Use of a hearing aid in the contralateral ear or bilateral cochlear implants are highly successful interventions. Indications are also being expanded to include patients with single-sided deafness (with normal hearing on the contralateral side), moderate hearing loss and tinnitus occurring in association with severe hearing loss.
Devices that incorporate a fusion of a cochlear implant with a hearing aid assist patients with residual aidable hearing. As most of these patients have residual hearing in the lower frequencies with severe high-tone hearing losses, the aim is for the cochlear implant to rehabilitate the higher (speech) frequencies while preserving the lower tones. When successful, this combination of ‘electroacoustic’ hearing can produce a hearing result with near normal listening experience; however, the risks of losing functional residual hearing during surgery to place the implant should be accepted.
Recognising potential candidates
Adult patients with severe hearing loss should be considered for a cochlear implant when their hearing aids are optimally adjusted but still give poor hearing experiences in quiet listening environments. In common terms, this level of hearing impairment is reached when the patient is having difficulty understanding phone conversations with familiar voices and subjects. If readjustment of the hearing aids by the hearing aid provider fails to improve the situation then referral of the patient to an ENT surgeon with an interest in cochlear implantation should be considered. A recent audiogram as well as the results of previous hearing tests will be useful in determining the rate of progression of the hearing loss.
Cochlear implant surgery
Surgery to place a cochlear implant has evolved considerably since the first operations were designed 40 years ago. The procedure takes about two hours and recovery usually requires an overnight stay in hospital. It can take four to five days before most patients can return to their usual routine and social activities, including driving and work.
Surgery involves performing a limited mastoidectomy to access the middle ear cleft and cochlear structures. A small opening measuring about 1 mm in diameter (cochleostomy) is then drilled into the cochlea to allow placement of the intracochlear electrode close to the auditory nerve endings (Figure 5). The implant is tested to confirm its function and correct placement within the cochlea. Patients are typically given a general anaesthetic; however, more recently, surgery has been performed under local anaesthetic with the patient fully awake. This obviates the need for general anaesthesia and its potential to cause postoperative confusion or further cognitive decline in the very elderly patient. The surgery is well tolerated.