[Results of Speech Audiometry Testing in Case of Transcranial CROS Depend on Duration of Deafness]

In single sided deafness, treatment with transcranial CROS makes pseudo stereophonic listening possible. This leads to improved speech understanding in noise. However, several reports show large variations between the individual results of the benefit by speech audiometry in noise. One possible factor is the duration and changes in the auditory pathway between the onset of deafness to CROS supply. 18 patients with single sided deafness have tested a transcranial CROS supply. The speech intelligibility thresholds were evaluated in 2 spatial hearing situations each with CROS and unaided. When speech was arriving at 45° from the deaf ear and noise at 45° from the hearing ear, a significant improvement of speech reception threshold for 50% intelligibility was detected by CROS supply compared the medians. Patients with longer duration of deafness showed higher benefit by an average of -4.0 dB, in contrast to patients with short duration of deafness. In the reversed situation, that speech on the hearing ear and noise on the deaf ear was a significant deterioration observed, an average of 3.1 dB at longer deafened patients. In addition, a highly significant correlation was found with the individual changes in the speech recognition threshold between the two situations. The duration of deafness is an essential factor in the individual benefit estimate for treatment with transcranial CROS supply. The time frame for audimetrically proven changes in the auditory pathway as a result of unilateral auditory deprivation can be estimated to about 1-3 years. Patients with short duration of deafness have low or no benefit from transcranial CROS supply.