[The monaural pseudo-stereophonic hearing aid (BAHA) in unilateral total deafness: a study of 29 patients].

For many years, unilateral total deafness has been considered a minor handicap which does not require the fitting of a hearing aid. If the condition did give a major problem, the usual recommendation for this type of hearing loss was a CROS system which, in addition to problems of function and aesthetics, gave poor results. Faced with increasing demands from these patients, and given the good performance of bone conduction implants (BAHA), we decided to try to implant these devices on the deaf side, which allowed, by way of transcranial conduction, stimulation of the functioning ear and the re-establishment of a certain degree of stereophonic hearing. This study of 29 patients who were tested by stereophonic audiometry pre- and post-implantation shows that this type of aiding is beneficial, with improvement of the threshold of intelligibility against background noise of between 5 and 15 dB during Hirsch's test, correction of the "dead angle" on the deaf side, and improvement in localisation of sound in space. From the functional point of view, 88% of patients were satisfied with their aid, which they wore for 8 or 9 hours per day, and had a marked improvement in their hearing performance under various conditions which had proved very difficult for them before they were fitted with the aid. These results all demonstrate the effectiveness of the implant used in this way. The fact that sounds are received on the totally deaf side goes a long way towards establishing satisfactory hearing. True stereophonic hearing could not be established in any of the cases, because this requires input from two ears. It is for this reason that we have termed this type of aid as monaural pseudo-stereophonic.