Rehabilitation of the Hearing Impaired

Rehabilitation of the Hearing Impaired

Aural rehabilitation is essential for individuals with hearing loss to improve communication and quality of life. It encompasses a combination of instrumental devices and training programs tailored to the individual’s needs.

1. Instrumental Devices

a) Hearing Aids

• • Conventional Hearing Aids: Amplify sound for individuals with residual hearing.
  • Bone-Anchored Hearing Aids (BAHA): Transmit sound via bone conduction, ideal for conductive or mixed hearing loss and single-sided deafness.
  • Implantable Hearing Aids: Surgically implanted devices that enhance sound transmission, suitable for moderate to severe hearing loss.

b) Implants

• • Cochlear Implants: Directly stimulate the auditory nerve, providing sound perception for individuals with severe to profound sensorineural hearing loss.
  • Auditory Brainstem Implants (ABI): Used for individuals with non-functional auditory nerves, stimulating the brainstem directly.

c) Assistive Devices for the Deaf. Include devices like FM systems, infrared systems, and captioning tools to improve accessibility in various environments.

2. Training Programs

• Speech (Lip) Reading. Teaches individuals to interpret visual cues from lip movements, facial expressions, and gestures to understand speech.
• Auditory Training. Focuses on improving the ability to recognize and interpret sounds, especially for new hearing aid or cochlear implant users.
• Speech Conservation. Helps individuals maintain clear speech by practicing articulation, pitch, and volume control.

 Conventional Hearing Aids

A hearing aid is an electronic device designed to amplify sounds for individuals with hearing loss. It consists of three essential components: (1) a microphone, which captures sound and converts it into electrical signals; (2) an amplifier, which increases the strength of these signals (amplification); and (3) a receiver, which transforms the amplified signals back into sound. This sound is then delivered to the ear through an ear mould, enhancing the user’s ability to hear.

Hearing aids are broadly categorized into two types: air conduction and bone conduction. Air conduction hearing aids transmit amplified sound through the ear canal to the tympanic membrane, making them suitable for most users. Bone conduction hearing aids, on the other hand, use a bone vibrator placed on the mastoid to directly stimulate the cochlea, making them ideal for individuals with conditions like actively draining ears, otitis externa, or ear canal atresia, where traditional ear inserts cannot be worn.

Types of Bone Conduction Hearing Aids

1. Body-Worn Hearing Aids: The microphone, amplifier, and battery are housed in a case worn at chest level, while the receiver is placed at ear level. These hearing aids offers high amplification with minimal feedback, making it suitable for severe hearing loss or congenital deafness in children.
2. Behind-the-Ear (BTE) Hearing Aids: All components are integrated into a single unit worn behind the ear, connected to the ear canal via tubing and an ear mould. These are ideal for mild to moderate hearing loss, particularly high-frequency loss.
3. Spectacle Hearing Aids: The hearing aid is embedded in the frame of eyeglasses. These are useful for individuals requiring both vision correction and hearing assistance, though less popular today.
4. In-the-Ear (ITE) Hearing Aids: The entire device is housed within a custom earmould that fits inside the ear. Popular for mild to moderate hearing loss due to its cosmetic appeal.
5. Canal Hearing Aids (ITC and CIC): Compact devices that fit entirely within the ear canal, with two subtypes: In-the-Canal (ITC) and Completely-in-the-Canal (CIC). Suitable for mild to moderate high-frequency hearing loss (1-4KHz), requiring a wide ear canal and user dexterity for operation.

Indications for Hearing Aids. Hearing aids are recommended for individuals with hearing loss that cannot be addressed medically or surgically. Key indications include:

1. Sensorineural Hearing Loss: For those whose daily activities are affected, though some may experience sound distortion or recruitment.
2. Deaf Children: Early fitting of binaural aids (one for each ear) is crucial for speech and language development, often combined with lip-reading training.
3. Conductive Hearing Loss: Used when surgery is refused, not feasible, or unsuccessful.

