The Anastomoses of the Recurrent Laryngeal Nerve in the Larynx

  • The vagus nerve:
    • Also known as the 10th cranial nerve
    • Gives rise to the superior laryngeal nerve (SLN) and recurrent laryngeal nerve (RLN) in the neck
    • After descending toward the larynx:
      • The SLN divides into:
        • The internal laryngeal nerve (ILN)
        • External laryngeal nerve (ELN)
  • The RLN innervates all of the intrinsic muscles of the larynx:
    • Except the cricothyroid muscle:
      • This muscle, tenses the vocal cords and adducts the vocal cords:
        • Is innervated by the ELN
  • The other branch of the SLN, the ILN:
    • Provides sensory innervation to the laryngeal mucosa
  • There are many exceptions to the normal innervation of the laryngeal muscles:
    • Which can influence the interpretation of laryngoscopy results or voice changes after thyroid surgery
  • A neural anastomosis:
    • That provides additional motor innervation to the muscles of the larynx normally innervated by the injured nerve:
      • Can contribute to an incorrect interpretation of injury during laryngoscopy or stroboscopy
  • According to recent clinical studies:
    • Electrical stimulation of the RLN can cause contraction of the cricothyroid muscle:
      • This suggests that extra-laryngeal branches and or other communications of the RLN:
        • Can sometimes contribute to innervation of this muscle
  • The laryngeal nerves:
    • Can form a great variety of anastomoses:
      • These various connections among the ILN, ELN, and RLN have been investigated by many anatomists over the centuries
  • Claudius Galen:
    • Was the first to describe the communication between the ILN and RLN
    • Currently, Galen’s anastomosis:
      • Is most commonly defined as:
        • The direct communication between the posterior branches of the ILN and the RLN
      • It can occur as:
        • A single trunk
        • A double trunk
        • A plexus
  • Besides Galen’s anastomosis, other communications have been observed and described as follows:
    • The arytenoid plexus:
      • Which links the anterior branch of the RLN with the arytenoid branch of the ILN
The arytenoid plexus and the cricoid communication. AP, arytenoid plexus; CA, cricoid communication; ILN, internal laryngeal nerve; RLN, recurrent laryngeal nerve (a, anterior; p, posterior).
  • The cricoid communication:
    • Which connects branches originating bilaterally from the RLNs with the superior branch from the deep portion of the arytenoid plexus
  • The thyroarythenoid communication:
    • Which is formed by the ascending branch of the RLN and the descending branch from the anterior branch of the ILN
The thyroarytenoid communication and the communication between the external laryngeal nerve (ELN) and the recurrent laryngeal nerve (RLN). CN, communicating nerve; ILN, internal laryngeal nerve; TAC, thyroarytenoid communication
  • The communication between the ELN and RLN:
    • Human communicating nerve
  • The communication between the ILN and ELN
  • The communication between the RLN and the sympathetic trunk
Communications between the internal laryngeal nerve (ILN) and the external laryngeal nerve (ELN) and between the recurrent laryngeal nerve (RLN) and the sympathetic trunk. SLN, superior laryngeal nerve; TF, thyroid foramen.
  • Despite progress in the development of new techniques:
    • Such as intra-operative nerve monitoring:
      • Which help to reduce the risk of iatrogenic injuries during thyroid surgeries and other procedures conducted in close proximity to the laryngeal nerves:
        • The laryngeal muscles are often paralyzed postoperatively due to iatrogenic injury to the laryngeal nerves
  • In view of the complexity and variability of the anatomy in this region:
    • Detailed anatomical knowledge is crucial if surgery is to be both successful and safe, and to reduce the risk of nerve injury
  • Observing an intra-laryngeal anastomosis during laryngeal surgery or an extra-laryngeal communication between laryngeal nerves during thyroid surgery:
    • Can lead to confusion, misidentification, and an increased risk of iatrogenic injury
  • A thorough understanding of the complex anastomoses between the laryngeal nerves is crucial in patients with laryngeal muscle paralysis
    • Paralyzed laryngeal muscles can be spontaneously reinnervated from an anastomosis between laryngeal nerves
    • Additionally, in cases in which surgical reinnervation is required, some of the nerves that form anastomoses can be used as grafts to restore damaged nerve connections
