperative sensorineural hearing loss or to a higher incidence of postoperative sensorineural hearing loss.
application/xml
1827-675X
213
en
Sébastien Schmerber
https://creativecommons.org/licenses/by-nc-nd/4.0
ACTA Otorhinolaryngologica Italica
bone conduction
Is the Carhart notch a predictive factor of hearing results after stapedectomy?
Text.Serial.Journal
https://www.actaitalica.it/
41
Otology
2021-03-19
2019-03-26
2021-03-19
2021-03-24
84-90
1
Sébastien Schmerber
2021/03/19
10.14639/0392-100X-N0213
84
Department of Otolaryngology-Head and Neck Surgery, Grenoble University Hospital, Grenoble Cedex 9, France
1827-675X
bone conduction
90
Is the Carhart notch a predictive factor of hearing results after stapedectomy?
https://www.actaitalica.it/article/download/213/528
41
ACTA OTORHINOLARYNGOLOGICA ITALICA 2021;41:84-90; doi: 10.14639/0392-100X-N0213




Otology


Is the Carhart notch a predictive factor of hearing
results after stapedectomy?
La tacca di Carhart è un fattore predittivo dei risultati uditivi dopo stapedectomia?
Elea Lamblin1, Alexandre Karkas2, Jérôme Jund3, Sébastien Schmerber1
1
  Department of Otolaryngology-Head and Neck Surgery, Grenoble University Hospital, Grenoble Cedex 9, France; 2 Department of
Otolaryngology-Head and Neck Surgery, Saint Etienne University Hospital, CHU de Saint-Étienne Hôpital Nord, Saint Etienne Cedex
2, France; 3 Department of Research and Clinical Investigation, Annecy Hospital, Metz - Tessy, Pringy Cedex, France


