Role of Fibreoptic Surgery (Flexible Fibreoptic Laryngoscopy) in Vocal Cord Palsy

Introduction

Anatomy Relevant to Vocal Cord Palsy

• The vagus nerve (CN X) supplies the larynx via two branches:
  • Recurrent laryngeal nerve (RLN): supplies all intrinsic laryngeal muscles except cricothyroid; responsible for abduction and adduction of the cords.
  • Superior laryngeal nerve (SLN), external branch: supplies cricothyroid (pitch control and cord tensioning).
• The left RLN loops under the aortic arch (longer course) - more commonly injured.
• The right RLN loops under the right subclavian artery.
• ~90% of cord paralyses arise from peripheral nerve injury; only ~10% are central in origin.

Causes of Vocal Cord Palsy

Types of Vocal Cord Palsy

1. Unilateral VCP

• Cord lies in paramedian position
• Voice is breathy, weak, easily fatigued
• Mild stridor (usually none)
• Aspiration possible, especially with thin liquids
• Contralateral cord may compensate over time

2. Bilateral VCP

• Both cords lie in paramedian position (bilateral abductor paralysis)
• Voice may be near-normal or good (cords close to midline)
• Inspiratory stridor is the dominant feature - the airway is at risk
• Tracheostomy may be required in ~50% of cases
• Classic congenital cause: hydrocephalus with Arnold-Chiari malformation

What is Fibreoptic Laryngoscopy?

Role of Fibreoptic Laryngoscopy in Vocal Cord Palsy

1. DIAGNOSIS - Primary Tool

• It directly visualises the movement (or absence of movement) of the vocal cords in real time
• Confirms whether immobility is due to nerve palsy or mechanical fixation (cricoarytenoid joint fixation, posterior glottic scarring after intubation) - a distinction of critical clinical importance (see below)
• Identifies the position of the paralysed cord: paramedian (most common in RLN palsy), median, or lateral (intermediate) positions
• Detects the anteromedial displacement of the arytenoid and dilatation of the pyriform sinus ipsilateral to the palsy
• Identifies associated findings: pooling in pyriform fossae (suggesting dysphagia/aspiration risk), laryngeal penetration, cord bowing, mucosal abnormalities

"Vocal cord function should be evaluated and documented by indirect laryngoscopy or flexible fiberoptic laryngoscopy, especially in patients who have had previous surgery." - Cummings Otolaryngology, Head and Neck Surgery

"Awake flexible endoscopy is particularly useful to assess dynamic abnormalities such as vocal cord palsy." - Scott-Brown's Otorhinolaryngology, Head & Neck Surgery

2. ASSESSMENT OF CORD POSITION

• Paramedian position: Typical RLN palsy; voice may be breathy but aspiration risk is moderate; often self-compensates
• Lateral (abducted) position: More pronounced dysphonia and aspiration; medialization more likely needed
• Median position: May occur with combined RLN + SLN palsy; more critical for airway
• Bilateral paramedian: Good voice but compromised airway; may need tracheostomy

3. DISTINGUISHING PARALYSIS FROM FIXATION

• In cord paralysis, the cord is flaccid and does not move - but the cricoarytenoid joint is mobile (palpable under GA)
• In cricoarytenoid joint fixation (from intubation, rheumatoid arthritis, post-inflammatory scarring), the cord also appears immobile, but FFL cannot always distinguish the two
• However, FFL may show subtle differences: in paralysis the cord may be slightly lower, bowed, and the arytenoid rotated anteromedially; in fixation the cord retains some tension
• Definitive distinction requires palpation of the arytenoid under general anaesthesia via rigid laryngoscopy (microlaryngoscopy)
• This distinction is especially important in children who have been previously intubated

"It should never be assumed that an immobile vocal cord is paralyzed. Vocal cord immobility in previously intubated children may be due to joint fixation or posterior glottic scarring." - Scott-Brown's Otorhinolaryngology

4. MONITORING AND FOLLOW-UP

• Documents return of function or continued paralysis at serial visits (typically every 3 months)
• Monitors contralateral cord compensation - the normal cord crosses midline to meet the paralysed cord
• Guides timing of surgical intervention: most surgeons wait 9-12 months before permanent medialization, using FFL to confirm no recovery
• In children with bilateral VCP (especially congenital), serial FFL monitors for the ~58% who eventually recover - some taking over 5 years

"Serial examinations should document a potential return of function or compensation by the contralateral vocal cord." - Cummings Otolaryngology

5. PRE-OPERATIVE ASSESSMENT

• Mandatory before thyroid, parathyroid, oesophageal, and skull base surgery to document baseline cord function
• Documents pre-existing palsy, protecting the surgeon from medico-legal liability for postoperative cord palsy
• After thyroid surgery, FFL is performed to confirm cord function before the patient is discharged or before the contralateral side is operated upon in staged procedures

