Hearing Preservation surgery in cochlear implantation

Cochlear implants are now proven options for patients with profound hearing loss, who do not derive benefit with hearing aids. The ability of hearing aids to sufficiently amplify sounds in frequencies over 2000Hz with losses over 90dB is poor. So, for someone who has hearing loss over this figure, especially children who are born with profound loss, speech is affected unless we interfere very early. Initial doubts about benefits from cochlear implantation and the fear of the deaf community that this surgery causes great pain and no benefit for deaf children are slowly fading away in the light of very strong scientific evidence. Good cochlear implant teams have shown that, with early surgery, right candidate and efficient habilitation, many young children with profound hearing loss speak and hear as well as their normally hearing peers.

While there is still euphoria among the researchers about the success of what arguably is the most amazing scientific discovery of the past fifty years, there is a growing population of people who are not so deaf, but cannot really be helped with hearing aids. They are ones with significant residual hearing in the low frequencies, but poor hearing in the higher frequencies. They miss finer aspects of speech and suffer in silence while still being told to “adjust” to their hearing aids.

Technology has come to the help of such patients. We are now faced with many options to preserve residual hearing. The first of them is the use of medication. From the Royal Australasian college of surgeons, Stephen O’Leary and colleagues have studied the use of steroids in the cochlea during surgery to preserve residual hearing. They discovered that by keeping a steroid soaked gel foam for twenty minutes on the round window membrane, significant preservation of residual hearing can be achieved, but this has not been statistically significant to be offered as a general recommendation.

Prof. Skazinsky and others in Warsaw, Poland prefer to give intravenous dexamethasone for patients with residual hearing who opt for cochlear implantation. He has a large series of over 2500 patients who have “Partial” deafness and in who over 65% of them retained their pre implant hearing levels. However, since he uses an exclusive round window insertion, it is doubtful whether it is the technique of surgery that prevents bone dust and blood from entering the cochlea, or the steroid, or both that is more instrumental in getting these results.

Round window insertion has obvious advantages. There is no drilling, so no shearing force on the basilar membrane. Since the round window membrane is opened with a pick, no blood or bone dust enters the cochlea, both detrimental to hearing preservation. No suctioning of the cochlear fluids happen, and the implant is positioned in the scala tympani, all positive factors for hearing preservation. There are some cons, too. It is technically difficult to perform. The surgery requires clear skeletonization of the facial nerve and its attendant dangers is unskilled hands. In every case, the round window may not be clearly visible. However, this holds promise as the most logically sound option for “safe” surgery.

In our Institute, we have been performing round window insertions for patients who have good low frequency residual hearing, and of late, have been doing this for all patients, as the results have been so encouraging. First, the facial nerve is clearly identified and the bone over it is thinned without the nerve being exposed. The round window membrane is identified and the edges drilled away till the whole membrane is clearly visible. The rest of the bone work including the well for the receiver stimulator and the electrode path are then drilled and the entire area cleaned with copious irrigation, and hemostasis secured. The implant is then taken out of its package and fixed to the well. Finally, the membrane of the round window is penetrated by a fine pick and the electrode is gently, but quickly inserted. This technique is easily adaptable with the very flexible Medel electrode. The other FDA approved companies are also coming up with very thin flexible electrodes to facilitate round window insertion.

This technique holds great promise. Data from our center and other centers worldwide shows that in people with serviceable residual hearing, over 85% of them have hearing preservation. Of course, thereal application of this technique would be to use “hybrid” implants, where the low frequency is aided by hearing aids, and the higher frequency with the cochlear implant. These devices are still partly investigational, but evidence is strongly building up for widespread use. However, surgical techniques have to be perfect and well validated for this ideal to be achieved. We too believe that hearing preservation is important for the future and we should be prepared when the time comes. Hence, this technique is now universally followed in our Institute.

This aspect of surgery also dispels the greatest argument that some had towards cochlear implants- in that it destroys whatever hearing that was left behind. Like the learned men say, the progress of scientific thought is inexorable. We may be saving the cochlea for future technologies like hair cell regeneration or genetic therapy for the future by following this soft approach to cochlear implantation

Welcome to my ENT department which offers comprehensive medical and surgical services at affordable cost to the patients in Kerala and beyond. The prime object behind this movement is to provide all sorts of advanced treatment in ENT,

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