**7. Hearing after cochlear implantation**

Acoustic hearing remains preserved in more than half of the patients after cochlear implantation; however, previously, it was believed that insertion of electrode into the cochlea destroys the natural mechanism of hearing [31]. Preserving physiologic pathway of hearing has several advantages such as ability to localize the sound, recognize the speech, and hear in complex listening environments [32]. A variety of factors and approaches have been considered for improving hearing preservation after cochlear implantation. Previous studies have reported that full electrode insertion makes the hearing preservation possible; however, electrode insertion depth and length are determining factors for intracochlear trauma [24, 33].

Studies believe that the most hearing preservation achieves when the electrode is entirely located in scala tympani [34]. The most appropriate surgical approach has remained controversial; some previous studies have mentioned that there is no significant difference between round window and cochleostomy approaches regarding hearing outcomes [35, 36], while others reported that each method is superior for maximizing atraumatic scala tympani insertion. Eventually, preoperative prescription of steroids and steroid-eluting implants have been reported to improve hearing preservation up to 1 year from implantation [32].

In another retrospective analysis of cochlear implanted patients, researchers investigated the impact of related factors on hearing preservation. They reported an overall preservation likelihood of 39% for patients operated by refined soft surgery technique with a higher conservation rate at low frequencies when compared to high frequencies [37]. Age at the time of implantation, etiology of deafness, side of implant, electrode array model, and insertion technique, as well as type of cochleostomy, are investigated factors, which are considered to possibly affect hearing preservation; however, there are a variety of opinions on their effects, and further studies are required for conclusive results [36, 38–52].
