Can you explain the anatomy of the vocal cords and describe vocal cord (recurrent laryngeal nerve) palsy, including its causes, symptoms, diagnosis, treatment, and provide a diagram?

Vocal Cord Anatomy and Vocal Cord Palsy

Vocal Cord Anatomy

The vocal cords (vocal folds) are twin infoldings of mucous membrane that extend from the anterior thyroid cartilage to the posterior arytenoid cartilages, consisting of epithelium and lamina propria overlying the vocalis muscle 1. They vibrate during phonation to modulate airflow from the lungs, producing voice.

Key Anatomical Components:

• Structure: Mucous membrane covering the vocalis (thyroarytenoid) muscle
• Attachments: Anterior - thyroid cartilage; Posterior - vocal process of arytenoid cartilage
• Layers: Epithelium, lamina propria, and underlying muscle

Innervation:

• Recurrent Laryngeal Nerve (RLN): Innervates all intrinsic laryngeal muscles except cricothyroid; controls vocal cord movement (abduction and adduction) 2
• External Branch of Superior Laryngeal Nerve (EBSLN): Innervates cricothyroid muscle; controls pitch and vocal tension 1
• Nerve Course: The RLN is a branch of the vagus nerve; the left RLN loops under the aortic arch, while the right loops under the subclavian artery, then both ascend in the tracheoesophageal groove 3

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Vocal Cord Palsy (Recurrent Laryngeal Nerve Palsy)

Vocal cord palsy results from neurological dysfunction affecting the vagus nerve, recurrent laryngeal nerve, or nucleus ambiguus, causing immobility of one or both vocal cords 3.

Causes

Peripheral lesions injuring the vagus nerve or its branches account for 90% of all vocal cord paralysis 4.

Common Etiologies:

• Iatrogenic injury (most common): Thyroid surgery historically caused ~30% of cases, now reduced to <5% with improved surgical techniques 4; also cardiac surgery in pediatrics 5
• Neoplasms: Mediastinal, thyroid, esophageal, or lung cancers compressing the nerve 3, 6
• Trauma: Blunt or penetrating injury to head, neck, or thorax 4
• Inflammatory conditions: Viral neuritis, autoimmune disorders 3
• Vascular causes: Aortic aneurysm, cardiovascular surgery 6
• Idiopathic: Significant proportion remains unexplained despite imaging 3

Symptoms

Unilateral Vocal Cord Palsy:

• Dysphonia: Breathy, hoarse voice with vocal fatigue 1
• Aspiration: Difficulty swallowing liquids, risk of pneumonia 2
• Reduced vocal volume and projection 1
• Acute presentation: Flaccid vocal fold, severe dysphonia to complete aphonia 2

Bilateral Vocal Cord Palsy:

• Severe stridor and respiratory distress 5
• Life-threatening airway obstruction 4
• May require tracheostomy 5

Diagnosis

Flexible laryngoscopy is the gold standard for diagnosing vocal cord paralysis 7, 5.

Diagnostic Approach:

1. Laryngoscopy findings:

   • Immobile vocal fold in paramedian or lateral position
   • Inadequate glottic closure during phonation
   • Possible vocal fold bowing or atrophy 1

2. Laryngeal Ultrasound (LUS):

   • Non-invasive alternative with pooled sensitivity of 0.90 and specificity of 0.98 8
   • Well-tolerated, easy to perform, particularly useful in infants and unstable patients 7
   • Can assess vocal cord mobility in real-time

3. CT Imaging:

   • Must include the entire course of the vagus and RLN from brainstem to mediastinum (left side to aorticopulmonary window, right side to brachiocephalic artery) 6
   • Identifies causative lesions: neoplasms, vascular abnormalities, inflammatory processes 3, 6
   • Key CT findings: asymmetric vocal cord position, dilated laryngeal ventricle on affected side 9

4. FDG PET-CT:

   • May show asymmetrically increased uptake in contralateral vocal cord due to compensatory hyperactivity 9
   • Helps identify underlying malignancy along nerve course

5. Electromyography (EMG):

   • May assist in determining prognosis (reinnervation vs. permanent paralysis) 2
   • Limited normative data currently available

Treatment

For unilateral vocal cord palsy with glottic insufficiency, surgical medialization techniques significantly improve voice quality and quality of life 10.

Treatment Algorithm:

Acute Phase (0-4 weeks):

• Early otolaryngology referral for laryngeal examination 1
• Voice therapy with speech-language pathologist 1
• Manage aspiration risk: dietary modifications, swallowing therapy

Subacute Phase (1-6 months):

• Injection medialization laryngoplasty:
  • Can be performed in office under local anesthesia or operating room 10
  • Provides immediate voice improvement
  • Temporary solution (collagen, hyaluronic acid) or longer-lasting (calcium hydroxylapatite) 10
  • Avoid polytetrafluoroethylene (Teflon) due to granuloma formation and airway compromise 10

Chronic Phase (>6-12 months if no recovery):

• Medialization thyroplasty (laryngeal framework surgery):

  • Permanent solution performed under local anesthesia with sedation 1
  • Immediate voice improvement
  • Can be combined with arytenoid adduction for better results

• Laryngeal reinnervation:

  • Anastomosis between ansa cervicalis and RLN 1
  • Prevents long-term denervation atrophy
  • Longer healing period but may provide superior long-term voice quality 2

Bilateral Vocal Cord Palsy:

• May require tracheostomy for airway management 5
• Surgical options: arytenoidectomy, cordotomy, or reinnervation procedures to facilitate decannulation 5

Key Clinical Pitfalls:

• Failing to image the entire nerve course: Always extend CT from brainstem through mediastinum to identify causative lesions 6
• Delaying otolaryngology referral: Early evaluation (within 4 weeks) maximizes treatment options and voice outcomes 1
• Using Teflon for injection: Associated with granulomas and voice deterioration 10
• Assuming idiopathic without complete workup: Vocal cord palsy may be the presenting sign of occult malignancy 6

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Diagram Request

Note: As a text-based system, I cannot generate visual diagrams. However, I recommend seeking anatomical diagrams showing:

1. Normal vocal cord anatomy: Coronal and axial views showing vocal fold position, arytenoid cartilages, and thyroid cartilage
2. RLN course: Bilateral vagus nerve descent, RLN branching (left under aortic arch, right under subclavian), and ascent in tracheoesophageal groove
3. Vocal cord palsy: Comparison of normal bilateral vocal cord adduction vs. unilateral paralysis with lateralized immobile cord and glottic gap