Abstract
Electrode array misplacement is an infrequent complication in cochlear implant surgery. A case report of electrode array insertion into the posterior semicircular canal, and its effects on the vestibular function is described. Video head impulse test (vHIT) has become an exceptional diagnostic tool to study vestibular function. We present our experience using the vHIT to detect a misplaced electrode array after cochlear implant surgery.
1
Introduction
Cochlear implantation is a well-standardized procedure for the treatment of severe to profound bilateral sensorineural hearing loss. Complications including infections, extrusion or flap-related are rare in cochlear implantation . Extracochlear electrode array misplacement is an even more infrequent complication with a published incidence rate between 0.2% and 5.8%, and an average of 0.37% in the literature .
Video Head impulse test (vHIT) is a novel test to study vestibular function of vestibule–ocular reflex, not only from the lateral semicircular canal but also vertical semicircular canal . We present a case report of electrode array misplacement into the posterior semicircular canal in cochlear implant surgery, and the use of vHIT to detect vestibular injury from array misplacement in the inner ear.
2
Case report
A 56-year-old female was referred to the cochlear implants unit for cochlear implant evaluation. Patient had suffered chronic otitis media in both ears, right worse than left hearing. Preoperative workup included audiometric testing and a CT of the temporal bone that showed only soft tissue opacification in the middle ear space, consistent with probable fibrosis. MRI showed normal inner ears. The patient was determined to be an appropriate candidate for cochlear implantation. Surgery was performed via standard mastoidectomy and facial recess approach to the round window. However, the round window was not clearly visualized intra-operatively due to fibrosis. A cochleostomy was performed superior to the round window after clearance of middle ear soft tissue/fibrosis as much as possible. Full electrode insertion of the implant was achieved. Intraoperative impedance testing was high but within normal range. Neural response telemetry (NRT) was measured in only 6 basal electrodes at high levels of stimulation, and absent in the middle and apical electrodes. Intraoperative X-ray study at the end of the procedure was inconclusive. In the immediate post-operative period, patient complained of acute vertiginous symptoms. Follow up CT temporal bone demonstrated the electrode array coursing through the vestibule and entering into the posterior semicircular canal ( Fig. 1 ).
Management options were discussed with the family. Two options considered were: concurrent implant removal and another attempt to reimplant in the same ear or implant removal and delay cochlear implantation in the contralateral side. The patient elected to undergo a cochlear implant placement in the contralateral ear (Left) next month. Electrode insertion through the round window was performed. Intraoperative impedance and NRT measurements were normal.
The video Head impulse test (vHIT) (otometrics, Denmark) was performed a week after her left cochlear implant surgery ( Fig. 2 ). It detected a low gain in the right posterior semicircular canal with delayed covert catch-up saccades, and a normal gain with small covert saccades in the left lateral semicircular canal. At two-year follow-up, the patient had a mild hearing loss (40 dB) with a 90% word speech recognition when aided with her left cochlear implant.