SUMMARY
The Carhart notch (CN) is a depression in the bone-conduction audiogram of patients with
clinical otosclerosis. The middle frequencies from 0.5 to 2 kHz, which correspond to the
resonance frequency of the middle ear, can be substantially improved upon following suc-
cessful stapes surgery. This retrospective audiometric database and chart review in a tertiary
referral centre was performed with the aim of assessing whether the presence of a CN could
be predictive of results after stapes surgery in otosclerosis, through improvement in bone
conduction (BC) thresholds. Nine hundred and thirty-one cases of stapes surgery over a
period of 25 years benefitted from audiological assessment before and 4 months after sur-
gery. A CN was considered present when the BC threshold at the notch frequency (0.5, 1 or
2 kHz) exceeded the mean thresholds at higher and lower adjacent frequencies by at least
7.5 dB. BC threshold improvement was better at 2 kHz (+14.1 ± 12.5 dB vs +12 ± 13.2 dB)
                                                                                                    Received: March 26, 2019
and lower at 4 kHz (+3.6 ± 13.5 dB vs +11 ± 14.7 dB) for the CN+ group compared to the
                                                                                                    Accepted: November 26, 2020
CN- group. Moreover, sensorineural hearing loss was more frequent in the CN+ group than
in the CN- group. These results indicate that a CN on preoperative audiogram should alert
                                                                                                    Correspondence
the clinician to lesser postoperative BC improvement at 4 kHz related to a preoperative sen-
                                                                                                    Sébastien Schmerber
sorineural hearing loss or to a higher incidence of postoperative sensorineural hearing loss.
                                                                                                    Department of Otolaryngology-Head and Neck
KEY WORDS: otosclerosis, stapedectomy, hearing, Carhart notch, bone conduction                      Surgery, Grenoble University Hospital, 1 avenue du
                                                                                                    marquis du Grésivaudan, 38043 Grenoble Cedex
                                                                                                    9, France
RIASSUNTO                                                                                           Tel. +33 4 76 76 56 62. Fax +33 4 76 76 51 20
La tacca di Carhart è una depressione della via ossea nell’audiogramma dei pazienti con             E-mail: SSchmerber@chu-grenoble.fr
otosclerosi clinica. Le frequenze medie da 0,5 a 2 kHz, che corrispondono alla frequenza
di risonanza dell’orecchio medio, possono essere efficacemente migliorate mediante un               Funding
intervento chirurgico di stapedectomia. Sono state eseguite la valutazione di un database           None.
audiometrico retrospettivo e la revisione delle cartelle cliniche dei pazienti afferenti in un
centro terziario con l’obiettivo di valutare se la presenza di una tacca di Carhart (CN) po-        Conflict of interest
tesse essere predittiva dei risultati dopo la chirurgia della staffa nell’otosclerosi, attraverso   The Authors declare no conflict of interest.
il miglioramento delle soglie di conduzione ossea (BC). Novecentotrentuno pazienti sotto-
posti a chirurgia della staffa trattati in un periodo di 25 anni sono stati sottoposti a valuta-      How to cite this article: Lamblin E, Karkas A,
zione audiologica prima e 4 mesi dopo l’intervento. Una CN è stata considerata presente               Jund J, et al. Is the Carhart notch a predictive fac-
quando la soglia BC alla frequenza del notch (0,5, 1 o 2 kHz) ha superato le soglie medie             tor of hearing results after stapedectomy? Acta
delle frequenze vicine superiori e inferiori di almeno 7,5 dB. Il miglioramento della soglia          Otorhinolaryngol Ital 2021;41:84-90. https://
BC è risultato migliore a 2 kHz (+ 14,1 ± 12,5 dB contro +12 ± 13,2 dB) e inferiore a 4 kHz           doi.org/10.14639/0392-100X-N0213
(+3,6 ± 13,5 dB contro +11 ± 14,7 dB) per il gruppo CN + rispetto al gruppo CN-. Inoltre,
la perdita neurosensoriale dell’udito era più frequente nel gruppo CN + rispetto al gruppo          © Società Italiana di Otorinolaringoiatria
CN-. Questi risultati indicano che una CN sull’audiogramma preoperatorio dovrebbe esse-             e Chirurgia Cervico-Facciale
re predittiva di un minore miglioramento postoperatorio della BC a 4 kHz correlato a una
perdita dell’udito neurosensoriale preoperatoria o a una maggiore incidenza di ipoacusia                           OPEN ACCESS
neurosensoriale postoperatoria.                                                                     This is an open access article distributed in accordance with
                                                                                                    the CC-BY-NC-ND (Creative Commons Attribution-Non-
PAROLE CHIAVE: otosclerosi, stapedectomia, udito, tacca di Carhart, conduzione ossea                Commercial-NoDerivatives 4.0 International) license. The
                                                                                                    article can be used by giving appropriate credit and mentio-
                                                                                                    ning the license, but only for non-commercial purposes and
                                                                                                    only in the original version. For further information: https://
                                                                                                    creativecommons.org/licenses/by-nc-nd/4.0/deed.en




84
                                                                                               The Carhart notch after stapedectomy




