**Section 1**

**Surgical Techniques** 

**1** 

*USA* 

**Cochlear Implant Surgery** 

Hakan Soken, Sarah E. Mowry and Marlan R. Hansen

*Department of Otolaryngology, University of Iowa Hospitals and Clinics, Iowa City, Iowa* 

Over the past quarter of a century, cochlear implants (CIs) have become recognized as highly successful auditory rehabilitation devices for individuals with severe to profound hearing impairment. There is ample evidence of the success of electrical stimulation of the

However, the majority of persons with hearing loss are not profoundly deaf and they have some remaining usable hearing. Encouraged by promising results in traditional cochlear implant patients and by improvements in the electrode design and the signal processing, investigators have expanded the indications for implantation. Now in addition to completely deaf patients, selected subjects with residual hearing are eligible for cochlear implantation with modified electrodes. The approach involves preserving existing residual acoustic hearing (low-frequency) in an ear to be implanted. Electrical stimulation is provided via a modified CI for the missing high frequencies to improve speech understanding via combined acoustic and electric (A + E) hearing. The prerequisite for this form of combined stimulation (ipsilateral A + E) is a sufficient degree of residual low frequency hearing in the implanted ear. Most patients with the modified electrodes are able to achieve improved sound perception and word understanding while preserving their residual acoustic hearing (Ching et al., 1998; Hogan & Turner, 1998). The listening condition using only A+E hearing and no hearing aid in the contralateral ear is referred to as "hybrid mode". However, these implant recipients benefit from using a hearing aid in their contralateral ear, a listening condition referred to as "combined mode". This listening situation has the potential to improve speech recognition in both quiet and noise (Gstoettner

Since Gantz and von Ilberg first discussed the possibility of using A+ E stimulation simultaneously in patients with significant residual hearing, the concept of combined electric and acoustic stimulation has provided a focus of interest and research (von Ilberg et al., 1999; Gantz & Turner, 2003). The Iowa Hybrid project stemmed from work by Shepherd and colleagues that showed that preservation of the apical regions of the feline cochlea could be spared anatomically and functionally following limited electrode insertion (Ni et al., 1992; Xu et al., 1997). Developments in technology and "soft" surgery techniques, combined with a better understanding of the structure and function of the inner ear allowed the first patient to be implanted with a modified electrode in 1999 (Gantz & Turner, 2003). Work by groups in Iowa and Frankfurt have targeted hearing-impaired

**1. Introduction** 

inner ear as a treatment for profound deafness.

et al., 2006; Turner & Cummings, 1999).
