1. What is a cochlear implant and how does it work?
When we consider what a cochlear implant is, it is first worthwhile considering how we hear normally.
Sound is vibration. Vibrations are transmitted by vibrating molecules Sound is usually transmitted through air - the vibration of the molecules in the air around us. Vibrations are channelled into our ear canal by the external part of the ear, and hit the ear drum. This causes vibration of the ear drum. There are three little hearing bones within the middle part of the ear, with one attached to the ear drum, and one to the hearing organ in the inner ear. These bones transmit the vibration from the ear drum into the inner ear. Within the inner ear, the vibrations are amplified and detected by hair cells. These hair cells then stimulate the hearing nerve which lies within the cochlea with small electrical impulses. The hearing nerve then passes to the brain, and stimulates the part of the brain that processes hearing.
The most common reason to have hearing loss meaning a cochlear implant is problems with the hair cells in the inner ear.
A cochlear implant is an electronic device that allows hearing rehabilitation. It includes an internal part (usually referred to as the implant, or the package) and an external hearing aid (usually referred to as the processor).
The processor has a microphone (actually usually more than one) that detects sounds, and processes those sounds into a digital signal. That signal is transmitted through an antenna in a headpiece to the implant beneath the skin. The transmitter only has a very short range, and so the antenna has to be held close to the implant through the use of a magnet.
Within the implant, the signal goes through a receiver-stimulator - which is an electronic device that channels electrical impulses into the electrode. The electrode is the part of the implant that is inserted into the cochlea. The electrical impulses pass from the electrode into the cochlea, and stimulate the hearing nerve that sits within the cochlea. In most people with hearing loss, the hearing nerve works normally, and stimulating it electrically can stimulate the brain and reproduce hearing. This works remarkably well, and adults who receive cochlear implants report being able to hear sounds as soon as they start wearing the device - and their hearing then improves (more detail below).
2. Why am I /my child having a cochlear implant?
By the time you have come to a cochlear implant department, you will have met a number of audiologists who will have tested you/your child’s hearing. The reason that they have referred you to a cochlear implant department is because they think that you/your child has a hearing loss that is not going to be adequately managed with conventional hearing aids. That is not to say that you/your child should not use hearing aids - indeed it is very important to use their hearing aids as much as possible (as they usually give a little bit of hearing, and if you’re used to wearing a hearing aid its easier to get used to wearing a cochlear implant)! However, it means that more hearing than a hearing aid can provide be required. When you have very little hearing, it can be difficult to hear loud sounds clearly, even when they are made much louder by a hearing aid. There are lots of causes of hearing loss. In adults, combinations of age and noise exposure are the most common causes of hearing loss. Most people lose hearing gradually, but it can be lost suddenly. Children can be born with hearing loss, or hearing may get worse over time (usually gradually, but this can happen suddenly). For the majority of children, we never find the exact cause of their hearing loss. We may suspect that the hearing loss has a genetic cause - but this does not mean we are currently able to identify the specific gene, or yet have an appreciation of what that gene means, other than it is associated with hearing loss. Our understanding increases each year, and hopefully in the future, we will be able to answer these questions. In children, the most common causes that we are able to identify are specific genetic causes - such as connexin 26 / GJB2, or children who have hearing loss as part of a pattern of other medical problems called a syndrome. The most common syndromes that we look for are Usher’s (which also causes visual impairment), Pendred’s (which can cause thyroid problems in older children), Waardenburg (which can cause changes to skin, eye and hair colour), Alport (which causes kidney problems) and Jervell-Lange-Nielson (which causes heart problems). While the cause of hearing loss is usually due to the functioning of the inner ear, it can also be a problem with the hearing nerve itself, or a problem with the structure of the inner ear. Nerve problems are referred to as ANSD (auditory neuropathy spectrum disorder) and may be a structural problem (small or absent nerves termed ‘cochlear nerve deficiency’), or a functional problem (most commonly seen in children born very early who develop jaundice). Structural problems are called cochlear dysplasia - and there are lots of different types. Cochlear implants may still be recommended in people with these problems, but they may not work as well (more below). These problems are more commonly seen in some syndromes, such as CHARGE syndrome (which causes issues in various parts of the body such as the heart and nose).
