Cochlear Implant

Question 1

What are the basic components of a CI?

Answer 1

1. Microphone
2. Speech processor
3. Implanted receiver-stimulator

Question 2

How does a CI work?

Answer 2

1. Sound is detected by external microphone
2. Conversion to an analog signal and directed to the external sound processor
3. Digital electronic code is sent by a transmitting coil situated over the receiver-stimulator via radiofrequency through the skin
4. The receiver-stimulator delivers electronic impulses to electrodes on a coil located w/in cochlea
5. Electrodes stimulate spiral ganglion cells

Question 3

Options of speech processors

Answer 3

1. BTE
2. Wear on belt, clothing, or small packs
3. Entirely implantable (under development)

Question 4

What is involved in speech processing?

Answer 4

1. Amplification (gain control)
2. Compression (must compress the signal to within a narrow range of 10-25 dB since the deaf ear responds to electrical stimulation w/ a dynamic response in this range)

Question 5

What are the electrical stimulation strategies

Answer 5

1. Multichannel strategies
2. Pulsatile stimulation
3. Spectral Analysis

Question 6

Can patients with partial hearing (hearing at low frequencies) benefit from CI?

Answer 6

Yes, there are hybrid or short electrode devices developed to allow preservation of native low-freq hearing while allowing for mid and high freq hearing assistance

Question 7

How is candidacy for CI determined in US?

Answer 7

Sentence recognition test scores with properly fitted hearing aids
-Hearing-in-Noise Test
-Arizona Biomedical Sentences (AzBio)
Score of 60% or less are candidates

Question 8

How are children evaluated for CI?

Answer 8

First, establish a hearing threshold
-OAE
-ABR
-Auditory steady-state responses
-Behavioral testing
Then, hearing aid trial to assess speech and language development

Question 9

What does the pre-op otologic assessment include?

Answer 9

• Kids must be clear of infxn before surgery (CI can safely coexist with PET but ideally pts have intact TM at time of surgery)
• Adults should have intact TM
• Cochlear patency with MRI (T2-weighted)
• Cochlear and vestibular malformations
• RF for infxn: I/S, DM, tobacco, malnutrition
• Vestibular evaluation (ENG); not required but helpful in selecting ear to implant

Question 10

What are complications that are more common with CI in the setting of cochlear/vestibular malformations?

Answer 10

• Incomplete device insertion
• CSF leak
• FN injury
• Vestibulopathy
• Poorer hearing outcomes

Question 11

Radiologic assessment before CI

Answer 11

Fine-cut CT and/or MRI

• CT preferred for bony anatomy
• MRI w/w/o gad + high-res T2 weighted images useful if cochlear patency is in question bc better assess soft tissue detail

Question 12

What are the 2 absolute contraindications for CI that can be found on radiologic assessment?

Answer 12

1. Michel deformity (congenital cochlear agenesis)

2. Absence of the auditory nerve

Question 13

Candidacy for CI in kid

Answer 13

1. B/l severe-to-profound HL
2. Lack of auditory development w/ a proper binaural HA trial as documented by objective testing or a parental questionnaire
3. Properly aided open-set word recognition scores < 20-30% in kids capable of testing
4. Suitable auditory development education plan
5. Lack of medical contraindication, w/ cochlea and auditory nerve present

Question 14

Candidacy for CI in adult

Answer 14

1. B/l severe-to-profound HL
2. Limited benefit from conventional HA
3. Unaided PTA 70 dB or worse
4. Sentence (hearing-in-noise test or AzBio) recog scores < 60% in better ear, <50% in implant ear
5. Lack of medical contraindication, w/ cochlea and auditory nerve present
6. Realistic expectations

Question 15

When should the implant be placed?

Answer 15

• Earlier implantation in kids yields more favorable results (routinely < 12 months)
• Adults do better w/ shorter duration of deafness

Question 16

Steps for surgery

Answer 16

1. Facial nerve monitoring (No paralysis)
2. Mark device location w/ use of templates
   - Internal device should be far enough posteriorly so that the processor does not lie against ear
3. Postauricular incision 3-4 cm; close to postauricular crease
4. Periosteal incision 1 cm posterior to skin incision (device extrusion less likely to occur since incisions separate)
5. Mastoidectomy
6. Open facial recess to gain access to promontory, round window niche, and stapes
7. Well may be drilled posterior to mastoid cavity in the cortex to harbor the receiver-stimulator package
   - Down to dura in kids
   - Just remove inner table in adults
8. Device can be placed in subperiosteal pocket or secured by various means such as suture
9. After device seated, cochleostomy made 1 mm anterior and inferior to round window to access scala tympani
   - A more inferior cochleostomy assures wide clearance of the osseous spiral lamina
10. Insert electrodes
11. Seal the cochleostomy with fascia or periosteum

Question 17

Can hearing be preserved with CI?

