Cochlear Implant

What Is a Cochlear Implant?

The cochlear implant, which can be distinguished from conventional hearing aids, is an electronic hearing aid that consists of two parts. An external component with a built-in microphone and speech processor is placed behind or in front of the auricle. An inner part, which is equipped with a receiver coil and electrodes, is implanted in the temporal bone and has direct contact with the human inner ear's cochlea.

The battery-operated outer component communicates wirelessly with the inner component. The energy supply is provided by induction via magnets located on the inside and outside. The signals are encoded via radio waves and transmitted as electrical impulses through the inner component to the auditory nerve and the brain's auditory center.

Hearing - Healthy People and Patients with Cochlear Implants

Typically, the hearing process in a healthy person proceeds as follows: sounds, speech, and music are picked up as sound waves by the auricles, which act as a large funnel, and transmitted from the external auditory canal to the eardrum. The eardrum is set in vibration and transmits the sound waves via the malleus, incus, and stapes in the middle ear to the inner ear. Up to this point, the sound waves are only transmitted. Once they reach the inner ear (cochlea), the sound waves are converted into electrical impulses. There is fluid in the cochlea, which winds like a snail shell, that is set in motion causing activation of the fine sensory cells in the membrane of the inner ear and transmits an impulse that reaches the hearing center in the brain via the auditory nerve, where it is processed further.

If this system is disturbed, and the inner ear's sensory cells no longer respond correctly to impulses, an electronic cochlear implant may be viable. The cochlear implant works as follows: the built-in microphone in the outer component receives sound waves in sounds, speech, and music and sends them to the speech processor. The speech processor filters important signals such as speech from unimportant noise, convert them into radio waves, and sends them directly through the skin and bone to the inner component. The radio waves reach the so-called receiver coil, which converts the radio waves into electrical impulses. The impulses are picked up by the electrodes and transmitted to the auditory nerve, which is stimulated and transmits the sensory stimulus to the brain for further processing, just like in healthy hearing.

Who Is Suitable for a Cochlear Implant?

All damage that is limited to the inner ear can theoretically be treated with a cochlear implant. The precondition for successful therapy is that the auditory nerve and the brain's auditory center are undamaged.

In principle, the cochlear implant can be used for adults and children. A distinction is made between post-lingual (predominantly adults) and pre-lingual (mainly children) deafness. In pre-lingual deafness, mostly children are affected who have not yet learned to speak. With the help of the CI and speech therapeutic and pedagogic support, they have to learn to understand what they hear and articulate. If therapy is started early, the chances of normal hearing and understanding are quite good.

Post-lingual deafness mostly affects adults who have become deaf or suffer a hearing loss due to trauma, infection, tumors, intoxication, or genetic causes. Since adults have usually already learned to speak, greater success is achieved sooner, but therapy should be started as early as possible, too.

Preliminary Examinations for a CI Implantation

Before a cochlear implant can be placed, the ENT physician must carry out specific examinations. He uses classic audiometric procedures (e.g., Weber & Rinne test) to check the functionality of the auditory nerves and the auditory pathway. The promontory test is also frequently used.

The ENT physician punctures the eardrum at the first turn of the cochlea (this is the so-called promontory) with a very fine needle and places it in the tympanic cavity. If the auditory nerve is functional, the patient typically perceives a hearing stimulus as soon as the fine needle is electrically stimulated. While adults' active feedback can support these examinations, the situation is more difficult in children, which requires a careful procedure for the ENT physician. To diagnose congenital deafness in children, the ENT physician also uses the otoacoustic emissions test, which already takes place during the screening examinations in children.

Besides these tests, CTs, MRIs, and X-rays, imaging procedures, in general, provide information about the patient's anatomical structures and possibilities, which determine and localize the surgical area. These images must, of course, be taken before any cochlear implant is placed.

Finally, the ENT physician analyzes the patient's social and psychological conditions together with psychologists and pedagogues to find out about the patient's general ability to communicate and psychosocial state. In children, factors such as the general level of language and development at the time of implantation are also considered. All these parameters determine the individual therapy plan and success.

How Is the Cochlear Implant Placed?

After a detailed consultation and informing the patient and possibly relatives regarding the surgery and aftercare, the cochlear implant is usually implanted under general anesthesia.

The ENT physician will drill a small hole in the mastoid process's bone bed, which is located at about the level of the earlobe just behind the ears. Then the ENT physician implants the prosthesis into this bone bed. The surgeon places the corresponding electrode, which converts the radio waves into electrical signals, directly in the cochlea. To restore three-dimensional hearing and improved speech understanding, patients often receive two cochlear implants, one for each ear. The surgery should be carried out in a specialized clinic or practice to ensure an uncomplicated procedure and avoid secondary damage. The surgery is quite simple, and postoperative complications such as nerve injuries and infections are quite rare.

How Is Aftercare?

The training and aftercare program is carried out by a team consisting of doctors, pedagogues, speech therapists, psychologists, audio therapists, and phoniatric specialists. If the patient is still a child, teachers who specialize in the deaf will also play a role. The wound healing time is about eight weeks after the successful surgery. After this time, the speech processor can be calibrated. At the same time, intensive speech and hearing training take place, which is much shorter for adults who have become deaf during their lives and have already learned to speak than for children who have been congenitally deaf. Children must first learn to perceive and understand hearing and speaking as a completely new sensory impression to articulate like healthy people.

How Promising Is the Cochlear Implant?

If the surgery has been successful, and the patient actively participates, the chances of achieving normal hearing and everyday speech are excellent. Patients can learn to recognize and block out background noise. They can distinguish between voices and gain a speech understanding that is so good that, statistically speaking, in 9 out of 10 cases, they can easily talk on the telephone.

The cochlear implant enables the patient to have an improved life quality. It allows them to communicate with their environment and break through the social wall.