6. ASSESSMENT OF ASPIRATION AND SWALLOWING

• FFL can be combined with swallowing assessment (FEES - Functional Endoscopic Evaluation of Swallowing) to assess:
  • Pooling of secretions or food bolus in the pyriform fossae (sign of pharyngeal weakness or VCP)
  • Laryngeal penetration or aspiration
  • Whether dysphagia is due to the cord palsy itself or associated pharyngeal weakness
• "Flexible nasolaryngoscopy is useful in identifying... vocal cord palsy, pooling within the pyriform fossae and laryngeal penetration that contribute to the overall assessment of patients' swallowing abilities." - Scott-Brown's Otorhinolaryngology

7. PAEDIATRIC-SPECIFIC ROLE

• Can be performed awake in infants who can be swaddled (most feasible under 9-12 months)
• Avoids general anaesthesia for initial diagnostic screening
• Monitors children with known congenital VCP for spontaneous recovery
• Used in sick neonates or infants unfit for endoscopy under GA
• Laryngeal ultrasound is an alternative in the very sick neonate, but FFL remains the standard
• Identifies synchronous airway pathology (up to 45% of VCP patients have coexisting airway anomalies)
• Flexible laryngoscopy under sedation in an endoscopy suite is "widely practised by paediatricians and pulmonologists as an adjunct to rigid endoscopy" - Scott-Brown's, Vol 2

8. FUNCTIONAL ASSESSMENT TOOLS USED WITH FFL

• Videostroboscopy: Strobe light source added to FFL allows slow-motion assessment of mucosal wave - demonstrates loss of mucosal wave in paralysed cord, distinguishes palsy from spasmodic dysphonia, and shows degree of glottic closure
• FEES (Flexible Endoscopic Evaluation of Swallowing): FFL scope used at bedside to watch swallowing with food/liquid boluses
• Video recording: Allows documentation, comparison over time, multidisciplinary review, and medicolegal record
• Narrow Band Imaging (NBI): Advanced imaging modality added to flexible scopes for mucosal lesion characterisation

Limitations of Fibreoptic Laryngoscopy in VCP

Comparison: FFL vs. Rigid Laryngoscopy (MLB) in VCP

Management Summary (where FFL guides decisions)

Unilateral VCP

1. FFL confirms diagnosis and cord position - check every 3 months
2. Wait 9-12 months for spontaneous recovery (FFL documents this)
3. If no recovery: medialization procedures
   • Temporary: Vocal cord injection (fat, collagen, calcium hydroxyapatite, carboxymethylcellulose) - can be performed under FFL guidance or rigid laryngoscopy
   • Permanent: Medialization thyroplasty (Type I) - laryngeal framework surgery, traditionally done under local anaesthetic with FFL monitoring of voice improvement
   • Arytenoid adduction - for posteriorly positioned arytenoids
   • Reinnervation - ansa cervicalis to RLN anastomosis

Bilateral VCP

1. FFL confirms bilateral immobility and position of cords
2. Manage airway: tracheostomy if needed (~50% require)
3. Wait for recovery (up to 58% spontaneous recovery in children)
4. If no recovery: surgical airway enlargement:
   • Endoscopic laser cordotomy (posterior division of one cord)
   • Laser arytenoidectomy
   • Endoscopic suture lateralization

Medialization Thyroplasty - Special Role of FFL

• In adults, Type I thyroplasty is typically done awake under local anaesthetic
• The surgeon places a silastic implant while the patient phonates
• FFL (or video monitoring of the glottis) is used intraoperatively to confirm optimal medialization in real time - this is one of the most direct surgical roles of fibreoptic assessment

Summary Points for Exam

1. FFL is the gold-standard first-line investigation for diagnosing vocal cord palsy in the clinical setting
2. It assesses cord movement, position, and symmetry in the awake, physiological state
3. Key advantage over rigid laryngoscopy: dynamic assessment - cord movement reflects true neurological function
4. Critical role in distinguishing palsy from fixation (though definitive distinction needs palpation under GA)
5. Serial FFL is used to monitor recovery or compensation, guiding timing of surgical intervention
6. Pre-operative documentation of cord function is mandatory before neck/thoracic/skull base surgery
7. Combined with FEES for dysphagia and aspiration assessment
8. Combined with videostroboscopy for detailed vibratory analysis
9. In children, awake FFL avoids GA; congenital VCP recovers spontaneously in ~58% - monitored by serial FFL
10. Limitation: Cannot perform therapeutic procedures; rigid MLB under GA is required for full assessment and for confirming joint fixation