Factors affecting residual hearing preservation in cochlear implantation

The likelihood of residual hearing preservation in cochlear implantation (CI) is related to surgical factors such as type of cochleostomy (trans-fenestral vs. promontorial), use of lubricants and protective drugs, and device-related factors such as shape, length and flexibility of the array. We investigated the impact of these factors on the hearing preservation rate in adults and children with conventional audiological indications to CI. Eighty-two children aged 1-9 years and 73 adults (16-79 years) received a CI in the right (59%) or left ear (41%). An anterior-inferior promontorial cochleostomy was performed in 143 ears (92%); a trans-fenestral approach was used in 12 (8%). A perimodiolar electrode was implanted in 144 ears (93%), and a straight electrode in the remaining 11 (7%). Overall, some post-operative hearing was retained in 39% of ears. The rate of preservation was higher at the low than at the high frequencies. When correlated with age, side of implant, implant model and type of cochleostomy, the mean threshold variations did not reach statistical significance for any of these variables. A slight trend in favour of better residual hearing preservation in children vs. adults was seen, especially at lower frequencies.