CI Atlas · The Labyrinth Next Door: Balance and the Cochlear Implant · Module 13

13The Vestibular and Cochleovestibular Implant Frontier

As bilateral implantation makes iatrogenic bilateral vestibular failure more likely, the same engineering that restored hearing is being turned on balance. A multichannel vestibular prosthesis stimulates the semicircular-canal ampullae to restore three-dimensional motion sensing, and combined cochleovestibular devices are on the horizon. The chapter closes where it began: the labyrinth next door, now a target for restoration rather than only a casualty.

TThe clinical need

Bilateral vestibular hypofunction causes disabling postural instability and oscillopsia, and most but not all patients compensate enough to resume normal activity Decades passed with little progress in treating vestibular disorders beyond surgery for superior canal dehiscence, intratympanic gentamicin and rehabilitation For hypofunctional disorders such as uncompensated unilateral or bilateral loss, no treatment exists beyond rehabilitation — the gap the implant addresses.[2004][2007]

CHow a vestibular implant works

A multichannel vestibular prosthesis uses motion sensors to electrically stimulate the semicircular canals and restore three-dimensional vestibular sensation, proposed as treatment for those disabled by bilateral hypofunction Push-pull pairing means a single unilateral implant can theoretically restore motion sensing in all planes even in bilateral disease Electrical stimulation of the vestibular nerve evokes a measurable nystagmus (evoked VOR); a brisk plane-appropriate nystagmus confirms correct ampullary placement.[2007][2011]

The vestibular implant restores head-motion sensing the way a cochlear implant restored hearing: motion sensors drive electrodes at the three ampullary nerves, generating an electrically evoked VOR locked to real movement. The Geneva-Maastricht/MED-EL group performed the first human implant in 2007; the Johns Hopkins multichannel device (Della Santina) achieved continuous 24/7 sensory restoration with sustained gains in posture, gait and quality of life — even when the loss predated surgery by decades. Schematic.

CDevice lineage and human data

The lineage runs from Gong and Merfeld's single-axis prototype (2000) through the Della Santina multichannel prosthesis (MVP1/MVP2) that restored 3-D VOR sensation in monkeys Appropriate evoked VORs have been measured in human subjects with dedicated vestibular implants and with a modified cochlear implant A UW/Nucleus device received FDA feasibility-trial approval for refractory definite Meniere disease and has been implanted in humans.[2000][2011]

CToward a combined cochleovestibular implant

Current narrow (~150 µm) electrodes preserved hearing in 5 of 8 implanted monkeys with only small threshold shifts, showing combined hearing-and-vestibular function preservation is feasible Integrated vestibular-cochlear prostheses to restore both balance and hearing have been proposed and prototyped Current spread to neighboring structures can cause auditory percepts, facial twitching or wrong-plane vertigo, and high-frequency/bipolar stimulation and current focusing limit it.[2012][2011]

Case 24.13 · The Vestibular and Cochleovestibul

During placement of a vestibular-implant electrode in the horizontal-canal ampulla, stimulation produces a brisk pure horizontal nystagmus.

What does this intraoperative finding indicate?

Self-assessment — Module 132 questions

Question 1

A multichannel vestibular prosthesis primarily restores function by stimulating:

Question 2

Which finding best demonstrates that combined hearing-and-vestibular preservation is feasible?

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