This cross-sectional study investigated vestibular function outcomes after cochlear implantation in patients with inner-ear anomalies.

Twenty-two patients with bilateral symmetric inner-ear anomalies and 28 patients with normal inner ears were included. All were congenitally or progressively deaf persons implanted unilaterally during the previous 15 years. Vestibular system function was assessed by vestibular-evoked myogenic potential and bithermal caloric tests.

The vestibular-evoked myogenic potential abnormality rate in implanted ears with an inner-ear anomaly was 81.8 per cent, compared with 39.3 per cent in implanted ears with normal anatomy. In the non-implanted sides, the rate was 45.5 per cent (10 out of 22 cases) in the inner-ear anomaly patients compared with 17.9 per cent in patients with normal inner-ear structure. The respective abnormal caloric test rates in inner-ear anomaly versus normal anatomy patients were 81.8 per cent and 17.9 per cent (implanted ears), 77.3 per cent and 14.3 per cent (non-implanted sides).

Inner-ear anomaly and implantation were both associated with more vestibular-evoked myogenic potential abnormalities; when occurring together, these factors showed a synergistic effect. Caloric test abnormality is mainly dependent on the presence of an inner-ear anomaly, but implantation is not associated with caloric abnormality.