3. How effective is a cochlear implant?
Cochlear implants are immensely effective at rehabilitating the hearing of people with low levels of hearing. This is because, unlike a hearing aid which still relies on acoustic hearing, they provide a new, electrical, way of hearing. In adults whose hearing loss means that even with hearing aids they are typically only able to identify less than half the words spoken at a set volume, cochlear implants will typically enable them to hear over 80% or 90% of words at the same volume. In children who without an implant would never have developed speech, some will develop speech more quickly than children without hearing problems.
It takes time to get used to electrical hearing. Initially voices may sounds electronic, or like a cartoon character talking. But over time, typically a few months, this way of listening will become more and more normal, until voices sound entirely normal. For this reason, wearing the cochlear implant a lot, and listening to sounds in context, is important to get the most out of an implant. This is particularly true in the first weeks and months after it is activated. Even then, appreciation of music generally does not return to the level it was at before.
Each person is an individual, and the amount a cochlear implant can do for any individual does vary. There are factors that we know make it more likely that you/your child will do really well with a cochlear implant. We know that in children who are born with very little hearing, that the younger they are they receive their implant (particularly if they are less than one year old), the more likely they are to benefit. In adults that develop progressive hearing loss, we know that the shorter the length of time they struggle with hearing, the more an implant will help them. We know that wearing hearing aids, good family support, and rehabilitation are important too. We know that some forms of hearing loss, like some specific genetic hearing losses, respond particularly well to cochlear implants. There are surgical factors that are important too - fully inserting the cochlear implant helps, as does keeping any remaining ‘acoustic’ hearing mechanisms.
Despite everything we do know about who will do best with a cochlear implant, there is still much we don’t know - indeed the main factors only account for about a third of the variation that is seen in outcomes. The vast majority of people will still benefit hugely from an implant, but a small proportion (around 2%) of people find that they can not get used to electrical hearing, and decide not to wear their implant much, or at all.
4. What does the cochlear implant process involve?
Having been referred to the cochlear implant programme, the first step in the pathway is the assessment. You will also meet an audiologist who will perform a range of tests of the ears and hearing. These vary quite a lot depending on age. You will meet a speech and language therapist who will assess language skills and listening. Children may undergo additional steps in assessment - focused on aspects like determining the cause of hearing loss. The aim of the assessment is to get enough information as possible to determine if we think cochlear implants would be the best option or not. You will meet a cochlear implant surgeon to discuss the operation.
A cochlear implant is a routine operation that is undertaken thousands of times every year in the UK.Usually, you will come to hospital on the day of your operation. The operation usually takes about 2 hours per side. In adults, having an implant on one side is usually a daycase procedure, in children having two implants usually means one night in hospital. We give a dose of antibiotics at the time of the operation, and no further antibiotics are usually required. Therefore, usually the only medication you require is simple painkillers such as ibuprofen and paracetamol (assuming you are able to take these medications). It is useful to take these regularly throughout the day for the first few days, and the amount can be reduced after 3-5 days depending on how you/your child is doing. Taking alternating doses of each drug can be useful to keep on top of the pain. It is usually worthwhile taking a dose of both paracetamol and ibuprofen just before going to bed to make sure you get as much rest as possible. After the operation it is important to keep the ear and wound dry for ten days to stop the wound from becoming infected.
Between 2 and 3 weeks after the operation, the device will be activated. This is known as ‘switch on’. You will be given the external processor(s) to wear. It is important to wear this/these as much as possible, as the more exposure to speech and sounds, the more their cochlear implant(s) will help. Initially, a low setting is used, and over time, the volume is ‘turned up’. This is done gradually. You may be given some different programs on the device and asked to build up the volume gradually whilst you are at home. The audiologist will give you information about this.
In the months and years after the implant has been inserted, you will see the team members who assessed you. The surgeons will check on your child’s progress, and ensure the ear holding the implant is not developing any problems. The audiologists will check the devices are working, and the speech therapists will give you exercises to develop your child’s hearing and speech.
5. What are the risks of cochlear implantation?
Cochlear implantation is a routine surgical operation. Complications are unusual, however, they can occur, and it is important you are aware of them. If you have any questions about them, please ask your surgeon.
A small amount of hair behind the ear will be shaved, and there will be a cut approximately 2-3 inches long behind the ear. This will leave a small scar, but this is hidden behind the ear, and after time it is unusual for this to be noticeable.
