Chapter 6 - Cochlear Implants

Front 1

THe critical residual neural elements stimulated by the cochlear implants appear to be the _________ or ______.

Back 1

spiral ganglion cells or axons

(damanged or mising hair cells of the cochlea are bypassed)

Front 2

What are the components of the cochlear implant system?

Back 2

1) A microphone
2) Externally worn speech processor
3) Surgically implanted electrode array places into the cochlea near the auditory nerve

Front 3

What are the names of the three commercially available cochlear implant systems that have FDA approval?

Back 3

Nucleus, MedEl, Clarion

Front 4

Several speech coding strategies exist.

Describe the 'feature extraction' stragegy.

Back 4

Feature extraction - key speech features such as amplitude and freq of vowel formans and the fundamental freq of voiced sounds are extracted.

Front 5

Several speech coding strategies exist.

Describe the 'continuous interleaved sampling (CIS)' stragegy.

Back 5

Continuous Interleaved Sampling (CIS) - the speech signal is filtered into a fixed number of bands and the speech envelope obtained and compressed for each channel into the narrow dynamic range of electrically evoked hearing. On each cycle of stimulation, a series of interleaved digital pulses rapidly stimulates consecutive electrodes in the array. The CIS strategy is designed to preserve fine temporal details in the speech signal by using high-rate, pulsatile stimuli.

Front 6

Several speech coding strategies exist.

Describe the 'analog' stragegy.

Back 6

Analog strategy - simultaneous analog stimulation (SAS) filters then compresses the incoming speech signal for simultaneous presentation to the corresponding enhanced bipolar electrodes. The relative amplitudes of information in each channel and the temporal details of the full speech waveform in each channel transmit speech information.

Front 7

What are the adult candidacy criteria for cochlear implantation?

Back 7

1) Above 18 yo with no upper age limit
2) Bilateral severe-to-profound HL
3) Minimal benefit from converntional hearing aids
4) Between 40-50% sentence recognition score in best-aided condition

Front 8

What are the pediatric candidacy criteria for cochlear implantation?

Back 8

1) Twelve months of age
2) Bilateral profound HL for 12- to 18-month oldds, severe to profound HL for those older than 18 months
3) Little or no benefit from hearing aids documented by parent questionnaire in children younger than 24 months; word recognition scores less than 30% correct in children older than 24 moths (the hearing aid trial is waived in postmeningitis children with radiographic evidence of inrtacochlear ossification)
4) No medical contraindications
5) Enrollment in an educational program that emphasizes auditory development
6) Appropriate family support and expectations

Front 9

Stimulable auditory neural elements are nearly alwas present regardless of cause of deafness, however, what are the two exceptions?

Back 9

1) Michel deformity - congenital agenesis of the cochlear
2) Small internal auditory canal syndrome - cochlear nerve may be congenitally absent

Front 10

What is the initial imaging of choice for evaluating the absence of presence of the cochlea?

Back 10

High resolution, thin-section CT scan

If soft-tissue obliteration occurs following sclerosing labyrinthitis, CT may not image the obstruction, in this case get a T2-weighted MRI.

Front 11

Do intracochlear ossification or congenitally deformed cochleas a contraindication to cochlear implantation?

Back 11

No, but it can limit the type and insertion depth of the elctrode array that can be introducted into the cochlea.

Front 12

The facial recess is opened during surgical implantation of a CI. What are the boundaries of the facial recess?

Back 12

Fossa incudis, chorda tympani nerve and facial nerve

Front 13

Name a few complications of cochlear implantation.

Back 13

1) Facial weakness or paralysis (rare)
2) Wound infection or flap breakdown
3) CSF drainage
4) Meningitis

Front 14

What are the identifiable risk factors related to the increased incidence of meningitis in cochlear implant recipients?

Back 14

1) Young age
2) Cochlear dysplasia
3) Temporal bone abnormalities
4) Use of a two-part electrode system

The importane of carefully packing the cochleostomy site (made anterior & inferior to the round window) with a soft tissue seal to prevent bacteria from entering the innter ea and intracranial spaces has been re-emphasized. Also consider vaccination against meningitis as a preventative measure.

Front 15

One factor reported to influence the benefit from cochlear implantation in congenitally deaf children is the __________.

Back 15

age at which the child receives the device

Front 16

_______ cochlear implants can provide salient inormation regarding all three dimensions of sound: intensity, timing and frequency.

Back 16

Multichannel cochlear implants

Front 17

Who are the most predictable beneficiaries of cochlear implants?

Back 17

Postlinguistically deafened adults

Front 18

Is a hearing aid trial required prior to cochlear implants?

Back 18

Yes; except in cases of HL due to meningitis

Front 19

What is the standard surgical approach for cochlear implants?

Back 19

Through the mastoid and facial recess, providing access to the round window.