Congenital Sensorineural Hearing Loss (SNHL)

Overview

1. Genetic Causes

A. Nonsyndromic (75% of genetic cases)

Autosomal Recessive (most common)

Autosomal Dominant

• Wolfram syndrome: Most common cause of dominantly inherited low-frequency SNHL; progressive course.

B. Syndromic Genetic Causes (>400 syndromes)

Autosomal Recessive Syndromes

• Accounts for ~2% of profound congenital SNHL
• Mutation in SLC26A4 (iodine-chloride transporter defect)
• Bilateral/unilateral SNHL + Mondini malformation + euthyroid goiter
• Work-up: SLC26A4 testing, TSH, T3, T4

• Affects 3% of the deaf population; 50% of the deaf-blind population
• Mutations in MYO7A, USH2A, and others (tip-link/usherin protein dysfunction)
• Three types:
  • USH1 (most severe): profound SNHL, vestibular dysfunction, early retinitis pigmentosa
  • USH2 (most common): moderate-severe SNHL, normal vestibular function, later retinitis pigmentosa
  • USH3 (~3%, mostly Norwegian): progressive SNHL, variable vestibular function

• 1 in 1,000 profoundly deaf patients
• Mutation in KVLQT1 - dysregulated potassium channel
• Severe/profound SNHL + prolonged QT interval + sudden death in young adults
• Treatment: beta-blockers; screen first-degree relatives for Romano-Ward syndrome

• Incidence: 1/60,000; screened in neonatal programs
• SNHL + hair loss + seizures + hypotonia
• Preventable/treatable with dietary biotin replacement

Autosomal Dominant Syndromes

• Mutation in neural crest cells → defective intermediate layer of stria vascularis
• Features: white forelock, dystopia canthorum, synophrys, heterochromia iridis, SNHL
• Four types: WS1 (PAX3), WS2A/Tietz (MITF), WS3 (Klein), WS4 (SOX10 + Hirschsprung)

• EYA1 mutation (only 40% confirmed by testing)
• Major features: branchial clefts/fistulas, outer/middle/inner ear anomalies
• Temporal bone findings pathognomonic: fused malleoincudal complex, funnel-shaped IAC, hypoplastic cochlear apex

• Sporadic microdeletion in CHD7 (chr 8) - only 50% have confirmed mutation
• Coloboma, Heart defects, Atresia choanae, Retardation, Genitourinary anomalies, Ear anomalies
• Inner ear: absent oval window, Mondini malformation, absent/hypoplastic semicircular canals

• Mutation in schwannomin (chr 22) → abnormal merlin protein
• Bilateral acoustic neuromas, hearing loss ~age 20, tinnitus, imbalance

• Mutation in chr 5q → abnormal treacle protein
• Bilateral: microtia, aural atresia, mid-face hypoplasia, downsloping palpebral fissures, coloboma of lower eyelid, micrognathia

• Progressive mixed hearing loss (80%)
• Myopia, retinal detachment, cataracts, Robin sequence, hypermobile joints

X-Linked

• Most common X-linked deafness
• Males: stable hearing at birth → progressive mixed/SNHL (bilateral in 75%)
• Large IAC, absent lamina cribrosa; risk of perilymphatic gusher during surgery

• COL4A5 mutation (X-linked) or COL4A3/COL4A4 (AR, 15%)
• Progressive high-frequency SNHL + glomerulonephritis + hematuria + anterior lenticonus

Chromosomal

• Down Syndrome (Trisomy 21): Stenotic EAC, middle ear disease, SNHL (common)
• Turner Syndrome (45,XO): Mixed conductive and SNHL
• Fetal Alcohol Syndrome: Microcephaly, mental retardation; conductive and SNHL

