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22 January 2025: Database Analysis  

Role of the Carhart Effect and Outcomes from Surgery: A Retrospective Study of 532 Patients with Conductive Hearing Loss Due to Otosclerosis, Otitis Media with Effusion, and Chronic Otitis Media

Kamila Szpak ORCID logo1ABCDEF, Agnieszka Wiatr ORCID logo2BCDE, Maciej Wiatr ORCID logo2ADEG*

DOI: 10.12659/MSM.947061

Med Sci Monit 2025; 31:e947061

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Abstract

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BACKGROUND: The Carhart effect consists of a reduction in bone conduction thresholds associated with conductive hearing loss. The aim of this study was to evaluate the role of the Carhart effect in predicting outcomes from surgery in 3 age groups.

MATERIAL AND METHODS: This study included 532 patients with conductive hearing loss due to otosclerosis, otitis media with effusion, and chronic otitis media who underwent surgery between 2010 and 2020.

RESULTS: The depth of the Carhart effect is a favorable prognostic factor for changes in BC (bone conduction) thresholds after ear surgery in younger patients. A deep Carhart effect in older people is an unfavorable prognostic factor for improving BC thresholds. The restoration of physiological amplification of the sound that was transmitted through the ossicular chain led to a statistically significant change in the Carhart effect and a strong positive correlation between the change in the Carhart effect and the change in average BC thresholds. The influence of the Carhart effect on the postoperative change in the ABG (air-bone gap) is most noticeable when the physiological strengthening of the middle ear is maintained.

CONCLUSIONS: This findings from this study have shown that the depth of the Carhart effect is one of many factors that should be considered when predicting the results of ear surgery. The depth of the Carhart effect is a favorable prognostic factor for the postoperative changes in BC threshold and for change in the ABG when the physiological strengthening of the middle ear is maintained.

Keywords: Aging, Bone Conduction, Ear, Middle, Hearing Loss, Hearing Tests

Introduction

Hearing loss is one of the main symptoms reported by patients with middle ear diseases and is one of the most important indications for surgical treatment. An integral part of the audiological assessment of patients with hearing impairment is the measurement of air and bone conduction thresholds [1,2]. At the beginning of the 20th century, Bárány described a single factor influencing the perception of sound through bone conduction [3]. In the following decades, numerous works were published describing the cumulative contribution of various factors influencing sound perception using the bone pathway [4–6].

Conductive hearing loss is common, but its etiology varies in different age groups. In young patients, the incidence of conductive hearing loss is estimated at 15–26%, of which 65–93% is caused by otitis media with effusion. In middle age, conductive hearing loss occurs in approximately 26% of cases and is most often caused by inflammation of the middle ear or otosclerosis. The incidence of otosclerosis in the White population ranges from 0.04% to 1%, but increases to 5% in Asians. In elderly people, conductive hearing loss is less common and the hearing disorder is usually sensorineural in nature and results from aging of the ear. Treatment for conductive hearing loss depends on the underlying condition. In some situations, it is helpful to restore the patency of the external auditory canal, treat inflammation of the outer ear, or conservatively treat acute otitis media. In cases of otitis media with effusion, conservative treatment is used, but in some cases it is necessary to incise the eardrum (myringotomy) with drainage of secretions from the middle ear and insertion of a ventilation tube into the eardrum. It is important to diagnose and treat the cause of eustachian tube dysfunction as the cause of otitis media with effusion. Diagnostics of the nasal part of the pharynx is important both in the youngest patients (hypertrophy of the adenoid) and in adults (assessment for the presence of a tumor in the nasopharynx). Surgery is the preferred treatment of chronic otitis media and immobilization of the stapes in the oval window in the course of otosclerosis [7].

