Influence of insertion depth in cochlear implantation on vertigo symptoms and vestibular function.

OBJECTIVES: The aim of the present study was to investigate the effect of the electrode insertion depth in vestibular function after cochlear implantation.
MATERIAL AND METHODS: In a retrospective observational study design, 41 adult patients who had undergone cochlear implantation between 2006 and 2012 at a tertiary referral university hospital were included. The postoperative performed radiograph images of the petrous bone were acquired according to the Stenvers method. These were analyzed to determine electrode insertion depth. Pre- and postoperative subjective vertigo symptoms were assessed by a questionnaire. The function of the horizontal semi-circular canal was evaluated by caloric irrigation and the function of the sacculus was tested by using cervical vestibular evoked myogenic potentials pre- and postoperatively.
RESULTS: The average electrode insertion depth was 464°. A certain variability of insertion depth existed among the different electrodes according to their designs. No statistical difference of the insertion depth was found between patients with or without vertigo. There was also no correlation between electrode insertion depth and alterations of the measurable vestibular function.
CONCLUSION: In our study the variability of insertion depth didn't have a significant influence on subjective vertigo, horizontal semi-circular canal function or saccular function. Plain radiography is a rapid, simple and cost-effective method to determine electrode insertion depth after implantation. However the scalar position of the electrode cannot be analyzed in plain radiography, so that an interscalar dislocation as a possible influence in vestibular function remains undetected.