2. Acquired Causes

TORCH Infections

Perinatal Causes

• Hypoxia / birth asphyxia
• Neonatal jaundice (kernicterus)
• Prematurity

Postnatal Causes

• Bacterial meningitis (Streptococcus most common organism)
• Mumps

Evoked response audiometry - a non-invasive objective test of hearing thresholds

3. Investigations / Diagnosis

4. Management

1. Early identification - Universal newborn hearing screening programs are now standard (UK: OAE at birth; ABR if failed)
2. Hearing aids - Fitting as early as possible to exploit neural plasticity of the developing auditory cortex
3. Cochlear implantation - For profound SNHL; early intervention essential; stimulates cochlear neurones (which usually remain intact even when hair cells are lost); insertion through round window
4. Auditory brainstem implant (ABI) - In cases of absent cochlear nerve (e.g., NF2, cochlear aplasia)
5. Sign language / habilitation - Complementary to amplification
6. Genetic counselling - Essential for families; test first-degree relatives
7. Condition-specific management:
   • Jervell-Lange-Nielsen: beta-blockers, screen relatives for Romano-Ward
   • Pendred: monitor thyroid; avoid unnecessary thyroid surgery
   • CMV: antiviral therapy (valganciclovir) may reduce progression of CMV-related SNHL
   • Biotinidase deficiency: dietary biotin replacement

• K.J. Lee's Essential Otolaryngology, pp.1001-1006
• Bailey and Love's Short Practice of Surgery (28th ed.), p.781
• Scott-Brown's Otorhinolaryngology Head & Neck Surgery (Vol 2)

Bilateral Abductor Palsy (Bilateral Vocal Cord Paralysis)

Definition & Anatomy

Causes

Three Principal Mechanisms

Neurological Causes

• Amyotrophic lateral sclerosis (ALS)
• Post-polio syndrome
• Charcot-Marie-Tooth neuropathy
• Arnold-Chiari malformation
• Guillain-Barré syndrome
• Idiopathic (same infectious agents as unilateral paralysis)

Important distinction: Bilateral vocal fold immobility following intubation may represent mechanical fixation (joint/scar) rather than true denervation. This matters because mechanical causes may be surgically correctable without destructive procedures.

Clinical Features

Laryngoscopic view in bilateral cord palsy, with the cords separated by the laryngoscope (a) prior to partial right laser arytenoidectomy

Investigations

Management

Acute Phase

• Immediate airway security - re-intubation or emergency tracheotomy if post-operative stridor after extubation
• Do NOT proceed to destructive surgery until recovery potential is excluded

Long-term Options

1. Tracheotomy

• Guarantees the airway
• Minimal compromise of phonation or swallowing
• May be a long-term option for some patients, especially the elderly or those who are poor surgical candidates

2. Reversible Glottic Enlargement Procedures (when recovery potential exists)

• Vocal cord suture lateralization (endo-extralaryngeal suture) - lateralizes one cord, reversible, buys time
• Arytenoid abduction suture - mimics PCA action; pulls the vocal process posterolaterally; does NOT abolish residual adductor activity during phonation

3. Definitive Glottic Enlargement (when no recovery expected)

• Endoscopic CO2 laser partial posterior cordectomy + partial arytenoidectomy - unilateral or bilateral; most widely used. Voice becomes breathier but remains functional. Shorter hospitalization; higher compliance.
• Open arytenoidectomy - rarely performed now with laser available
• Restenosis of the glottis is the main complication requiring reoperation

4. Reinnervation (Selective Reinnervation)

• Indicated for stridor due to bilateral abductor paralysis
• Selective reinnervation procedure: C3 root of phrenic nerve → cable graft (great auricular nerve, Y-shaped) → both PCA muscles; PLUS ansa hypoglossi anastomosed to RLN bilaterally
• Technically demanding; performed via extended anterior neck incision
• Aim: selectively restore abductor function while adductors are separately reinnervated

5. Laryngeal Pacing (Experimental)

• Electrodes implanted into both PCA muscles → automatic abduction/adduction
• Connected to subcutaneous pacemaker device (similar to cardiac pacemaker)
• Currently in clinical trials; not yet standard of care

Summary Table

• Scott-Brown's Otorhinolaryngology Head & Neck Surgery, Vol 3, pp.1134, 1152
• Cummings Otolaryngology Head and Neck Surgery, Ch. 63
• Fishman's Pulmonary Diseases and Disorders, p.436
• Goldman-Cecil Medicine, p.3979

