The Vestibular Implant: Hearing Preservation during Intralabyrinthine Electrode Insertion-A Case Report

Abstract

Objective: The vestibular implant seems feasible as a clinically useful device in the near future. However, hearing preservation during intralabyrinthine implantation remains a challenge. It should be preserved to be able to treat patients with bilateral vestibulopathy and (partially) intact hearing. This case study investigated the feasibility of hearing preservation during the acute phase after electrode insertion in the semicircular canals.

Methods: A 40-year-old woman with normal hearing underwent a translabyrinthine approach for a vestibular schwannoma Koos Grade IV. Hearing was monitored using auditory brainstem response audiometry (ABR). ABR signals were recorded synchronously to video recordings of the surgery. Following the principles of soft surgery, a conventional dummy electrode was inserted in the lateral semicircular canal for several minutes and subsequently removed. The same procedure was then applied for the posterior canal. Finally, the labyrinthectomy was completed, and the schwannoma was removed.

Results: Surgery was performed without complications. No leakage of endolymph and no significant reduction of ABR response were observed during insertion and after removal of the electrodes from the semicircular canals, indicting no damage to the peripheral auditory function. The ABR response significantly changed when the semicircular canals were completely opened during the labyrinthectomy. This was indicated by a change in the morphology and latency of peak V of the ABR signal.

Conclusion: Electrode insertion in the semicircular canals is possible without acutely damaging the peripheral auditory function measured with ABR, as shown in this proof-of-principle clinical investigation.

Keywords: bilateral vestibular areflexia; bilateral vestibulopathy; electrode design; hearing preservation; neural prosthesis; vestibular implant; vestibular prosthesis; vestibulo-ocular reflex.

Figures

Figure 1

Preoperative audiogram of the patient.

Figure 2

Auditory brainstem response audiometry (ABR) artifacts during drilling. The left panel shows the surgical drilling, and the right panel shows the synchronized ABR signal. It illustrates that surgical drilling induces ABR artifacts, making it impossible to draw any precise conclusions about the ABR signal during drilling.

Figure 3

Illustration of electrode placement and fenestrations in the semicircular canals. The LSCC and PSCC were fenestrated at points away from their ampullae. The electrode was first inserted into the LSCC, up to the cupula (1). After removal of the electrode out of this canal, it was inserted into the PSCC, up to the cupula (2). Abbreviations: SSCC, superior semicircular canal; LSCC, lateral semicircular canal; PSCC, posterior semicircular canal.

Figure 4

Surgical steps and obtained auditory brainstem response audiometry (ABR) signals. The left column presents the surgical steps, the right column the ABR measurements obtained during those steps. In the last row, four ABR signals are shown in the same box. These signals illustrate the last four ABR measurements of the study procedure. Their timing can be found in Table 1.