Fitting a Hearing Aid. The fitting process considers several factors:

1. Degree and configuration of hearing loss (type of frequencies affected).
2. Type of hearing loss (conductive or sensorineural).
3. Presence of recruitment or uncomfortable loudness levels.
4. Patient’s age, dexterity, and cosmetic preferences.
5. Condition of the outer and middle ear.
6. Type of ear mould and fitting (monoaural, binaural, or contralateral routing of signals).

Disadvantages of Conventional Hearing Aids

• Cosmetic Concerns: Visibility of the device may be undesirable.
• Acoustic Feedback: Whistling sounds due to sound leakage.
• Spectral Distortion: Altered sound quality.
• Occlusion Effect: Blockage of the ear canal, leading to discomfort and wax build up.
• Skin Sensitivity: Irritation from ear moulds.
• Discharging Ears: Difficult to use in cases of active ear discharge.

CROS Hearing Aids. Contralateral Routing of Signals (CROS) aids are designed for individuals with unilateral severe hearing loss. A microphone is fitted on the deaf ear transmits sound to a receiver fitted in the better-hearing ear which helps in sound localization coming from the side of the deaf ear. However, bone-anchored hearing aids are increasingly preferred for single-sided deafness, offering a more effective solution.

Bone-Anchored Hearing Aid (BAHA)

The Bone-Anchored Hearing Aid (BAHA) is a specialized hearing device that operates on the principle of bone conduction. It is particularly beneficial for individuals with conductive hearing loss, mixed hearing loss or unilateral hearing loss, who are unable to use traditional “in-the-ear” or “behind-the-ear” hearing aids. By bypassing the external auditory canal and middle ear, BAHA directly transmits sound vibrations through the skull bone to the cochlea, offering an effective auditory solution for those with specific hearing impairments.

How BAHA Works. The BAHA system consists of three key components:

1. Titanium Fixture: Surgically implanted into the skull bone.
2. Titanium Abutment: Attached to the fixture and protruding through the skin.
3. Sound Processor: Externally attached to the abutment.

The titanium fixture undergoes osseointegration, a process where it fuses with the surrounding bone tissue over 2–6 months. Once osseointegration is complete, the sound processor is connected to the abutment. The device captures sound waves, converts them into vibrations, and transmits these vibrations through the skull to the cochlea, enabling sound perception.

Surgical Procedure

• Adults: The procedure is typically performed in a single stage (both fixture and fixture are implanted), with a 3-month osseointegration period before attaching the sound processor.
• Children: A two-stage approach is recommended. The titanium fixture is implanted in the first stage, followed by a second procedure 6 months later to connect the abutment.

Complications. While BAHA is generally safe, potential complications include:

• Failure of osseointegration.
• Localized infections or inflammation at the implant site.

Candidacy for BAHA. BAHA is recommended for individuals who meet the following criteria:

1. Chronic Ear Conditions: Patients with persistent ear canal infections or inflammation that prevent the use of conventional air-conduction hearing aids.
2. Congenital Malformations: Children with microtia or canal atresia (malformed or absent outer ear and ear canals).
3. Single-Sided Deafness (SSD): Individuals with hearing loss in one ear. For patients with SSD, BAHA offers a significant advantage over traditional Contralateral Routing of Signal (CROS) hearing aids. Unlike CROS aids, which have limitations in performance and aesthetics, BAHA is implanted on the deaf side and transmits sound via bone conduction to the functional cochlea on the opposite side. This eliminates the “head shadow” effect, improving speech recognition in both quiet and noisy environments.

Indications for BAHA. BAHA is indicated in the following scenarios:

1. When Air-Conduction Hearing Aids Are Ineffective:

• • Children with microtia or canal atresia (malformed or absent outer ear and ear canals).
  • Chronic ear discharge unresponsive to treatment. Not able to wear conventional hearing aids due to persistent ear in the canal.
  • Discomfort or excessive feedback from air-conduction devices.

1. Conductive or Mixed Hearing Loss: Cases such as otosclerosis or tympanosclerosis where surgical intervention is not feasible.
2. Single-Sided Deafness: To restore binaural hearing and improve auditory localization.