The first half of the operation involves removing part of the bone behind the ear to access the cochlea. The final part of this involves drilling a hole between the nerve that moves the face (the facial nerve) and one of the tongue’s taste nerves (the chorda tympani). Injury to the facial nerve causes weakness to movement of the face which has a number of implications. It is very rare (maybe around 1 in 1000), and when it does occur, is usually temporary, although recovery can take many months. Injury to the chorda tympani can cause an unusual taste in the mouth that usually settles after 6-8 weeks.
The second part of the operation involves inserting the whole cochlear implant into the cochlea as gently as possible. We want to be as gentle as possible to preserve any small amount of remaining hearing. This can be useful to hear fire alarms or similar sounds when you’re not wearing the implant. Residual hearing also helps get the most out of an implant as it gives context to sounds you hear. We also want to be gentle to avoid injury to the balance organ. This can make you feel dizzy and affect the balance, although this is usually temporary. Interestingly, for reasons we don’t understand, it appears some children can balance better when they are wearing their implant. The operation can also cause a ringing sound in the ear, although this usually stops on its own, it can take some time. This can also stop when you start using the implant.
We balance wanting to be gentle with wanting to insert the whole implant (what is termed a ‘full insertion’). This is so the implant can provide as much hearing as possible. In some cases, the implant will only be partly inserted, or indeed overinserted, and whilst this may not have any noticeable effects, it might mean that you/your child gets marginally less hearing.
In a small proportion of people, there is a connection between the fluid in the cochlea and the fluid in the inside of the head. Sometimes this means that when a cochlear implant is inserted, this fluid can then leak out into the ear. If this happens, it has to be repaired, as this increases the risk of meningitis. If this does not happen, but there is still a connection, then there is still a very small risk of meningitis. To reduce this very small risk, we recommend pneumococcal vaccination. Specifically, we recommend vaccination with Pneumovax (pneumococcal polysaccharide vaccine) for all adults and children over 2. Also, children who receive cochlear implants before this should receive this vaccine when they are 2. Children younger than 10 who have not completed their regular vaccination schedule with Prevenar (Pneumococcal conjugate vaccine) will additionally need a single vaccination with this.
Of the complications to occur, infection is probably the most common, happening to about 1 in 200 cochlear implants in the weeks and months after the operations. When it occurs, we treat it with antibiotics, but the infection often persists, and this may mean the implant has to be removed. If this happens, we usually offer to replace the implant after a period of 3-6 months. Infections can also occur years after the implant is inserted if bacteria reach the implant through the ear or the skin breaks down. Problematic bleeding from the ear is very rare. You may have bruising on their lip or eyebrow from needles used to monitor the function of the facial nerve.
General anaesthetics are very safe, and the anaesthetist you see will be very experienced at putting children to sleep and waking them up. Risks of allergic reactions to anaesthetic drugs, breathing problems, or other similar issues are very very small, but if they do occur, they may need treatment, and even potentially treatment in the intensive care unit. After the operation, it is not unusual to have a sore throat or some vomiting as a consequence of the anaesthetic.
When we insert bilateral devices, we try and make them symmetrical as possible on each side of the head. However, this is not always possible, and so they may sit at different heights.
The implants inserted are electrical devices, and as such, they have a life-expectancy. We would expect an implant to last for 20-30 years, although they may last much longer, or equally they may fail after a much shorter period. Injuries to the head from falling over increase this risk by a very small amount, and so implants in children tend to have a slightly shorter life expectancy. If an implant fails, it can be replaced, although this involves an operation similar to the operation to insert the implant.
5. What are the long term implications?
People with cochlear implants can hear very well, and as such go to school, get normal jobs, and undertake daily activities entirely normally. They need to wear their implants to hear similarly to people needing to wear hearing aids to hear, or glasses to see. Like glasses, for some sports which require protective head wear, you may need to make specific measures.
Implants generally need to be checked annually, to ensure the settings are giving you the best hearing possible. This goes hand in hand with hearing rehabilitation provided by speech therapists. Furthermore, if there are issues with the implant or hearing, you may need to see a cochlear implant team member.
People with cochlear implants can swim. There are swimming accessories to put the processor in, or otherwise, the processor can be removed and they can swim without hearing. We do, however, advise against SCUBA diving at any stage having had a cochlear implant.
