---

Cochlear Implant (CI) - Complete ENT Textbook Overview

---

1. WHAT IS A COCHLEAR IMPLANT?

1. Transmission of the electrical signal to the auditory cortex
2. Appropriate central processing for understanding speech

---

2. DEVICE COMPONENTS

External Components

Internal Components (surgically implanted)

---

3. PRINCIPLES OF HEARING WITH CI

• High-pitched sounds → spiral ganglion cells at the basal turn of the cochlea
• Low-pitched sounds → spiral ganglion cells at the apex

---

4. INDICATIONS

Adults (FDA/Standard Criteria)

• Bilateral moderate-to-profound sensorineural hearing loss (SNHL)
• Aided sentence recognition scores ≤50% in the ear to be implanted and ≤60% in the best-aided condition (binaural hearing aids)
• Failure to benefit from hearing aids after adequate trial
• No upper age limit - patients aged 65-80 years show significant improvement in speech perception and quality of life

Children

Special/Non-Traditional Indications

• Auditory Neuropathy Spectrum Disorder (ANSD): Normal OAEs but absent ABR - reliable open-set speech recognition can be achieved with CI
• Single-Sided Deafness (SSD): CI can reduce tinnitus and improve sound localization (not FDA-approved but widely practiced)
• Far-Advanced Otosclerosis: CI outcomes equivalent to or better than other causes of deafness
• Neurofibromatosis Type II with bilateral vestibular schwannomas: CI can achieve open-set speech recognition when cochlear nerve is intact
• Elderly patients: No upper age limit; good evidence for improvement even in patients aged 70-80
• Pre-lingual deafness: Early implantation gives language development rates comparable to normal hearing children

NICE Criteria (England & Wales)

• Severe to profound deafness defined as hearing only sounds louder than 90 dBHL at 2 kHz and 4 kHz without hearing aids
• Hearing aids used for at least 3 months unless contraindicated
• Adequate benefit with hearing aids = score of ≥50% on BKB sentence testing at 70 dB SPL (adults) or appropriate speech/language milestones (children)
• Simultaneous bilateral CI recommended for children and blind adults

---

5. CONTRAINDICATIONS

Absolute Contraindications

• Cochlear aplasia (absent cochlea) - no structure for electrode insertion
• Cochlear nerve aplasia - no nerve to stimulate; MRI is the preferred investigation to identify this preoperatively
• Active middle ear infection or cholesteatoma - must be fully eradicated before implantation due to increased risk of meningitis

Relative Contraindications

• Cochlear ossification (post-meningitis, cochlear otosclerosis) - may complicate electrode insertion; requires specialized surgical approaches
• Unfavorable anatomy: Low-lying dura, anterior sigmoid sinus, anomalous facial nerve - may require alternative surgical approaches
• Previous canal wall-down mastoid surgery - mastoid and middle ear must be obliterated before implantation
• Tympanic membrane perforation - must be repaired before CI to prevent infection pathway
• Patients unfit for general anesthesia - though CI under local anesthesia is possible in exceptional cases
• Severe cognitive impairment or autism - psychologist assessment required; may impact device usage and rehabilitation outcomes

---

6. PRE-OPERATIVE ASSESSMENT (Multidisciplinary)

Audiological Assessment

• Pure tone audiometry (PTA)
• Speech discrimination testing (CNC word scores, AzBio sentences in noise)
• Hearing aid trial (3-6 months minimum)

Imaging

• MRI (preferred first): Identifies cochlear nerve aplasia, cochlear aplasia, acoustic neuromas, inner ear anomalies - most important in infants
• CT scan: Identifies cochlear lumen obliteration (post-meningitis ossification), otosclerosis, anatomical variants (low dura, anterior sigmoid sinus), middle ear pathology; used selectively in infants to limit radiation exposure

Psychological Assessment

• Counseling to ensure realistic expectations
• Assessment of cognitive ability, developmental disorders
• Family support evaluation

Pre-operative Vaccinations

• Children 2-5 years: At least 2 previous doses of PCV13 and 1 dose of PPSV23 (8 weeks after last PCV13)
• Children 6-19 years: At least 1 previous dose of PCV13 and 1 dose of PPSV23 (at least 8 weeks apart)
• (To reduce risk of post-implantation meningitis)

---

7. SURGICAL PROCEDURE - STEP BY STEP

Approach

Anesthesia

---

STEP 1 - INCISION

• A postauricular (retroauricular) skin incision is made, sufficiently long to allow introduction of the receiver-stimulator
• The incision is deliberately not placed directly over the receiver-stimulator to minimize wound complications
• The soft tissue is dissected down to the periosteum
• An anteriorly or posteriorly based periosteal flap is created

---

STEP 2 - CREATING THE RECEIVER-STIMULATOR BED

• A subperiosteal pocket is created under the temporalis muscle to house the receiver-stimulator
• Alternatively, a shallow bony well (trough) may be drilled into the outer cortex of the skull for secure implant placement
• A gutter/trough is drilled in the cortical bone for the electrode lead as it passes toward the mastoid cavity
• Some surgeons use tie-down sutures to secure the device

---

STEP 3 - CORTICAL MASTOIDECTOMY

• A simple (cortical) mastoidectomy is performed with a drill to open the mastoid air cells
• The posterior EAC wall is carefully thinned for better visualization through the facial recess
• The posterior and inferior mastoid cavities are NOT saucerized - bony overhangs are preserved to retain the electrode array coiled within the mastoid
• The incus and ossicular chain are carefully preserved, especially in patients with residual hearing