Introduction                                                    tive tools predicting BC threshold improvement 5,12. The
                                                                main goal of our study was to determine whether preopera-
Patients with a middle ear pathology have increased air con-
                                                                tive audiological assessment as the presence of a CN were
duction (AC) thresholds. There is often also an accompa-        predictive factors for postoperative hearing results such as
nying depression of the bone conduction (BC) thresholds.        BC threshold improvement.
The increase in BC thresholds for otosclerosis, maximal at
2 kHz, is called the “Carhart notch” (CN) 1. This effect may
be explained by BC mechanisms. The inertial component           Materials and methods
seems to be the most important factor contributing to BC        Patients
hearing 2. The ossicular and inner ear fluid inertia are less   All patients treated for otosclerosis were included in this
efficient due to the higher impedance of the fixed stapes       retrospective consecutive case-series study. Patients were
footplate in otosclerosis and an increase in BC thresholds is   operated on by the same senior surgeon over a period of 25
observed. The middle ear inertia is the most effective in the   years in our tertiary referral centre. The surgical procedure
mid frequencies close to the resonance frequency vibration      consisted of a stapedotomy with interposition of either a
which is 1.5 kHz 3. In a model simulation of BC excitation      perichondrium or a vein graft, and placement of a Causse-
of the inner ear, Stenfelt et al. 3 hypothesised that the CN    type Teflon stapes 0.4 mm diameter prosthesis 14, the loop
close to 2 kHz could be simulated as a result of increas-       of which was anchored to the long process of the incus.
ing the impedance at the oval window seen from inside the
inner ear. This explains the predominant presence of CN         Audiological assessment
around 2 kHz in otosclerosis.                                   Assessment of hearing status was performed before and
Definite criteria for the detection of a CN are unclear and     after surgery (at 4 months and at 1 year). The audiologi-
previous studies were conducted with different defini-          cal assessment included the preoperative and postoperative
tions 4-8. Hence, the reported CN prevalence in otosclerosis    AC and BC thresholds. We used a 4-frequency pure-tone
varies considerably among authors, ranging from 31% to          average (PTA) for AC and BC thresholds (0.5, 1, 2 and 4
80%. We propose a new definition of CN in order to stand-       kHz). The thresholds at 3 kHz were not available in the
ardise the reporting of audiometry results in future studies.   database at its implemention and were replaced in all cases
In 1950, Carhart 1 was the first to observe that BC thresh-     with those at 4 kHz.
olds were improved following successful fenestration            Only AC and BC results that were obtained at the same
surgery for otosclerosis: this BC improvement is called         time postoperatively were used for calculation of the post-
“overclosure” 9. Although the initial diagnosis of senso-       operative air-bone gap (ABG). Audiometry was assessed
rineural hearing loss (SNHL) is usually made on the ba-         according to the American Academy of Otolaryngology
sis of abnormal BC hearing thresholds, this apparent BC         Head and Neck Surgery guidelines 9, except for thresholds
loss is not a true indicator of the inner ear function, since   at 3 kHz which were substituted in all cases with those at
it could improve following successful surgery; it reflects      4 kHz. This was necessary because 3 kHz measurements
the successful reestablishment of the former impedance of       were not performed at the beginning of this study.
the oval window by surgery 10. Thus, the term overclosure,
while widely used, remains confusing. We prefer to use BC       Carhart notch definition
improvement.                                                    Choosing relevant factors for a precise definition of a CN
Bone lesions in otosclerosis were reported to affect in-        was necessary (Fig. 1). First, we identified a CN at various
tracochlear structures and also cause SNHL 11. In some          frequencies from 0.5 to 2 kHz. To avoid underestimation,
cases the audiogram is unusual and may be attributed to         we determined that the minimum differences between the
sensorineural impairment: this could be the case if the BC      CN frequency and the adjacent frequencies was 7.5 dB and
curve shows a notch which is duplicated on the air conduc-      not 10 dB as reported in other studies 4, otherwise some
tion (AC) curve; this AC-notch is usually called a “cookie      audiograms (e.g. type B in Figure 1) were not defined as in-
bite” 12. Indeed, the question of BC improvement is par-        cluding a CN pattern. Finally, to avoid overestimation, the
ticularly pertinent in patients with mixed hearing loss to      CN frequency had to be higher than the adjacent frequen-
determine the influence of preexisting SNHL. We aimed           cies, or other audiograms (e.g. type A in Figure 1) were
to determine whether different types of AC curve impacted       considered as including a CN pattern 6-8. Indeed, a CN was
BC threshold improvement.                                       defined by BC threshold at the notch frequency (0.5, 1 or 2
Audiological predictive factors of successful surgery are       kHz) ≥ 7.5 dB above the mean of thresholds at higher and
well known 13, but few authors have focused on preopera-        lower adjacent frequencies. Another criterion was that the



                                                                                                                               85
E. Lamblin et al.




Figure 1. CN considered present or not on various type of BC curves according to previous CN definitions and according to our definition (example of right ear).


