10-Mark Question: Hearing Rehabilitation (Final Year MBBS ENT)

QUESTION

MODEL ANSWER / EXAMINER'S GUIDE

1. Introduction (1 mark)

• Non-surgical: Hearing aids, auditory training, speech therapy, lip reading
• Surgical: Ossiculoplasty, tympanoplasty, cochlear implants, bone-anchored hearing aids (BAHA)

2. Hearing Aids (3 marks)

Components of a Hearing Aid

1. Microphone — picks up sound and converts it to electrical signals
2. Amplifier/Signal Processor (DSP) — processes, filters, and selectively amplifies speech while suppressing noise
3. Receiver (loudspeaker) — converts processed electrical signal back into acoustic energy delivered to the ear
4. Power source — usually a zinc-air disposable battery or rechargeable battery

Types / Styles of Hearing Aids

Indications for Hearing Aid Use

• Primary option after medical/surgical causes of hearing loss are excluded
• Predominantly used in sensorineural (88%) and mixed (11%) hearing loss; rarely for pure conductive loss (<1%)
• Candidacy based on: degree of hearing loss, word recognition score, dynamic range, patient motivation
• Two predictors of hearing aid success: word recognition score ≥50% and wide dynamic range (Dynamic range = UCL – SRT)

Electroacoustic Properties

• Frequency response: extends up to 3–4 kHz
• Gain: ratio of output to input power
• OSPL-90: maximum output; prevents uncomfortable over-amplification

Limitations of Conventional Hearing Aids

• Insufficient gain for severe-profound loss (max ~75–82 dB for BTE)
• Acoustic feedback limits usable gain
• Poor performance in background noise
• Occlusion effect; cosmetic concerns

3. Implantable Hearing Devices (2 marks)

Bone Conduction Devices / BAHA (Bone-Anchored Hearing Aid)

• Indicated for conductive, mixed, or single-sided deafness (SSD)
• Titanium fixture osseointegrated into the temporal bone transmits vibrations directly to cochlea via bone conduction
• Bypasses diseased external/middle ear
• Indicated when conventional hearing aids cannot be worn (e.g., atresia, chronically discharging ear)
• For SSD: eliminates the head shadow effect, improves speech in noise (but does not restore sound localization)

CROS / Bi-CROS Aids

• CROS (Contralateral Routing of Signal): microphone on deaf ear transmits signal wirelessly to receiver on the better ear — for SSD
• Bi-CROS: additional amplification added for the better ear when it also has some hearing loss

Active Middle Ear Implants

• Transducer coupled directly to the ossicular chain or round window
• Provide higher, more selective gain than conventional aids
• Overcome acoustic feedback limitation

4. Cochlear Implants (3 marks)

Definition

Components

• External: microphone → sound processor → transmitter coil
• Internal: receiver-stimulator (implanted) → electrode array inserted into scala tympani

Candidacy Criteria (FDA Guidelines)

Outcomes

• Marked improvement in speech perception in quiet and in noise
• Best outcomes in postlingual deafened adults and children implanted early
• Combined Electric and Acoustic Stimulation (EAS/Hybrid CI): for patients with residual low-frequency hearing and high-frequency profound loss
• Cochlear implants also used for single-sided deafness — improves noise performance, sound localization, and relieves tinnitus

Preoperative Considerations

• Pneumococcal vaccination mandatory (PCV13 + PPSV23) before implantation — meningitis risk
• High-resolution CT temporal bone ± MRI to assess cochlear anatomy and auditory nerve
• Multidisciplinary team: otologist, audiologist, speech-language pathologist, psychologist

5. Other Rehabilitative Measures (1 mark)

• Auditory training / Aural rehabilitation: improves listening skills after hearing aid or CI fitting; particularly important in CI recipients
• Speech therapy: especially for children with prelingual deafness
• Lip reading (speech reading) and sign language: for profoundly deaf who do not benefit from devices
• Ossiculoplasty: PORP or TORP for conductive hearing loss due to ossicular chain disruption
  • PORP (stapes suprastructure intact): better outcomes; ~2/3 patients achieve air-bone gap ≤20 dB
  • TORP (stapes footplate only): inferior long-term results

