Surgical therapy of deafness: cochlear implant and implantable prostheses
When is this procedure indicated?
Hearing loss is a decrease in hearing ability that can be caused by several diseases and conditions. Hearing loss can be of following types:
- Transmissive, i.e. due to poor sound conduction by the outer and middle ear (eardrum and ossicular chain): earwax plugs, acute and chronic otitis, otosclerosis, etc.;
- Neurosensory, caused by diseases that affect the "noble" parts of the hearing (cochlea and auditory nerve): presbyacusis, sudden hearing loss, Meniere's disease, acoustic neurinoma, meningitis, trauma, ototoxic drugs, complications of otitis, genetic and autoimmune diseases, etc.
Generally, while transmissive hearing loss can be treated with drugs or surgery to restore good hearing, in cases of neurosensory hearing loss the therapeutic alternatives are represented by different hearing aids.
Up to a certain hearing loss, a traditional hearing aid may be used. A hearing aid is an instrument that uses a microphone that captures sound, amplifies it (increases the volume) and through a small speaker sends the amplified sound to the ear. There are different types and models of hearing aids: they are worn behind the ear (behind-the-ear) or inside the ear canal (in-the-ear) and have different characteristics and degrees of "power". All of them, however, have a limit in the amplification of the signal, that is, they work up to a certain degree of deafness: the more the device has to increase the volume, the more the sound is distorted, of poor quality, and therefore you will not understand anything ("I hear some noise, but I do not understand the words").
At this point, that is, when the hearing loss is "severe / profound" (or at least when the prosthesis no longer offer a "gain" for hearing), for some years it is possible to intervene with a special prosthesis: the cochlear implant.
How is it performed?
Basically, the implant consists of 2 parts:
- Processor : is similar to the hearing aid, it is worn behind the ear, contains the battery and microphones that capture sounds;
- Coil : is a magnet connected by a small cable to the processor and used to make the external part communicate with the internal one;
- The actual implant , which encodes the sounds transmitted by the processor and converts them into electrical stimuli;
- Array : a series of electrodes that are inserted directly into the cochlea in order to electrically stimulate the auditory nerve; the electrical impulse is transformed into a nerve impulse and from here the impulse reaches the brain which interprets the sound as auditory sensation, with all its load of information.
After surgery, the implant will not be functional. The commissioning of the implant, i.e. the activation of the implant will take place 3-4 days after surgery.
When the implant is turned on, patients are often unable to understand everything they hear. In order to achieve a good recovery of hearing, it will be necessary for the patient to follow a program of speech therapy rehabilitation in the hospital and practice at home, following the instructions provided by the speech therapist.
With continued use of the implant and subsequent speech therapy and mapping sessions, the performance of the implant increases week by week as the recognition of sounds and noises improves.
Logopedic rehabilitation in adults is initially carried out with 3 sessions per week of approximately one hour per session. As results are achieved, the frequency of sessions is reduced. Generally, the rehabilitation process lasts from 4 to 6 months. The speed of learning is variable and depends on many factors and in particular on the patient's willingness and psychological state.
During the rehabilitation period, the patient must undergo continuous adjustments, known as "mapping," of the cochlear implant. Adjustments are made over time to adapt hearing perception to the needs of each individual. Mapping and fitting can be performed either in the hospital or through telemedicine.
In the case of foreign patients, the assistance of the speech therapist, rehabilitation and mapping are also guaranteed in the country of origin. It will be the surgical team that will make contact with the countries of origin to ensure the possibility of therapy. In addition, speech therapy can also be carried out at Ospedale San Raffaele, through a cultural mediator, although it is still preferable to carry it out in the country of origin.
The surgery is performed under general anesthesia, so evaluation must be performed by the Anesthesiologist to verify the general conditions (comorbidities and other diseases, commonly used medications, cardiopulmonary function, etc.).
The most common (though generally rare) complications are: hemorrhage, temporary facial nerve palsy, dysgeusia (altered taste).
To minimize risks and complications, facial nerve monitoring is used during surgery; at the end of surgery, before the patient wakes up, electrophysiological tests are performed to assess proper implant placement and function.
In addition, the patient undergoes a CT scan of the ear post-operatively.