CN frequency threshold had to be higher than the adjacent                         Statistical analyses
frequency thresholds.                                                             We used SPSS software (V13.0; SPSS Inc., Chicago, IL,
                                                                                  USA). Quantitative data were expressed as mean and stand-
Hearing outcomes                                                                  ard deviation. We used the Chi-square and Fisher’s exact
BC threshold improvement was measured by the preopera-                            test for the analysis. Univariate analysis was used to identi-
tive minus the postoperative pure-tone BC average follow-                         fy a CN as a possible predictive factor for hearing outcome.
ing successful surgery. Various AC curve types were de-                           A P value < 0.05 was considered significant.
scribed to determine whether preoperative AC thresholds
impact postoperative BC thresholds (Fig. 2): 1) a flat AC                         Results
curve; 2) a downward AC curve (defined by high frequency
                                                                                  Population studied
AC hearing loss > 2 kHz); 3) an AC-notch or “cookie bite”                         This retrospective study was conducted on 1,029 patients
(defined by a notch in the AC threshold along with the CN                         who underwent 1,250 stapes surgeries for otosclerosis in
at 2 kHz). The success rate in stapes surgery was defined in                      our tertiary referral centre. Seven hundred and ninety-nine
two ways. Firstly, an AC PTA < 30 dB as primary criterion                         patients (931 surgical cases) were followed at 4 months af-
alone. Secondly, combined criteria of this primary assess-                        ter surgery and 355 patients (415 surgical cases) at 1 year.
ment with 2 additional criteria: absence of postoperative
sensorineural hearing loss (SNHL defined by a 4 kHz BC                            Preoperative data: Carhart notch description
threshold postoperative increase > 10 dB) and a postopera-                        A CN was observed in 495 (53.1%) of the 931 surgical
tive ABG < 10 dB.                                                                 cases in the preoperative audiogram according to our defi-



86
                                                                                                                 The Carhart notch after stapedectomy




                                                                                  mean BC threshold improvement for cases with successful
                                                                                  surgery at 4 months of follow-up was: +5.4 dB at 0.5 kHz,
                                                                                  +3.8 dB at 1 kHz, +13.8 dB at 2 kHz and +8.5 dB at 4 kHz.
                                                                                  The mean BC threshold improvement decreased in cases of
                                                                                  failed hearing restoration but remained in positive values.
                                                                                  The results were stable at 1 year after surgery.

                                                                                  Preoperative audiological predictive factors affecting au-
                                                                                  diological results
                                                                                  Improvement of BC thresholds 4 months after surgery
                                                                                  were significantly different if a CN was observed on pre-
                                                                                  operative audiogram (495 cases with CN: CN+ group) or
                                                                                  not (436 cases without CN: CN- group). BC thresholds
                                                                                  improvement for the CN+ group were better at 0.5 and 2
                                                                                  kHz (+7.1 ± 11 dB vs +3.8 ± 10.3 dB, p = 0.00015, Ano-
                                                                                  va; +14.1 ± 12.5 dB vs +12 ± 13.2 dB, p = 0.017, Anova)
                                                                                  and lower at 4 kHz (+3.6 ± 13.5 dB vs +11 ± 14.7 dB,
                                                                                  p = 0.00019, Anova) compared to the CN- group (Fig. 3).
                                                                                  We measured the likelihood of a > 10 dB BC thresholds
                                                                                  improvement and found it to be greater in the CN+ group at
                                                                                  0.5 kHz (odds ratio = 2; 95% CI = 1.5-2.7; p = 0.029) and
                                                                                  at 2 kHz (odds ratio = 1.6; 95% CI = 1.3-2.1; p = 0.035).
Figure 2. BC improvement for cases with a 2 kHz CN preoperatively depend-
                                                                                  The likelihood of a > 10 dB BC thresholds improvement
ing on the AC curve type (a flat AC curve; a “cookie-bite” AC curve defined by    was lower at 4 kHz (odds ratio = 0.4; 95% CI = 0.3-0.5;
“CN duplication” on an AC curve 4 months after surgery (*: p < 0.05, Anova).      p = 0.022).
                                                                                  Figure 3 shows that if a CN was observed at 2 kHz in the
                                                                                  preoperative audiogram there is no BC threshold improve-
nition. Notches were distributed according to the peak fre-                       ment (negative overclosure) at 4 kHz if the AC thresholds
quency as follows: 273 (29.2%) surgical cases at 2 kHz, 44                        presented a corresponding notch. The likelihood of a > 10
(4.7%) at 1 kHz and 178 (19.1%) at 0.5 kHz. The CN dip                            dB BC threshold improvement was significantly lower
means (corresponding to the difference of mean adjacent                           (odds ratio = 0.08; 95% CI = 0.01-0.6; p = 0.016). On the
thresholds minus CN threshold) were: 13 ± 4.7 dB for 2                            other hand, in the event of a “downward” AC curve, BC
kHz CN, 11.3 ± 4.4 dB for 1 kHz CN, and 11.5 ± 4.7 dB                             threshold improvement at 2 kHz was significantly bet-
for 0.5 kHz CN.                                                                   ter (p = 0.0001, Anova). The likelihood of a > 10 dB BC
                                                                                  threshold improvement was significantly higher (odds ra-
Postoperative data: BC threshold improvement                                      tio = 3.6; 95% CI = 1.1-10.1; p = 0.0013).
Table 1 is a list of BC threshold improvement using prima-                        The univariate analysis did not allow any significant rela-
ry successful surgery criteria from 931 cases and 415 cases                       tionship to be determined between the presence of a preop-
respectively, 4 months and 1 year after stapes surgery. The                       erative CN and successful surgery, considering the primary