KEY REFERENCES FROM STANDARD TEXTBOOKS

1. Cummings Otolaryngology Head and Neck Surgery (Primary Reference)

• Chapter 164 — Hearing Aid Technology: Indications, components, styles, digital technology, fitting and verification
• Chapter 160 — Cochlear Implantation in Adults: Candidacy criteria, EAS/hybrid CI, outcomes
• Chapter 161 — Cochlear Implantation in Children: Pediatric criteria, speech-language outcomes
• Chapter 163 — Implantable Hearing Devices: Limitations of conventional aids; active middle ear implants; BAHA/osseointegrated devices
• Chapter 43 — Pediatric Otology (Hearing Rehabilitation and Cholesteatoma): Ossiculoplasty in children, PORP vs TORP outcomes

2. K.J. Lee's Essential Otolaryngology, Head and Neck Surgery

• Chapter on Hearing Aid Basics (pp. 396–398): Components, electroacoustic properties, styles, CROS, word recognition scores, dynamic range
• Chapter on Cochlear Implant Design (pp. 406–408): External/internal components, candidacy table, meningitis risk and vaccination in CI recipients
• Chapter on Ossiculoplasty (pp. 399–401): PORP/TORP, prosthesis materials, mechanics

KEY POINTS FROM DHINGRA'S DISEASES OF EAR, NOSE AND THROAT

Hearing Aids — Dhingra Points

1. A hearing aid is an electronic amplifying device worn on or in the ear; it does not treat the underlying disease but improves communication
2. Minimum hearing loss for prescription: typically ≥40 dB in the better ear (speech frequencies)
3. Hearing aids are most beneficial in bilateral moderate SNHL with good speech discrimination
4. Types described: BTE (most commonly prescribed in India), ITE, ITC, CIC, and Body-worn aids
5. Body-worn aids: most powerful; for profound/severe loss; microphone separated from receiver by wire — avoids feedback
6. CROS aid: for unilateral deafness; microphone on bad ear, speaker on good ear
7. Essential components (as per Dhingra): microphone, amplifier, receiver, battery, and volume control
8. Hearing aid fitting requires pure tone audiometry and speech audiometry (speech reception threshold + word recognition score)
9. Tolerance/adaptation period: 4–6 weeks recommended before judging benefit

Cochlear Implant — Dhingra Points

1. Indicated in patients with bilateral profound SNHL who gain no benefit from hearing aids
2. Works by electrical stimulation of the spiral ganglion cells (first-order auditory neurons)
3. Internal component = receiver-stimulator + electrode array (22 electrodes in Nucleus device); inserted into scala tympani via cochleostomy or round window
4. External component = speech processor + microphone + transmitter coil
5. Candidacy (Dhingra criteria):
   • Bilateral profound SNHL (>90 dB PTA)
   • Age ≥12 months (prelingual) or any age (postlingual)
   • No benefit from optimally fitted hearing aids for 3–6 months
   • Absence of cochlear ossification (assess by HRCT)
   • No active middle ear disease
6. Best results in: postlingually deafened adults; children implanted before age 2–3 years (critical period of auditory cortex plasticity)
7. Complications: device failure, facial nerve injury, perilymph gusher, meningitis (reduced by pneumococcal vaccine)
8. Post-implant auditory-verbal therapy (AVT) is mandatory for speech development in children

BAHA — Dhingra Points

1. Osseointegrated titanium implant in the mastoid bone
2. Sound bypasses external and middle ear, stimulates cochlea via bone conduction
3. Indicated in: conductive/mixed hearing loss where conventional aids cannot be worn (bilateral atresia, chronic otorrhea, fibrosed EAC) and SSD
4. Procedure: two-stage surgery in children; one-stage in adults
5. Transcutaneous BAHA (magnetic coupling) is now preferred over percutaneous (skin-penetrating abutment)

