Cochlear Implantation: Candidacy Criteria & Audiological Evaluation

A Comprehensive Answer for 50 Marks | RGUHS ENT

1. INTRODUCTION

2. DEVICE DESIGN (Brief Overview)

External Components

Internal Components

• Advanced Bionics Corporation (Valencia, CA, USA)
• Cochlear Corporation (Lane Cove, Australia)
• Med-El GmbH (Innsbruck, Austria)

3. COCHLEAR IMPLANT TEAM (Multidisciplinary)

┌─────────────────────────────────────────────┐
│           COCHLEAR IMPLANT TEAM             │
├─────────────────────┬───────────────────────┤
│ CORE MEMBERS        │ EXTENDED TEAM         │
├─────────────────────┼───────────────────────┤
│ Otolaryngologist/   │ Psychologist          │
│ Neurotologist       │ Radiologist           │
│ (Surgeon)           │ Ophthalmologist       │
│ Audiologist         │ Neurologist           │
│ Speech-Language     │ Pediatrician/         │
│ Pathologist         │ Geriatrician          │
│                     │ Social Worker         │
│                     │ Teacher of the Deaf   │
└─────────────────────┴───────────────────────┘

4. CANDIDACY CRITERIA

4.1 Evolution of Candidacy

• 1980s: Profound bilateral SNHL (PTA ≥ 100 dB), no residual hearing
• 1990s: Severe-to-profound SNHL; limited open-set speech recognition
• 2000s onward: Moderate-to-profound SNHL; expansion to single-sided deafness, auditory neuropathy, cochlear malformations

4.2 FDA/Standard Candidacy Criteria (Table 20-1, KJ Lee)

4.3 Indications — FLOWCHART

                    PATIENT WITH HEARING LOSS
                            │
                            ▼
              ┌─────────────────────────────┐
              │  Pure Tone Audiogram (PTA)  │
              └─────────────┬───────────────┘
                            │
              ┌─────────────▼───────────────┐
              │ Severe-to-Profound SNHL     │
              │ (≥70 dB bilateral)          │
              └─────────────┬───────────────┘
                            │
              ┌─────────────▼───────────────┐
              │  Trial with Hearing Aids    │
              │  (3–6 months minimum)       │
              └─────────────┬───────────────┘
                            │
              ┌─────────────▼───────────────┐
              │ Speech Discrimination Score │
              │ (in best-aided condition)   │
              └──────┬──────────────┬───────┘
                     │              │
              ≤50%   │              │  >50%
                     ▼              ▼
          ┌──────────────┐   ┌────────────────────┐
          │  CI CANDIDATE│   │ Continue HA;        │
          │  (proceed to │   │ Reassess periodically│
          │  full workup)│   └────────────────────┘
          └──────────────┘

4.4 Specific Candidacy Categories

A. Adult Candidates (Cummings)

1. Bilateral severe-to-profound SNHL
2. Limited benefit from hearing aids (≤50% open-set sentence recognition in best-aided condition)
3. No retrocochlear pathology as etiology
4. Medical fitness for surgery

• Single-sided deafness (SSD): CI provides binaural benefit, tinnitus suppression; FDA-approved for SSD with tinnitus
• Asymmetric SNHL: One ear meets CI criteria; contralateral ear ≤80%
• Auditory Neuropathy Spectrum Disorder (ANSD): Good outcomes reported; cochlear neural stimulation bypasses dysfunctional hair cells
• Hybrid/Electric-Acoustic Stimulation (EAS): Low-frequency residual hearing (≤60 dB HL at 500 Hz) with profound high-frequency loss; implanted ear CNC score 10–60%; contralateral ear ≤80% CNC

B. Pediatric Candidates

1. Age ≥12 months (FDA-approved age); earlier implantation indicated in post-meningitic ossification risk
2. Bilateral severe-to-profound SNHL
3. Limited benefit from hearing aids (≤30% word recognition)
4. Appropriate family motivation and support