Bilateral Adductor Palsy

Definition & Physiology

• Airway is patent - no obstruction, no stridor
• Glottis cannot close - phonation fails, cough fails, airway protection fails

Anatomy of Adduction

• Lateral cricoarytenoid (LCA) - primary adductor; rotates arytenoid to bring vocal process medially
• Transverse and oblique arytenoids (interarytenoids) - close the posterior glottis
• Thyroarytenoid (TA/vocalis) - tenses and shortens the cord

Causes

Surgical / Iatrogenic (most common)

Malignancy

• Thyroid carcinoma invading both RLNs
• Tracheal, oesophageal, or lung malignancy
• Mediastinal lymphadenopathy compressing both nerves

Neurological

• Amyotrophic lateral sclerosis (ALS)
• Post-polio syndrome
• Guillain-Barré syndrome
• Charcot-Marie-Tooth neuropathy
• Arnold-Chiari malformation
• Brainstem stroke or tumour (nucleus ambiguus)

High Vagal Injury (more severe syndrome)

• Glottic insufficiency (RLN component)
• Hemi-laryngeal anaesthesia (internal branch of SLN)
• Pharyngeal constrictor atony
• Cricopharyngeal hyperfunction This combination produces far greater aspiration risk than RLN palsy alone.

Idiopathic / Infectious

• Viral neuropathy (same agents as unilateral palsy)
• Post-intubation cricoarytenoid joint injury (mechanical, not true palsy - important to distinguish)

Clinical Features

Important: The degree of glottic insufficiency depends on cord position. Residual or regenerated innervation of adductors may hold cords near the midline (paramedian), allowing some phonation and aspiration protection. Truly cadaveric (lateralized) cords indicate complete flaccid denervation.

Comparison: Bilateral Adductor vs. Abductor Palsy

Investigations

Management

Principle: Medialization

1. Vocal Fold Injection (Injection Laryngoplasty)

• Injection of bulking agent (collagen, fat, hydroxylapatite, carboxymethylcellulose) lateral to the thyroarytenoid muscle
• Ideal when recovery is anticipated within weeks (use temporary/absorbable material)
• Can be done under local or general anaesthesia
• For bilateral palsy: bilateral injections described for aspiration, though they do not prevent all aspiration and carry risk of causing airway compromise - must be done with care
• Used as a test of medialization suitability before permanent thyroplasty

2. Medialization Thyroplasty (Isshiki Type I)

• Permanent implant (Silastic, Gore-Tex, titanium, hydroxylapatite/VoCoM) inserted through a window in the thyroid lamina to push the cord medially
• Done under local anaesthesia so the patient can phonate during the procedure - allows real-time optimisation
• For bilateral adductor palsy with aspiration: bilateral medialization thyroplasty has been described
  • Posterior edge of implant must sit anterior to the vocal process to allow abduction in non-aspiration cases (presbyphonia/bowing)
  • For aspiration: adduction of the entire vocal cord (including vocal process) is required
  • Works in carefully selected cases of mild aspiration; does not prevent all aspiration; risk of converting to airway obstruction requiring tracheostomy
• Indicated when likelihood of recovery is negligible
• Can be considered early (even before recovery excluded) if aspiration or severe dysphonia requires urgent intervention

3. Arytenoid Adduction

• Suture placed in the muscular process of the arytenoid; traction applied anteriorly (mimicking lateral cricoarytenoid action) to internally rotate the arytenoid → medial displacement of the vocal process
• Closes the posterior glottic gap which thyroplasty alone cannot reliably close
• Combined with thyroplasty for superior acoustic and aerodynamic results
• Most valuable when vocal process is significantly laterally displaced (cadaveric position)
• More technically demanding than thyroplasty alone

4. Reinnervation (Non-selective)

• Ansa cervicalis to RLN anastomosis - restores bulk and tone to the thyroarytenoid muscle without restoring purposeful motion; provides neuromuscular medialization without an implant
• Does not restore voluntary adduction but prevents progressive cord atrophy
• Indicated in unilateral adductor palsy (hoarseness from unilateral palsy)

