Cochlear implant (CI)
For 30 years now, cochlear implantations have been performed in the ENT Clinic at the Klinikum rechts der Isar. At our clinic itself, as well as in cooperation with other institutes of the Technical University of Munich and our international cooperation partners, we are involved in several research projects in order to offer our patients state-of-the-art care.
The CI consultation before a possible operation as well as the follow-up treatment takes place in the friendly rooms of the Munich Comprehensive Hearing Center (Hörzentrum München).
A cochlear implant is not a hearing aid, but a hearing prosthesis. Unlike a hearing aid, it does not act as a sound amplifier to support an injured ear. Rather, it replaces the function of the inner ear by directly electrically stimulating the auditory nerve.
For this purpose, a stimulation electrode is placed as close as possible to the auditory nerve fibers. In CI implantation, it is inserted into the fluid-filled cavities of the cochlea.
The CI system consists of internal and external components:
The sound vibrations are picked up via microphone on the speech processor (1). The speech processor processes the acoustic signal by performing frequency and volume coding (which otherwise takes place in the inner ear) and calculates an electrical pulse pattern. This information is transmitted from the transmitter coil (2), held by a magnet, through the skin to the implant (3). The implant checks the received information and stimulates the auditory nerve (5) via the electrode (4).
Figure: with kind permission of the company MED-EL, Innsbruck
The CI is not an alternative to a hearing aid: A CI is basically only suitable for patients whose hearing ability is no longer sufficient for free speech communication despite the use of powerful conventional hearing aids in the affected ear.
Cochlear implantations are performed in both children and adults. The age range of patients who have been fitted with a CI at the Klinikum rechts der Isar is between nine months and 93 years. If infants born deaf are promptly provided with a CI, almost normal speech development is usually guaranteed.
Both the bilateral treatment with a CI has been established for many years, as well as the CI treatment of patients with unilateral deafness (and hardly restricted opposing ear). Only hearing with both ears enables directional hearing. Hearing with both ears improves speech understanding in noisy environments and is less strenuous.
Especially for children and their parents, hearing/speech development with CI is associated with an intensive work and learning process. In order to get a realistic assessment of the individual requirements, some points should be given special attention and clarified in advance with infants and children. These include the precise diagnosis of possible developmental disorders and chronic diseases, as well as ensuring that the child's environment allows for continuous technical care and language.
Understanding with a cochlear implant must first be practiced: This is because the CI electrode generates a pulse pattern on the auditory nerve that is not identical to the stimulus pattern produced by a healthy inner ear.
When the CI is switched on for the first time (which happens about 4 - 6 weeks after the operation, when all wounds have healed accordingly), the patients immediately perceive sounds or noises over a wide range of frequencies, but they often cannot interpret them correctly and therefore cannot understand speech immediately.
For the initial fitting, we admit our adult CI patients for another week. For most of them the new sound is very unfamiliar. Together with our speech therapists, the patients practice recognizing speech step by step in this new sound experience. In children, in the absence of cooperation, an "objective setting" is also possible using the deducible stimulus responses of the auditory nerve (NRT, ART). In general, a large proportion of patients manage to follow a conversation in a quiet environment after the first week. In adults, the first follow-ups after fitting take place after 3, 6 and 12 months. Subsequently, we perform an annual medical and technical follow-up examination.
Despite optimal fitting and aftercare, only in a few exceptions does a CI achieve a hearing performance comparable to that of a normal hearing person. In general, hearing with the CI requires a significantly increased concentration and as soon as louder ambient noise is added, even a very good CI patient will have difficulties with speech comprehension, especially if the fitting is only one-sided.
The implant is inserted in a one to two hour operation under general anesthesia.
First, the skin is opened directly behind the auricle (the scar is later no longer visible under the hair). In the bone behind the ear a hollow is created for the implant housing, so that it cannot slip later and is not visible as a bulge under the scalp. Now the bone process behind the auricle (the so-called mastoid process) is drilled out millimeter by millimeter under the surgical microscope - this is done with special drills with spherical drill bits.
In this way, the surgeon reaches the middle ear. On the way there, the surgeon identifies the organ of balance, the facial nerve and the gustatory nerve. The integrity of the facial nerve is monitored throughout the entire operation with a so-called neuromonitoring.
In the middle ear, the approximately 1 cm large air-filled space behind the eardrum, there is (in addition to the ossicles) also the entrance to the inner ear, the cochlea. The cochlea is usually opened in the round window niche by cutting the round window membrane, through which the stimulation electrode is inserted about 20 - 30 millimeters deep into the two and a half spiral coils of the cochlea. The opening of the cochlea and insertion of the electrode is done atraumatically (so-called soft surgery) in order to preserve any residual hearing in the best possible way. This site is immediately sealed again, then the electrode cable and the implant are fixed and the skin is closed with sutures.
Directly after the operation, dizziness may occasionally occur, otherwise the procedure is relatively easy and painless. Our patients can usually be discharged within four days.