**8. Other applications of cochlear implant**

### **8.1. Cochlear implantation for single-sided sensorineural hearing loss**

Recently, a new topic has come up about cochlear implantation in setting of single-sided sensorineural hearing loss [53]. So far, options such as hearing aids, bone-anchored implants, and contralateral routing of signal (CROS) devices were applied for single-side deaf patients. While these options improve hearing by healthy ear, cochlear implantation restores hearing by deaf ear. Sound localization is a special challenge for patients with unilateral hearing loss. A proper localization involves a good bilateral hearing and sound stimulation, as well as intraaural time differences, which allow complex processing of sounds. Recent studies have mentioned some advantages for cochlear implantation in unilateral hearing loss, and some has reported a better sound localization in comparison with bone-anchored implants [54]. Additionally, it has been shown that cochlear implants resolve tinnitus up to an acceptable extent in patients with single-sided deafness and may improve speech perception [34, 55].

### **8.2. Hybrid cochlear implants**

implantation occurring in 2.5–6% of cases [18, 27]. Vestibular symptoms, such as vertigo and disequilibrium, are present in about one-third of patients postoperatively and are believed to last for more than 1 week after surgery. Most of these symptoms are resolved in weeks; however, patients over 70 years of age are more likely to have permanent vestibular weakness [30].

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

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

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,

Recently, a new topic has come up about cochlear implantation in setting of single-sided sensorineural hearing loss [53]. So far, options such as hearing aids, bone-anchored implants, and contralateral routing of signal (CROS) devices were applied for single-side deaf patients. While these options improve hearing by healthy ear, cochlear implantation restores hearing by deaf ear. Sound localization is a special challenge for patients with unilateral hearing loss.

insertion depth and length are determining factors for intracochlear trauma [24, 33].

reported to improve hearing preservation up to 1 year from implantation [32].

and further studies are required for conclusive results [36, 38–52].

**8.1. Cochlear implantation for single-sided sensorineural hearing loss**

**8. Other applications of cochlear implant**

**7. Hearing after cochlear implantation**

142 An Excursus into Hearing Loss

A hybrid cochlear implant was developed by Gantz et al. with the aim of preserving residual hearing, which has only 10 mm of height [56]. This provides the possibility for stimulating the region responsible for high-frequency hearing in cochlea without stimulating regions responsible for low frequency hearing. Primary studies have revealed that hybrid implant application is associated with better hearing preservation and increased speech perception [35, 36, 57, 58]. In addition to the comparable performance of hybrid implants with conventional ones, patients with hybrid implants had improved music appreciation as a result of acoustic and electrical stimulation combination [56, 57]. Replacement of hybrid implant with full-length implant in a progressive hearing loss improves hearing and word recognition; however, it is associated with a notable additional cost [59, 60].

#### **8.3. Cochlear implantation and Meniere's disease**

Cochlear implantation has been utilized for Meniere's disease, a condition consisted of episodic attacks of tinnitus, hearing loss, and debilitating vertigo spells. Previous studies have shown resolution of related symptoms after cochlear implantation in Meniere's disease patients, although the hearing outcomes are not as acceptable as patients implanted for other reasons [61, 62].