 Implantable Hearing Aids

Implantable middle ear hearing aids represent an innovative category of hearing devices that operate on the principle of direct drive. Unlike traditional hearing aids, which deliver sound acoustically through the ear canal, these devices use mechanical vibrations to directly stimulate the ossicular chain, leaving the ear canal open. This approach offers a unique solution for individuals with moderate-to-severe sensorineural hearing loss who seek an alternative to conventional hearing aids.

Types of Implantable Middle Ear Devices. Implantable hearing devices are broadly classified into two types based on their mechanism of action:

1. Piezoelectric Devices: These devices utilize a piezoceramic crystal that changes shape when an electric current is applied, generating vibrations. The crystal is coupled to the ossicles, directly driving the ossicular chain by vibrations. Examples include the Envoy, Middle-Ear Transducer (MET), Rion, and Totally Integrated Cochlear Amplifier (TICA).
2. Electromagnetic Devices: These devices function by passing an electric current through a coil, creating a magnetic field that drives an adjacent small magnet attached to one of the ossicles. This magnet transmits vibrations to the cochlea. A well-known example is the Vibrant Sound bridge, manufactured by MED-EL.

The Vibrant Sound bridge Device. The Vibrant Sound bridge is a semi-implantable system consisting of two main components:

• • Internal Component (VORP): This includes a receiver, a Floating Mass Transducer (FMT), and a conductor link between the receiver and FMT. The FMT is surgically attached to the incus, enabling direct vibration of the ossicular chain.
  • External Component (Audio Processor): Worn behind the ear, this component captures sound via a microphone and transmits it as radiofrequency signals to the internal component receiver.

Candidacy for Implantable Hearing Aids. Ideal candidates are adults aged 18 and older with moderate-to-severe sensorineural hearing loss having dissatisfaction with the traditional hearing aids due to issues such as:

• Poor sound quality.
• Discomfort from the occlusion effect.
• Frequent wax build-up in the ear canal or hearing aid mould.
• Sensitivity of the ear canal skin.
• Persistent acoustic feedback.

Surgical Procedure. The implantation of the internal device is performed under general anaesthesia. The receiver is placed under the skin over the mastoid bone using a cortical mastoidectomy and posterior tympanotomy approach. The FMT is attached to the long process of the incus without modifying the middle ear structures, preserving the patient’s residual hearing. After 6–8 weeks, the external audio processor is fitted and programmed.

Advantages of Direct Drive Systems. Direct drive hearing devices offer several benefits over conventional hearing aids:

1. Improved Sound Quality: By delivering mechanical energy directly to the ossicles, these devices provide clearer sound, especially in noisy environments.
2. Elimination of Common Issues: Problems such as occlusion, feedback, discomfort, and wax build-up are avoided, as the ear canal remains open.
3. Enhanced Comfort: The absence of ear canal obstruction makes these devices more comfortable for long-term use.

Cochlear Implants

Cochlear implants are advanced electronic devices designed to provide hearing for children and adults with severe to profound sensorineural hearing loss. The cochlear implant provides direct electrical stimulation to the auditory nerve, bypassing the damaged parts of the inner ear and degenerated hair cells in the cochlea, which are damaged to such a point that amplification provided by hearing aids is no longer effective. The auditory nerve then carries the signals to the auditory cortex in the brain for hearing perception.

Components and Mechanism of a Cochlear Implant. A cochlear implant consists of two main components: an external unit and an internal unit.

1. External Component: It consists of
   • Speech Processor: This can be worn behind the ear or on the body, with the behind-the-ear type being more common. It captures sound through a microphone, processes it, converts it into digitally coded signals, and sends them to the transmitter coil. The speech processor converts sound into electrical pulses using a variety of advanced coding strategies, such as the Simultaneous Analogue Strategy (SAS), Continuous Interleaved Sampling (CIS), Spectral Peak (SPEAK), and Advanced Combination Encoder (ACE).
   • Transmitter coil: The external transmitter sends digitally coded signals to the receiver-stimulator package via radiofrequency waves.
     
