Hearing Assessment in Newborns

Why Is Newborn Hearing Assessment Important?

Background: Why the Old Method Failed

Universal Newborn Hearing Screening (UNHS) - The Current Standard

• 95% of babies are screened by 4 weeks of age (hospital-based programmes) or within 5 weeks (community-based)

• Refer rate: ~2.5%, bilateral refer rate: ~0.5%
• Yield for bilateral PCHI: 1.01 per 1,000 screened
• Importantly, 40-50% of affected babies have NO risk factors at birth - this is why universal (not just targeted) screening is necessary

The Two Core Tests Used

1. Automated Otoacoustic Emissions (AOAE)

• A small soft probe is placed in the ear canal
• A click or tone is played
• A microphone in the probe detects the returning "echo" (the OAE)
• Result: PASS or REFER

2. Automated Auditory Brainstem Response (AABR)

• Soft electrodes placed on the baby's scalp and forehead
• Clicks are delivered through small earphones
• The brainstem response (waves I-V) is recorded automatically
• Result: PASS or REFER

Which Test for Which Baby? - The Protocol

High-Risk Factors for Hearing Loss in Newborns

• TORCH infections - Toxoplasmosis, Rubella, CMV (most common cause of non-hereditary congenital SNHL), Herpes
• Teratogen exposure
• Prematurity and low birth weight
• Low APGAR scores
• Hyperbilirubinemia (associated with ANSD and SNHL)
• Sepsis, meningitis
• Ototoxic medications (aminoglycosides)

• Family history of congenital hearing loss
• Craniofacial anomalies
• Syndromes associated with hearing loss (e.g., Down syndrome)

Auditory Neuropathy Spectrum Disorder (ANSD) - A Special Case

• Accounts for up to 10% of all children with confirmed PCHI
• Predominantly found in the NICU population
• Only 5-7% come from the "well baby" population
• Hyperbilirubinemia is a major associated factor
• These babies are missed if OAE is the only screening tool

What Happens After a "Refer" Result?

1. Refer on AOAE → Retest AOAE (many refer results are due to fluid/vernix in canal at birth)
2. Refer on repeat AOAE → AABR testing
3. Refer on AABR → Full audiological diagnostic assessment

• Electrophysiological tests: ABR threshold series (click and tone-burst ABR), Cochlear Microphonic
• Behavioural Observation Audiometry (BOA): for very young infants - observing head turns, startle, eye widening
• Imaging: MRI/CT temporal bone to assess cochlear nerve and inner ear anatomy
• Medical history: full prenatal/perinatal history, family history, syndromic features
• Genetics referral

Behavioural Hearing Tests Used in Infants (Post-Neonatal Period)

Surveillance After a Pass Result

1. Progressive hearing loss (normal at birth, deteriorates with time)
2. Acquired hearing loss (meningitis, ototoxic drugs, trauma)
3. Late-onset genetic hearing loss
4. Mild hearing loss missed by the screen (screen only detects ≥40 dBHL)
5. Babies who moved from countries without UNHS

• Syndromes associated with hearing loss (other than Down)
• NICU baby who referred on OAE but passed AABR
• Craniofacial anomaly
• Down syndrome
• Congenital infection (especially CMV)
• Family history of progressive genetic hearing loss

Summary: The NHSP Protocol at a Glance

ALL NEWBORNS
      ↓
   AOAE Test
   /       \
PASS      REFER
  ↓          ↓
Discharge  Retest AOAE
           /        \
         PASS       REFER
           ↓           ↓
       Discharge    AABR Test
                   /        \
                PASS        REFER
                  ↓             ↓
              Discharge   Audiological
                          Diagnostic
                          Assessment

NICU BABIES → AOAE + AABR (both mandatory)

Key Points (from Scott-Brown's ENT Textbook)

• Newborn hearing screening of all babies is the most effective and cost-effective method to identify congenital hearing loss
• Early identification before 6 months leads to significantly better language outcomes
• AOAE alone is insufficient for NICU babies - AABR must be added due to risk of ANSD
• 40-50% of deaf babies have NO risk factors - universal screening beats targeted screening
• A pass result means the child can hear at the time of screening; late-onset or progressive hearing loss can still develop
• Screening and assessment must be the first steps in a family-centred, multidisciplinary service including ENT, audiology, education, and social services

Types of Paediatric Deafness and Prerequisites for Cochlear Implantation

PART 1: TYPES OF PAEDIATRIC DEAFNESS

How to Classify Childhood Hearing Loss

Axis 1: TYPE (Anatomical)

ANSD is a special category: outer hair cells work normally (OAEs present), but neural transmission is disrupted (ABR absent or abnormal). Up to 10% of children with confirmed permanent hearing impairment have ANSD.

