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Otology > Cochlear Implant > Flashcards

Cochlear Implant Flashcards

1
Q

What are the basic components of a CI?

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

How does a CI work?

A
  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
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3
Q

Options of speech processors

A
  1. BTE
  2. Wear on belt, clothing, or small packs
  3. Entirely implantable (under development)
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4
Q

What is involved in speech processing?

A
  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)
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5
Q

What are the electrical stimulation strategies

A
  1. Multichannel strategies
  2. Pulsatile stimulation
  3. Spectral Analysis
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6
Q

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

A

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

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7
Q

How is candidacy for CI determined in US?

A

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

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8
Q

How are children evaluated for CI?

A 
First, establish a hearing threshold
-OAE
-ABR
-Auditory steady-state responses
-Behavioral testing
Then, hearing aid trial to assess speech and language development
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9
Q

What does the pre-op otologic assessment include?

A
  • 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
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10
Q

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

A
  • Incomplete device insertion
  • CSF leak
  • FN injury
  • Vestibulopathy
  • Poorer hearing outcomes
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11
Q

Radiologic assessment before CI

A

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
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12
Q

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

A
  1. Michel deformity (congenital cochlear agenesis)

2. Absence of the auditory nerve

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13
Q

Candidacy for CI in kid

A
  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
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14
Q

Candidacy for CI in adult

A
  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
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15
Q

When should the implant be placed?

A
  • Earlier implantation in kids yields more favorable results (routinely < 12 months)
  • Adults do better w/ shorter duration of deafness
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16
Q

Steps for surgery

A
  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
17
Q

Can hearing be preserved with CI?

A

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)

18
Q

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

A

Intraoperative electrical tests by audiology

Evoked potentials and stapedial reflexes

19
Q

What imaging can confirm CI location?

A

Stenver’s view XR post-op

20
Q

What happens if the pt has cochlear ossification?

A

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)
21
Q

What happens if the pt has cochlear malformation?

A

Use specifically designed electrodes

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

22
Q

When is the device engaged and programmed postop?

A

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
23
Q

Complications of CI

A

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
24
Q

Subjective improvement after CI

A
  • 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%)
25
Q

Objective improvement after CI

A
  • Open-set sentence recogn scores of 60-70%

- WRS of 30-50%

26
Q

Improvements in kids after CI

A
  • 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
27
Q

Who benefits from CI (per ENT secrets)?

A
  • 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
28
Q

What 2 crucial factors influence auditory performance after CI?

A
  1. Age of onset of deafness

2. Duration of profound HL

29
Q

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

A

Loss of central auditory processing

30
Q

Preop imaging w/ CT vs MRI

A

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

31
Q

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

A

No

32
Q

Which ear should you implant?

A
  • 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)

Otology (10 decks)

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