     
2. Internal Component:
   • Receiver-Stimulator package: It consists of a magnet, which holds the external transmitter in place and an electronic system that decodes signals received from the external transmitter, converts them into electrical impulses and transmits them to the electrode array by using a speech strategy. It is surgically implanted behind the ear beneath the skin.
   • Intracochlear electrode Array: It is a thin, flexible wire inserted into the scala tympani of the basal turn of the cochlea (the entire length of the cochlear duct). This array contains multiple electrodes that deliver electrical impulses to the spiral ganglion cells in the cochlea. These cells are bipolar neurons that connect the cochlea to the auditory nerve. When the electrodes stimulate the spiral ganglion cells, the auditory nerve carries these signals to the auditory cortex in the brain, where they are interpreted as sound. For effective speech perception, it is essential to stimulate at least 10,000 of the approximately 35,000 nerve fibres in the auditory nerve. This ensures that the brain receives sufficient information to get good speech perception and distinguish speech sounds, especially in noisy environments.

Candidacy for Cochlear Implants. Cochlear implants are suitable for both children and adults who meet specific criteria:

1. Severe to Profound Sensorineural Hearing Loss.
2. Fracture of the cochlea following temporal bone fracture.
3. Auditory neuropathy or dyssynchrony (ANDS) patients.
4. Inability to achieve functional hearing with conventional devices.
5. No medical contraindications for fitness for surgery and general anaesthesia.
6. Realistic Expectations: Understanding the potential outcomes and limitations.
7. Strong family and social support for post-implantation rehabilitation.
8. Adequate Cognitive Function: Ability to use and adapt to the device.

Candidates are categorized as prelingual (deafened before acquiring speech) or postlingual (deafened after acquiring speech). Early intervention is critical for prelingual children, as auditory deprivation during early development can lead to degeneration of central auditory pathways, limiting the benefits of implantation.

Outcomes of Cochlear Implantation. The success of cochlear implantation depends on several factors:

1. Prior Auditory Experience: Postlingual patients or those with prior hearing aid use tend to achieve better outcomes.
2. Age at Implantation: Younger children, especially those implanted before 12 months, show improved speech and language development.
3. Duration of Deafness: Shorter periods of deafness correlate with better outcomes.
4. Neural Plasticity: Early diagnosis and rehabilitation (ideally before age 5) are critical for prelingually deaf children due to neural plasticity. Neural plasticity is the brain’s ability to adapt to new auditory stimuli. Without early stimulation, the brain’s auditory areas may be repurposed for other functions, limiting the potential for speech and language development.

• Postlingual patients often achieve significant benefits, including the ability to understand speech without visual cues and use the telephone.
• Prelingual children also develop speech and language skills over time, though this requires consistent auditory-verbal therapy.
• Prelingual adults with no prior auditory experience may gain only sound awareness.

Evaluation for Cochlear Implantation. A thorough evaluation is essential to determine candidacy and set realistic expectations. The evaluation process includes:

1. Medical Evaluation:
   • Detailed history and physical examination to assess fitness for surgery.
   • Preoperative tests and vaccinations, particularly against meningitis (e.g., Haemophilus influenza, meningococcus).
   • Check for any ear infections. Pt should be free from all ear infections. Myringoplasty or mastoid exploration if required, should be 03 months before the cochlear implant surgery.
2. Imaging Studies: 
   • HRCT of Temporal Bone: Identifies inner ear abnormalities, cochlear lumen obliteration, middle ear pathology, and anatomical variations (e.g., low-lying dura, anterior sigmoid sinus). It detects conditions like cochlear hypoplasia, enlarged vestibular aqueduct, and labyrinthitis ossificans, which can impact surgical planning and candidacy for cochlear implants (CI).
   • MRI: Diagnoses cochlear nerve aplasia, a contraindication for CI, necessitating an Auditory Brainstem Implant (ABI) instead.
3. Audiological Evaluation:
   • Pure tone audiometry, speech discrimination tests, tympanometry, otoacoustic emissions (OAE), auditory brainstem responses (ABR), and auditory steady-state responses (ASSR).
   • A mandatory hearing aid trial to assess the extent of benefit from conventional devices.
4. Speech and Language Evaluation: Assesses the patient’s current communication abilities and identifies any developmental delays or disorders.
5. Psychological Evaluation: Evaluates cognitive function and identifies any additional disabilities, helping to set realistic expectations for post-implantation outcomes.