Pathological lesions that disrupt sound conduction through the middle ear, in addition to increasing the air conduction threshold, also have a negative impact on bone conduction thresholds. This phenomenon owes its name to Raymond Carhart, who in 1950 described an increase in the bone conduction threshold in audiometric testing at a frequency of 2000 Hz (hertz) in patients with otosclerosis [8]. The Carhart effect, or notch, consists of a reduction in bone conduction thresholds associated with conductive hearing loss [9].

The variability of the bone conduction threshold because of pathological changes affecting the middle ear was presented by Huizing based on his own experience, introducing the concept of pseudoperceptual deafness. Depending on the type of disease and its location, the Carhart effect was observed to be between 500 Hz and 4000 Hz [10].

The presence of a disease process in the oval window with immobilization of the base of the stapes and the associated increased stiffness of the ossicular chain causes a preoperative increase in the bone conduction threshold in the range of 2000 Hz. This increase has been observed in the course of otosclerosis and chronic cholesteatoma otitis media or chronic otitis media with inflammatory granulation tissue with changes to the mucous in the oval window. The presence of adhesions, mainly in the area of the malleus and promontorium, lead to an increase in the preoperative bone conduction threshold of 4000 Hz. In the course of exudative otitis media, pseudoperceptual deafness was observed significantly more often at 4000 Hz and 2000 Hz [11,12].

The frequency of the Carhart effect depends on the location of the abnormalities in the middle ear, and this issue was the subject of a separate study conducted by our team [13], which analyzed the change in bone conduction thresholds in a group of patients with middle ear diseases such as chronic otitis media, otosclerosis, or exudative otitis media, finding presence of the Carhart effect in 54.5% of all analyzed patients. The Carhart effect was most often observed in patients with chronic otitis media (62.7% of patients), in the case of otosclerosis it was observed in 61.5%, while the Carhart effect was least frequently observed in the case of exudative otitis media (30.29% of patients). In exudative otitis media, the Carhart effect was observed significantly more often at the frequency of 4000 Hz and in individual cases also at 500 and 2000 Hz. In otosclerosis, the Carhart effect was most often observed at the frequency of 2000 Hz, and in a significant percentage of patients it also affected the frequency of 4000 Hz. In chronic otitis media, the frequency of the Carhart effect significantly depended on the location and not the type of observed lesions. The presence of cholesteatoma in the attic area (37.2% of patients with chronic cholesteatoma media), in the immediate vicinity of the ossicular chain, correlated with the Carhart effect at a frequency of 4000 Hz. The presence of cholesteatoma masses close to the oval window was associated with the Carhart effect at a frequency of 2000 Hz and affected 10.98% of patients with cholesteatoma. The Carhart effect at 2000 Hz was also observed for chronic otitis media with inflammatory granulation tissue. An increase in the bone conduction threshold in the 2000 Hz range occurred in almost 60% of patients with the Carhart effect in this group of patients. In the case of chronic simple otitis media, the presence of the Carhart effect in our observation depended on the presence of adhesions in the tympanic cavity. Immobilization of the ossicular chain through the presence of adhesions close to the malleus and promontorium significantly increased the bone conduction threshold at 4000 Hz. This previously published research was the basis for conducting the presented study, which examines the impact of the Carhart effect in various middle ear diseases on the improvement of hearing after treatment.

The extent of the disease process in the middle ear can only be precisely assessed intraoperatively. Therefore, in many cases, it is difficult to predict postoperative hearing test results and precisely answer patients’ questions about the expected effects of surgical treatment.

Predicting the postoperative effects of surgical treatment for middle ear diseases based on preoperative audiometric test results remains a possibility; in addition to imaging tests (temporal bone high resolution computer tomography, magnetic resonance imaging), this prediction will allow patients to avoid disappointment with the effects of treatment and provide doctors with the opportunity to estimate the benefits of other treatment methods.

Therefore, the present study included 532 patients with conductive hearing loss due to otosclerosis, otitis media with effusion, and chronic otitis media, and aimed to evaluate the role of the Carhart effect in predicting outcomes from surgery in 3 age groups.