Table I. BC threshold improvement according to surgical results after stapes surgery.
                                                                                                   BC threshold improvement (dB)
 Follow-up                                                               n (%)          500 Hz        1000 Hz         2000 Hz          4000 Hz
 4 months                               Total                           931              5.6            2.6             13.2              7.1
                         Successful surgery (AC PTA < 30dB)           609 (65%)          5.4            3.8             13.8              8.5
                              Failed hearing restoration              322 (35%)           6             0.4              12               4.3
 1 year                                 Total                           415              5.1            2.3              13               6.5
                                  Successful surgery                  263 (63%)          4.8            3.5             14.2              9.2
                              Failed hearing restoration              152 (37%)          5.5            0.2             11.1              1.8
AC PTA: air conduction threshold pure tone average.




                                                                                                                                                 87
E. Lamblin et al.




                                                                                           nition we propose helps to describe with accuracy if a CN
                                                                                           is present or not, but it does not account for notches with
                                                                                           broader spectrum.
                                                                                           CN was renamed “the Carhart effect” by Gatehouse 15 since
                                                                                           increases in bone conduction thresholds are reported from
                                                                                           0.5 to 4 kHz. This increase of BC thresholds are not an in-
                                                                                           dicator of the inner ear function since BC thresholds were
                                                                                           demonstrated to improve after surgery 1. The Carhart ef-
                                                                                           fect is due to the lack of excitation mainly from the inertial
                                                                                           component of the ossicles close to a resonance frequency
                                                                                           of 1.5 kHz, and to a lesser extent from the inertia of the
                                                                                           cochlear fluid for lower frequencies 3. Indeed, the presence
                                                                                           of a CN in a patient with conductive hearing loss cannot be
Figure 3. BC improvement according to the presence of a CN, 4 months af-                   used for the specific diagnosis of otosclerosis 4 because the
ter surgery (*: p < 0.05, Anova).                                                          CN can also be due to other disorders of the middle ear that
                                                                                           reduce the movement of ossicles, such as otitis media with
                                                                                           effusion, tympanosclerosis, or ossicular malformations 4,6-8.
criterion alone or the 3 associated criteria (Tab. II). How-
                                                                                           The mean BC improvement in our series was +5.4 dB at
ever, SNHL if considered separately, was more frequent in
                                                                                           0.5 kHz, +3.8 dB at 1 kHz, +13.8 dB at 2 kHz, and +8.5
the CN+ group than in the CN- group at 4 months (odds
                                                                                           dB at 4 kHz. The authors of previous studies confirmed
ratio = 3.1; 95% CI = 1.7-5.7; p = 0.00016) and at 1 year of
                                                                                           the finding of largest BC improvement at 2 kHz 5,15-17. The
follow up (odds rati = 2.6; 95% CI = 1.3-5.4; p = 0.0013).
                                                                                           values of BC improvement in our study correlated with
                                                                                           those of Gatehouse 15 who also assessed the magnitude of
Discussion                                                                                 the Carhart effect in his series from precise criteria of suc-
In our study, a CN was observed according to our defini-                                   cessful surgery (ABG < 10 dB, mean BC thresholds not
tion in 53.1% of the 931 preoperative audiograms, mainly                                   worsened by > 5 dB, AC improved by > 10 dB). BC im-
at 2 kHz. Definite criteria for the detection of a CN were                                 provement varies considerably according to the author, but
not yet clearly established, and the authors of previous                                   Gatehouse demonstrated that discrepancies were markedly
studies used different definitions. The definition that we                                 reduced when the appropriate selection criteria were used.
propose describes CN at various frequencies (0.5, 1 and 2                                  Thus BC improvement can be underestimated with other
kHz), whereas some authors suggested defining CN only                                      methods such as comparing BC thresholds of patients with
at 2 kHz. In addition, as shown in Figure 1, some defini-                                  BC in an age-matched healthy population, or including
tions used previously to define the presence of a CN were                                  only patients whose BC improved 15. Gatehouse also dem-
inadequate, leading to over- or underestimation. The defi-                                 onstrated that BC values before and after surgery underes-


