Laryngeal Reinnervation: Selective and Non-Selective Procedures

Introduction

Anatomical Basis for Reinnervation

• Posterior cricoarytenoid (PCA) - the sole abductor; activated synchronously with inspiration, 40-100 ms before the diaphragm. Contains ~50% type 1 (slow) fibers; peak contraction time ~40 ms.
• Thyroarytenoid (TA) - fast-twitch adductor; peak contraction time 14 ms, <36% type 1 fibers.
• Lateral cricoarytenoid (LCA) - fast adductor; peak contraction time 19 ms.
• Interarytenoid (IA) - has bilateral innervation.

• Donor nerve activity pattern should match recipient muscle activity.
• PCA requires a nerve active during inspiration (abduction) → phrenic nerve is ideal.
• Adductor muscles need a tonically active nerve → ansa cervicalis is used.

Classification of Reinnervation Procedures

LARYNGEAL REINNERVATION
├── NON-SELECTIVE
│   ├── Ansa cervicalis to RLN anastomosis (ansaNSR) ← most common
│   ├── RLN-to-RLN anastomosis (direct or with nerve graft)
│   ├── Hypoglossal to RLN (HNSR)
│   └── Neuromuscular pedicle (NMP) technique
└── SELECTIVE
    ├── Selective abductor reinnervation (phrenic → PCA)
    ├── Selective adductor reinnervation (ansa → adductor branch RLN)
    └── Combined abductor + adductor (for bilateral paralysis)

I. NON-SELECTIVE REINNERVATION

Principle

"Non-selective reinnervation results in a laryngeal synkinesis without coordinated movement of the vocal fold and is used clinically for unilateral paralysis." - Cummings Otolaryngology

Indications

• Unilateral vocal fold paralysis with hoarseness and voice dysfunction
• Best results when performed within 1-2 years of denervation (before irreversible muscle atrophy)
• Preferred when patient age <60 years and denervation <2 years

A. Ansa Cervicalis-to-RLN Transfer (ansaNSR)

• First described by Frazier (1924), popularized by Crumley & Ibzdebski (1986)
• The ansa cervicalis (C1-C3 loop) innervates the infrahyoid strap muscles - a tonically active nerve ideal for maintaining adductor muscle tone

1. Ipsilateral neck incision at the level of the cricoid cartilage under general anaesthesia
2. Identify the ansa cervicalis and the distal stump of the RLN
3. End-to-end anastomosis using 9/0 nylon suture
4. The ansa cervicalis provides tonic activity to the entire hemilarynx via the distal RLN

• Replaces unfavorable synkinesis from partial axonal regrowth with favorable synkinesis from ansa cervicalis
• Restores muscle tone, bulk, and position to the vocal fold
• No synchronized movement expected

• Improvement in voice begins at 3-4 months, continues for up to 2 years
• Significant improvement in GRBAS scores, MPT, and acoustic parameters
• Studies report high rates (>70-80%) of voice improvement

1. Relatively straightforward in an unoperated neck
2. Minimal learning curve
3. Provides tone, position, and bulk - superior rehabilitation vs. thyroplasty alone
4. Can be combined with temporary vocal fold injection at time of surgery
5. No permanent implant - avoids migration/foreign body risk
6. Thyroplasty/injection still possible later if needed
7. Reversible by dividing the anastomosis
8. Sacrifice of sternothyroid is clinically insignificant

1. Requires general anaesthesia
2. Delay of several months before voice improvement
3. Eliminates possibility of spontaneous RLN recovery (RLN must be divided)
4. More complex dissection than thyroplasty
5. Requires intact ansa cervicalis - may be unavailable post-neck surgery
6. If performed on wrong side (non-paralyzed side) → bilateral paralysis and airway obstruction

• Bilateral neck surgery with sacrifice of both ansa cervicalis nerves
• Anticipated spontaneous recovery within months
• Active malignancy in the neck

B. Hypoglossal to RLN Transfer (HNSR)

• Described by Paniello (2000)
• Hypoglossal nerve (CN XII) is used as donor; transposed to distal RLN
• Higher morbidity (tongue weakness/atrophy) has limited its use
• Less commonly used than ansa cervicalis transfer

C. RLN-to-RLN Anastomosis (RRNSA / RRNSANG)

• Direct RLN-to-RLN anastomosis when nerve continuity is disrupted intraoperatively (e.g., during thyroid surgery)
• With interposition nerve graft (RRNSANG): First described by Berendes & Miehlke (1968) using great auricular nerve graft
• Best results when performed immediately after nerve injury
• Poor outcomes when significant gap exists without graft

