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Cochlear implants: candidacy, bimodal and EAS, single-sided deafness, ABI and outcomes
A cochlear implant bypasses the hair cells and stimulates the spiral ganglion neurons and the cochlear nerve directly. So the decision rests on two things: are well-fitted hearing aids no longer enough, and is there a nerve to stimulate. Time matters a great deal — the longer the deafness, the weaker the result.
Why it matters in the exam
In an adult deafened after acquiring language, candidacy is set mainly by speech recognition (words and sentences) with fitted, verified aids; very poor recognition despite good aids is the main reason to implant. In children, a bilateral profound loss with no auditory and language progress on verified aids is a clear indication, and implantation is as early as possible (usually around one year or earlier). If MRI shows no cochlear nerve (aplasia), a cochlear implant will not help, and an auditory brainstem implant (ABI) is considered — which also suits an absent cochlea or a destroyed nerve, as after removing bilateral schwannomas in NF2. After bacterial meningitis implantation must be quick, before the cochlea ossifies (labyrinthitis ossificans).
Bimodal listening pairs an implant on one side with acoustic amplification on the opposite side: the aid adds low-frequency information — F0, voicing and music — that the implant carries poorly. EAS (hybrid) suits good low-frequency hearing (up to about 500 Hz) with a profound high-frequency loss: in the same ear the implant stimulates the base electrically and the aid amplifies the lows acoustically, so preserving hearing in surgery matters. In single-sided deafness only an implant gives input back to the deaf ear and allows some binaural benefit; in congenital single-sided deafness the cochlear nerve must be checked first. Outcomes: the longer the ear went without sound before surgery, the poorer the result tends to be; in children implanted by about 3.5 years P1 latency reaches normal, and in those implanted after about 7 years it usually does not. Dizziness is a relatively common, usually passing complication; serious complications are rare.
Key points
- Adult: candidacy by speech recognition with verified aids.
- Child: profound loss without progress — early implant.
- No nerve or NF2 — ABI; meningitis — quickly.
- Bimodal adds the lows; EAS in the same ear.
- Single-sided deafness — implant; short deafness — good result.
Summary table
| Situation | Decision | Reason |
|---|---|---|
| Adult with progressive loss | Implant if recognition with verified aids is very poor | Speech recognition is the main candidacy test |
| Infant with bilateral profound loss | Early implant if there is no progress with aids | Developmental window |
| No cochlear nerve / NF2 | ABI | No nerve for a cochlear implant to stimulate |
| After meningitis | Urgent implantation | Risk of cochlear ossification |
| Bimodal | Implant and aid in different ears | F0, voicing and music from the aid |
| EAS | Implant and aid in the same ear | Lows acoustic, highs electric; hearing preservation |
| Single-sided deafness | Implant — the only option that gives input back to the deaf ear | In congenital cases check the nerve first |
A free exam question
In which of the following is the prognosis for cochlear implant success very poor?
- A. A profound mixed loss due to advanced otosclerosis
- B. A congenital profound sensorineural loss due to a Connexin 26 mutation
- C. A profound loss due to hypoplasia of the auditory nerve
- D. A profound loss due to auditory neuropathy related to Otoferlin
In the full version for subscribers
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Sources
- Niparko (ed.), Cochlear Implants: Principles and Practices, 2nd edition (2009) — Candidacy, surgery and outcomes
- Kral & Sharma, Trends in Neurosciences, 2012 — Developmental neuroplasticity after cochlear implantation
- Van de Heyning et al., Audiology and Neurotology, 2017 — Towards a unified testing framework for single-sided deafness studies (cochlear implants in SSD)
Sources are given for further reading; the text is written afresh and not copied from them.
Reviewed by the Examqo AI Professor · 2026-11-02. The text may contain errors; when in doubt, check the source.