Deafness, also known as hearing impairment, is the most common birth defect and one of the most significant disabling factors. The results of the Second National Sample Survey of Persons with Disabilities, published in December 2006, showed that there are 20.04 million people with simple hearing disabilities in China, second only to physical disabilities in terms of disability rate. Therefore, how to provide more optimal hearing rehabilitation programs for this large population of patients has become an important topic of medical research.
From the use of tympanoplasty for conductive deafness in the 1950s to the rise of cochlear implants for severe sensorineural deafness in the 1980s, from early tube hearing aids to integrated circuit digital hearing aids, from artificial hearing bone pseudo-replicas to various electronic artificial hearing implants, from single cochlear implants to various artificial hearing implants, the treatment of deafness has been a major medical concern. The treatment of deafness has been progressing and developing, among which, surgical procedures, especially artificial hearing implants, have been rapidly developed in the last decade or so along with technological advances, solving many hearing problems that could not be solved by hearing aids alone. The following is an introduction to the surgical treatment of deafness and artificial hearing implants.
1.Traditional ear surgery
(1) Classical treatment for chronic otitis media – tympanoplasty
Since the development of tympanoplasty in the 1950s, it has gradually developed into four types of such surgery according to physiological functions. In recent years, tympanoplasty has developed rapidly, and its treatment indications include: removal of focal middle ear lesions, repair of the tympanic membrane, reconstruction of the auditory chain, and restoration of the physiological function of the middle ear. Therefore, the advantages of tympanoplasty therapy are: it can efficiently treat almost all ear diseases and complications, minimize residual lesions, and fully restore the continuity of the auditory chain, and all chronic suppurative otitis media can be treated in one go. Repair of the auditory chain and reconstruction of hearing. After the surgery, the perforated tympanic membrane is closed and the mobility and continuity of the reconstructed auditory chain is good, so that the physiology and morphology of the middle ear are close to normal and the hearing will gradually improve after the surgery. By surgical operation with ear microscope instruments under a microscope, the operation is less harmful and has fewer complications.
(2) Classical treatment of otosclerosis – artificial stapes surgery
There is a not uncommon clinical category of otosclerosis that manifests as conductive deafness with normal tympanic membrane and progressive hearing loss. The main cause of otosclerosis is that the stapes in the auditory chain becomes fixed and its movement is limited, which affects the sound transmission function of the auditory chain, resulting in hearing impairment and clinical symptoms. The main treatment for otosclerosis is stapes surgery, which aims to restore the movement of the stapes floor or vestibular window, restore the conduction of the auditory chain, and then restore hearing.
(3) Classical treatment of congenital external ear deformity – atresia hearing reconstruction
Congenital external auditory atresia is a congenital birth defect, which is seen after birth as abnormal development of the external ear in newborns, manifested by small or no auricle, no external auditory canal, and possibly accompanied by malformation of middle ear development.
Currently this category can be well restored by artificial hearing implants such as vibrating acoustic bridges and bone-anchored hearing aids (BAHA), but traditional hearing reconstruction for congenital external auditory canal atresia still has its use, especially for some children with basically normal development of the bony external auditory canal and middle ear and only membranous external auditory canal atresia. Depending on the development of the external auditory canal, tympanic chamber and auditory chain, simple external otolaryngoplasty or external otolaryngoplasty can be performed.
2.Artificial Hearing Implant
(1) Cochlear implantation, a boon for patients with extreme deafness
Cochlear implantation is a technique of implanting an artificially manufactured electronic hearing device into the cochlea of patients with severe or profound sensorineural deafness (replacing the function of the cochlea) to directly stimulate the auditory nerve fibers in the cochlea. This means that external sound is converted into electrical stimulation to produce electrical hearing, and the patient needs to learn and train to re-establish the appropriate connection between sound and electrical hearing, thus enabling the patient to re-understand speech and return to the audible world.
