1. What is a cochlear implant?
The human cochlear hair cells are the sensory cells that receive sound. When the cochlear hair cells are severely damaged, severe deafness can occur. A cochlear implant is an electronic device that replaces damaged hair cells and regains sound signals through the electric auditory nerve.
2. Structure of the cochlear implant
The cochlear implant consists of an in vitro and an in vivo device. The in vitro part consists of a microphone, a speech transducer, and a transmitter coil; the in vivo part consists of a receiver coil, a processor, a stimulating electrode, and a reference electrode.
3. How a cochlear implant works
The microphone receives the acoustic signal, which is digitally encoded by the speech processor and transmitted through the transmitter coil via the skin to the receiver coil inside the cochlear implant, where it is transmitted to the stimulation electrodes with the appropriate frequency and current intensity.
4. What is speech coding strategy?
A speech processor’s approach to processing auditory signals is called a speech coding strategy. The main speech compilation strategies commonly used today are the fast continuous interval sampling strategy (CIS strategy), the spectral peak sampling strategy (SPEAK strategy), and the multiple peak sampling strategy (MPEAK strategy).
5. Who is suitable for cochlear implantation?
Cochlear implantation varies from country to country and region to region, with most countries having the following selection criteria
Selection criteria for pediatric patients
(1) Severe or very severe sensorineural hearing in both ears (PTA 3Fs ≥ 80 dB).
(2) Age 18 months (FDA approved) to 9 years.
(3) Hearing improvement is basically ineffective or minimally effective after 3 to 6 months of hearing rehabilitation training with appropriate hearing aids.
(1) Children under the age of 5 cannot establish effective auditory communication skills.
②Children above 5 years old, open speech cognition ≤ 50%.
(③Auditory hearing threshold at 2KHz and above is outside the range of the speech spectrum.
(4) No contraindication to surgery. For example, acute and chronic external otitis media episodes and other systemic organs are not suitable for surgery.
(5) Parents and family have a strong desire to improve the hearing of the child.
(6) Good family support and good family listening environment.
(7) Correct understanding of cochlear implants and appropriate expectations.
(8) A complete hearing and speech rehabilitation program is needed for pediatric patients.
Selection of adolescent prelingually deaf patients (generally defined as prelingually deaf patients aged 9-20 years): refers to deafness that occurred prior to having language learning experience.
(1) Severe or very severe sensorineural deafness in both ears (PTA 3Fs ≥ 80 dB).
(2) History of hearing aid wear since childhood, history of hearing or speech training.
(3) Ineffective or very ineffective hearing aids with a speech recognition rate test score ≤ 40% in the best hearing aid listening environment
(4) Can use oral/aural communication or lip-reading communication.
(5) No contraindications to surgery. If acute and chronic external otitis media episodes and other systemic organs are not contraindicated for surgery.
(6) Have the support of family and friends, a strong personal desire to return to the audible world, and good psychological qualities.
(7) There is a good environment for acquiring cultural knowledge. If you continue to study at a school for the deaf, you should have a good listening training environment.
(8) Have a correct understanding of cochlear implants and appropriate expectations.
Post-lingual deafness patient selection: refers to deafness that occurs after existing language and oral language learning experience.
(1) Severe or very severe sensorineural deafness in both ears (PTA 3Fs ≥ 80 dB).
(2) Ineffective or very ineffective hearing aids, with a sentence perception test score of ≤ 40% in the listening environment of the best hearing aid.
(The latest FDA supplemental criteria for adults with open phrase recognition test scores ≤ 30% in the best hearing aid listening environment).
(3) No contraindications to surgery. For example, acute and chronic external otitis media episodes and other systemic organs are not contraindicated for surgery.
(4) Have the support of family and friends.
(5) Have a correct understanding of the cochlear implant and appropriate expectations.
(6) Have appropriate psychological quality and subjective motivation.
6. Can I get a cochlear implant if I have an inner ear malformation?
Cochlear implants can be performed with good results for many inner ear malformations, such as large vestibular canal syndrome, Mondini syndrome, and common cavity malformation. If the inner ear cavity itself is small, some of the electrodes will need to be closed. Too many closed electrodes can affect the hearing results. In severe dysplasia, such as Micheal malformation, severe malformation such as absence and narrowing of the inner auditory canal. Cochlear implantation is generally not done because the electrodes cannot be implanted.
7. Why is it important to have cochlear implant surgery as early as possible?
Around 1 to 3 years old is the best time for language learning and the development of the auditory center. Due to deafness, the auditory center will atrophy if it is not stimulated by acoustic signals for a long period of time. Once atrophy occurs, it will be very difficult to regain it. Therefore, it is important to receive cochlear implant treatment as soon as possible once the diagnosis is clear. Patients with post-lingual deafness can have a wider time frame, but again, the earlier the cochlear implant is performed, the better the outcome.
