9Choosing the Ear: Vestibular Risk and Bilateral Implants

TThe selection rule

If pre-op vestibular function is asymmetric, implant the ear with poorer vestibular function first, retest post-op, and reconsider the second side if function dropped Cochlear implantation of an 'only balancing ear' should be performed only after carefully weighing the risk of inducing severe bilateral vestibular hypofunction Choosing the worse-balancing ear preserves the patient's better labyrinth against surgical injury.[2004][2016]

CThe bilateral-CI hazard

Iatrogenic bilateral vestibular sensory failure has so far been rare, but growing use of bilateral implantation heightens its likelihood Bilateral hypofunction can cause disabling postural instability, disequilibrium and oscillopsia (degraded visual acuity during head movement) Among five patients implanted contralateral to an ear with profound vestibular loss, two became bilaterally hypofunctional and one lost vestibular reflexes entirely.[2004][2022]

TWhen simultaneous bilateral may be reasonable

In pre-existing bilateral vestibular loss (for example after meningitis), simultaneous bilateral implantation can be reasonable because vestibular responses are already reduced or absent Meningitic candidates also face cochlear ossification, favoring early and possibly simultaneous surgery and fewer procedures Counseling must still address the residual risk and the possibility of oscillopsia if any vestibular function remains.[2016][2004]

CSurgical and patient modifiers of risk

Patients with good pre-op function have more to lose, while those with pre-op dizziness may have unstable structures prone to further damage Older age increases the likelihood of losing vestibular function (thresholds reported variously >59, >60, >70 years) Electrode position matters: arrays in the scala vestibuli or vestibule increase dizziness, and stiffer arrays produce greater caloric reduction.[2003][2016]