Surgical Procedure. Cochlear implant surgery is performed under general anaesthesia and involves the following steps:

1. Patient Positioning: The surgery is performed under general anaesthesia, with the patient in a supine position and the head turned 45-60 degrees from the surgeon.
2. Incision: A C-shaped postauricular incision is made.
3. Flap Elevation and Mastoidectomy: The skin flap , subcutaneous tissue, and part of the temporalis muscle (palva flap) are elevated. A cortical mastoidectomy is performed, preserving overhanging edges.
   
4. Formation of the well. A subperiosteal pocket is made in the posterior and superior to the mastoidectomy cavity. A bony well is created for the receiver-stimulator placement.
   
   
5. Posterior Tympanotomy: The middle ear is accessed via the facial recess, and the round window niche is visualized.
   
   
   
   
6. Cochleostomy: A cochleostomy is done with Rosen’s pick instrument. Cochleostomy is created anteroinferior or inferior to the round window, ensuring the electrode enters the scala tympani.
   
   
7. Receiver-Stimulator Placement: The receiver-stimulator is placed tightly in the subperiosteal pocket and the electrode array is passed through the bony well, which is secured with non-absorbable sutures.
   
   
   
8. Electrode Insertion: The electrode array is inserted into the cochlea, either through the cochleostomy or the round window (the latter is preferred for reduced trauma and postoperative complications).
   
   
9. Cochleostomy sealing. Temporalis muscle pieces or fat are used to seal the cochleostomy site. Electrophysiological testing is done to confirm proper functioning.
   
   
10. Verification and Closure: Neural response telemetry checks electrode functionality. The incision is closed in layers, and a postoperative X-ray (Stenver’s view) is done to confirm the electrode position.
    
    

Postoperative Mapping and Rehabilitation

1. Device Activation: The implant is activated 3–4 weeks post-surgery.
2. Mapping (Programming): The speech processor is programmed to optimize sound perception. Regular adjustments are made during follow-up visits.
3. Habilitation: Auditory-verbal therapy is essential for all patients, particularly prelingual children. This therapy focuses on developing listening and speaking skills without relying on visual cues. Consistent effort from the patient, family, and therapists is crucial for successful adaptation.

Cochlear implants have transformed the lives of individuals with severe to profound hearing loss, offering them the opportunity to experience sound and develop communication skills. With careful patient selection, precise surgical techniques, and dedicated postoperative rehabilitation, cochlear implants can provide life-changing benefits, particularly for children who receive early intervention. This technology continues to evolve, promising even greater outcomes for future recipients.

Auditory Brainstem Implant (ABI)

The Auditory Brainstem Implant (ABI) is a groundbreaking device designed to provide auditory stimulation for individuals who cannot benefit from cochlear implants due to the absence or dysfunction of the auditory nerve (CN VIII). Unlike cochlear implants, which stimulate the auditory nerve, the ABI directly targets the cochlear nuclear complex in the brainstem. This makes it a vital option for patients with specific conditions, such as bilateral vestibular schwannomas in neurofibromatosis type 2 (NF2), where the auditory nerve is damaged or severed.

Indications for ABI. The primary indication for an ABI is bilateral damage to the auditory nerve, typically resulting from the surgical removal of vestibular schwannomas (acoustic neuromas). In cases of unilateral acoustic neuroma, an ABI is unnecessary because hearing can still be preserved or restored through the contralateral ear. However, in bilateral cases, such as those seen in NF2, the ABI becomes a critical tool for auditory rehabilitation.

How the ABI Works. The ABI is conceptually similar to a multichannel cochlear implant but differs in its placement and target. Key components include:

1. Multielectrode Array: Attached to a Dacron mesh, which is positioned on the surface of the brainstem within the lateral recess of the fourth ventricle.
2. Receiver/Stimulator: Contains a removable magnet, allowing patients to safely undergo MRI scans if needed.

