Cochlear Implants ent

Cochlear Implants

Definition: Electronic device providing useful hearing and communication for persons with severe to profound sensorineural hearing loss who cannot benefit from hearing aids.

Principle: Produces meaningful electrical stimulation of the auditory nerve (bypassing damaged hair cells).

1. Components

External Component Internal Component (Surgically Implanted)
  • Speech Processor: Body worn or BTE (Behind-the-ear is preferred).
  • Transmitter: Sends signal to internal part.
  • Receiver/Stimulator: Receives signal via RF.
  • Electrode Array: Linear array of contacts placed in cochlea.
Cochlear Implant
Cochlear Implants

2. Mechanism of Action

Current implants are multichannel processors delivering current to different places along the basilar membrane.

Microphone (Picks up sound)
↓
Speech Processor (Codes sound into electrical pulses)
↓
Transmitting Coil (Sends signal via Radiofrequency)
↓
Receiver/Stimulator (Decodes signal)
↓
Electrode Array (In Scala Tympani)
↓
Spiral Ganglion Cells → Auditory Nerve → Brain
Coding Strategies: Techniques to deliver meaningful speech parameters.
Examples: CIS (Continuous Interleaved Sampling), ACE (Advanced Combination Encoder), SPEAK, SAS.

3. Candidacy Profile

Used in both Children and Adults.

Selection Criteria

  1. Bilateral severe to profound SNHL.
  2. Little/No benefit from hearing aids.
  3. No medical contraindication for surgery.
  4. Realistic expectations.
  5. Good family/social support (for habilitation).
  6. Adequate cognitive function.

Candidate Types

  • Prelingual: Deafened before acquisition of speech/language.
  • Postlingual: Deafened after acquisition of speech/language.

4. Importance of Early Intervention

⚠ Auditory Deprivation: Lack of stimulus in early childhood causes degeneration of central auditory pathways.

Early implantation (as early as 12 months) is vital to preserve potential for speech and language acquisition.

5. Outcomes & Prognosis

Predictors of Success

  • Previous auditory experience (Postlingual > Prelingual).
  • Younger age at implantation.
  • Shorter duration of deafness.
  • Neural Plasticity of the auditory system.

Results by Group

Group Expected Outcome
Postlingual (Adults/Kids) - Very good benefit.
- Recognize speech with minimal/no lip reading.
- Can eventually use telephone.
Prelingual Children - Good speech/language over time (takes years).
- Requires constant auditory-verbal training.
Prelingual Adults - Limited benefit.
- Mostly obtain sound awareness rather than speech understanding.
📚 Source: Dhingra ENT

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