Material and Methods

ETHICS STATEMENT:

Consent to conduct the research was obtained from the local Bioethics Committee (no. 122.6120.206.2016). All patients included in the analysis gave informed written consent to participate in the study.

MATERIAL:

A retrospective analysis of 532 consecutive patients who underwent surgery for middle ear diseases between 2010 and 2020 was performed. The youngest patient was 18 years old, the oldest was 82 years old, and the average age was 43 years. The analysis included 289 women and 243 men. The study cohort included 139 patients with otosclerosis (OTO), 73 with exudative otitis media (OME) treated with surgical drainage, and 320 patients with chronic otitis media (COM).

GROUPS OF PATIENTS:

Among patients with otosclerosis, those who underwent stapedotomy in which the prosthesis was suspended on the long process of the incus were considered. Patients with otitis media with effusion who were included in the study were those with a thick “glue ear” secretion who were qualified for surgical drainage of secretions from the middle ear space and in whom previous conservative treatment had failed. To illustrate the impact of the extent of ossicular chain damage, patients with COM were additionally divided into a group that underwent type 1 tympanoplasty and a group that underwent type 3 tympanoplasty.

To determine the impact of aging of the hearing system on the analyzed parameters, the participants were divided into the following 3 age groups within each disease group:

The inclusion criteria for the study were: age older than 18 years, OTO, OME treated with surgical drainage, COM, first ear surgery, no history of ear/head trauma, informed consent to participate in the study, and Carhart effect observed in preoperative pure tone audiometry.

The exclusion criteria for the study were: age younger than 18 years, external ear diseases, middle ear diseases other than those listed in the study inclusion criteria, ear reoperation, history of ear/head trauma, congenital hearing defects, lack of informed consent to participate in the study, or withdrawal of consent at any stage of the research.

METHODS:

In each patient included in the study, a medical history was collected and typical otolaryngological examination, an acumetric examination, and tuning fork tests (Weber test and Rinne test) were performed. We performed pure tone audiometry and, if the ear pathology allowed, impedance audiometry. The middle ear procedures were performed by otosurgeons with similar experience and surgical methodologies. This made it possible to treat the analyzed patients as a homogeneous group.

SURGICAL METHODOLOGY:

In the case of otosclerosis, the study included patients undergoing surgery for the first time, in whom a prosthesis was suspended on the long process of the incus and inserted into an orifice created in the stapes footplate during stapedotomy. After putting on the prosthesis, the orifice in the stapes footplate was sealed with 3 pieces of connective tissue. To treat the group as a homogeneous group, we considered patients who used the same type of prosthesis and method of its attachment. In the course of otitis media with effusion, the procedure included myringotomy, drainage of thick secretions from the middle ear spaces and insertion of a ventilation tube into the eardrum.

Considering the influence of the degree of damage to the ossicular chain and the extent of opening of the middle ear space on the Carhart effect, 2 extremely different subgroups of patients with chronic otitis media were identified. The type 1 tympanoplasty group included patients with eardrum perforation as the only abnormality, with normal middle ear lining and intact ossicular chain. To reduce the impact of the size of the eardrum defect on the observed result, an additional division was made into small (up to 50%) and large (over 50%) eardrum defects. In these cases, the treatment consisted of reconstruction of the eardrum.

The next group included patients with type 3 tympanoplasty. The advancement of the disease process required extensive opening of the temporal bone with removal of the posterosuperior wall of the external auditory canal and performance of the canal wall-down tympanoplasty. The damage to the ossicular chain affected the malleus and incus, and the ossiculoplasty involved placing an eardrum graft directly on the stapes. Due to damage to the bony canal of the facial nerve and the risk of compression of the VII nerve in the event of displacement, a prosthesis was not used between the stapes and the eardrum.