4.5 CONTRAINDICATIONS

┌──────────────────────────────────────────────────────────────────┐
│                      CONTRAINDICATIONS                           │
├──────────────────────────┬───────────────────────────────────────┤
│    ABSOLUTE              │    RELATIVE                           │
├──────────────────────────┼───────────────────────────────────────┤
│ • Cochlear aplasia       │ • Chronic otitis media (manageable    │
│   (Michel deformity)     │   with staged approach)               │
│ • Complete ossification  │ • Narrow internal auditory canal      │
│   precluding electrode   │   (hypoplastic cochlear nerve)        │
│   insertion              │ • Congenital malformations (less      │
│ • Absence/aplasia of     │   dysplastic ear preferred)           │
│   cochlear nerve         │ • Active middle ear infection         │
│ • Narrow IAC with no     │ • Unrealistic expectations            │
│   primary afferent       │ • Lack of family support (pediatric)  │
│   innervation            │ • Significant cognitive impairment    │
│ • Active retrocochlear   │ • Medical fitness concerns            │
│   disease (untreated     │                                       │
│   acoustic neuroma)      │                                       │
└──────────────────────────┴───────────────────────────────────────┘

5. PRE-IMPLANT AUDIOLOGICAL EVALUATION

5.1 Overview Flowchart

            AUDIOLOGICAL EVALUATION FOR CI CANDIDACY
                            │
            ┌───────────────┼───────────────────┐
            ▼               ▼                   ▼
    UNAIDED TESTING   AIDED TESTING      SPECIAL TESTS
    (PTA, SRT,        (with optimal      (AABR, OAE,
    speech tests)      hearing aids)      ECAP, Promontory
                                         stimulation)
            │               │                   │
            └───────────────┴───────────────────┘
                            │
                    CANDIDACY DECISION
                            │
                 ┌──────────┴────────────┐
                 ▼                       ▼
          CI INDICATED           CI NOT INDICATED
          (proceed to            (optimize HA,
           MDT review)            reassess)

5.2 Unaided Audiological Tests

A. Pure Tone Audiogram (PTA)

• Air conduction and bone conduction thresholds
• Each ear tested individually
• Confirms severity and type of hearing loss
• Documents bilateral severe-to-profound SNHL
• PTA (500, 1000, 2000, 4000 Hz)

B. Speech Reception Threshold (SRT)

• Confirms PTA findings
• Establishes baseline for speech awareness

C. Tympanometry & Acoustic Reflexes

• Rules out middle ear pathology
• Type B/C tympanogram indicates middle ear disease to be treated pre-operatively

D. Otoacoustic Emissions (OAE — DPOAE/TEOAE)

• Absent in cochlear SNHL (confirms hair cell dysfunction)
• Present OAE with absent ABR → suspect auditory neuropathy

5.3 Aided Audiological Tests

A. Aided Sound Field Audiogram

• Performed with optimally-fitted bilateral hearing aids
• Warble-tone stimuli presented in sound field
• Assesses residual benefit from amplification
• Can reveal recruitment limiting HA benefit

B. Speech Perception Tests (The Minimum Speech Test Battery — MSTB)

5.4 Electrophysiological Tests

A. Auditory Brainstem Response (ABR/BERA)

• Waveform morphology assesses auditory pathway integrity
• Click and tone-burst ABR
• Absent Wave I/II with present Wave III/V → ANSD pattern
• Threshold estimation in children unable to cooperate for behavioral audiometry

B. Auditory Steady-State Response (ASSR)

• Frequency-specific threshold estimation
• Useful for profoundly deaf infants
• Thresholds ≥90 dB across frequencies → supports CI candidacy

C. Cortical Auditory Evoked Potentials (CAEP)

• P1 latency — cortical maturational marker
• Delayed P1 in older implanted children → poorer prognosis
• P1 normalization after CI correlates with auditory cortical maturation

D. Promontory Stimulation Test

• Electrical stimulation of the promontory/round window niche
• Tests survival of spiral ganglion cells
• Positive response (patient perceives sound) → favorable prognosis
• Absent response → may still proceed (not an absolute contraindication)

E. Electrically Evoked Compound Action Potential (ECAP/NRT/ART)

• Performed intra-operatively or post-operatively via implant
• Confirms electrode-neural interface
• Helps initial device programming (MAP setting)

5.5 Pediatric-Specific Assessment

PEDIATRIC AUDIOLOGICAL ASSESSMENT PROTOCOL
                    │
      ┌─────────────┼─────────────┐
      ▼             ▼             ▼
  ABR/BERA      OAE          Behavioral
  (click &    (DPOAE/        Audiometry
  tone-burst)  TEOAE)             │
                           ┌──────┴──────┐
                           ▼             ▼
                       BOA            VRA
                    (0–6 mo)        (6–30 mo)
                                       │
                                  CPA/Play
                                 Audiometry
                                 (>2.5 yr)
                                       │
                                  PTA (>4 yr)