Answer 17

Only if implanting a shortened electrode that doesn’t extend into the apical cochlear neural elements
-There is potential for delayed HL usu w/in first 3-6 mo (unknown etiology)

Question 18

How can proper functioning of the device be confirmed after implant?

Answer 18

Intraoperative electrical tests by audiology

Evoked potentials and stapedial reflexes

Question 19

What imaging can confirm CI location?

Answer 19

Stenver’s view XR post-op

Question 20

What happens if the pt has cochlear ossification?

Answer 20

Various approaches

• Drill out the ossification (usu the first few mm of the basal turn)
• Partial electrode insertion
• Insertion into scala vestibuli
• More elaborate drill out approaches
• Split electrodes (one inserted partially into scala tympani and other in scal vestibuli or further along scala tympani)

Question 21

What happens if the pt has cochlear malformation?

Answer 21

Use specifically designed electrodes

Anticipate CSF leak (may require plugging ET and packing ME)

Question 22

When is the device engaged and programmed postop?

Answer 22

1-4 wks postop

• Initial programming is done over 2-3 days
• 1st day, reports of sound like static or Donald Duck/metallic voices
• Quality of sound improves over next 24 hrs
• Learning occurs over 3-6 months

Question 23

Complications of CI

Answer 23

Overall 5-10% complication rate

• Wound infxn – m/c complication of CI; post-auricular and AOM
• FN injury
• Taste disturbance (resolves in 6 mo; 2-3% permanent)
• Loss of residual hearing in implanted ear
• Tinnitus (usu improves w/ device programming)
• Balance problems
• Device failure
• ?Meningitis

Question 24

Subjective improvement after CI

Answer 24

• 60% can communicate on phone and converse w/o lip reading
• Improved reception of environmental sounds
• Augmented lip reading capabilities
• Decreased tinnitus
• Decreased depression
• Improved QOL (96%)

Question 25

Objective improvement after CI

Answer 25

- Open-set sentence recogn scores of 60-70% | - WRS of 30-50%

Question 26

Improvements in kids after CI

Answer 26

- Harder to measure - Mainstream schooling (achieve communication abilities sufficient to allow enrollment in mainstream schooling by 2nd grade) - Word understanding test scores 3 yrs after implant documented to reach as high as 100% in post-lingual kids

Question 27

Who benefits from CI (per ENT secrets)?

Answer 27

- At least 12 months old - Binaural severe to profound SNHL - Intact CN 8 fnc - Little to no benefit from HA (at least 6 month trial) - Audiologic criteria - -PTA at 500, 1000, 2000 Hz higher than 70 dB - -WRS 50% on open-set testing for ear to be implanted and 60% in nonimplant ear

Question 28

What 2 crucial factors influence auditory performance after CI?

Answer 28

1. Age of onset of deafness | 2. Duration of profound HL

Question 29

Why do pts w/ prolonged duration of profound HL do worse?

Answer 29

Loss of central auditory processing

Question 30

Preop imaging w/ CT vs MRI

Answer 30

CT adv: - Excellent inner ear morphology - Course of intratemporal FN - Aeration of mastoid CT limitations: - Can't evaluate retrocochlear path - Can't evaluate cochlear patency in pts w/ fibrosis of cochlea as precursor to cochlear ossification - Ability to detect absent cochlear n also limited MRI addresses these limitations but cost and anesthesia needs in kids

Question 31

Is cochlear hypoplasia (seen in Mondini's deformity) a contraindication to CI?

Answer 31

No

Question 32

Which ear should you implant?

Answer 32

- Most patent cochlea is usu chosen - Ear w/ shortest duration of deafness - Ear not used w/ HA - Ear on side of dominant hand If there is no diff acoustically, chose the better surgical ear (least ossification or fibrosis w/in scala tympani)