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Cochlear Implantation in Adults


A cochlear implant is an implanted medical device that restores the ability to perceive sound. The two patient populations that have benefited most from cochlear implants are children with congenital or early-onset profound hearing loss and postlingual adults who no longer benefit from amplification.

Key Operative Learning Points

  • The middle ear is accessed via mastoidectomy through a facial recess approach between the facial and chorda tympani nerves.

  • The round window is located inferior to the incudostapedial joint and is the key landmark for insertion of the electrode array.

  • The receiver-stimulator portion of the cochlear implant is positioned 2 cm posterior to the mastoidectomy cavity.

  • Slow insertion of the electrode is thought to minimize trauma to the inner ear and potentially preserve hearing.

Preoperative Period

History

History of Present Illness

  • Details of hearing loss: When did the hearing loss begin? Has its progression been gradual, rapid, or sudden? Is there a known cause for the hearing loss—hereditary, noise-related, ototoxic medications, meningitis? Which ear is the better-hearing ear?

  • Amplification history: How long has the patient used amplification in each ear? If/when did the patient stop wearing a hearing aid on either side?

  • Current communication ability: How much lip-reading ability does the patient have? Which environments are problematic? Is the patient socially isolated?

Past Medical History

  • Prior treatment: Sudden hearing loss, chronic ear disease, previous ear infections, radiation therapy

  • Medical illness: Any conditions precluding 3 hours of general anesthesia? Cardiac, pulmonary status?

  • Surgery: Prior implants? Stapes surgery? Chronic ear surgery? Craniotomy?

  • Medications: Surgery on patients using anticoagulants: nonsteroidal anti-inflammatory drugs (NSAIDs), warfarin, rivaroxaban. Inquire about oral narcotic with acetaminophen abuse.

Physical Examination

  • General appearance: Ability to communicate in office setting? Eye contact? Syndromic features?

  • Ear: Postauricular skin characteristics? Previous surgical scars? Ear canal and tympanic membrane intact, free of infection? Otorrhea?

  • Vestibular: Nystagmus? Gait?

  • Cranial nerves: Facial nerve function? Weber and Rinne tests?

Imaging

  • Standard preoperative computed tomography (CT) imaging to assess temporal bone anatomy. Check for abnormal cochlear morphology (ossification in setting of meningitis); enlarged vestibular aqueduct; and characteristics of the facial nerve, sigmoid sinus, and tegmen.

  • Magnetic resonance imaging (MRI) may be used in patients where there is concern for cochlear nerve aplasia in order to visualize the nerve within the internal auditory canal. It may also help in assessing the patency of the cochlea.

Indications

  • Children with prelingual deafness

    • Children 1 to 2 years of age: Pure tone average (PTA) >90 dB in bilateral condition

    • Children above 2 years of age: Pure tone average (PTA) >0 dB in bilateral condition or failure to progress with auditory amplification

  • Adults with postlingual deafness

    • Bilateral moderate to profound sensorineural hearing loss no longer benefiting from amplification

    • Open set sentence bilateral testing less than 60% in best-aided condition, less than 50% in the better ear (non-Medicare)

    • Hybrid cochlear implant

      • Normal to moderate hearing loss in low frequencies and severe to profound loss in the middle to high frequencies

      • Consonant-nucleus-consonant (CNC) word score between 10% and 60% in the ear to be implanted in the preoperative aided condition and the other ear equal or better but not above 80%

      • Previous suitable hearing aid trial if not already using amplification

Contraindications

  • Cochlear nerve aplasia

  • Cochlear aplasia

  • Active middle ear infection

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