AUDIOMETRIC TESTS:

The hearing test was performed by 1 person in a soundproof and sound-absorbing audiometric cabin using an audiometer meeting ISO (International Organization for Standardization) standards. Pure tone audiometry was performed immediately before surgical treatment and during a follow-up 6 months after surgical treatment. In patients with OME with a ventilation tube in place, a follow-up audiometric test was performed no sooner than 30 days after the tube was removed.

The changes in average bone conduction thresholds and average air conduction thresholds were assessed at frequencies of 500 Hz, 1000 Hz, 2000 Hz, and 3000 Hz in accordance with the recommendations of the American Academy of Otolaryngology, Head and Neck Surgery. Committee on Hearing and Equilibrium [14].

For all analyzed diseases, the conditions for inclusion in the analysis were the presence of the Carhart effect in audiometric tests. The audiometric criterion for the Carhart effect was an increase of a minimum of 10 dB (decibel) in the BC (bone conduction) threshold for 1 frequency in relation to neighbouring frequencies. To assess the impact of the depth of the Carhart effect on the change in bone conduction threshold values after surgical treatment, we divided patients into 2 groups according to depth of the Carhart effect. Within each disease group, patients were divided into 2 groups according to the depth of the Carhart effect assessed preoperatively: those with a Carhart effect up to 15 dB and those with a Carhart effect above 15 dB. Analyses were carried out for patients with a given diagnosis as a whole and in specific age groups. Within each disease, regardless of the depth of the Carhart effect, the aging of the hearing system was also considered and the patients included in the study were analyzed in established age groups.

STATISTICAL ANALYSIS:

The audiometric test results obtained preoperatively and in follow-up tests 6 months after surgery were subjected to statistical analysis using STATISTICA 13 (StatSoft, Cracow, Poland). Descriptive statistics were used to describe the characteristics of the study group: mean, median, and standard deviation (SD). The normality of the distribution of individual parameters assessed in the study was checked using the Shapiro-Wilk test. The obtained results were subjected to statistical analysis via the χ2 test of independence, Fisher’s test, and the t test. The level of statistical significance was set to P<0.05.

Results

RELATIONSHIP BETWEEN PREOPERATIVE DEPTH OF CARHART EFFECT AND CHANGE IN AVERAGE BONE CONDUCTION THRESHOLD VALUES AFTER TREATMENT:

Within each disease group, patients were divided into 2 groups according to the depth of the Carhart effect assessed preoperatively: those with a Carhart effect up to 15 dB and those with a Carhart effect above 15 dB. Statistical analysis revealed that the depth of the Carhart effect, assessed jointly for all patients with a given disease, had no impact on the change in mean BC values (Table 1).

The next stage of the study looked for the relationship between the preoperative depth of the Carhart effect and the change in average bone conduction threshold values after treatment in established age groups. To determine the impact of aging on the observed results, the analyzed patients were considered in 3 age groups: 18–29 years old, 30–59 years old, and over 60 years old.

In patients with otosclerosis, significant differences were found between all age groups regarding the change in mean BC values in patients with a preoperative Carhart effect up to 15 dB (P=0.008). Additionally, in patients with a preoperative Carhart effect >15 dB, significant differences were found for the changes in the mean BC values between the analyzed age groups (P=0.008).

In patients with otosclerosis, the preoperatively assessed depth of the Carhart effect had a significant impact on the postoperative change in mean BC values in younger patients. A greater change in BC was observed in patients with a Carhart effect >15 dB, in both the age group up to 29 years of age and the age group of 30–59 years (Figure 1). In the oldest patients, the preoperative depth of the Carhart effect had no significant impact on the postoperative change in BC, which may be explained by aging of the hearing system. Age-related changes in the inner ear were indicated by the lack of statistically significant differences in the observed change in BC observed in patients over 60 years of age between the Carhart effect depth groups with the same reconstruction (stapedotomy) and while maintaining the physiological amplification of the sound transmitted through the auditory ossicular chain (P=0.448).

