The Early Postoperative Effects of Cochlear Implantation on Horizontal Semicircular Canal Function

To use video head impulse testing to examine the effect of cochlear implantation (CI) on horizontal SCC vestibulo-ocular reflex (VOR) gain early after surgery, and to relate outcomes to subjective imbalance.

Prospective cohort study.

Academic tertiary referral center.

Thirty-seven (23F:14M) adult cochlear implant recipients (mean age, 55; age range, 20-80).

Cochlear implantation.

The VOR of the horizontal semicircular canal of both the operated and non-operated ears was examined using video head impulse testing before surgery and at days 1, 7, and 28 following surgery. VOR gain, VOR gain asymmetry, and the change in VOR gain from preoperative baseline where the primary outcome measures. Subjective imbalance was assessed using a structured questionnaire.

VOR gain value for the operated ear was 0.88 ± 0.21. Mean VOR gain on day 1 postoperatively was 0.86 ± 0.19; on day 7, 0.87 ± 0.17, and on day 30, 0.91 ± 0.21. Before surgery median asymmery was -5.50%, on day 1 it was -5.30%, at day 7, -6.44%, and at day 30 it was -2.61%. There was no significant difference between these measures for the cohort across the four time points. Thirteen of 37 (35%) of patients experienced imbalance in the follow-up period, but this was not correlated to changes in VOR gain.

Horizontal semicircular canal function is preserved in the immediate and early postoperative period. This suggests that horizontal semicircular canal impairment is not likely to be responsible for postoperative imbalance.