The ABI bypasses the cochlea and auditory nerve entirely, delivering electrical stimulation directly to the cochlear nucleus in the brainstem. This enables the brain to perceive sound, albeit with less clarity and precision compared to cochlear implants.

Benefits and Limitations. ABIs provide several functional benefits, including:

• Improved Communication: Enhanced ability to understand speech, especially when combined with lip-reading.
• Environmental Sound Awareness: Better recognition of everyday sounds, such as alarms, doorbells, and approaching vehicles.
• Safety and Orientation: Increased awareness of surroundings, contributing to improved quality of life.

However, ABIs are not as effective as multichannel cochlear implants. The sound perception they provide is often less refined, and users may not achieve the same level of speech recognition. Despite these limitations, ABIs represent a significant advancement for individuals who have no other options for hearing restoration.

Surgical Procedure. The ABI is surgically implanted during the removal of a vestibular schwannoma. The procedure involves:

1. Accessing the Brainstem: The lateral recess of the fourth ventricle is exposed.
2. Placing the Electrode Array: The Dacron mesh with the multielectrode array is carefully positioned on the cochlear nucleus.
3. Securing the Receiver/Stimulator: The internal device is placed under the skin, and the electrode array is connected.

Postoperative imaging and electrophysiological testing are performed to ensure proper placement and functionality.

Technological Developments. ABIs are still relatively rare, with a limited number of procedures performed worldwide. Ongoing research and technological advancements aim to improve their effectiveness, particularly in enhancing speech perception and sound quality. Innovations in electrode design, signal processing, and surgical techniques are expected to expand the potential of ABIs in the future. The Auditory Brainstem Implant (ABI) is a specialized solution for individuals with bilateral auditory nerve damage, particularly those with NF2. While it does not match the performance of cochlear implants, it offers meaningful auditory benefits, including improved communication and environmental sound awareness. As technology continues to evolve, ABIs hold promise for further enhancing the quality of life for patients with profound hearing loss due to brainstem-level auditory pathway damage.

 

———— End of the chapter ————

Download full PDF Link: Reference Textbooks.

• Scott-Brown, Textbook of Otorhinolaryngology-Head and Neck Surgery.
• Glasscock-Shambaugh, Textbook of Surgery of the Ear.
• P L Dhingra, Textbook of Diseases of Ear, Nose and Throat.
• Hazarika P, Textbook of Ear Nose Throat And Head Neck Surgery Clinical Practical.
• Mohan Bansal, Textbook of Diseases of Ear, Nose and Throat Head and Neck Surgery
• Hans Behrbohm, Textbook of Ear, Nose, and Throat Diseases With Head and Neck Surgery.
• Salah Mansour, Middle Ear Diseases – Advances in Diagnosis and Management.
• Logan Turner, Textbook of Diseases of The Nose, Throat and Ear Head And Neck Surgery.
• Rob and smith, Textbook of Operative surgery.
• Anirban Biswas, Textbook of Clinical Audio-vestibulometry.
• Arnold, U. Ganzer, Textbook of  Otorhinolaryngology, Head and Neck Surgery.
• Gordon B. Hughes, Myles L. Pensak, H. B. Broidy. Textbook of Clinical Otology.
• Mario Sanna. Textbook of Color Atlas of Endo-Otoscopy Examination–Diagnosis–Treatment.

Author:

Dr. Rahul Bagla
MBBS (MAMC, Delhi) MS ENT (UCMS, Delhi)
Fellow Rhinoplasty & Facial Plastic Surgery.
Renowned Teaching Faculty
Mail: msrahulbagla@gmail.com
India

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• Please read. Anatomy of External Ear. https://www.entlecture.com/anatomy-of-ear/
• Please read. Anatomy of Temporal Bone. https://www.entlecture.com/anatomy-of-temporal-bone/
• Please read. Stenger’s, Chimani Moos, Teal test. https://www.entlecture.com/special-tuning-fork-tests/

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