Deafness has always plagued human beings and has become one of the most common diseases. The World Health Organization estimates that 250 million people worldwide suffer from moderate hearing loss, and the second China Disability Sample Survey in 2006 showed that the total number of people with various types of disabilities in China is 82.96 million, including 27.8 million people with hearing disabilities, and about 800,000 people with severe to profound deafness, and 20,000 to 30,000 new cases of congenital deafness each year. There are many ways to rehabilitate deafness, depending on the nature and degree of deafness, such as outer or middle ear surgery, hearing aids, bone anchored hearing aids or bone bridges, vibrating sound bridges, and cochlear implants. In clinical practice, many deaf patients or parents often ask: “Do I need a cochlear implant if I have a hearing problem? The answer to this question is complex and involves audiology, imaging, genetics, psychology, pediatric or medical evaluation, psychological, intellectual and learning abilities, family conditions and rehabilitation conditions. In general, cochlear implants are currently indicated mainly for patients with severe or profound sensorineural deafness who have poor hearing aid results, meaning that the lesion causing the deafness is located in the cochlea or in the synaptic portion of the cochlear nerve (lesions that are truly located in the cochlear nerve and/or its neural pathways may be less effective or ineffective for cochlear implants). However, the suitability for cochlear implantation depends on whether there are contraindications when the hearing level is sufficient. According to the latest “Guidelines for Cochlear Implantation (2013)” of the Chinese Medical Association’s Otolaryngology-Head and Neck Branch, these questions are answered in detail with regard to audiological and imaging assessments, as follows.
I. The nature and extent of deafness should be clarified.
According to the Cochlear Implant Guidelines (2013), cochlear implants are primarily used to treat severe or profound sensorineural deafness in both ears. To answer the question of the nature and extent of deafness, the necessary audiological tests are required, including pure tone audiometry (children need directional conditioned reflex audiometry), acoustic conductance, 40 Hz correlation potential (AERP) threshold, auditory brainstem evoked potential (ABR) threshold, steady-state evoked potential (ASSR), distortion product otoacoustic emissions (DPOAE), and hearing threshold for hearing aids. All kinds of audiological examinations cannot replace each other, and need to be used in a comprehensive way to complement each other’s strengths and weaknesses. Patients who do not respond to a combination of pure tone audiometry ABR, 40 Hz AERP and ASSR testing have the possibility of an incomplete auditory nerve, and need to be explained to the patient and/or parents that there is a possibility of no auditory response after CI surgery, with a small percentage of false positives and negatives, and that the integrity of the auditory nerve and pathways cannot be completely and accurately evaluated by audiometric testing alone. A combination of imaging tests is required to determine the incompleteness of the auditory nerve and auditory pathway and to decide whether a cochlear implant is appropriate.
The purpose of pure-tone audiometry is to determine the patient’s hearing status (whether there is residual hearing), the degree of hearing loss, and the nature of the hearing loss and the location of the lesion when combined with acoustic conductance. Advantages: simple, easy to operate, can play a role in the initial screening, laying the foundation for other tests. Disadvantages: certain limitations, subjective examination, subject to more interfering factors, related to the operator’s proficiency and the patient’s cooperation, so the credibility is relatively low, to some extent, only for our reference. The test cannot be performed on infants, uncooperative children or adults.
The ABR is an objective test of the auditory pathway from the auditory nerve to the brainstem, and the ABR threshold reflects the electrical activity of the auditory nerve and pathway in response to stimulation (3-4 kHz). 40 Hz AERP threshold is an auditory steady-state response, named for the maximum amplitude of the potential evoked at a stimulation rate of 40 Hz. 40 Hz AERP may originate in the cortex or subcortical midbrain and thalamus, and is primarily a response to low-frequency hearing (3-4 kHz). The ABR is characterized by the fact that it is not influenced by factors such as anesthesia, sedation, sleep and concentration, and can better reflect behavioral hearing thresholds.The ABR has a lower limit: the ABR lacks frequency specificity and mainly reflects hearing at 3 kHz-4 kHz. The determination is an artificial determination, i.e. objective examination subjective judgment, closely related to the state of the machine and equipment, the presence of interference, and the experience of the operator. 40 Hz AERP test can well compensate for the lack of reflection of low and mid-frequency hearing level by ABR, but 40 Hz AERP test is affected by factors such as sleep and sedation anesthesia.
The modulated sound waves are given simultaneously in both ears, and several modulated sounds activate the cochlear basilar membrane at the same time to produce the ASSR. At lower modulation frequencies, the ASSR mainly originates from the cortex; at higher modulation frequencies, the ASSR mainly originates from the brainstem. Whether ASSR is elicited or not is based on a statistical basis, using the so-called signal-to-noise ratio to eliminate the interference of noise, so there are false positives and false negatives. advantages of ASSR: rapid, non-invasive, good frequency specificity, good correlation with behavioral hearing threshold, objective test method and objective result determination. Limitations: There are false positives and false negatives.
