Single Sided Deafness
This term usually applies to a situation where a patient has a severe to profound sensorineural (nerve) hearing loss in one ear, and near normal hearing in the other ear. There are a number of causes of this including congenital abnormalities, trauma, infections, trauma, Meniere’s disease and the sudden sensorineural hearing loss syndrome.
The main advantage we gain from having two ears working together is directional sense and improved hearing when there is background noise. Therefore patients with a single sided deafness often manage very well in a one to one situation, but struggle when there is any additional noise, and also struggle with their directional sense.
In general terms there are three options:
1. Adaptation: Many patients can adapt very well with hearing only from one ear, and it does not bother them to any great degree. The most important issue here is to be vigilant with any problems with the only remaining hearing ear.
2. Re-routing strategies. This involves using a receiver on the deaf side and sending an audiologic signal to the hearing ear. This creates the illusion of hearing from two ears. The main advantage is improved hearing in small group environments and in situation like being in the car. Given that we are not stimulating the non-functioning or dead ear, this does not improve directional sense, nor does it have the advantage of suppressing tinnitus that often accompanies severe hearing loss.
This can be done by using a BiCross hearing aid, which uses Bluetooth technology to send a signal to the good ear, or by utilising bone anchored technology. There are advantages and disadvantages of both:
o A BiCross hearing aid is especially effective if the good hearing ear has a degree of hearing loss, and obviously does not require surgery.
o A Bone anchored hearing aid has the advantage of not having to wear a hearing aid in the good ear, and the sound from the deaf side is transferred to the good ear via bone conduction. There are a number of different devices that can achieve this result, all with their own particular advantages and disadvantages.
The cochlear company provides the BAHA connect, which requires a small pin or abutment to be inserted into the bone behind the ear, and protrudes through the skin by a couple of millimetres, and the Baha attract, where a magnet is attached to a similar pin, but remains underneath the skin. The hearing aid component (or processor) then either attaches like a press stud for the BAHA connect, or via a transcutaneous magnet in the BAHA attract. The obvious advantage of the attract is that there is no transcutaneous component, but some sound efficiency is lost though transfer through skin.
The Medel Company produces the BoneBridge, which is an active bone anchored hearing aid. This means that the internal component is made up of a floating transducer, that is connected via a transcutaneous processor. Placement of this device does require appropriate anatomy, but the external processor has a lower profile than does the BAHA attract.
3. Restimulation of the ‘dead’ ear
In more recent times the option of directly restimulating the dead ear has become an option with the use of cochlear implantation. This is obviously only an option in people who have a residual cochlear and cochlear nerve. This is often not the case if we have needed to surgically remove a tumour involving these structures.
The major advantage here is that there is actual re-stimulation of the deafened ear, allowing the potential of true binaural hearing as well as a much better chance for tinnitus suppression.
Traditionally it was thought that the brain would not be able to process an electrically generated signal with essentially normal hearing on the other side. In a high percentage of appropriately selected cases, cochlear implantation has allowed significant improvements in the fields of hearing in background noise and directionality.
The downside is that this requires slightly more interventional surgery, but also requires a more dedicated period of audiologic retraining and adjustment. It is those patients who are highly motivated, especially those who need to function in demanding audiologic conditions that report the biggest degrees of improvements.
How to decide
In most cases there is no great urgency in deciding which of these options to choose. The rare circumstance where a patient has suffered bacterial meningitis which can lead to ossification of the cochlear is an example where a more rapid decision may need to be made.
Usually a period of observation is recommended to allow the patient to ascertain the degree of handicap the single sided deafness is causing them.
A discussion surrounding the advantages and disadvantages, the risks and benefits involved is then arranged. Normally we would then recommend a trial of both a BiCross and a BAHA to see what degree of improvement is gained. If adequate we would then head in that direction.
If there is no great improvement, and the patient wished to head in that direction we then head in the direction of cochlear implantation.