In patients with OME, no statistically significant differences were found among the individual age groups in terms of the change in BC in patients with a preoperative Carhart effect up to 15 dB (P=0.161). Additionally, in patients with a Carhart effect >15 dB, there were no statistically significant differences in BC change among individual age groups (P=0.359).

In patients with OME, the preoperatively assessed depth of the CE had a significant impact on the postoperative change in BC in all age groups. A greater change in BC was observed in patients with a Carhart effect >15 dB in all age groups. Compared with patients with OTO, there were more patients with a Carhart effect up to 15 dB in each OME age group (Figure 2).

In patients with COM, statistically significant changes in BC were observed among the created age groups for patients with a preoperative Carhart effect up to 15 dB (P=0.039). When the preoperative Carhart effect was >15 dB, the observed BC changes among age groups were not statistically significant (P=0.258).

The preoperatively assessed depth of the Carhart effect had a statistically significant impact on the postoperative change in BC in younger age groups. A greater change in BC was observed in patients with a preoperative Carhart effect >15 dB in both the up to 29 years age group and the 30–59 years age group.

In the oldest patients, the preoperative depth of the Carhart effect did not have a statistically significant impact on the postoperative change in BC, which may be explained by the aging of the hearing system. However, there was a trend that a greater change in BC was observed in patients with a preoperative Carhart effect >15 dB (Figure 3).

RELATIONSHIP BETWEEN PREOPERATIVE DEPTH OF CARHART EFFECT AND CHANGE IN AVERAGE ABG (AIR-BONE GAP) VALUES AFTER TREATMENT:

In patients with otosclerosis, a greater statistically significant change in the ABG was observed in patients with a preoperative Carhart effect of up to 15 dB (P=0.012). Similarly, in patients with OME, a significantly greater change in the ABG after surgical treatment was observed in patients with a preoperative Carhart effect of up to 15 dB (P=0.004). In patients with COM, no statistically significant differences were found for the change in ABG after ear surgery between the groups with a different depth of the preoperative Carhart effect (P=0.442) (Table 2).

To determine the impact of aging on the observed results, the next stage of the study assessed the relationship between preoperative depth of the Carhart effect and the change in ABG values after treatment in established age groups.

In patients with otosclerosis, no statistically significant changes in the ABG were observed among the age groups for patients with a preoperative Carhart effect up to 15 dB (P=0.245). When the preoperative Carhart effect was >15 dB, the observed changes in the ABG among age groups were statistically significant (P<0.001).

In the youngest group of patients with otosclerosis, a significantly greater change in the mean ABG after surgical treatment was observed in patients with a preoperative Carhart effect up to 15 dB (P<0.001). After stapedotomy, a statistically significant change in the mean ABG was also observed in patients aged 30–59 years, but unlike in younger patients, patients with a preoperative Carhart effect >15 dB were affected (P<0.001).

In the oldest age group, differences in change in the mean ABG depending on the preoperative depth of the Carhart effect were not statistically significant, but the results indicated a tendency similar to the change in mean ABG in patients aged 30–59 years, which can be explained by the impact of aging of the hearing organ and other factors adversely affecting inner ear function (Table 3).

In the group of patients with otitis media with effusion, statistically significant changes in the mean ABG were observed among the age groups for patients with a preoperative Carhart effect up to 15 dB (P<0.001). When the preoperative Carhart effect was >15 dB, the observed changes in the mean ABG among age groups were not statistically significant (P=0.188).

In the youngest group of patients, after surgical drainage of secretions from the middle ear space in the course of OME, a significantly greater change in the mean ABG was observed in patients with a preoperative Carhart effect up to 15 dB (P<0.001). In patients with OME aged 30–59 years, a statistically significant change in the mean ABG was also observed, but unlike in younger patients, patients with a preoperative Carhart effect >15 dB were affected (P=0.018). Additionally, in the oldest age group, after surgical treatment of patients with OME, a statistically significant change in the mean ABG was observed for patients with a preoperative Carhart effect >15 dB (P<0.001) (Table 4).