5. Laryngeal Closure Procedures (Severe Intractable Aspiration)

• Montgomery-type glottic closure - median laryngofissure, cord mucosa stripped, cords sutured together; patient becomes tracheostomy-dependent and loses all voice; not easily reversible
• Supraglottic laryngeal closure - two-layer closure of the supraglottis via pharyngotomy; similarly renders patient voiceless and tracheostomy-dependent
• Epiglottoplasty / tracheoesophageal diversion - reserved for the most severe cases

6. Non-surgical / Adjunctive

• Speech and swallowing therapy - compensatory swallowing techniques, postural manoeuvres (chin tuck, supraglottic swallow)
• Dietary modification - thickened fluids, texture-modified food
• Nasogastric / PEG feeding - if aspiration risk prohibits safe oral intake
• Antibiotics - for aspiration pneumonia episodes
• Cricopharyngeal myotomy - combined with medialization for high vagal injuries where UOS dysfunction compounds the aspiration

Summary

• Scott-Brown's Otorhinolaryngology Head & Neck Surgery, Vol 3, pp.554-578, 2156-2205
• Cummings Otolaryngology Head and Neck Surgery, Ch. 62-63, pp.1152-1164
• Schwartz's Principles of Surgery (11th ed.), p.1656
• Goldman-Cecil Medicine, p.3973

Unilateral Recurrent Laryngeal Nerve (RLN) Palsy

Anatomy Review - Why the RLN is Vulnerable

Causes

Surgical / Iatrogenic (most common overall)

Malignancy

• Thyroid carcinoma (most common on right)
• Lung carcinoma / apical tumour (most common non-surgical cause on left - Pancoast)
• Oesophageal carcinoma
• Mediastinal lymphadenopathy (lymphoma, metastatic nodes)

Neurological / Central

• Brainstem lesions (stroke, tumour, demyelination) - affect nucleus ambiguus
• Guillain-Barré syndrome, ALS, post-polio syndrome
• Skull base tumours or jugular foramen syndrome (co-involves CN IX, X, XI)

Vascular

• Thoracic aortic aneurysm (classically left RLN)
• Aortic arch anomalies

Idiopathic / Viral

• Accounts for 10-40% of cases in large series
• Presumed viral neuropathy (similar to Bell's palsy)
• Generally good prognosis for recovery

Iatrogenic - Post-intubation

• Arytenoid dislocation or cricoarytenoid joint injury
• Cuff-pressure neuropathy
• Accounts for ~5-11% of cases in large series

Key epidemiological data from pooled studies: Across series, causes break down approximately as - surgical trauma 12-75%, tumour 7-52%, idiopathic 10-41%, intubation 5-11%. The wide variation reflects referral patterns and era.

Pathophysiology - Cord Position

Important: Cord position does NOT reliably indicate the site of injury or prognosis. Position is determined by the balance of residual innervation, not by where the nerve is damaged.

Prolapsed Arytenoid

Clinical Features

Symptoms

• Hoarseness / dysphonia - the cardinal complaint; ranges from subtle vocal fatigue to near-total aphonia
• Breathy voice - excessive air escape through the incompetent glottis
• Weak/ineffective cough - inability to generate adequate subglottic pressure
• Dysphagia and aspiration - especially in 'high vagal' injury (see below)
• Phonation-induced dyspnoea - breathlessness from air escape rather than obstruction; often mistaken for asthma
• 'Wet' voice quality - secretions pooling in the laryngeal introitus; sign of penetration/aspiration
• Laryngospasm - reactive to unexpected aspiration
• 'Paralytic falsetto' - patient uses intact cricothyroid (SLN intact) to increase pitch and raise vocal fold resistance; characteristic strained high-pitched voice

Signs on Laryngoscopy

• Immobile vocal fold on the affected side
• Use the 'eee-sniff' manoeuvre to exaggerate cord asymmetry on examination
• Spindle-shaped gap: membranous portion fails to close, cartilaginous portion approximates (relatively common)
• Posterior gap: wide distance between vocal processes; indicates complete denervation; associated with prolapsed arytenoid; responds poorly to injection/thyroplasty alone
• Supraglottic hyperfunction (false cord squeezing) - compensatory mechanism for glottic insufficiency
• Jostle sign (positive in mechanical fixation): the paralysed arytenoid is passively pushed laterally by the contralateral arytenoid during phonation; negative in true denervation where the arytenoid is flaccid

Figure 78.3: Left - good vocal process closure despite malignant mediastinal lymphadenopathy. Right - posterior gap following thyroidectomy. Compare cord positions and gap configurations.

