Cochlear implant: Prosthesis for the inner ear

The inner ear implants also help with complete deafness, which can occur, for example, as a result of a cerebral disease such as meningitis , a skull fracture, after infections such as mumps and measles or a chronic middle ear infection.

What is a cochlear implant and how does it work?

A conventional hearing aid only amplifies sound waves, so its use depends heavily on the residual hearing ability. A cochlear implant, on the other hand, bypasses the inner ear and sends signals directly to the auditory cells. It thus replaces the function of the inner ear.

The cochlear implant takes its name from the cochlea (Latin: cochlea) into which electrodes are implanted. The device consists of two parts. Outside the ear, a microphone and speech processor unit is worn behind the ear like a hearing aid. There is also a magnetic coil that sits on the outside of the scalp and creates the connection to the inner coil on the implant. The acoustic signals picked up from the environment are first converted digitally and transmitted wirelessly to the implant, which is inserted in the skullcap behind the ear. From there, electrical impulses are transmitted to the electrodes, which stimulate the auditory nerves directly in the cochlea. The brain can process the signals and interpret them as noises, tones and voices.

Who is a cochlear implant suitable for?

In most cases, hearing loss can be corrected with hearing aids. But it is not uncommon for those affected to no longer hear adequately, even with a hearing aid, because their hearing ability continues to decrease or they become completely deaf. Then a CI can bring those affected back into the world of hearing. However, implants only make sense if only the function of the cochlea is impaired. The auditory nerve and auditory center must be intact. The CI can be implanted in one ear or on both sides.

In addition to the classic indication for the cochlear implant, there are now other areas of application. For example, patients are provided with a hybrid solution who still have a residual hearing ability for low tones but not for speech. A conventional hearing aid is combined with a cochlear implant. It is also possible to fit a hearing aid in one ear and an implant in the other.

Cochlear implants in children

The implantation of the inner ear prosthesis is of great importance in the treatment of children born deaf or in children who become hard of hearing during speech acquisition. In the first three and a half years after birth , the brain’s ability to process external acoustic stimuli develops. The training of the hearing and speech center is important for learning spoken language and further intellectual development.

If there are no stimuli on the brain, the innate abilities wither away and later can no longer be learned or can only be learned to a limited extent. That is why the use of cochlear implants in children who are deaf, who become deaf very early or who have severe hearing loss is now the common treatment method. Doctors recommend implantation before the age of two, and infants under the age of one are sometimes treated. In the case of older, deaf children and adolescents, the use of a cochlear implant only makes sense if they have previously been fitted with a hearing aid and have thus been able to learn spoken language.

In principle, the chances of being able to hear adequately again with a cochlear implant, both in children and in adults, are better the shorter the time between complete deafness and implantation.

The implantation, the subsequent rehabilitation and aftercare are very expensive: costs of 40,000 euros are normal. However, if there is a corresponding indication, the statutory health insurance companies pay 100 percent of the CI care, including maintenance, technical adjustments and possibly the replacement of individual components. In contrast to hearing aids, the battery supply is also paid for by the health insurance company. With private health insurance companies, this depends on the provider and the selected tariff.

Contraindications for cochlear implants

A prerequisite for the use of a cochlear implant is that the auditory nerve is functioning. This is the only way that the signals sent by the implant can be transmitted to the brain. The cochlea – the cochlea – must also be developed and intact.

After the insertion of the cochlear implant, an extensive rehabilitation and learning phase is necessary so that the implant can also successfully help the CI wearer. The basis for this is a certain degree of learning ability and cooperation with the patient. In the case of severe mental and psychotic illnesses, the most severe intellectual deficits and psychomotor development disorders, CI care will therefore be avoided.

Serious general illnesses with the risk of impaired wound healing, chemotherapy for cancer, cramps or active infections (e.g. middle ear infections) are further contraindications. A cochlear implant can be used in these cases after successful treatment.

This is how the implantation works

Since the operation and subsequent therapy is expensive and lengthy, a hearing aid that is already in use should also be optimized beforehand. Extensive tests and examinations are necessary before doctors recommend cochlear implants. This includes:

• Examination by general and ENT doctor
• extensive hearing tests in which residual hearing ability and other values ​​are determined
• Examination of the anatomical ear structures of the middle ear and inner ear
• Magnetic resonance imaging of the head and auditory canals

The vaccination status is also checked and, if necessary, vaccinated against pneumococci and Haemophilus influenzae type B to reduce the risk of meningitis (inflammation of the meninges).

The operation itself takes between two and four hours and is performed in specialized clinics under general anesthesia . First, a skin incision is made on the bone behind the auricle, the skin is folded away and the skull bone is exposed. The surgeon mills an indentation into the bone in which the implant can be placed. From there, direct access to the cochlea in the inner ear is drilled through the skull bone. The electrodes are placed and fixed there. During the operation, it is checked whether the signals sent out can actually reach and stimulate the auditory cells.