5.6 Ear Selection Protocol

WHICH EAR TO IMPLANT?
        │
   ┌────┴────┐
   ▼         ▼
Better     Worse
hearing    hearing
  ear        ear
   │         │
   │    ← Generally preferred for
   │      unilateral CI (poorer aided
   │      performance, less to lose)
   │
In cases of:
• Bilateral deafness (prelingual, early) → Better ear OR simultaneous bilateral
• Long auditory deprivation (>10 yr) → Better ear (greater spiral ganglion survival)
• Cochlear malformation → Less dysplastic ear (safer, better outcomes)
• Ossification → Less ossified ear

6. MEDICAL AND RADIOLOGICAL EVALUATION

6.1 Imaging (Pre-implant)

• Standard pre-operative imaging
• Evaluates: cochlear anatomy, mastoid, middle ear, ossification, IAC diameter, facial nerve course
• Detects: cochlear malformations (Michel aplasia, Mondini, common cavity, IP-I/II/III), labyrinthitis ossificans

• MRI without contrast: evaluates cochlear nerve patency/aplasia, membranous labyrinth
• Recommended when: congenital deafness, small IAC on CT, suspected retrocochlear pathology
• "Some authors advocate complementary use of HRCT and MRI without contrast in all CI recipients" — Cummings, p. 3708
• Cochlear nerve hypoplasia/aplasia → relative/absolute CI contraindication

6.2 Medical Evaluation

• Fitness for general anesthesia
• Immunization status (pneumococcal vaccine mandatory pre-CI: PCV13 ≥2 weeks before implantation)
• Ophthalmic evaluation (Usher syndrome — combined deaf-blindness)
• Neurological evaluation (when relevant)
• Otological evaluation: treat active infection before implantation

7. RECOMMENDATIONS FOR REFERRAL (Cummings Otolaryngology)

Adult Referral Criteria:

• Bilateral severe-to-profound SNHL (PTA ≥70 dB HL)
• Open-set sentence recognition ≤50% in best-aided condition
• No benefit improvement expected from hearing aid optimization
• Medical suitability for surgery

Pediatric Referral Criteria:

• Bilateral severe-to-profound SNHL confirmed by ABR and behavioral audiometry
• ≤30% word recognition scores with optimal amplification
• Age ≥12 months (FDA), or younger if risk of cochlear ossification post-meningitis
• Enrolled in early intervention program

8. BILATERAL COCHLEAR IMPLANTATION

Advantages:

1. Binaural summation → improved speech perception in quiet and noise
2. Squelch effect → improved directional hearing
3. Redundancy — backup if one device fails
4. Both ears stimulated → guarantees "better ear" is implanted
5. Critical for prelingual deaf children — optimal auditory cortex development

Simultaneous vs Sequential:

9. HYBRID/ELECTRIC-ACOUSTIC STIMULATION (EAS)

• Low-frequency hearing: Normal to moderate HL (≤60 dB HL at ≤500 Hz)
• High-frequency hearing: Severe-to-profound loss (PTA at 2,3,4 kHz ≥75 dB HL in ear to be implanted; ≥60 dB HL contralateral)
• Word recognition: CNC score 10–60% in ear to be implanted; contralateral ear CNC ≤80%
• Uses shorter electrode array to preserve residual acoustic hearing
• Combines acoustic amplification (low frequencies) + electrical stimulation (high frequencies)

10. RECENT ADVANCES IN CI CANDIDACY (RGUHS Relevance)

1. Expansion of audiometric criteria — bilateral CI now considered for moderate SNHL with poor speech discrimination
2. Single-sided deafness (SSD) — FDA-approved; CI suppresses ipsilateral tinnitus and restores binaural input
3. Auditory Neuropathy Spectrum Disorder (ANSD) — CI stimulates spiral ganglion cells directly; outcomes variable but generally good in cochlear (synaptic/IHC) type ANSD
4. Cochlear ossification management — drill-out technique; shorter electrode arrays; bi-cochleostomy approach
5. Pre-lingual deafness in adults — poor prognosis; counseling essential; not an absolute contraindication
6. Older adults (geriatric CI) — age alone not a contraindication; significant QOL improvement demonstrated
7. Neurocognitive testing — new role in candidacy for older adults with cognitive decline
8. Remote/telehealth audiological follow-up — post-COVID advancement in mapping and rehabilitation
9. MRI compatibility — newer devices (Cochlear Nucleus Profile Plus, AB Naída CI M90) compatible with 3.0 Tesla MRI
10. Totally implantable CI (TICI) — experimental; eliminates external processor; under clinical trials