'High Vagal' Injury (above origin of SLN)

• Hemi-laryngeal anaesthesia - absent sensation, greatly increases silent aspiration
• Pharyngeal constrictor atony - pooling in pyriform fossa
• Cricopharyngeal hyperfunction - UOS dysfunction worsening dysphagia
• Associated CN deficits (IX, XI) if jugular foramen involved; Horner syndrome if cervical sympathetics involved

Voice Assessment Tools

Investigations

LEMG Prognostic Accuracy (Table 78.3, Scott-Brown's)

Management

Decision Framework

Unilateral RLN Palsy diagnosed
├── Cause identified post-surgically? → No further workup for cause needed
├── Unknown cause → CT skull base to aortic arch (mandatory)
│
└── Treatment decision guided by:
    ├── Severity of aspiration/dysphagia (trumps all other factors)
    ├── Degree of vocal disability
    ├── Prognosis for recovery
    └── Glottic gap configuration

1. Observation + Voice Therapy

• No aspiration
• Intact nerve (structurally) with recovery potential
• Minimal vocal disability or demand
• Significant comorbidities

2. Injection Laryngoplasty (Temporary / Early)

• Recovery anticipated (use absorbable material)
• Small glottic gap (2-3 mm)
• No posterior glottic gap
• Aspiration / high vocal demand
• Short life expectancy (avoids open surgery)
• As test of medialization suitability

• Hyaluronic acid preparations (shortest duration)
• Micronized human dermis (Cymetra)
• Autologous fat
• Carboxymethylcellulose-glycerine gel
• Calcium hydroxylapatite (CaHA) - most durable injectable; ~1 year effect

• Cannot correct posterior glottic gap or height discrepancy
• Requires over-injection (allowing for reabsorption) - fine tuning impossible
• Superficial injection into lamina propria stiffens the mucosa and impairs vibration
• All available materials stiffen the lamina propria

3. Medialization Thyroplasty (Laryngeal Framework Surgery)

• Poor prognosis for recovery
• Large glottic gap or posterior gap
• High degree of vocal disability
• Dysphagia / aspiration

• Airway obstruction (post-op oedema + medialization narrows airway; some surgeons keep overnight)
• Lumen perforation → infection/extrusion
• Suboptimal voice (revision rate 5.4-33%) - causes: persistent posterior gap, under-medialization, superior/anterior implant malposition

4. Arytenoid Adduction (± Thyroplasty)

• Significant posterior glottic gap
• Prolapsed / poorly supported arytenoid
• Height mismatch between cord levels

5. Reinnervation

• Restores muscle bulk and tone to the thyroarytenoid; prevents atrophy
• Does not restore purposeful cord motion (due to synkinesis from complex innervation)
• Provides neuromuscular medialization without an implant
• Ideal if RLN was knowingly sectioned during surgery - immediate re-anastomosis (or reinnervation if tension-free anastomosis impossible) is the treatment of choice when the cut is recognized intraoperatively
• If considering later in the disease course, must confirm patient is not depriving the cord of spontaneous reinnervation
• Improvement takes weeks to months; sometimes combined with other procedures

6. Prognosis for Spontaneous Recovery

• Good prognosis: Post-intubation, idiopathic/viral (Ramsay Hunt, Bell's equivalent), blunt trauma
• Poor prognosis: Complete nerve section during tumour resection, nerve invasion by tumour, thoracic aortic aneurysm, progressive neurological disease

Summary

• Scott-Brown's Otorhinolaryngology Head & Neck Surgery (Vol 3), pp.2114-2563
• Cummings Otolaryngology Head and Neck Surgery, Ch. 62-63
• Schwartz's Principles of Surgery (11th ed.), p.1656
• Goldman-Cecil Medicine, p.3973