Hearing without ears (auditory brainstem implant)

August 15, 2011 by Dr Denis Pouliot

Hearing without ears (auditory brainstem implant)

Nowadays, it is possible to hear without ears. People who are completely deaf in both ears and who do not have an auditory nerve between the brain and the ear can now benefit from a new auditory technology.

An auditory implant can be implanted in a part of the brain that is accessed via the ear and mastoid. The implant is placed in the wall of the lateral recess of the fourth ventricle in the area where the axons (nerve fibres) and cochlear nucleus (synapses)—which transport sounds picked up by the ear to the cerebral cortex—are found. This is the normal oto-neurological channel that detects sound and speech. Practically speaking, a microphone is placed externally behind the hearing-impaired person’s pinna (ear flap). This transmits sound to a receiver embedded in the skin, which subsequently transforms electrical impulses to small electrodes placed in the brain (cochlear nucleus).

An ENT surgeon (ear and mastoid) and a neurosurgeon (brain) jointly perform the implantation of this type of implant. The first auditory brainstem implant was performed in 1979 at the House Ear Institute, in Los Angeles. After basic studies, the implant was marketed officially in 2000, and the first implantation in Québec was carried out in 2005 at Hôpital de l’Enfant-Jésus du CHAUQ by Dr. Denis Pouliot, ENT specialist, and Dr. Claude Picard, neurosurgeon. Located in Québec City, Hôpital de l’Enfant-Jésus is the only hospital in the province that performs this surgery.

A multitude of participating partners

First of all, CHAUQ is a health care, teaching and research establishment, as well as an affiliated university centre. For over 20 years, a multidisciplinary team, primarily comprising ENT specialists and neurosurgeons, has developed cutting-edge expertise in the treatment of basal skull tumours. For its part, Hôtel-Dieu de Québec du CHUQ carried out Canada’s first cochlear implant in 1984. Since then, the nationally and internationally renowned Québec Cochlear Implant Program has become an ultra-specialized centre in auditory implants, thanks to the participation of a number of partners. Given the expertise developed in cochlear implants at Hôpital-Dieu de Québec and that of basal skull surgery at Hôpital de l’Enfant-Jésus, access to state-of-the-art technology, requiring the involvement of this team, is now possible. Then there is the Institut de réadaptation en déficience physique de Québec (IRDPQ), a university institute that offers habilitation and rehabilitation services, as well as social integration, counselling and family support to individuals involved in the rehabilitation of patients receiving auditory brainstem implants. Finally, since its creation in 1984, the Quebec Cochlear Implant Research Foundation has funded all new and research activities in the field of auditory implants, and has also financed the cost of the first two auditory brainstem implants.

Patients who most often received the auditory brainstem implant are those presenting with type 2 neuro-fibromatosis. These patients have benign tumours that destroy the auditory nerves, making it impossible to use a standard hearing aid or a cochlear implant due to the complete absence of the nerve. Some patients who have suffered from meningitis resulting in total deafness, due to the destruction of the cochlear nerve and new bone formation within the cochlea, may also benefit from the auditory brainstem implant.

Following surgery, recipients should receive speech therapy and audiology follow-up to relearn how to interpret new sounds. Post-surgery studies show that 84% of patients who have received these implants are satisfied with the results and would advise others to undergo the same procedure.

Thus, patients presenting profound deafness in both ears with a destroyed cochlea and/or auditory nerve can benefit from this new auditory technology. Without this implant, these patients are completely isolated from the world of sound. With an implant, they are able to enjoy greater interaction with their surroundings and experience a more fulfilling social life.