    • On the other hand, variations in the normal anatomy of the laryngeal nerves can disrupt selective surgical laryngeal reinnervation:
      • A procedure based on the assumption that each laryngeal muscle is supplied by only one nerve branch originating from the RLN
    • Anastomoses among laryngeal nerves can result in exceptions to this rule
    • Such anastomoses have been widely described in the literature:
      • However, there is still no consensus about their prevalence and functionality
    • The significant heterogeneity among studies reporting data on anastomoses between the laryngeal nerves is noteworthy:
      • For example, the reported prevalence of the most common communication, Galen’ s anastomosis:
        • Ranges from 25% to 100%
  • Prevalence of Galen’s anastomosis:
    • A total of 14 studies (n = 890 hemilarynges) presented data on the prevalence of Galen’s anastomosis
    • The overall pooled prevalence rate:
      • Was 76.7% (95% confidence interval [CI]: 59.0– 90.0)
    • Subgroup analysis revealed no significant difference in the prevalence of Galen’s anastomosis between the right and left sides
    • Subgroup analyses by gender (males vs females) and geographical origin, and the sensitivity analysis, also revealed no significant differences:
      • However, although the difference was not significant:
        • The prevalence of the anastomosis was highest in Europeans (88.2%) and lowest in North Americans (44.8%)
    • Analysis of the different types of Galen’s anastomosis (two studies, n = 261 anastomoses):
      • Showed a significant difference in the prevalence between single versus double trunk and plexus formation
      • But no significant difference between double trunk and plexus formation
      • The most common type of Galen’s anastomosis was a single trunk:
        • With a pooled prevalence rate 92.3% (95% CI: 84.1–97.5)
      • This was followed by the double trunk anastomosis type:
        • With a pooled prevalence of 4.2% (95% CI: 0.5– 10.7)
      • The plexus formation type with a pooled prevalence of 3.5% (95% CI: 0.2–9.5) (I2: 70.4%, 95% CI: 0–93.3; Co- chran’s Q, value = 0.066
  • Prevalence of a communication between the ELN and RLN
    • A total of eight studies (n = 639 hemilarynges) provided data on the prevalence of the communication between the ELN and RLN
    • The overall meta-analysis revealed that this communication was present in:
      • 21.3% of hemilarynges (95% CI: 3.8–46.0)
    • A subgroup analysis showed no significant difference between left and right sides
    • Although the difference was not statistically significant:
      • The pooled prevalence rate calculated for the North American subgroup (32.0%) was twice that for the European subgroup (14.4%)
  • Prevalence of the arytenoid plexus:
    • Five studies (n = 478 hemilarynges) included data on the prevalence of the arytenoid plexus:
      • The pooled prevalence rate was 79.7% (95% CI: 41.1–100)
    • In the European subgroup:
      • The arytenoid plexus was observed in 96.9% of hemilarynges (95% CI: 83.6–100)
    • Subgroup analysis revealed no significant difference with respect to side
  • Prevalence of the cricoid communication:
    • Two studies (n = 120 hemilarynges) reported prevalence data for the cricoid communication:
      • The pooled prevalence rate was 19.7% (95% CI: 0–100)
    • There was no significant difference in sub- group analysis based on side
  • Prevalence of the thyroarytenoid communication:
    • A total of three studies (n = 430 hemilarynges) presented data on the prevalence of the thyroarytenoid communication:
      • The overall pooled prevalence was 6.3% (95% CI: 0.4–16.9)
    • In subgroup analysis, there was no significant difference in pooled prevalence between the right and left sides:
      • The calculated pooled rate for the left side (15.9%) was almost twice that for the right side (8.8%)
  • Communication between the ILN and ELN:
    • A total of two studies (n = 280 hemilarynges) reported data on a communication between the ILN and ELN
      • The pooled prevalence estimate of this communication in hemilarynges was 8.8% (95% CI: 0–35.3; I2 97.0%, 95% CI: 92.2–98.8; Cochran’s Q, value <0.001)
  • References:
    • Journal of Voice, Vol. 31, No. 4, 2017

#Arrangoiz #HeadandNeckSurgeon #CancerSurgeon #ThyroidSurgeon #ParathyroidSurgeon #ThyroidExpert #ParthyroidExpert #Teacher #Miami #Mexico

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