Pr Olivier Sterkers, head of the Orl department at the Beaujon Hospital, explains the benefits of the latest electroacoustic implant, demonstrated at the recent Congress of the French Society of Orl and Head and Neck Surgery at the Palais des Congrès in Paris.
Can you briefly explain how the ear receives sounds?
Pr Olivier Sterkers.They reach the inner ear (cochlea) through the external auditory canal, the eardrum, and then the ossicles. The main role of this inner ear is to transform sound energy into electrical energy (mechano-electrical transduction). This coding is done by means of specific cells, called “hair cells”, which are connected to the nerve endings of the auditory nerve. This electrical message is then transferred along the brainstem to the brain, in the areas of hearing. The ciliated cells are different and distributed according to the frequency of the sounds (treble or bass) that they code like the keys of a piano. The coding of these high-pitched sounds is provided by the lower part (or base) of the cochlea, and the bass sounds by the upper part (or vertex).
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What are the most common forms of deafness?
Pr OS These are degenerations that occur in the course of life and increase with age. They always concern the inner ear where, with the years, progressively a loss of the ciliated cells which process the acute sounds, becomes a dead region of the cochlea: consequently, an auditory discomfort settles, particularly painful in a noisy environment. When the attack is more advanced, there is this time loss of intelligibility. Then persist only the low frequencies, which always allow to analyze the rhythm of the sound messages but more to integrate them in the brain. Up to a certain level of loss
What type of prosthesis is placed then?
Prof. OS There are two types of these external hearing aids: 1 Single-ear implants are indicated in cases where the hearing decline is not too large. 2 In cases requiring more powerful help, a contour prosthesis is used, the tip of which is connected to a tiny device placed behind the ear and amplifies the sounds. But at a later stage, the prosthesis is not enough anymore. It is then necessary to consider the surgical placement of a cochlear implant.
How does a cochlear implant work?
Pr OS The process involves placing electrodes inside the cochlea to stimulate the sensory cells of the inner ear, which will then send neurological impulses to the brain. The apparatus implanted behind the ear consists of different elements. Outside, a tiny receiver receives the sounds, then transfers them (through a magnetic system introduced under the skin) to an electronic processor that turns them into electrical messages. These signals are transmitted to the electrodes implanted in the cochlea where it will be possible to analyze the high-pitched sounds.
What results do we get with this implant?
Pr OS Patients can understand speech again, while retaining limited hearing when in a noisy environment. This understanding is optimized by reading the movements of the lips of the interlocutor.
Does this method have disadvantages?
Pr OS Yes, this implant technique involves the destruction of the remaining healthy auditory cells. The patient is left with a totally artificial hearing, which requires adjustments to the device and a re-education to follow.
What is the new approach using two implant techniques?
Pr OSThis method associates the stimulation of the low frequencies for the hearing aid with that of the nerve endings allocated to the high frequencies for the cochlear implant. But there, a new minimally invasive surgical technique allows to preserve the hearing cells remained healthy, in 80 to 90% of the cases. Instead of practicing a large opening to introduce a rather large electrode, the surgeon, using micro-instruments, makes a small millimeter window to place a much finer diameter electrode. The operation is performed under a microscope (the operative field is enlarged) with regular electrophysiological checks of the hearing. The first settings of the implant are made fifteen days after the operation to optimize speech recognition