Auditory Training / Aural Rehabilitation — Dhingra Points

1. Encompasses listening training, lip reading/speech reading, and auditory-verbal therapy
2. Especially important post-cochlear implant in children — must begin within weeks of activation
3. Cued speech: uses hand cues alongside lip movements to distinguish phonemes that look similar on lips
4. Total communication: combines oral, manual (sign language), and written methods for profoundly deaf

MARKING SCHEME GUIDE (10 marks)

• Cummings CW et al. Cummings Otolaryngology Head and Neck Surgery, 7th ed. Elsevier, 2021. (Chapters 160, 161, 163, 164)
• Lee KJ. Essential Otolaryngology Head and Neck Surgery, 11th ed. McGraw-Hill, 2019. (pp. 396–408)
• Dhingra PL, Dhingra S. Diseases of Ear, Nose and Throat & Head and Neck Surgery, 7th ed. Elsevier India, 2018. (pp. 49–66)

Hearing Rehabilitation — 10-Mark Answer

Definition

Methods of Hearing Rehabilitation

• Non-surgical — Hearing aids, auditory training, lip reading, sign language
• Surgical — Ossiculoplasty, cochlear implants, bone-anchored hearing aids (BAHA)

1. Hearing Aids

Components

Types

• BTE (Behind the Ear) — most powerful; all degrees of loss
• ITE (In the Ear) — moderate to severe loss
• ITC (In the Canal) — mild to moderate loss
• CIC (Completely in the Canal) — cosmetically superior; mild loss
• Body-worn — most powerful; for profound loss; microphone-receiver separation eliminates feedback

All modern hearing aids are digital, using nonlinear compression — amplifying soft sounds more and loud sounds less, which is ideal for SNHL with recruitment.

Indications

• Bilateral moderate SNHL (≥40 dB PTA) with good speech discrimination
• After medical and surgical causes are excluded
• Two key predictors of success: word recognition score ≥50% and wide dynamic range (Dynamic range = UCL − SRT)

Special Types

• CROS aid (Contralateral Routing of Signal) — microphone on the deaf ear transmits wirelessly to the better ear; used for single-sided deafness
• Bi-CROS — same as CROS with additional amplification for the better ear

2. Bone-Anchored Hearing Aid (BAHA)

Indications

• Conductive/mixed hearing loss where conventional aids cannot be used (bilateral atresia, chronic ear discharge, fibrosed EAC)
• Single-sided deafness — eliminates the head shadow effect and improves speech in noise

Transcutaneous (magnetic coupling) BAHA is now preferred over percutaneous (skin-penetrating abutment).

3. Cochlear Implant (CI)

Components

Candidacy Criteria

Outcomes

• Best results in postlingually deafened adults and children implanted before age 2–3 years (critical period of auditory cortex plasticity)
• EAS (Electro-Acoustic Stimulation / Hybrid CI): for patients with residual low-frequency hearing and profound high-frequency loss — combines electrical stimulation at the base with acoustic amplification at the apex
• Also used for single-sided deafness — improves noise performance, sound localization, and relieves tinnitus

Complications

4. Ossiculoplasty

• PORP (Partial Ossicular Replacement Prosthesis) — stapes suprastructure intact; ~2/3 patients achieve air-bone gap ≤20 dB; better outcomes
• TORP (Total Ossicular Replacement Prosthesis) — stapes footplate only; inferior long-term results
• Materials: hydroxyapatite, titanium, plastipore

5. Auditory Rehabilitation & Training

• Auditory-Verbal Therapy (AVT): mandatory post-CI in children; begins within weeks of device activation
• Lip reading / Speech reading: for profoundly deaf patients
• Cued speech: hand cues + lip movement to distinguish similar-looking phonemes
• Sign language / Total Communication: combines oral, manual, and written methods
• Speech therapy: essential in children with prelingual deafness

Summary Table

References

• Dhingra PL, Dhingra S. Diseases of Ear, Nose and Throat, 7th ed. — pp. 49–66
• Cummings CW et al. Cummings Otolaryngology, 7th ed. — Chapters 160, 163, 164
• Lee KJ. Essential Otolaryngology, 11th ed. — pp. 396–408