Describe the different components of cochlear implant. Mention patient selection criteria for cochlear transplant surgery. What are the advantage of multi channel over single channel cochlear implant?

→The different components of cochlear implant are:

1. Internal part (implant): placed surgically beneath the scalp
   • Array of electrode inside cochlea
   • Body of implant which contains a receiver/stimulator: decodes the signals from the external prosthesis and send the electrical charges to the individual electrodes.
2. External part:
   • Microphone
   • Speech processor
   • Transmitting coil

→The two main strategies used:

I. Continuous interleaved sampling (CIS): Med-EL(TM) and Clarion (TM)

II. Spectral peak processing (SPEAK): Cochlear(TM)

The patient selection criteria for cochlear transplant surgery have evolved over times as advances in cochlear implant technology produced subsequent improvement in performance outcomes. At any point, however, candidacy resolves around three basic questions:

• Is physical implantation of the device possible and/or advisable given the medical status of the patient?
• Is it likely that an individual will receive more communication benefit from a cochlear implant than from a hearing aid or alternatively, from no hearing prosthesis at all?
• Do the necessary supports exit in the individual psychological, family, education and  rehabilitative situation to keep a cochlear implant working and integrate into the patient’s life? If not, can they be developed?

Initially, only individuals with bilateral profound SNHL with no open set speech recognition were considered candidates for cochlear implants.

	1995	1990	1998	Today
Age of implantation	18 years or Older	Adults and children age 2 years or older	Adults and children age 18 months+	Adults and children age 12 months+
Onset of hearing loss	Postinguistic	Postlinguistic adults & pre/postlinguistic children	Pre/postlinguistic adults & children	Pre/postlinguistic Adult and children
Degree of SNHL	Profound	Profound	Severe-profound adults profound children	Severe-profound adults, children>2, profound children<2 years
Adult speech scores (open set)	0%	0%	40% or less sentences in quiet	50% on sentences in quiet in ear to be implanted, with 60% or less in contralateral ear or binaurally
Paediatric speech scores	N/A	0%	Lack of auditory progress, less than 20% paediatric word tests	Lack of auditory progress 30% or less on paediatric word tests.

The evaluation of candidacy process is a team approach:

• Audiologist
• Speech and language specialists
• Social worker
• Education consultant operating surgeon

ADULTS:

• Individual 18 years of age or older
• Severe to profound sensorineural hearing loss in both ears.
• Recently individuals with mild to moderate low frequency hearing with absent high frequencies are considered candidates for cochlear implantation using EAS.
• 2- speech recognition scores:
  • Advanced bionics specified sentence recognition up to 50% in the best aided condition.
  • Cochlear specified sentence recognition up to <50% sentence recognition in the ear to be implanted and <=60% in the opposite ear or binaurally, in the best aided condition.
  • Med El listed sentences recognition up yo 40% correct in the best aided condition.

CHILDREN (2-17 years)

• Severe to profound sensorineural hearing loss
• Limited benefit from binaural amplification.
• Multi-syllabic Lexical Neighborhood Test (MLNT) or Lexical Neighborhood Test (LNT) scores <=30%.
• FDA preimplant word recognition performance candidacy criteria for older children ranges range from 12-30% correct in the best aided condition.
• During the hearing aid trial (3 months period, children should be making at least month to month auditory progress as well as speech and language developmental progress.
• Regular speech therapy should be considered a part of the hearing aid trial for all children being seen for implant evaluation.

Children(12-24 months)

• B/I Profound sensorineural hearing loss
• Child must weigh about 9-10 kg from an anaesthesia viewpoint.
• Limited benefit from binaural amplification
• Specific circumstances may allow for earlier implantation. A child with meningitis is implanted as early as possible as the condition causes cochlear ossification. It also help to decrease the duration of auditory deprivation and its deleterious effects on the auditory pathways.

OTHER CANDIDACY CRITERIA:

• Family willingness to follow recommendations: enroll in speech, language and auditory therapy; and return from the follow up appointments.
• Educational and home environments that is supportive of cochlear implants
• Having no medical contraindications to electrode insertion or receiver placement. Otitis media must be diagnosed and managed prior to implantation.Prior ear or prosterior fossa surgery must be investigated preoperatively.

The candidates can be divided into three categories. Among these, change over at an earlier age candidates make excellent implants as some plasticity for articulation still remains.

Postlingual	Onset of deafness has occurred after completion of speech development
Perillngual	Onset of deafness has occurred while speech development was occuring
Prelingual	Onset of deafness occurred prior to any development of speech a. Primary candidates: have not acquired language by any other means of communication b. Secondary candidates: have used another mode of communication (usually sign) to develop language c. Change over candidates: have developed auditory skulls using a hearing aid.

Post lingual category can be divided into:

• Post pubertal: adults and teenager who becomes deaf after experiencing normal hearing during their childhood and they are excellent candidates.
• Prepubertal group: 2-12 years and younger the child more likely speech will be lost.

In cochlear implant systems, the channel refers to the number of stimulation sites within the inner ear, or cochlea, and is defined by a range of frequencies or pitches. All sounds, ranging from low pitch (bass) to high pitch (treble) sound are separated into the number of available channels. The advantages of multi channel over single channel cochlear implant are:

 

	Single channel system	Multi channel system
Delivery	All sound information is delivered to only one channel.	Divides the incoming sound signal into various frequency bands
No. of electrodes	Use single pair of electrodes (signal and ground) through which current passes	Use at least 4 active electrodes to mimie the frequency analyzing capabilities of normal ear (basilar membrane)
Area of stimulation	All informationis transmitted to single area of stimulation within the cochclea, regardless of the pitch of the incoming signal.	Incoming information are transmitted to various sites of stimulation spanning the inner ear.
Frequency organization	Absent	Low pitch sounds are sent to apical part of the cochlea and high pitch sound to another (basal).Thus sounds are organised by frequency.
Sound processing	Simple	Complex
Speech understanding	Poor	Better
Insertion and fabrication	Less difficult	Difficult because it needs to be flexible and smooth enough to negotiate the 1st turn of the cochlea without causing extensive damage.
Improvement	Performance improvement reach s palteau by 1.5 years post implant	Improvement continues after 2 or more years post implant
Miscellaneous(not to write in difference)	> Preferred in patient with severely ossified cochlea which can be prevent a significant insertion depth for the electrode. > The possibility of using an ear level device in place of body worn box > The situation where simplicity of construction and low cost are paramount.	> multichannel implant is not strongly influenced by: -Age of onset of deafness when deafness occurs before 3 years . -Children with congenitial deafness have potential to obtain the sense of benefit as those with acquired loss.

 

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