Cochlear Implant - Risks and Disadvantages

Risks and Disadvantages

Some effects of implantation are irreversible; while the device promises to provide new sound information for a recipient, the implantation process inevitably results in shaving of the hair cells within the cochlea, which can result in a permanent loss of some or all residual natural hearing. While recent improvements in implant technology, and implantation techniques, promise to minimize such damage, the risk and extent of damage still varies. Still, the cause of deafness is not always identified before the surgery. It is possible but rare that the surgery does not restore hearing at all.

In addition, while the device can help the recipient better hear and understand sounds in their environment, it is not as robust as the quality of sound processed by a natural cochlea. The main factor in success is with the age of recipient. While cochlear implants restore physical ability to hear, this does not mean the brain can learn to process and distinguish speech if the recipient has passed the critical period of adolescence. As a result, those born profoundly deaf who receive an implant as an adult can only distinguish simple sounds, such as a ringing phone vs. a doorbell, while others who receive implants early can understand speech. The success rate depends on a variety of factors, most critically the age of recipient but also the technology used and the condition of the recipient's cochlea.

The United States Food and Drug Administration reports that cochlear implant recipients may be at higher risk for meningitis. A study of 4,265 American children who received implants between 1997 and 2002 concluded that recipient children had a risk of pneumococcal meningitis more than 30 times greater than that for children in the general population. A later, UK-based, study found that while the incidence of meningitis in implanted adults was significantly higher than the general population, the incidence in children was no different than the general population. As a result, the Centers for Disease Control and Prevention and the Food and Drug Administration both recommend that would-be implant recipients be vaccinated against meningitis prior to surgery.

Rarely, necrosis has been observed in the skin flaps surrounding cochlear implants. Hyperbaric oxygen has been shown to be a useful adjunctive therapy in the management of cochlear implant flap necrosis.

As the location of the cochlea is close to the facial nerve, there is a risk that the nerve may be damaged during the operation. The incidence of the damage is infrequent.

There are strict protocols in choosing candidates to avoid risks and disadvantages. A battery of tests is performed to make the decision of candidacy easier. For example, some patients suffer from deafness medial to the cochlea - typically vestibular schwannomas. Implantation into the cochlea has a low success rate with these people, as the artificial signal does not have a healthy nerve to travel along. Historically, patients with severe congenital anatomic anomalies of the cochlea were considered poor candidates for cochlear implantation. Many studies since 1980s have demonstrated successful hearing outcomes after CI in this group. Blake Papsin et al. in 2005 published the largest series of patients with cochleovestibular anomalies undergoing implantation and found no significant difference in outcomes versus patients with normal anatomy. Michael Pakdaman et al. in 2012 presented a systematic review of studies reviewing cochlear implantation in anomalous inner ears and found increased surgical difficulty and lower speech perception among patients with more severe inner ear dysplasia. With careful selection of candidates, the risks of implantation are minimized.