Table II. Hearing results at 4 months and 1 year after surgery according to the presence of a CN (Chi 2 Pearson).
                                                                                             CN-                                          CN +
                                                                                                n                %                 n                %                 p
 4 months after surgery                               Total, n                                436                                 495
                                              PTA AC< 30 dB:1 criterion                       276             63.3%               333             67.3%            0.204
                                                     3 criteria                               246             56.4%               290             58.6%            0.505
                                                     ABG < 10                                 376             76.0%               316             72.0%            0.225
                                                       SNHL                                    14             3.2%                 46             9.3%            0.00016
 1 year after surgery                                 Total, n                                201                                 214
                                             PTA AC < 30 dB :1 criterion                      121             60.0%               142             66.4%             0.193
                                                     3 criteria                               111             55.2%               118             55.1%             0.986
                                                     ABG < 10                                 135             67.2%               164             76.6%             0.032
                                                       SNHL                                   11              5.4%                28              13.1%             0.013
CN-: absence of Carhart notch; CN+: presence of a Carhart notch; PTA AC: air conduction threshold pure tone average; ABG: air bone gap; SNHL: sensorineural hearing loss.




88
                                                                                                         The Carhart notch after stapedectomy




timated the Carhart effect for low frequencies compared to       14%, Ib 8%, II 52%, III 10% and IV 12% 25. Age was not
theoretical considerations, with an experimental model in        considered in our study since functional results do not vary
which pressure changes were applied to the external canal        according to age group 26. Likewise, there was no difference
to simulate the Carhart effect. Indeed, our results could be     in initial or late postoperative hearing outcome, depending
underestimated for low frequencies.                              on vein or tragal perichondrium interposition 27.
We found that a CN observed at 2 kHz with a correspond-
ing AC-notch in the preoperative audiogram was correlated        Conclusions
to lesser BC thresholds improvement at 4 kHz (negative
overclosure). Therefore, an AC-notch on preoperative au-         CN or more appropriately the Carhart effect was observed
diogram is a warning sign for the lack of postoperative BC       at a wide range of frequencies, predominantly at 2 kHz. It
improvement related to a preoperative SNHL or to a high-         is illustrated by the improvement in BC thresholds, which
er incidence of postoperative SNHL. The assessment of            is predominant at 2 kHz, but that is not an indicator of suc-
whether SNHL was preoperative or postoperative is diffi-         cessful surgery. We identified preoperative audiological
cult to know as postoperative BC thresholds were the result      factors influencing BC improvement: 4 kHz BC improve-
of a combination of improvement by adequate impedance            ment was significantly lower in case of preoperative CN or
change and loss by surgical trauma. Cook et al. 18 described     in presence of an AC–notch at 2 kHz. These findings should
a method allowing changes in BC to be predicted according        alert the clinician to mixed hearing loss with preoperative
to air conduction at any frequency by a linear regression.       SNHL or to an incidence of postoperative SNHL.
In Cook’s model, changes in BC other than those expected
could be attributed to other causes than the Carhart effect,     Acknowledgements
and help assess the degree of SNHL in the presence of con-
                                                                 We are grateful to Pierre-Emmanuel Colle, University Gre-
ductive hearing loss. Our findings using our new definitions
                                                                 noble Alpes, for copy editing.
have never been described.
We did not find any relationship between the presence of a
CN and successful surgery rate, according to our criteria.       References
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case series of 931 stapes surgery should be large enough to           of Otolaryngology-Head and Neck Surgery Foundation, Inc. Oto-
cover all CT-scan grades with a distribution similar to that          laryngol Head Neck Surg 1995;113:186-7. https://doi.org/10.1016/
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