The observed results in individual age groups of patients with OME confirm that the removal of effusion is more important for change in the mean ABG than were patient age or depth of the Carhart effect.

In patients with chronic otitis media, statistically significant changes in the mean ABG were observed among the age groups for patients with a preoperative Carhart effect up to 15 dB (P<0.001). When the preoperative Carhart effect was >15 dB, the observed changes in the mean ABG among age groups were also statistically significant (P=0.025).

In the youngest group of COM patients, a significantly greater change in the mean ABG after surgical treatment was observed in patients with a preoperative Carhart effect up to 15 dB (P<0.001). In patients aged 30–59 years, no statistically significant relationship was observed between the change in the mean ABG and the preoperative Carhart effect. In the oldest age group, a statistically significant change in the ABG was observed, but unlike in younger patients, patients with a preoperative Carhart effect >15 dB were affected (P=0.008) (Table 5).

Finally, the influence of the preoperative depth of the Carhart effect on the change in mean ABG values after treatment was considered by comparing patients who underwent type 1 tympanoplasty with those who underwent type 3 tympanoplasty. In patients who underwent type 1 tympanoplasty, a significantly greater change in the ABG after myringoplasty was observed in patients with a preoperative Carhart effect >15 dB (P=0.038). Reconstruction of the eardrum led to a significant improvement in hearing, as indicated by a change in the ABG, especially in the group with a preoperative Carhart effect >15 dB, which indicates the restoration of the influence of middle ear mechanics on the function of the inner ear (Table 6).

In patients who underwent type 3 tympanoplasty, no statistically significant differences were found between the ABG change after ossiculoplasty and the depth of the preoperative Carhart effect (P=0.083). This observation indicates that due to the extent of damage to the ossicular chain and the impact of inflammation on the inner ear, the observed change in the ABG was small and unrelated to the preoperatively observed depth of the Carhart effect (Table 7).

Discussion

The present study assessed the preoperative value of the Carhart effect in predicting surgical outcomes in patients who underwent surgery for middle ear diseases in various age groups.

In the group of patients with otosclerosis, a statistically significant change in BC threshold values in the 2 kHz range was observed in the case of preoperative Carhart effect >15 dB in patients up to 59 years of age. In this study, age-related changes in the inner ear were indicated by the lack of statistically significant differences in the observed change in BC threshold values in patients over 60 years of age in the Carhart effect depth groups with the same reconstruction of the sound conduction system in the tympanic cavity (stapedotomy).

In patients with OME, the preoperatively assessed depth of the Carhart effect was significantly associated with the postoperative change in BC threshold values in all age groups. A greater change in BC thresholds was observed for patients with a Carhart effect >15 dB.

In the group of patients with chronic otitis media, the preoperatively assessed depth of the Carhart effect was significantly associated with the postoperative BC change in younger age groups. In the oldest patients (>60 years of age), the preoperative depth of the Carhart effect did not have a statistically significant association with postoperative change in BC threshold values.

When considering the relationship between the depth of the Carhart effect and the change in average ABG values, a repeating pattern was found among the age groups. In patients under 29 years of age, a greater improvement in hearing, expressed by a greater change in the average ABG, was observed for patients with a preoperative Carhart effect up to 15 dB. Due to the aging of the hearing system, the duration of the disease, the effects of toxic factors, and exposure to noise, in patients 30–59 years of age, a significantly greater change in the average cochlear reserve was observed for patients with a preoperative Carhart effect >15 dB. This was particularly noticeable in patients with OTO and OME. In patients who underwent type 1 tympanoplasty, a significantly greater change in the ABG after myringoplasty was observed in patients with a preoperative Carhart effect >15 dB. In patients who underwent type 3 tympanoplasty, no statistically significant differences in the ABG change after ossiculoplasty were found between the groups according to the depth of the preoperative Carhart effect. In younger age groups, a greater change in the mean bone conduction threshold values was observed, which influenced the change in the mean ABG.