8. How is the cochlear implant procedure performed?
Under general anesthesia, a curved incision is made behind the ear, the skin is cut, subcutaneous, and the mastoid bone is exposed. A bone bed of the appropriate size is ground into the posterior mastoid bone with an electric drill according to the size of the graft. Several small holes are ground around the bone bed with a small cutting drill to allow for threading and fixation of the graft. A mastoid opening is performed to open the bulbar sinus. The posterior tympanic chamber is opened. The anvil stirrup joint and the tympanic capsule are exposed, and a 1.2 mm diameter diamond drill bit is used to open a window in the tympanic capsule. The test electrode is inserted. The cochlea to be transplanted is then placed into the prepared bone bed, and the stimulation electrode is inserted into the cochlea through the window in the tympanic capsule, with the reference electrode placed under the temporalis muscle. The graft is secured with sutures. The subcutaneous tissue and skin are sutured layer by layer. The wound is bandaged with pressure.
9. What are the complications of cochlear implant surgery?
1) Postoperative wound non-healing or hematoma formation.
2) Facial paralysis, which occurs in about 2% of cases. Most of them are transient and can be treated conservatively.
3) Non-auditory irritation, including facial nerve irritation, pain, vestibular spinal nerve reflex, etc.
4) Electrode dislocation, which often occurs in the mastoid radical cavity and requires re-surgical implantation. Therefore, attention should be paid to the intraoperative fixation of the electrode.
5) The implant malfunctions and needs to be replaced. According to European statistics, 95 percent of cochlear implants are still in use after 10 years. The main reasons for replacing the cochlear implant are: trauma, mechanical failure, and the patient’s own desire to replace the product.
10. What do I need to be aware of after the surgery?
(1) First of all, an X-ray will be taken on the first day after surgery to observe whether the electrodes are correctly implanted.
(2) Change the dressing daily and pay attention to the condition of the flap.
(3) The stitches are removed 10 days after the operation, which is later than the normal operation.
(4) Turn on the cochlear implant in one month after the surgery, and perform the commissioning as needed thereafter.
11. Why do I need speech training after cochlear implantation?
Post-operative rehabilitation includes commissioning and comprehensive hearing and speech training. Children with prelingual deafness are just starting to hear sounds after the cochlear implant is turned on. They have a hearing age of 0 and need to start from the beginning, hear sounds, gradually discriminate, understand, and then begin to speak. Therefore it takes longer than normal children to adapt to training.
12. Do I need to wear a hearing aid in the other ear without a cochlear implant?
The hearing center without acoustic stimulation will atrophy over time. In a survey, patients who wore hearing aids on one side for a long period of time had a significant decrease in speech intelligibility during a hearing test, although the pure tone threshold did not change much on the side without hearing aids, indicating a degenerative change in the auditory center. Therefore, in order to avoid atrophy of the auditory center on the other side, it is theoretically possible to use a cochlear implant while wearing a hearing aid on the other side. However, the prerequisite for wearing a hearing aid is a certain number of hair cells. If too many hair cells are missing, the sound heard after using the hearing aid is often distorted, and this can interfere with the use of the cochlear implant. For this reason, patients are often reluctant to use their hearing aids after cochlear implantation.
13. What are the advantages of bilateral cochlear implants?
(1) It conforms to normal hearing physiology and provides a sense of stereo sound.
(2) Improved speech resolution, especially in the presence of environmental noise.
(3) Improved hearing threshold.
(4) Enhanced orientation.
(5) Improved balance.
14. What is the timing of bilateral cochlear implant surgery?
(1) Phase I surgery: Bilateral cochlear implants can be performed simultaneously.
(2) Phase II surgery: Bilateral cochlear implants > 6 months apart
15. What is the speech training after cochlear implantation?
The ability of a deaf child to communicate with others in a more fluent spoken language will increase their self-confidence and will play an important role in their return to mainstream society.
We must be more tolerant and considerate of deaf children in the early stages of learning to speak. Even for an able-bodied child in the early stages of learning to speak, speech can change from unclear to clear, from a sound to a sentence, which is the inevitable process of language development.
Speech is the material basis of spoken language, and functional language training is necessary for deaf children to acquire spoken language. Language function training can help deaf children appreciate the essentials of pronunciation, master pronunciation skills, develop correct phonological habits, and lay a solid foundation for them to be able to speak every word sound fluently in the country.
Pronunciation ability is closely related to hearing, so pronunciation training cannot be carried out in isolation, but must be closely coordinated and synchronized with auditory training.