D. Neuromuscular Pedicle (NMP) Reinnervation

• Described by Tucker (1976)
• A block of omohyoid muscle with its branch from the ansa cervicalis is inserted directly into the adductor muscle complex (thyroarytenoid/LCA) through a thyroid cartilage window
• Strictly speaking, this is a selective technique targeting only adductor muscles, but classically grouped with non-selective methods
• Often combined with arytenoid adduction (AA) for optimal arytenoid positioning (NMPR+AA)
• Results show voice improvement in up to 70% of patients

II. SELECTIVE REINNERVATION

Principle

• PCA (abductor) ← phrenic nerve (respiratory/inspiratory nerve)
• Adductor complex ← ansa cervicalis or descending hypoglossal branch

"Early clinical results show that selective reinnervation can provide vocal fold motion." - Cummings Otolaryngology

Indications

• Bilateral abductor vocal fold paralysis (stridor, airway compromise) - primary indication
• Selected cases of unilateral paralysis where motion restoration is desired
• Younger patients in whom long-term dynamic function is the goal

A. Selective Abductor Reinnervation (Phrenic Nerve to PCA)

• PCA activity normally precedes diaphragm activation by 40-100 ms - the phrenic nerve provides this inspiratory signal
• Both phrenic nerve and PCA contain similar proportions of type 1 (slow) muscle fibers

1. Extended anterior neck skin incision at the level of the cricoid cartilage under general anaesthesia
2. Identify the C3 root of the phrenic nerve on one side
3. Harvest a Y-shaped cable graft from the great auricular nerve
4. Anastomose phrenic nerve to the Y-graft, with each limb inserted into both PCA muscles (bilateral innervation of abductors)
5. Identify the descending branch of ansa hypoglossi and RLN bilaterally
6. Perform bilateral ansa-to-RLN anastomoses for adductor tone (prevents arytenoid instability)

• Animal models (Berke, Chhetri) confirm functional abduction with phrenic nerve reinnervation
• Clinical trials show restoration of respiratory abduction in BVFP
• Vocal fold motion with inspiration seen in majority of cases at 6-12 months

B. Selective Laryngeal Adductor Denervation and Reinnervation (SLAD-R)

• Developed by Berke and colleagues at UCLA
• Primary indication: Adductor spasmodic dysphonia (SD)
• Involves selective denervation of the adductor branch of the RLN (to eliminate spasm) followed by reinnervation with the ansa cervicalis
• Long-term results show sustained voice improvement, superior to botulinum toxin injections

C. Combined Selective Reinnervation (for Bilateral Paralysis)

• Abductor reinnervation: Phrenic nerve → PCA (one or both sides)
• Adductor reinnervation: Ansa cervicalis → RLN (bilateral)
• The combined approach prevents both airway obstruction (via abductor reinnervation) and vocal fold atrophy (via adductor tone maintenance)

Comparison: Selective vs. Non-Selective Reinnervation

Factors Affecting Outcomes of Reinnervation

1. Duration of denervation - most important factor; <2 years preferred; irreversible muscle atrophy occurs after prolonged denervation
2. Patient age - <60 years: better outcomes (threshold based on current evidence)
3. Etiology - iatrogenic (post-thyroid surgery) vs. idiopathic
4. Integrity of donor nerve - ansa must be intact
5. Degree of muscle atrophy at time of surgery
6. Fiber-type matching between donor nerve and recipient muscle

Other Reinnervation-Related Procedures

Laryngeal Pacing

• Still under clinical trial evaluation
• Electrodes implanted in each PCA muscle, connected to subcutaneous pacing device (similar to cardiac pacemaker)
• Causes automatic abduction/adduction of vocal cords based on respiratory signals

Summary Points for Exam

1. Non-selective reinnervation = ansa cervicalis → distal RLN trunk → synkinesis → no motion, but improved tone/bulk/position → treats unilateral paralysis (voice)
2. Selective reinnervation = donor nerve matched to individual muscle → coordinated motion possible → treats bilateral paralysis (airway) and spasmodic dysphonia
3. Phrenic nerve = best donor for abductor (PCA) reinnervation (both are inspiratory/type 1)
4. Ansa cervicalis = best donor for adduction and non-selective reinnervation (most widely used)
5. Non-selective: ipsilateral neck incision, GA, 9/0 nylon, ansa-to-RLN end-to-end
6. Selective (BVFP): extended anterior neck incision, GA, phrenic C3 root + great auricular Y-graft to bilateral PCAs + bilateral ansa-to-RLN for adductors
7. Voice improvement starts at 3-4 months, continues for up to 2 years
8. Key predictors of success: age <60 years, denervation <2 years