If you need an MRI scan, this can be an issue. The magnet in the cochlear implant will be pulled on by the magnet in the MRI scanner. Whilst a scan is almost always possible, there are some important considerations. You may have to have a bandage to wrap around the head to hold the magnet in place. The scan may be painful, and may have to be stopped because of pain. The implant may heat up, and the magnet in it can become less powerful. There have been cases where the implant has had to be replaced as the internal magnet has moved out of position. The magnet can be removed and reinserted, but this involves two operations and carries a risk of infection. The quality of the image that the scan produces will be affected by the implant (particularly the images of the head). You may have a device that is compatible with MRI scans (see below), in which case there are unlikely to be issues, although the quality of the image that the scan produces will still be affected, and these devices have weaker magnets, which can cause problems, especially if you have thick skin.
6. Which cochlear implant should I have?
There are four cochlear implant manufacturers currently in use throughout the UK. These are:
Cochlear
Advanced Bionics
Med-El
Oticon
The differences between each of the devices is very small. Sometimes, there are specific surgical or audiological reasons to have an implant, and we will strongly recommend on one manufacturer or type. Sometimes, it will be a clear decision, sometimes it will take time to make, although it shouldn't cause you undue concern - all manufacturers provide excellent devices.
All of the companies have their strengths and weaknesses, however the differences between them are all very small compared to the differences between cochlear implant and a hearing aid. For this reason, it is best to focus on the similarities between devices rather than their differences. Overall, there are probably no significant differences in auditory function between each device. All companies invest large amounts in developing their products. At any one time, one manufacturer may be ahead in one area (such as the size of their processor, or the MRI compatibility of their magnet, or any one of a hundred other areas), but over subsequent years, other manufacturers will catch up in those areas, and may get ahead in other areas. The external processor can be replaced easily, and whilst the internal package is not straightforward to replace, it is almost always compatible with new technology in the external processor.
Reliability and device failure (as discussed above) are important considerations. All manufacturers publish reliability reports, which are freely available on the internet. It must be said, that academic articles published on the topic indicate that device failure may be more common than these figures - although that may be because some peoples devices get removed for infection and skin break down and so on. Some devices used previously have had higher rates of device failure. This happens because as they refine and develop their devices, they necessarily have to make them in new ways. There is a limit to the amount that testing in laboratories can show, and so after some years of an implant being used, there are some devices that begin to show a higher rate of problems, although these issues have still only affected a minority of patients. When such an issue is identified, we would not use any devices in which we know there is such an issue, however, these issues generally emerge after some years of using a device. There is therefore a balance between wanting the latest, newest device, and wanting a device that has been used for many years without problems.
Magnet type is also a consideration. MRI compatible magnets are less powerful than conventional magnets, and whilst this is not usually a problem, this may mean the antenna is more likely to become dislodged. Ways to deal with this, if it does occur include cutting hair over this area, using sticky tape, or wearing a head band. Under exceptional circumstances, the magnet can be replaced, although this carries small risks.
7. What about future technologies for hearing rehabilitation?
A question that we are frequently asked is about delaying cochlear implantation to see if emerging technologies. Generally that is not something that we recommend for the following reasons:
Having lost hearing, it is important to start hearing again as soon as possible. Children need to learn how to speak, and thrive at school. Adults need to interact with others, and avoid conditions like depression and dementia.
In those with some retained hearing, this is less important, although regaining hearing as early as possible tends to be useful for school, or for work, or for communicating with friends, and putting it off indefinitely can mean rehabilitation when hearing is restored is more difficult.
The below future technologies are not currently being used to treat people (although they are being researched), and even when they are, they will need to be refined. When cochlear implants were first invented and used in people, they worked, but they had not been refined, and so didn’t help patients nearly as much as current implants.
Many of the below future technologies will carry an element of unknown risk when they are first used. This is the case for everything new that we do to our bodies. Cochlear implants have been used safely for decades, and so the risks and benefits are much better understood.
Some of these therapies may not be relevant for people with hearing loss caused by certain causes - for example hair cell regeneration may not help someone with an issue with their auditory nerve.
The therapies we are asked about most commonly include:
Totally implantable cochlear implants. It is likely that these will be introduced in the coming years. There is a totally implantable middle ear implant, although this is not commonly used in the UK currently (it has been withdrawn), and hearing is best using an external microphone. This may change in due course, as there are hearing devices being developed that use the ear itself as a microphone.
Stem cell therapies. Stem cells have been shown to be able to regenerate hair cells and auditory neurones, however it has proven very difficult to get these cells into, and keep them alive in, the human inner ear. Furthermore, particularly in neuronal regeneration, it might be that this therapy is more effective performed at the same time as cochlear implantation.