Otoacoustic emissions (DPOAE) are divided into spontaneous and induced OAE. otoacoustic emissions induced by transient sound and aberrant products are called transient otoacoustic emissions (TEOAE) and aberrant products otoacoustic emissions (DPOAE), respectively. The OAE test is used for rapid screening to identify auditory neuropathies (the outer cochlear hair cells can function normally in auditory neuropathies), but not lesions of the inner, outer, or middle ear.
Acoustic field hearing threshold test is the hearing result obtained from the primary observational hearing test, which is closer to the patient’s actual condition, and the hearing threshold can determine the effectiveness of the hearing aid and whether it is suitable for surgery. It also indicates that there is residual hearing and that the hearing aid is effective.
For patients with cochlear implants wearing hearing aids has many roles.
(1) Patients who cannot have surgery as early as possible at the specified age for various reasons can wear hearing aids temporarily. Although they cannot communicate normally through hearing aids, they can stimulate the development of the auditory and speech centers; hearing aid effectiveness is one of the indications for cochlear implantation, and there is no significant improvement in auditory speech ability after 3 to 6 months of hearing rehabilitation training;
(2) Ineffective or poor hearing aid is defined as open phrase recognition rate ≤ 30% or two-word recognition rate ≤ 70% in the best hearing aid listening environment. Cochlear implantation is expensive, but of course, it is not the most expensive one that is the best one.
(3) After cochlear implantation, hearing aids can be worn in a slightly better ear, and the effect of hearing aids in both ears is better than in one ear.
(2) Cochlear implants cannot be done in the following cases (contraindications to cochlear implant surgery).
1. Contraindications to surgery include
(1) Severe deformities of the inner ear, such as Micheal deformity and cochlear deformity, where there is no space for cochlear electrodes.
(2) Patients with auditory nerve (or cochlear nerve) deficiency, extreme narrowing of the internal auditory canal, or no auditory response on preoperative examination along with MRI water imaging of the internal auditory canal suggesting hypoplastic or undeveloped cochlear nerve; such patients can only be considered for auditory brainstem implantation.
(3) Severely mentally handicapped; those who cannot cooperate with language training; severe mental illness; those with acute or chronic inflammation of the middle ear mastoid that has not been cleared, and those with chronic otitis media with tympanic membrane perforation, if the inflammation is under control, they can opt for one-stage or staged surgery. One-stage surgery refers to the eradication of the middle ear mastoid lesion, tympanic membrane repair (or mastoid cavity temporal muscle filling and closure of the external ear canal) and cochlear implantation at the same time. Staged surgery means removing the lesion first, repairing the tympanic membrane perforation or closing the external ear canal, and performing cochlear implantation 3-6 months later.
(4) Others. Relative contraindications include poor general condition, uncontrollable epilepsy, and lack of reliable rehabilitation.
The absence of cochlear malformation is an absolute contraindication to cochlear implantation.
Stenosis of the internal auditory canal and undeveloped cochlear nerve are absolute contraindications to cochlear implantation.
2. Severe inner ear or auditory nerve malformations require the necessary imaging tests, which commonly include high-resolution temporal bone CT and cranial magnetic resonance imaging (MRI). CT of the temporal bone is a routine preoperative examination that provides a good visualization of the bony structures of the inner ear, with the aim of observing the morphology of the cochlea and adjacent structures. The following can be understood: the degree of pneumatization of the mastoid, the thickness of the phosphorus of the temporal bone, the presence or absence of malformation of the cochlea, the enlargement of the vestibular canal, the thickness of the bony promontory, the narrowing of the internal auditory canal, and the malformation of the facial nerve course. CT can well display the bony structures of the inner ear, but there are limitations in the observation of the vagus and neurovascular lesions of the inner ear membrane; it is not enough to estimate the ossification and fibrosis of the cochlea.
Significance of imaging examination.
(1) It can objectively and accurately understand the condition and anatomical characteristics of important anatomical areas related to surgery, such as the presence of facial nerve malformation, abnormal facial nerve alignment, anterior displacement of the facial nerve and anterior displacement of the sigmoid sinus, and the presence of middle ear lesions, increasing the safety of surgery, reducing the occurrence of surgical complications, and shortening surgery time.
(2) For patients with cochlear deformity, cochlear axis deficiency or partial deficiency, such as Mondini inner ear deformity, only direct electrodes can be used to achieve relatively good results.
(3) To anticipate the complications of Gusher, to prepare well before surgery, and to reduce the occurrence of cerebral crest fluid leakage during surgery.