Diseases that disrupt sound conduction in the tympanic cavity not only result in increased air conduction thresholds but also have an adverse effect on bone conduction thresholds. The results obtained in this study showing the relationship between the type and location of middle ear lesions and the occurrence of the Carhart effect are consistent with our previously published findings [13]. This issue was also discussed by other researchers. Hilly et al observed this phenomenon for the frequency range 500–4000 Hz, with the greatest intensity at the frequency of 2000 Hz [15]. According to Yasan et al and Ahmad et al, the frequency affected by the Carhart effect does not depend on the disease entity, but on the type and location of lesions in the middle ear [16,17]. The Carhart effect observed at the frequency of 4000 Hz often coexists with changes in the attic, within the hammer and incus, while at the frequency of 2000 Hz it is partially associated with pathological changes affecting the oval window. The presence of thick fluid in the tympanic cavity significantly disrupts the influence of the system of sound transmission through the middle ear on the function of the inner ear, especially at a frequency of 4000 Hz [13].

The lack of a statistically significant change in bone conduction threshold values in the oldest age group of patients with otosclerosis is consistent with the observations of other authors. The progression of the otosclerotic process with age and secondary changes related to the remodelling of articular surfaces between elements of the ossicular chain further exacerbates hearing loss [18,19]. Many authors concur on the impact of toxic factors on the inner ear in patients with otosclerosis and the relationship between the duration of the disease and its progression [20–22]. Hinojosa and Marion showed that the degeneration of peripheral sensory elements of the inner ear in patients with otosclerosis is very similar to the changes observed in processes related to aging of the system, such as presbycusis [23].

According to previous studies, the Carhart effect is accompanied by the presence of thick effusion in the tympanic cavity, in contrast to cases of otitis media with effusion without the Carhart effect, in which the effusion was generally thin and serous [17,24]. In OME, blockage of the round window by retained fluid and impairment of stapes function in the oval window lead to impaired window mobility via a mechanism similar to that described by Bae et al in otosclerosis (“zero windows”) [20].

The changes in bone conduction thresholds observed in the COM group resulted from both the negative effect of inflammatory toxins on the structures of the inner ear and the effect of mechanical disruption of window function related to the location of inflammatory changes in the tympanic cavity. According to the literature, the postoperative deterioration of bone conduction thresholds observed in 1.2% of cases is related to acoustic trauma caused by use of a drill during surgery, and by improper manipulations of the auditory ossicular chain [25–28]. According to Vartiainen et al, in patients with cholesteatoma and an intact ossicular chain, performing procedures such as canal wall-down tympanoplasty increases the risk of damage to the inner ear [29].

Rosito et al described the influence of cholesteatoma size on the deterioration of postoperative bone conduction thresholds but did not observe any relationship between the location of inflammatory lesions and postoperative changes in BC conduction thresholds [28]. Mejzlik et al did not demonstrate an influence of the type of surgery according to the IOOG (International Otology Outcomes Group) tympanomastoid surgery classification on the deterioration of the bone conduction threshold, with the exception of obliteration of the mastoid cavity, which is closely related to the presence of cholesteatoma in its spaces [26,30,31].

The preservation of all auditory ossicles, after eliminating coexisting abnormalities of the eardrum and middle ear lining, creates optimal conditions for hearing improvement. This finding is consistent with previous reports that a significant improvement in hearing, as measured by a change in ABG, was observed not only in patients with an intact ossicular chain but also in patients after type 2 tympanoplasty and in patients where the ossicular chain was reconstructed using a partial ossicular replacement prosthesis [32,33].

