CI Atlas · Candidacy & Evaluation · Module 11

11Vestibular assessment at candidacy

The inner ear is an organ of balance as well as hearing, and implantation puts that balance at risk. Surgery in the cochlea carries a real chance of damaging the labyrinth on the operated side, so the candidacy work-up includes a focused look at vestibular function — not as a gate that excludes patients, but as a step that shapes which ear is implanted. The key fact is asymmetry: if the two labyrinths differ, the surgeon would rather implant the already-weaker one and spare the better balancer, and if the other side is already dead, implanting the sole functioning balance organ can be disastrous. Because no single vestibular test can declare a labyrinth dead, candidacy combines several, each probing a different frequency, into a picture much like an audiogram. This module covers balance testing as part of choosing whether and where to implant.

TWhy balance belongs in candidacy

Every candidate should have a focused vestibular history, a brief (under five minutes) bedside screen, and a review of the planning CT/MRI for labyrinthine anatomy; equivocal findings trigger quantitative testing. The aim is not exclusion — it is to detect a side-to-side asymmetry so the surgeon can preferentially implant the weaker labyrinth. Significant pre-existing unilateral vestibular loss is common, found in roughly 11–23% of candidates depending on the method.[2009]

Tap a cell to cycle normal → reduced → absent. No single test certifies a labyrinth as “dead,” just as one audiometric frequency does not condemn a cochlea — so candidacy combines caloric (very low frequency), head-shake, head-impulse (higher frequencies) and VEMPs (otolith) into a multifrequency picture. The aim is not exclusion but ear selection: detect a side-to-side asymmetry and preferentially implant the already-weaker labyrinth, sparing the better-balancing ear — crucial because implantation itself risks vestibular loss, and sacrificing an only-balancing ear can cause disabling oscillopsia. Schematic, after Della Santina.

CA multifrequency panel

No single test certifies a labyrinth as dead, just as a loss at one audiometric frequency does not condemn a cochlea. The tests probe different frequencies: caloric irrigation reads very low-frequency canal function (~0.003 Hz), head-shake nystagmus around 1–2 Hz, and head-impulse testing across 1–15 Hz. Combining them yields a multifrequency picture analogous to an audiogram, and VEMPs add a quantitative read of otolith (saccular) function — useful for choosing the ear in CHARGE-type dysplasia where the canals may be absent but the otolith organs intact.

CThe only-balancing-ear caution

Implantation itself carries roughly a 38% risk of some vestibular loss and about a 10% risk of severe loss in the operated ear. If the contralateral labyrinth is already dead, implanting the sole functioning balance organ can precipitate bilateral vestibular hypofunction — disabling oscillopsia (the world bouncing with every head movement) and postural instability. This reframes ear selection as a balance-preservation decision: it is an explicit argument to implant the poorer-balancing side, and to counsel carefully any patient with pre-existing contralateral loss (the link to ear selection in Module 18).

CAetiology and children

Certain deafness aetiologies predict labyrinthine involvement and raise vigilance during selection — Usher type I, congenital rubella, Waardenburg, Pendred, Jervell–Lange–Nielsen, and the CHARGE association with canal aplasia. In children, a vivid clinical clue is delayed motor milestones: failure to reach head control, independent sitting and independent walking by about 3, 8 and 18 months can mark bilateral vestibular hypofunction worth factoring into ear choice and counselling. Routine blanket caloric screening of every candidate was abandoned because it poorly predicts post-operative dizziness; its modern use is targeted ear selection, not a pass/fail gate.

Two facts make balance part of candidacy. First, a meaningful share of candidates — about 11–23% — already have asymmetric vestibular function before any surgery. Second, implantation itself damages the operated labyrinth surprisingly often: roughly 38% lose some vestibular function and about 10% lose it severely. Put together, they are the quantitative case for detecting asymmetry and implanting the weaker-balancing ear — and for never operating on a sole remaining balance organ. Illustrative figures; schematic.

Case 11.11 · The only balancing ear

A candidate's better-hearing left ear has a normal caloric response; the right ear is profoundly deaf with an absent caloric response. Imaging is otherwise unremarkable.

How should vestibular findings inform the plan?

Self-assessment — Module 112 questions

Question 1 · Trainee

What is the main purpose of vestibular assessment at candidacy?

Question 2 · Clinician

Why are several vestibular tests combined rather than relying on one?

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