CI Atlas · Beyond Hearing: The Implant for Tinnitus and the Balance System · Module 09

9Checking the Balance System Around Surgery

If the implant can cost balance, the team should know what each ear's labyrinth is worth before choosing where to operate. A short history and bedside screen, backed by targeted canal and otolith tests, documents the baseline, points to the safer ear, and gives a reference for the recipient who turns up dizzy afterwards.

FThe focused history and bedside screen

Ask specifically about vertigo, unsteadiness in the dark, oscillopsia (the world bouncing when walking) and falls, because these flag a pre-existing vestibular deficit that ear choice should respect. A few-minute bedside screen, head-impulse test, head-shake, Romberg and gait, and a Dix-Hallpike where indicated, separates a compensated chronic loss from an active problem. Reported symptoms correlate poorly with measured function, so a normal history does not exclude vestibular loss and an objective baseline is still worthwhile in the candidate at risk. The full structured history and screen are detailed in the Balance chapter; this module covers the implant-specific use of them.[2017][2020]

No single bedside test sees the whole labyrinth, so a peri-operative battery samples each part. The caloric probes the lateral canal at low frequency and is the least sensitive to surgical change, while the vHIT tests all three canals at high frequency and is often preserved. The otolith reflexes are the fragile ones: the cVEMP (saccule) is the most vulnerable to insertion trauma, and the oVEMP (utricle) is frequently affected. Reading the canals and otoliths together is what lets you decide which ear is safer to implant. Schematic.

TThe targeted test battery

The caloric test and the video head-impulse test (vHIT) assess the horizontal canal across low and high frequencies; caloric is the least sensitive to post-implant change while vHIT is often preserved. Cervical and ocular VEMP probe the saccule and utricle; cVEMP loss is the most frequent objective abnormality after implantation, reflecting the saccule's proximity to the basal cochlea. A combined battery (canal plus otolith) is needed because no single test captures the whole labyrinth, and objective and subjective findings diverge in roughly a third of patients. Around 30% of recipients show a measurable change on this battery after surgery, which is why a pre-operative baseline is the only way to attribute later change to the implant.[2015][2008][2017]

The vestibular-sparing rule says to implant the worse-hearing, worse-vestibularear wherever audiological candidacy allows, so that any vestibular loss the surgery may cause lands on the side that already has the least balance function to lose. This tool slides each ear toward the green “safer to implant” corner; when the two ears are close, the choice is marginal and other factors — cochlear nerve, anatomy, patient preference — decide. The rule protects the better-balancing ear as a reserve, which matters most in patients already at risk of bilateral vestibular failure. Illustrative.

CUsing the results to pick the ear

The guiding principle is to implant the worse-hearing and, where they coincide, the worse-vestibular ear, sparing the better balance organ. If both ears hear equally but one has a clearly weaker labyrinth, the weaker-balance ear is generally the safer surgical target. When the candidate depends on a single functioning labyrinth, the team should weigh the balance cost against the hearing gain and counsel explicitly, especially before bilateral surgery. Tinnitus, hearing-preservation goals and anatomy also feed the choice, so the vestibular result is one weighted input rather than an override.[2006][2020]

Overlaying the pre-operative baseline on the post-operative result shows where the dizziness comes from: in this recipient the canals are largely held (caloric and vHIT barely move), while the otolith organs collapse— the saccular cVEMP falls furthest, the utricular oVEMP next. Switching the device on adds a small extra disturbance the baseline could never have predicted, pointing to an electrically driven, device-on component layered on top of surgical loss. Comparing canal-versus-otolith change and device-on-versus-off is how you separate a structural injury from a programmable one. Illustrative.

CTesting the dizzy recipient afterwards

When a recipient becomes dizzy, repeat the same battery and compare with the pre-operative baseline to see whether the canals, otoliths or both have changed. Check whether the dizziness is switched on with the device, which points to electrical spread to vestibular afferents rather than a structural deficit. Most post-implant vestibular loss compensates with reassurance, vestibular rehabilitation and consistent device use; persistent or position-triggered symptoms warrant a fuller neurotologic work-up. The detailed management of the dizzy recipient is carried in the Balance chapter; the role here is to document, localise and triage.[2018][2015]

Case 30.9 · Checking the Balance System Around

A 47-year-old with symmetric bilateral profound loss has no dizziness history. As part of work-up you obtain caloric, vHIT and cVEMP for both ears: the right shows reduced caloric response and absent cVEMP, the left is normal on all three.

Which ear should generally be implanted, and why test at all when she is asymptomatic?

Self-assessment — Module 93 questions

Question 1

Which combination of tests best documents both canal and otolith function before implantation?

Question 2

When ears hear equally, which is generally the safer ear to implant on balance grounds?

Question 3

A recipient reports dizziness only when the processor is switched on. What does this most suggest?

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