Predictive impact of the behavior of the Carhart's notch after stapedotomy on speech audiometry parameters

<b>Introduction:</b> Stapedotomy improves air conduction thresholds and restores one of the components of bone conduction (BC): sound transmission to the inner ear via vibrations of the ossicular chain. This results in a measurable improvement in BC thresholds. Audiometric confirmation of pseudoperceptual hearing loss is the loss of the Carhart's notch (CN) observed after surgery. Sensorineural hearing loss is characterized by varying degrees of speech incomprehension impairment, particularly clinically apparent when the impairment affects frequencies essential for communication. <br><br><b>Aim:</b> The aim of the study was to analyze the influence of the occurrence and behavior of the CN on selected speech audiometry parameters after stapedotomy in patients with otosclerosis. <br><br><b>Materials and methods:</b> A retrospective analysis of 116 patients undergoing otosclerosis surgery between 2016 and 2019 was conducted. Patients were divided into groups based on the presence of a CN in the operated ear, based on pure-tone audiometry (PTA) performed preoperatively and during postoperative follow-up after 2-3 years of stapedotomy. Speech audiometry analysis considered changes in speech detection threshold (SDT), speech reception threshold (SRT), and speech discrimination threshold. <br><br><b>Results:</b> In the group of patients who did not have a CN on PTA preoperatively, improving mean BC threshold values after stapedotomy had a beneficial effect on SDT improvement. This association was not confirmed when assessing the effect of mean BC values on SRT. More profound sensorineural hearing loss in the preoperative assessment was associated with poorer SDT, SRT, and speech discrimination threshold in the absence of a CN on PTA. In the group of patients who had a CN on PTA preoperatively, a strong correlation was found between CN disappearance and improvement in SDT and SRT after surgery. A persistent CN after surgery proved to be an unfavorable prognostic factor for improvement in speech audiometry parameters. <br><br><b>Conclusions:</b> 1. The disappearance of the preoperatively observed CN after stapedotomy is a significant prognostic factor for improving the SDT and speech reception threshold; 2. A CN persisting after surgical treatment is an unfavorable factor in improving speech audiometry parameters; 3. Profound sensorineural hearing loss in the absence of the CN in the preoperative assessment is an unfavorable factor in improving the SRT, SDT and speech discrimination threshold; 4. Improvement of mean BC threshold values after stapedotomy, regardless of the preservation of the CN, has a beneficial effect on the improvement of SDT but not on SRT (the study showed that the improvement of SRT correlates with CN disappearing).