Cochlear Implants - Uses and Innovations

Hearing loss can occur in both children and adults. It can be categorized into mild, moderate, moderately severe, severe and profound hearing loss. Profound hearing loss refers to a condition when a person cannot hear sounds softer than 90 dB.

Causes of Hearing Loss

There are various causes of hearing loss. They are:

• Genetic conditions.
• Viral infections.
• Loud noise.
• Head trauma.
• Old age.

So, you have a hearing problem which does not improve with wearing hearing aids. Your doctor asks you to get a hearing test done and tells you that the hearing report says 'very severe or profound hearing loss' and you need to have a cochlear implant for this condition. Here, we discuss the cochlear implants, their uses, indications, contraindications, precautions, surgical procedure, and recent innovations.

A cochlear implant is an electronic device which is implanted in the cochlea and it directly stimulates the auditory nerve and aids hearing.

Parts of a Cochlear Implant

1. Sound processor containing a microphone, battery, coil, and electronics which is fitted on the outer skin behind the ear.
2. The implant, which is placed in the cochlea, houses a coil which receives signals and an array of electrodes for stimulation of the cochlear nerve.

Uses

Various conditions where cochlear implants are required include:

1. Severe to profound sensorineural hearing loss.
2. Patients not benefitted from hearing aids.
3. Patients not preferring hearing aids.
4. Can also be implanted in infants earlier for a better outcome, that is, better oral communication in later life.

CT or MRI imaging is done prior to implantation for evaluation of facial nerve, cochlea, cochleovestibular nerve, brain and brainstem as any aplasia/hypoplasia of cochlea, an absence of cochlear/auditory nerve or congenital malformations may alter the outcome.

Contraindications of Cochlear Implants

1. An absence of cochlea.
2. An absence of cochlear nerve.
3. Active middle ear infection.

Get vaccinated with Prevnar or Pneumovax vaccine to prevent a risk of meningitis before cochlear implantation. The vaccines are available for both children and adults.

Complications

Complications are few:

1. Risk of meningitis.
2. Facial nerve paralysis 1 %.
3. Device failure requiring reimplantation 2 to 6 %.
4. Transient vertigo.
5. CSF (cerebrospinal fluid) leak.

Precautions

• Not MRI compatible. Recent innovations are compatible with MRI also.
• Avoid head trauma. Children with implants should wear helmets while playing for implant protection.
• X-ray and CT scan are to be done with caution, as it can affect the external processor.

Surgical Procedure

Surgical procedure for implantation is performed under general anesthesia. It involves making an incision behind the ear to create a well for placing the receiver and small cochleostomy for insertion of the electrode array.

Facial nerve monitoring is required during the procedure to prevent injury to the facial nerve.

In the case of bilateral hearing impairment, implantation is preferably done in the ear with better hearing.

Patients can be sent home one to two hours after surgery with dressing on the ear and follow up for seven days.

Preoperative and postoperative steroids are given.

Types

Various types of cochlear implant systems are available which includes Clarion, Med El, Nucleus systems. Various innovations in implant design are available.

MRI compatible implants are also available with a removable magnet, which can be replaced later on after the procedure.

Recent innovations include cochlear implants that use laser pulses to trigger auditory signals from hair cells into the inner ear.

Research is being carried out to design better implants for the best communication outcome.