The procedure can be performed in pediatric patients as young as 12 months of age (FDA approved), and in some special cases, the age of implantation can be several months earlier. Patients with prespeech deafness have better results before the age of 8 years, especially before the age of 4 years. If the patient can wear a hearing aid for 3-6 months before the surgery and undergo aural rehabilitation, it will help a lot to improve the speech ability after the surgery. For adults with post-speech deafness, there is no significant age limit, and cochlear implants have been reported worldwide in people as young as 84 years old. In Western developed countries, the number of cochlear implants for deafness in the elderly is as high as that of children, greatly improving the quality of life of the elderly.
(2) Middle Ear Implantable Hearing Devices – Vibrating Sound Bridge
In the past 10 years or so, a new deafness treatment option, the vibrating sound bridge implant, has been more and more widely used in Europe and the United States. In May 2010, this new deafness treatment option, the vibrating sound bridge, began to enter mainland China and will increasingly build a bridge for deafness patients to transmit sound and allow unimpeded communication.
Deafness can be caused by a variety of causes, including diseases of the outer ear, middle ear or inner ear. Clinically, deafness is often divided into three main categories, namely sensorineural deafness, conductive deafness and mixed deafness. For patients with sensorineural deafness, hearing aids are often used for the less severe cases (where there is residual hearing available) and cochlear implants for the more severe cases (where hearing aids are ineffective or inefficient), while for patients with conductive or mixed deafness, the traditional treatment options are middle ear surgery or direct hearing aids.
When a deaf patient has a vibrating sound bridge implanted, sounds from the outside world and from themselves are captured by the processor’s microphone and then encoded into a sophisticated electromagnetic signal that is sent across the skin to the implant. Once the implant receives the signal, it instructs the floating mass sensor to vibrate. Finally, this mechanical vibration is transmitted precisely into the inner ear, and the patient hears a clear and natural sound, which is significantly better than traditional methods, and this is the biggest advantage of the vibrating sound bridge.
(3) New hearing rehabilitation technology – Bone Anchored Hearing Aids (BAHA)
BAHA, or Bone Anchored Hearing Aid (BAHA), is a device for treating deafness through bone conduction, which requires surgical implantation. 1996 U.S. FDA approved BAHA for treating conductive and mixed deafness, and 2002 U.S. FDA approved BAHA for treating unilateral sensorineural deafness. The BAHA is used to help patients with chronic otitis media, congenital external atresia and unilateral deafness who cannot use conventional hearing aids. This system requires surgical implantation and conducts sound to the inner ear through the bone conduction rather than the middle ear.BAHA’s hearing aid principle uses its own cranial bone conduction principle to send sound directly through the bone to the hearing part of the ear, bypassing the outer or middle ear hearing impaired area and producing clear sound without the distortion, feedback and uncomfortable ear mold that conventional hearing aids tend to cause.
(4) The perfect combination of hearing aids and cochlear implants – combined acoustic and electrical stimulation
Acousto-electric co-stimulation is still a kind of cochlear implant in a broad sense, and is suitable for patients with severe speech-frequency sensorineural deafness with good low-frequency hearing on one side, and total deafness with <50% monosyllabic speech recognition on the other side, without progressive hearing loss. The principle of combined acoustic and electrical stimulation is to use short electrodes to stimulate only the auditory nerve fibers in the bottom turn part of the cochlea, and no electrode stimulation in the top part of the cochlea.
(5) Auditory brainstem implantation
Auditory brainstem implantation is mainly indicated for patients with bilateral auditory neuroma or multiple neurofibromatosis after resection, cochlear ossification or auditory nerve hypoplasia. The working principle is similar to that of cochlear implantation, except that cochlear implantation is performed by stimulating the auditory nerve fibers in the cochlea, while auditory brainstem implantation is performed by implanting electrodes into the lateral saphenous fossa of the fourth ventricle to directly stimulate the auditory neurons in the brainstem cochlear nucleus complex. However, intraoperative positioning of the brainstem cochlear nucleus is much more complex than cochlear implantation and is influenced by a variety of factors, such as brainstem deformation due to early tumor compression, scar adhesions from previous surgery or radiation therapy, and operator experience. Incorrect electrode placement or postoperative electrode displacement may cause non-auditory responses such as myoelectric activity of the facial and linguopharyngeal nerves, which are not commonly performed in China.