Diagnostic significance of the carhart's notch in patients with chronic otitis

Aim: The present study to evaluate the changes in the air bone gap (ABG) at 500, 1000, 2000 and 4000 Hertz frequencies and bone conduction thresholds by comparing the results of pure-tone audiometry tests obtained in the preoperative period and at 6 months after surgery between patients with chronic otitis undergoing type 1 tympanoplasty. With this study,we set out to investigate the effects of air conduction on the bone conduction, evaluate the effects of the surgical correction of air conduction on bone conduction threshold, determine the presence of Carhart's notch in patients with chronic otitis media and evaluate the effects of surgical treatment on the Carhart's notch. Type and Place of the Study: Retrospective, Tertiary Health Care Center Materials and Methods: 104 patients took part in this study who underwent type 1 tympanoplasty with the diagnosis of chronic otitis media between January 2012 and March 2017. In audiometry test, air conduction thresholds at 250, 500, 1000, 2000, 4000 and 8000 Hz, bone conduction thresholds at 500, 1000, 2000 and 4000 Hz and air-bone gap (ABG) between 500-4000 Hz were evaluated. Pure-tone averages were calculated at frequencies of 500, 1000, 2000 and 4000 Hz. Male and female patients aged 8-70 years, who were diagnosed with chronic otitis media paticipated in the study. Patients with cholesteatoma and those with chronic otitis media manifesting retraction of the tympanic membrane, and patients who are found to have tympanosclerosis, ossicular fixation or discontinuity during the operation were excluded. Discussion: Various studies have suggested the importance of middle ear in bone conduction threshold between 1-3 kHz. In the present study, patients with significant improvement in ABG between 500-4000 Hz following tympanoplasty also showed significant improvement in bone conduction threshold at 2000 Hz. The decrease in the bone conduction threshold at 2000 Hz is known as the Carhart's notch and it is widely believed that these findings indicate stapes fixation (48). The relevant studies also report that middle ear does not contribute to bone conduction at frequencies below 1000 Hz. Kashio et al. used a formula in an attempt to calculate whether the Carhart's notch does exist. Accordingly, bone conduction threshold at 2,000 Hertz was subtracted from bone conduction thresholds at 1,000 Hertz, and 4,000 Hertz and the Carhart's notch was considered to exist if the result was 10 dBor higher. The present study also determined the value of Carhart's notch using this formula. In this study, Carhart's notch was present in 46 out of 104 patients (44.2%) who underwent tympanoplasty. Of the 46 patients, Carhart's notch disappeared in 25 patients (54.3%) after surgery. This finding was statistically significant (p=0.029). In their study, Kashio et al. divided patients into three groups as stapes fixation, incudostapedial joint separation, and malleolus and incus fixation. Carhart's notch was found to be present in 31.4% of patients with stapes fixation, 26.3% of patients with incudostapedial joint separation, and 30% of patients with malleolus and incus fixation (48). In the study by Kumar et al., Carhart's notch was present in 37 out of 95 patients (38.9%) with serous otitis media (49). Shishegar et al. found out that Carhart's notch was present in 25.3% of patients with otitis media with effusion (50). When we compare these three studies from the literature, the present study found a higher rate the presence of Carhart's notch. Conclusion: With significant improvement in ABG following tympanoplasty, patients with chronic otitis media and with an intact and mobile ossicular chain may show improvement in bone conduction at 2000 Hz. Carhart's notch is not a specific finding for the diagnosis of otosclerosis, and it may also be found in patients with chronic otitis media.