(4) Selection of the operative ear: try to select an ear without deformity or with relatively mild deformity (large vestibular canal can be equated to a normal ear), middle ear pathology can affect the surgery and should also be one of the conditions for the selection of the operative ear.
(5) Judgment of whether there are contraindications and relative contraindications to CI, such as severe malformation of the bony vagus structure of the inner ear, or even undeveloped cochlea and undeveloped auditory nerve (complete atresia of the internal auditory canal and thin or abnormal shape of the auditory nerve) are absolute contraindications, and surgery for narrowing of the internal auditory canal and fibrous ossification of the cochlea are relative contraindications.
(6) Determination of electrode implantation location: The location of the round window and oval window as well as the thickness of the tympanic capsule there will affect electrode implantation.
(3) The indications for cochlear implantation are widening.
1. Patients with unilateral severe or profound sensorineural deafness: With the progress of science and technology and the increasing demand for quality of life, unilateral severe or profound sensorineural deafness is also considered as a candidate group for cochlear implantation in Europe and the United States, and is also carried out in China one after another.
2. Unilateral severe to profound sensorineural deafness combined with severe tinnitus: Studies have shown that in addition to hearing and speech rehabilitation, about 60-70% of patients with severe tinnitus have their tinnitus relieved or disappeared after cochlear implantation.
3. Patients with previous unilateral cochlear implants: Studies have shown that bilateral cochlear implantation is one of the ways to obtain binaural hearing. The advantages of bilateral implantation are: sound source localization, speech recognition, and the ability to hear in complex environments such as avoiding head shadow effect and recognition under noise will have better performance.
Fourth, with the necessary family conditions, rehabilitation conditions and appropriate expectations.
The majority of patients with cochlear implants around the age of 1 have good results and can attend normal kindergartens and elementary school, and can communicate by telephone. However, patients with prelingual deafness older than 7 years old may have only auditory responses, and can hear horns and fire alarms, and so on, and can have emergency evacuation. The understanding of language may be crossed, that is, they can hear the sound of speech, but cannot understand the content.
2. There are conditions for hearing and language rehabilitation education. After cochlear implantation, it is equivalent to re-starting the exposure to sound and learning to speak again. It is necessary to strengthen the auditory and speech training, and it is recommended to learn or master the scientific rehabilitation methods in professional rehabilitation institutions.
3. Have the support of your family. In addition to financial support, spiritual support must be provided, and then reinforcement of auditory and verbal communication with the patient is beneficial to rehabilitation.
V. Special groups
1. Auditory neuropathy (the site of the lesion determines the efficacy): the site of the lesion that causes deafness is located in the cochlea or the synaptic part of the cochlear nerve (the real lesion is located in the cochlear nerve and/or its nerve pathway, the cochlear implantation may be less effective or ineffective).
2. Cochlear fibrosis and ossification. Deafness due to meningitis and inner ear trauma requiring cochlear implantation requires early surgery, before fibrosis and ossification develop (within 1 month), adequate preoperative evaluation, MRI water imaging to understand the presence and extent of fibrosis, and intraoperative preparation of test electrodes if necessary to determine whether the electrodes can be successfully implanted.
3. Cerebral white matter disease. Cochlear implantation should be performed with caution for cerebral leukoencephalopathy located in the temporal lobe (the central part of hearing and speech) and progressive cerebral leukoencephalopathy.
4. For severe middle ear and facial nerve deformities, if it is difficult to determine the position of the cochlear opening during surgery, facial nerve monitoring and intraoperative CT are the guarantee of smooth implantation.
Age requirements for cochlear implantation
The age requirement for cochlear implantation varies depending on the time of deafness. We classify deafness into pre-speech and post-speech deafness depending on whether or not the deafness has learned language at the time of deafness. The best age for prelingual deafness is 12 months to 6 years old, because the auditory and speech centers need to be stimulated by sound in order to develop. and a history of hearing or speech training since childhood. Cochlear implants are available for all ages of postlingually deaf patients. The oldest patient in our department is 91 years old, provided that the patient is well evaluated before surgery, is in good general condition, and can tolerate about 2 hours of general anesthesia for cardiopulmonary function.
Summary
(1) Severe to profound sensorineural deafness with poor hearing assistance is a basic requirement for cochlear implantation, but whether cochlear implantation can be performed must be evaluated by audiology and imaging to rule out contraindications to cochlear implantation.
(2) The indications for cochlear implantation have been appropriately relaxed, such as unilateral deafness and cochlear implantation on one side already.
(3) Special conditions such as cerebral leukodystrophy, auditory neuropathy, otitis media and cochlear fibrosis osteosynthesis may affect implantation or post-implantation outcomes.
(4) Cochlear implantation requires financial support from the family for implantation and assistance with rehabilitation, and both financial and time commitment are critical in determining the efficacy of cochlear implantation.