Axis 2: SEVERITY (Hearing Level in dBHL)

Axis 3: TIMING (Onset Relative to Speech Development)

Axis 4: AETIOLOGY (Cause)

A. Congenital Deafness

• Non-syndromic (70% of genetic): No other abnormalities
  • Autosomal recessive 80% - usually pre-lingual. Most common mutation: Connexin 26 (GJB2) - accounts for ~50% of all non-syndromic AR hearing loss (ARNSHL). Next most common: Pendrin gene (SLC26A4)
  • Autosomal dominant 15-20% - more often progressive/post-lingual
  • X-linked 5%
  • Mitochondrial - maternal inheritance
• Syndromic (30% of genetic): Hearing loss as part of a syndrome:
  • Pendred syndrome - SNHL + enlarged vestibular aqueduct + thyroid goitre
  • Usher syndrome - SNHL + retinitis pigmentosa (progressive visual loss)
  • Waardenburg syndrome - SNHL + heterochromia, white forelock
  • Branchio-oto-renal syndrome - SNHL/CHL + branchial anomalies + renal defects
  • Down syndrome - mainly conductive due to craniofacial abnormality
  • Treacher Collins syndrome - conductive loss due to ossicular/external ear abnormalities

• CMV (Cytomegalovirus) - now the most common cause of non-hereditary SNHL in the developed world. Affects 0.3-0.5% live births in UK. Hearing loss can be delayed onset and progressive; 30-50% begin as unilateral
• Congenital rubella syndrome (CRS) - deafness + cataracts/glaucoma + cardiac defects (PDA, pulmonary stenosis) + microcephaly. Almost eliminated in vaccinated countries
• Congenital syphilis - Hutchinson's triad: SNHL (VIII nerve) + interstitial keratitis + Hutchinson's teeth. Usually appears at 8-10 years
• Toxoplasmosis - SNHL, requires annual audiological monitoring if untreated
• Drugs in pregnancy - aminoglycosides, anti-epileptics, cytotoxics, diuretics
• Maternal diabetes / thyroid dysfunction
• Hyperbilirubinemia, low birth weight, birth asphyxia

B. Acquired Deafness

• Hypoxia (low Apgar, difficult delivery, ventilation) - apoptosis of hearing cells can occur
• Hyperbilirubinemia - damages auditory brainstem nuclei and inferior colliculi; often causes ANSD; associated with ototoxic drug exposure (aminoglycosides, furosemide) in NICU

Aetiology at a Glance (Figure from Scott-Brown's)

PART 2: PREREQUISITES FOR COCHLEAR IMPLANTATION IN CHILDREN

1. AUDIOLOGICAL PREREQUISITES

• Failure to reach auditory milestones despite adequate hearing aid use
• Speech perception score <20-30% on word tests (MLNT or LNT) in verbal children
• Poor and declining speech discrimination
• Evidence of increasing educational disadvantage despite amplification

• Post-meningitic hearing loss with risk of cochlear ossification - this is a surgical emergency; delay makes insertion difficult or impossible
• Known genetic mutations causing profound deafness
• Off-label implantation <12 months is increasingly common and has shown language comprehension comparable to normal hearing children

• ABR (acoustic + electric) to establish true thresholds
• Cochlear microphonic / ECoG (especially in ANSD)
• Aided thresholds and soundfield testing
• Behavioural audiometry age-appropriately (BOA, VRA, play audiometry)
• IT-MAIS scale (Infant-Toddler Meaningful Auditory Integration Scale) for very young infants

2. MEDICAL/SURGICAL PREREQUISITES

• Complete absence of a cochlea
• Severe cochlear ossification that completely precludes electrode placement (consider Auditory Brainstem Implant/ABI in these cases)

• MRI temporal bone - to assess cochlear nerve, cochlear anatomy, internal auditory canal
• CT temporal bone - to assess cochlear patency, ossification, cochlear malformations

• Pneumococcal vaccine (PCV13 + PPSV23) before implantation - CI recipients have increased susceptibility to meningitis
• PCV13 at least 2 weeks before surgery

3. SOCIAL/FAMILY PREREQUISITES

• Patient or caregivers unwilling to permit access to auditory input

• Family commitment to post-operative rehabilitation (device use, therapy appointments, school support)
• Understanding that CI does not produce "normal" hearing - gains require intensive habilitation and consistent device use
• Willingness to comply with long-term follow-up, speech therapy, and audiology appointments
• Realistic expectations counselled throughout the process

4. THE COCHLEAR IMPLANT TEAM (Multidisciplinary)

• ENT surgeon (cochlear implant surgeon)
• Audiologist (pre- and post-operative assessment, device mapping)
• Speech and Language Therapist (assessment + post-CI rehabilitation)
• Educational specialist (IEP planning, classroom support)
• Psychologist (cognitive assessment, autism screening, family coping)
• Social worker (family support, access to care)
• Community providers: early interventionists, teachers of the deaf

5. BILATERAL vs. UNILATERAL IMPLANTATION

• NICE (UK) 2009 guidelines: All eligible children should receive bilateral simultaneous CI
• Bilateral CIs improve speech in noise, sound localization, and reduce fatigue
• The European Bilateral Paediatric CI Consensus (2010): Any child who is an unambiguous CI candidate should receive bilateral simultaneous CI as soon as possible after diagnosis
• Sequential bilateral implants with >1 year delay show asymmetries in brainstem/cortical function and poorer scores in the second ear
• Children implanted earlier have quicker language acquisition, earlier binaural skills, better language scores, and higher rates of mainstream school attendance

Summary Box: Prerequisite Checklist for Paediatric CI