Gene therapy. A lot of research has been undertaken in gene therapy for hearing loss in animals, but very little in humans. It is likely that this technology would have to be different for each cause of hearing loss. It is also possible that the treatment would need to be undertaken within a specific window of opportunity that may even be before birth for some children who are born with hearing loss.
Growth factors and inner ear drug therapies. A variety of drugs and growth factors have been proposed and trialled to prevent or reverse hearing loss, with some success. Some of these drugs are for specific causes of hearing loss - particularly the prevention of ototoxicity. However, none is at a stage where it can improve hearing to the extent that it could replace the need for hearing aids or cochlear implants.
8. Specific situations
This leaflet is as general as possible for people who are in the position of considering cochlear implantation. And whilst everyone considering an implant is in a different position, there are some situations that have important differences.
Auditory Neuropathy In auditory neuropathy, the hearing problem is not within the hair cells in the cochlea, but rather in the nerve that runs between the cochlea and the brain. In children, this is most commonly (but not always), associated with prematurity and jaundice. Assessing the amount of hearing loss in these situations can be difficult, as the hearing nerve can give confusing signals. There is a balance between wanting to restore hearing with an implant, and to see the potential of the ear to hear without an implant. Also, as a cochlear implant still relies on the auditory nerve to transmit hearing to the brain, implants are not always as effective in people with auditory neuropathy. Making these assessments depends on the specific cause of auditory neuropathy - and so additional tests can be recommended for patients in this situation.
Cochlear Dysplasia and Cochlear Nerve Deficiency The term ‘cochlear dysplasia’ refers to an abnormal shape of the cochlea. This has a few implications. It is likely to be the cause of hearing loss, as the shape of the cochlea is important to it working properly. Depending on the shape, it may be that a cochlear implant is less effective than in normally shaped cochleas. The reason for this is that the cochlea is arranged so that high pitched sounds stimulate the cochlea near its entrance, and low pitched sounds near the inner part of the coil. When the shape is different, it can be difficult for this distribution of pitch to be recreated. Also, cochlear dysplasia is more likely to be linked to connections between the cochlea and the inner part of the head, meaning leaking of fluid, and things like meningitis are slightly more likely than they are for other people having a cochlear implant.
Cochlear nerve deficiency means the hearing nerve is small or it is missing. Whilst it is always possible to say whether there is a relatively normally sized nerve, the very best scans can have difficulty telling whether there is a very small nerve or nothing at all, so the term ‘cochlear nerve deficiency’ (CND) is sometimes used to cover all situations. People with small nerves tend to get less hearing from a cochlear implant, and it can take many years to see the full potential of an implant - a much longer period than for most people.
Ear Infections / Glue Ear / Chronic Otitis Media If you/your child has had lots of ear infections, or problems like glue ear, the surgery to insert a cochlear implant can be more difficult. This is because the lining of the middle part of the ear becomes swollen, and tends to bleed more. Sometimes, if you/your child has had surgery for conditions such as cholesteatoma, an operation needs to be done to prepare the ear for a cochlear implant at a later stage.
The Young Child Where possible, for children born with severe-profound hearing loss, we try to insert cochlea implants before their first birthday, or even earlier. The reason for this is that it has been shown that the younger the child who receives an implant, the more effective the implant will be, and the easier the child will find it to develop speech normally. When they are young, the cochlear implant is more visible beneath skin that tends to be thinner, and tends to have less hair, but it will become less apparent over time. It can feel frightening for your child to have an operation at such a young age, but it is entirely routine, and frequently performed in children of this age.
9. One versus two
There are a number of hearing benefits to having two cochlear implants. Two implants also help listening to speech in noisy environments – particularly when someone is talking to your child from one side, rather than straight ahead. Having two implants is also useful should an implant have reliability issues, as you/your child would then have a working hearing ear to rely upon while the implant is fixed. Spatial hearing and localisation of sound is also important – and being able to hear from both ears lets you/your child orientate yourself in the world around them much more effectively. We know that people with deafness on one side have worse visuospatial memory for example, working out from which direction a sound is originating. However, having two implants commits you to cochlear implantation on a lifelong basis, and having two implants does involve operations on both ears, and their associated risks.
10. Additional Resources
The below resources provide more information about cochlear implants.