11. SUMMARY FLOWCHART — COMPLETE CANDIDACY PROCESS

┌─────────────────────────────────────────────────────────┐
│          COCHLEAR IMPLANT CANDIDACY PATHWAY             │
└─────────────────────────┬───────────────────────────────┘
                          │
              ┌───────────▼──────────────┐
              │  STEP 1: REFERRAL        │
              │  Severe-profound SNHL    │
              │  HA trial ≥3 months      │
              └───────────┬──────────────┘
                          │
              ┌───────────▼──────────────┐
              │  STEP 2: AUDIOLOGICAL    │
              │  EVALUATION              │
              │  • PTA (aided + unaided) │
              │  • Speech tests (MSTB)   │
              │  • ABR / OAE / ASSR      │
              │  • MAIS (infants)        │
              └───────────┬──────────────┘
                          │
              ┌───────────▼──────────────┐
              │  STEP 3: MEDICAL         │
              │  EVALUATION              │
              │  • ENT exam              │
              │  • HRCT + MRI temporal   │
              │    bone                  │
              │  • General fitness       │
              │  • Immunizations         │
              └───────────┬──────────────┘
                          │
              ┌───────────▼──────────────┐
              │  STEP 4: PSYCHOLOGICAL   │
              │  / SOCIAL EVALUATION     │
              │  • Motivation            │
              │  • Realistic expectation │
              │  • Family support        │
              │  • Education plan        │
              └───────────┬──────────────┘
                          │
              ┌───────────▼──────────────┐
              │  STEP 5: MDT MEETING     │
              │  (Surgeon + Audiologist  │
              │  + SLP + Psychologist)   │
              └───────────┬──────────────┘
                          │
               ┌──────────▼─────────────┐
               ▼                        ▼
        CI INDICATED            CI NOT INDICATED
               │                        │
    ┌──────────▼──────────┐    ┌────────▼──────────┐
    │ STEP 6: SURGERY     │    │ Optimize HA        │
    │ Cochlear Implant    │    │ Auditory training  │
    │ (unilateral /       │    │ Reassess in 6 mo   │
    │  bilateral)         │    └───────────────────┘
    └──────────┬──────────┘
               │
    ┌──────────▼──────────┐
    │ STEP 7: DEVICE      │
    │ ACTIVATION &        │
    │ PROGRAMMING (MAP)   │
    └──────────┬──────────┘
               │
    ┌──────────▼──────────┐
    │ STEP 8: AUDITORY    │
    │ REHABILITATION      │
    │ (AVT / Listening &  │
    │  Spoken Language)   │
    └─────────────────────┘

12. REFERENCES (As per RGUHS ENT Curriculum Sources)

KEY POINTS TO REMEMBER FOR 50-MARK ANSWER

1. Candidacy = Audiological + Medical + Psychological + Radiological + Social criteria (not just audiogram)
2. PTA criteria: Adults >70–90 dB; Children >40–70 dB bilateral SNHL
3. Speech criteria: ≤50% sentence recognition in best-aided condition (adults)
4. Hearing aid trial is mandatory before CI candidacy is confirmed
5. Age: ≥12 months (FDA); earlier in post-meningitis ossification risk
6. Critical period: 0–2 years — peak neural plasticity (cross-modal plasticity if missed)
7. Absolute contraindications: Michel aplasia, cochlear aplasia, absent cochlear nerve, complete cochlear ossification
8. HRCT + MRI temporal bone mandatory pre-op
9. Vaccination: PCV13 mandatory ≥2 weeks before implantation
10. Bilateral CI — superior to unilateral; simultaneous preferred over sequential in children
11. Recent advances: SSD, EAS/Hybrid, ANSD, MRI-compatible devices, telehealth programming

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