---

STEP 4 - POSTERIOR TYMPANOTOMY (FACIAL RECESS APPROACH)

• The facial recess (triangular space bounded by the facial nerve posteriorly, chorda tympani anteriorly, incus buttress superiorly) is opened
• This gives access to the round window niche through the middle ear without entering the EAC
• Care is taken to preserve the chorda tympani (taste nerve) - dividing it risks dysgeusia
• The round window niche is visualized; removal of bone around it exposes the round window membrane

---

STEP 5 - COCHLEAR ENTRY (COCHLEOSTOMY or ROUND WINDOW)

1. Round Window Insertion (preferred for hearing preservation):
   • The round window membrane is opened in an anteroinferior direction
   • Minimally traumatic entry into the scala tympani
2. Cochleostomy:
   • A small opening is drilled anteroinferior to the round window
   • Directly enters the scala tympani
   • Used when round window is not accessible due to poor visualization or ossification

---

STEP 6 - ELECTRODE INSERTION

• The flexible electrode array is inserted slowly and gently into the scala tympani in a controlled atraumatic motion ("soft surgery" principles)
• Most conventional-length electrodes are inserted to a minimum angular depth of 360°-400° (just over one full cochlear turn)
• Residual perilymph is NOT suctioned (to preserve inner ear environment)
• The electrode is inserted very slowly to minimize intracochlear pressure changes

Soft Surgery Principles (for Hearing Preservation)

• Use of flexible, thin electrodes requiring less insertion force
• Preference for round window insertion over cochleostomy
• Slow electrode insertion
• No suctioning of perilymph
• Preserving ossicular chain integrity
• Perioperative steroids (e.g., dexamethasone at induction; triamcinolone soaked onto spongistan placed on round window membrane)

---

STEP 7 - INTRAOPERATIVE TESTING

• Electrocochleography (ECochG) may be used during insertion to monitor for cochlear damage in hearing preservation cases
• Neural response telemetry (NRT) / Electrically evoked compound action potentials (ECAP) confirm electrode function
• Impedance testing to verify electrode integrity
• Intraoperative imaging (X-ray or fluoroscopy) may confirm electrode position

---

STEP 8 - SEALING AND WOUND CLOSURE

• After electrode insertion, the cochlear opening is sealed with small pieces of fascia or muscle to prevent perilymph leak
• The residual electrode wire is coiled within the mastoid cavity
• The receiver-stimulator is seated in its subperiosteal pocket or bony well
• The wound is closed in layers (periosteum, subcutaneous tissue, skin)
• A mastoid dressing is applied

---

8. CHALLENGING SURGICAL SITUATIONS

---

9. POST-OPERATIVE CARE

• The external processor is NOT activated immediately after surgery
• Device activation ("switch-on") and mapping occurs approximately 4-6 weeks after surgery once wound healing is complete
• Mapping/Programming: The audiologist programs each electrode's stimulation levels (T-levels = threshold, C-levels = comfort levels)
• Intensive auditory rehabilitation: Speech therapy, auditory training, listening exercises
• More than 85% of implant recipients can use telephone speech understanding after implantation

---

10. COMPLICATIONS

Intraoperative Complications

Early Post-operative Complications

Late Complications

---

11. SPECIAL TOPICS

Electric-Acoustic Stimulation (EAS) / Hybrid Cochlear Implant

• For patients with "ski-slope" hearing loss: normal/moderate low-frequency hearing + severe-to-profound high-frequency hearing loss
• A shorter electrode array covers only the basal (high-frequency) cochlea
• A hearing aid provides low-frequency acoustic hearing in the same implanted ear
• Requires meticulous hearing preservation surgery with soft surgery principles

Bilateral Cochlear Implants

• Advantages over unilateral: improved sound localization, spatial acuity, better speech understanding in noise
• Recommended for children and visually impaired adults
• Sequential implantation: relative increase in quality of life is higher after the first implant

Auditory Outcomes

• More than 85% of CI recipients can use telephone for speech understanding
• Music perception remains generally poor despite advances (limited melody/pitch/timbre identification, but normal rhythm recognition)
• Postlingual deafened adults perform better than prelingual deafened recipients
• Children implanted earlier have language development rates comparable to normal-hearing peers

---

Summary Flowchart

Referral for CI
       ↓
Audiological evaluation (PTA, speech discrimination, hearing aid trial)
       ↓
Imaging (MRI first, then CT if needed)
       ↓
Multidisciplinary team assessment (psychologist, speech therapist, audiologist, surgeon)
       ↓
Pre-op vaccinations (pneumococcal)
       ↓
SURGERY (GA, no muscle relaxant, facial nerve monitoring throughout)
  → Postauricular incision
  → Receiver-stimulator bed creation (subperiosteal pocket or bony well)
  → Cortical mastoidectomy
  → Posterior tympanotomy (facial recess approach)
  → Round window visualization
  → Cochlear entry (round window membrane or cochleostomy)
  → Electrode insertion into scala tympani (slow, atraumatic "soft surgery")
  → Intraoperative testing (ECAP, impedance, imaging)
  → Fascia seal at cochlear opening
  → Layered wound closure + mastoid dressing
       ↓
Post-op wound healing (4-6 weeks)
       ↓
Device activation + audiological mapping
       ↓
Intensive auditory rehabilitation (speech therapy, listening training)

---

---