Statistically significant changes in the postoperative threshold values of BC, AC, and ABG were associated with changes in the area of windows in COM or OME patients. This finding is consistent with those of other reports, according to which the highest risk of increased postoperative bone conduction thresholds is observed in patients with adhesions in the round window [34,35].

Regardless of the disease process taking place in the middle ear, in the diseases considered there is an adverse impact on the inner ear and disruption of its function. In the course of otosclerosis, apart from impaired mobility of the stapes in the oval window, the progression of the disease and the development of otosclerotic changes in the cochlea lead to the development of the sensorineural component of hearing loss (cochlear otosclerosis). Another important factor is the adverse effect of chronic inflammation of the middle ear on the inner ear, which can increase bone conduction thresholds.

This study has some limitations. We used subjective audiometric tests in the diagnosis of hearing loss. There were unequal numbers of patients with the analyzed diseases, and there was unequal distribution of patients in the analyzed age groups within the analyzed diseases. Research results are influenced by limitations of the surgical methodology. In the case of otosclerosis surgery, the limitation is the repeatability of fixing the prosthesis on the long process of the incus, especially its clamping force and sealing of the hole in the stapes footplate. The limitations of the results obtained in patients with otitis media with effusion are the unrepeatability of the place and size of the tympanic membrane incision, the use of several types of ventilation tubes, and the variable duration of its insertion. In the case of chronic otitis media, the limitation is the different size and location of the eardrum perforation and the possibility of using different materials in its reconstruction. Another limitation in patients operated on due to chronic otitis media is the lack of a repeatable pattern of location and type of changes in the lining of the middle ear, which forced the adoption of simplifications to create the analyzed groups.

Conclusions

The depth of the Carhart effect is one of many factors that should be considered when predicting the results of ear surgery. The depth of the Carhart effect is a favourable prognostic factor for the postoperative changes in BC threshold values, especially in younger patients, and the influence of the Carhart effect on change in the ABG is most noticeable when physiological strengthening of the middle ear is maintained.

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Tables

Table 1. Association of depth of Carhart effect assessed preoperatively with change in average bone conduction threshold values after surgical treatment.Table 2. Association of depth of Carhart effect assessed preoperatively with change in average cochlear reserve after surgical treatment.Table 3. Otosclerosis. Association of preoperative depth of Carhart effect with change in average values of cochlear reserve after surgical treatment in the considered age groups.Table 4. Exudative otitis media. Association of preoperative depth of Carhart effect with change in average values of the cochlear reserve after surgical treatment in the considered age groups.Table 5. Chronic otitis media. Association of preoperative depth of Carhart effect with change in average values of cochlear reserve after surgical treatment in the considered age groups.Table 6. Association of depth of Carhart effect assessed preoperatively with change in average cochlear reserve after surgical treatment in patients with type 1 tympanoplasty.Table 7. The influence of the depth of the Carhart effect assessed preoperatively on the change in the average cochlear reserve after surgical treatment in patients with type 3 tympanoplasty.Table 1. Association of depth of Carhart effect assessed preoperatively with change in average bone conduction threshold values after surgical treatment.Table 2. Association of depth of Carhart effect assessed preoperatively with change in average cochlear reserve after surgical treatment.Table 3. Otosclerosis. Association of preoperative depth of Carhart effect with change in average values of cochlear reserve after surgical treatment in the considered age groups.Table 4. Exudative otitis media. Association of preoperative depth of Carhart effect with change in average values of the cochlear reserve after surgical treatment in the considered age groups.Table 5. Chronic otitis media. Association of preoperative depth of Carhart effect with change in average values of cochlear reserve after surgical treatment in the considered age groups.Table 6. Association of depth of Carhart effect assessed preoperatively with change in average cochlear reserve after surgical treatment in patients with type 1 tympanoplasty.Table 7. The influence of the depth of the Carhart effect assessed preoperatively on the change in the average cochlear reserve after surgical treatment in patients with type 3 tympanoplasty.

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