What is the difference between a cochlear implant and a hearing aid? Is it effective in improving hearing?

Author: Li Yongxin, Chief Physician, Beijing Tongren Hospital, Capital Medical University

Member of the Otolaryngology and Head and Neck Surgery Branch of the Chinese Medical Association

Reviewer: Liu Yuhe, Chief Physician, Beijing Friendship Hospital, Capital Medical University

Vice Chairman of the Science Popularization Branch of the Chinese Medical Association

A cochlear implant is an electronic device that helps deaf patients regain their "new voice". Everyone is familiar with hearing aids, but is relatively unfamiliar with cochlear implants. Today we will learn about cochlear implants.

1. What is the difference between a cochlear implant and a hearing aid?

Cochlear implants and hearing aids are two different devices, essentially different in nature and with completely different mechanisms of action.

Hearing aids amplify sounds so that people can hear better.

How does a cochlear implant enable deaf patients to hear sounds? Under normal circumstances, the auricle collects sound waves and transmits them to the ear canal, stimulating the eardrum and ossicular chain to vibrate. The eardrum and ossicular chain vibration transmit the sound stimulation to the spiral ganglion cells of the cochlea through the inner ear hair cells. The spiral ganglion cells transmit the action potential to the auditory nerve, which transmits this potential to the brain, thereby producing hearing. This is a normal auditory pathway.

A cochlear implant replaces the hair cells in the cochlea and directly stimulates the spiral ganglion cells of the cochlea, also called auditory cells, through electrodes. The auditory cells then transmit the electrical stimulation impulses to the brain through the auditory nerve fibers, thereby producing hearing.

In the traditional impression, most hearing aids are hung on the ears. With the rapid development of science and technology, nowadays, hearing aids can also be hidden deep in the ears.

The cochlear implant consists of two parts: an internal device and an external device. The internal device is implanted in a suitable position behind the ear. In addition, electrodes need to be implanted into the cochlea. The external device and the implant are attached by magnets. The internal and external devices are combined together to form a cochlear implant.

Figure 1 Original copyright image, no permission to reprint

Generally speaking, hearing aids are for patients with moderate or moderately severe hearing loss, while cochlear implants are for patients with severe, profound, or even complete hearing loss. They are suitable for different groups of people.

2. Will the effect be better if a deaf patient receives a cochlear implant earlier?

Deaf patients are divided into two categories: one is that they cannot hear before they learn a language, which is called pre-lingual deafness. The other is that they lose hearing due to disease or trauma after they learn to speak, which is called post-lingual deafness.

Both pre-lingual and post-lingual deafness can use cochlear implants, but the effect is closely related to the timing of implantation. For example, a 7-year-old child with bilateral extremely severe sensorineural hearing loss, or even complete deafness, has never worn hearing aids and has never received auditory stimulation in both ears. The effect of cochlear implants is usually worse than that of children who have had cochlear implants implanted earlier, because his speech center is likely to have degenerated. For example, if a person becomes deaf in adulthood and has a cochlear implant implanted very shortly after the deafness, the effect may be very good. If a cochlear implant is implanted after 30 years of deafness, the effect will definitely be different from that of the former.

Therefore, once it is clear that drug treatment is ineffective after hearing loss, a cochlear implant should be performed as soon as possible. The shorter the history of hearing loss, the better the effect of the implant. There is a bottom line to this shorter period. Generally, cochlear surgery is not performed within a short period of time (3-6 months) after the onset of hearing loss, because theoretically there is still a possibility of recovery. Once it is confirmed that there is no recovery, it is recommended that the patient consider cochlear implantation as soon as possible, of course, with the exception of patients with cochlear ossification.

Figure 2 Original copyright image, no permission to reprint

In theory, deaf patients of all ages can have cochlear implants. Even 90-year-olds, if in good physical condition, can tolerate general anesthesia, and have high requirements for hearing quality, can undergo cochlear implant surgery without being affected.

3. Is cochlear implant a minimally invasive surgery?

Initially, cochlear implant surgeries were performed with large incisions, which were relatively traumatic and rough. In order to minimize trauma, achieve better results, and achieve aesthetic results, the concept of minimally invasive surgery was introduced.

The concept of minimally invasive surgery can be divided into two parts: Aesthetically speaking, it is a small incision, but this is not all of minimally invasive surgery. The true meaning of minimally invasive surgery is that the trauma inside is also small. From the outside, it is a small incision, and from the inside, the trauma is also small. This is the goal of minimally invasive surgery.

When implanting a cochlear implant, a small incision is usually made behind the ear along the skin texture to insert the cochlea. This will not cause a large scar or hair loss. We also draw on plastic surgery techniques to suture the wound, using absorbable sutures, small needles, and thin threads to suture layer by layer. After the incision has healed, you will generally not feel any traces of the incision if you touch it with your hands, except for people with scar-causing constitutions, which may leave scars.

At present, whether for children, adults or the elderly, minimally invasive surgery is being sought. From the beginning of the incision to the end of the cochlear implantation, it takes about 40 minutes to 1 hour. Of course, for some special cases, such as severe deformity and severe ossification, the time will be relatively longer.

4. Does a cochlear implant require regular adjustments?

A cochlear implant is like a miniature computer and needs to be debugged according to the patient's needs and rehabilitation level. It is usually turned on 3-4 weeks after surgery. After the first turn-on, it may be adjusted once a month, and then again once a month. Depending on the patient's adaptation, it may be debugged again in 1-3 months, and finally debugged at least once a year. In theory, regular debugging is beneficial to patients, but cochlear implants need lifelong debugging.

Whether you are elderly, middle-aged, or a child, theoretically, you can get certain benefits after a cochlear implant. The key lies in the timing and cause of the implant, whether there is inner ear malformation, and whether the patient is pre-lingual or post-lingual. If the doctor recommends a cochlear implant and you have a great need for hearing, then do it as soon as possible and actively rehabilitate in the later stage to achieve the best results.