Is binaural hearing achievable in subjects with congenital unilateral conductive hearing loss?

The main problem of rehabilitation of unilateral conductive hearing loss (UCHL) with a hearing device or surgical repair is that the treated impaired ear has to compete with the normal hearing ear. Because of the impressive capacities of a normal hearing ear, rehabilitation results in a significant hearing asymmetry (20 -30 dB in children), and unilateral absence of spectral information processing. We review binaural hearing data as obtained after treatment in a population of subjects with congenital UCHL. Several measures addressing binaural hearing after treatment have been studied, e.g. directional hearing (detection of interaural time and level differences), binaural summation, binaural squelch and the effective use of head shadow. Whenever possible, binaural outcomes are compared with values obtained in normal hearing subjects, using the same tests. Included in this review are 11 papers, describing results in 169 subjects with treated unilateral aural atresia. Six papers presented binaural data gathered after atresia repair and five papers after application of either a percutaneous bone-conduction device (BCD), an active transcutaneous BCD, a passive transcutaneous BCD or an active middle ear implant. Binaural scores were collected and compared to norm values. Mean binaural scores are expressed, as z-scores; if z < 2 then the mean score falls within the normal range. Subjects with unilateral amplification do not perform as good as normal hearing listeners. It remains uncertain to conclude whether subjects with congenital UCHL have an equal chance for optimal rehabilitation compared to subjects with acquired UCHL. Subjects from the latter group can benefit from a maturated auditory system once they are aided. The congenital group might benefit from auditory system development while in the aided situation. When consistent amplification, although resulting in an asymmetrical input, is present during a certain critical period, it might result in better handling of the listening situation. [ABSTRACT FROM AUTHOR]