The operation is performed with the help of microscopes and requires a lot of manual skills and experience from the surgeon. Because in the surgical field there are important blood vessels and facial nerves as well as the center of balance.

After the operation, the patient receives antibiotics for a few days. Healing takes about four weeks before the rehabilitation phase begins with speech processor adjustment and auditory training.

Risks of CI surgery

Basically, complications during the implantation of the hearing prosthesis are rather rare. Possible risks are:

• Infections of the middle ear, which can also spread to the inner ear and, in rare cases, can lead to meningitis or adhesions in the inner ear
• Taste disturbances and paralysis in the face due to injury to the facial nerve and taste bud
• Violation of the structures of the cochlea and auditory nerve fibers
• loss of residual hearing
• Wound healing disorders
• Intolerance of implantation material
• Swelling of the auditory structures, dizziness and tinnitus during the healing phase
• rare technical complications, defects of the implanted parts

Disadvantages of the cochlear implant and limitations for the user

Cochlear implants are designed for understanding spoken language. Other acoustic signals often require technical accessories (such as microphones, amplifiers, phone adapters) to improve hearing in certain environments (classrooms, offices, conferences) and situations (when listening to music or on the phone). The sound is also initially perceived by many as unnatural. However, this usually changes after the first few weeks of listening with the new device.

Implant wearers depend on the technology throughout their lives and are usually tied to a clinic, a manufacturer, its system and accessories. Although defects in the outer parts can be corrected, technical faults in the actual implant often make explantation or reimplantation necessary.

The external appearance with the apparatus behind the auricle and additional transmission coil next to or above the ear may also take some getting used to. Some CI wearers find this annoying because their hearing impairment is obvious.

The parts of the hearing prosthesis that are attached to the outside of the head are sensitive and must be protected from water, sand, dust and impacts. The microphone and sound processor must be removed when showering, swimming and bathing or protected with a case.

There are a number of other restrictions for CI wearers in sports. In sports that involve physical contact or where balls are involved ( football , volleyball , squash), the external parts of the hearing prosthesis should also be removed. Alternatively, the system can also be secured with a headband or tape. Certain martial arts that can result in hits to the head (boxing, rugby, judo, and others) are not recommended for CI recipients.

Headgear and helmets (for motorcycling, cycling , horseback riding) usually do not pose a problem. The implant and the external parts are well protected, the padding of the helmets may need to be adjusted so that there is no pressure on the implanted site.

Security checkpoints with metal detectors, such as those used at airports or in shopping malls, can cause interference in the cochlear implant that those affected can hear. An alarm can also be triggered. CI wearers are recommended to switch off the device in such situations or to inform the staff about the implant.

A number of medical examinations and therapies are only possible to a limited extent for CI wearers. During the examination in the magnetic resonance tomograph (MRT), the magnetic fields can lead to disturbances in the cochlear implant and to the implanted magnetic coil being displaced. However, most implants are suitable for MRI examinations with low magnetic field strengths. In addition, the manufacturers prescribe safety measures (e.g. compression bandages on the head, certain positions in the MRI device).

Other examinations such as X-rays are possible without any problems. Certain treatment methods that use strong radiation, electric currents or magnetic fields are also only possible to a limited extent. Usually, the sound processor must be turned off and removed prior to such examinations or therapy. The CI wearer receives further rules of conduct during the initial briefing.

Hearing training after CI operation

The hearing prostheses enable the patient to participate in social life. However, they cannot be compared with natural hearing or common hearing aids: environmental noises, voices and music sound completely different to CI users. Patients report that it sounds metallic and like Mickey Mouse.

The alienation of the acoustic world is so pronounced that new CI wearers have to learn to reassign the noises. In any case, they need hearing training from a therapist, for example a speech therapist or audio therapist. In addition, the new world of noise can also be depressing. Anyone who has had a few hours of muffled hearing after a flight will be able to understand this: they have the feeling of being outside of everything. The hearing experience for CI wearers is similar: at first they may feel isolated from their environment or stressed and may develop psychological problems.

During the hearing training, the CI wearer is played various everyday noises and sounds of musical instruments, for example, which he has to identify. The patient also practices recognizing speech sounds. Initially, it is difficult for patients to recognize individual sounds. That’s why the listening training is done in stages: you start with whole sentences and then move on to words. Only then are individual vowels and consonants trained.

The rehabilitation and training after the implantation of the hearing prosthesis is a lengthy process and demands patience and motivation from the person concerned. He starts the basic therapy about four weeks after the operation – now the speech processor is set up and the first hearing and speech tests are carried out. During this basic therapy, the CI wearer also learns how to use and care for their device and how to recognize faults.

In the first month after the initial appointment, another four to eight sessions take place, then one to two sessions per month up to the sixth month. Hearing and speech tests as well as settings on the CI are then repeated at increasingly longer intervals. At least one session per year is recommended. CI wearers are therefore dependent on lifelong care from doctors, language trainers and technicians.