The investigators assume that cochlear implants in this indication are not only effective but also cost-effective. The investigators' experimental protocol relies on real life therapeutic strategy, where a cochlear implant may be proposed once CROS and bone conductions systems have failed. Thus, all subjects enrolled in our study will try CROS and bone conduction devices. If these trials are ineffective, the remaining subjects will be randomized between two arms (cochlear implantation vs 6 months abstention followed by cochlear implantation). A comparative cost-utility analysis between the two arms, of medical consequences measured in terms of quality of life will identify a preference for a strategy. Specific binaural hearing measurements with respect to each treatment option (abstention, CROS, bone conduction device, cochlear implant) will also be collected.

Single sided deafness and profound asymmetrical hearing loss are impairments that significantly alter quality of life. Behavioural problems and scholar delays have been reported in children. Speech recognition with background or competing noise and sound localization are both impaired. 1/1000 new borns are affected and the incidence tends to rise in the adult population. At the moment, there is no guideline regarding the treatment of single sided deafness and asymmetrical hearing loss. Some patients don't even receive any therapeutic proposition.

Three treatment options are available :

• CROS (Contralateral Routing Of the Signal) systems that convey the auditory information from the deaf ear to the good ear using wi-fi
• bone conduction devices which use transcranial conduction to convey auditory information from the poor ear to the good ear
• cochlear implants that directly stimulate afferent fibers of auditory nerve in the poor ear Cochlear implantation is therefore the only treatment which restores stimulation in the poor ear. Its efficacy in single sided deafness associated with incapacitating tinnitus have been demonstrated by Pr Van de Heyning (Leeuven, Be) and colleagues. Its interest has been compared to CROS systems and bone conduction devices in a valuable study conducted by S. Arndt (Pr Laszig, Freibourg, Ger). Cochlear implants provided better speech in noise recognition scores in dichotic hearing, i.e when speech and noise sources are spatially separated. Their first publication involved 11 patients but to date, more than 110 patients with single sided deafness have been included in their protocol. The efficacy of cochlear implantation has thus been validated in the treatment of single sided deafness and asymmetrical hearing loss.

The investigators assume that cochlear implants in this indication are not only effective but also cost-effective. The investigators' experimental protocol relies on real life therapeutic strategy, where a cochlear implant may be proposed once CROS and bone conductions systems have failed. Thus, all subjects enrolled in our study will try CROS and bone conduction devices. If these trials are ineffective, the remaining subjects will be randomized between two arms (cochlear implantation vs 6 months abstention followed by cochlear implantation). A comparative cost-utility analysis between the two arms, of medical consequences measured in terms of quality of life will identify a preference for a strategy. Specific binaural hearing measurements with respect to each treatment option (abstention, CROS, bone conduction device, cochlear implant) will also be collected.

Inclusion Criteria:

• Social security affiliation
• Single sided deafness or profound asymmetrical hearing loss confirmed using pure tone audiometry and auditory brainstem responses, with or without tinnitus
• Written consent to the protocol

Exclusion Criteria:

• Retrocochlear pathology (vestibular schwannoma, severe central auditory processing disorder)
• Major cochlear ossification or malformation
• Subjects under juridical protections or tutelage measure