Recurrent Laryngeal Nerve

Course

• Branch off the Vagus Nerve
  • Originates from the Vagus Nerve in the Superior Mediastinum
• Left Recurrent Laryngeal Nerve
  • Originates from the Vagus Nerve in the Superior Mediastinum
  • Recurves around Arch of Aorta in Superior Mediastinum
    • Hooks around the Ligamentum Arteriosum to pass upwards on the right- hand side of the Arch
    • Hooks around posterior to the Ligamentum Arteriosum, not anterior
  • Passes into root of neck moving from left towards the midline to enter trachea- oesophageal groove
  • More likely to have entered the groove and lie posterior to Inferior Thyroid Artery
• Right Recurrent Laryngeal Nerve
  • Originates from the Vagus Nerve in the neck
  • Recurves around Right Subclavian Artery at Root of the Neck
    • NB: This is NOT in the Superior Mediastinum
  • May be more lateral to the Trachea
  • Passes anterior or posterior to Inferior Thyroid Artery or in between its branches
  • More vertical course than the left
• Each nerve is behind the Pretracheal Fascia
  • Runs medial or lateral or through a thickening of the fascia attached to the Cricoid Cartilage and upper Tracheal Rings (the Suspensory Ligament of Berry)
• Both nerves pass behind the lateral lobe of the Thyroid in close association with the Inferior Thyroid Artery in the region of the Tubercle of Zuckerkandl
  • Variable relationship to ITA - most commonly posterior, then anterior then in-between branches. Posterior is more common on the left
• Nerve runs behind the Cricothyroid joint
• Passes upwards under cover of the Inferior Constrictor
  • NB: May also be seen disappearing below the inferior border of the Cricopharyngeus muscle
  • May supply a branch to the Inferior Constrictor Muscle before entering the larynx
• Reaches the lower part of the Piriform Recess and penetrates the Laryngeal wall
• At level of upper border of Isthmus, nerve often divides into two
  • If so, anterior (larger) branch is motor branch to laryngeal muscles and posterior branch sensory only
• Note: Relationships are not constant with considerable anatomical variation however, the Recurrent Laryngeal Nerve usually passes close to and behind the Tubercle of Zuckerkandl, under Berry ligaments and is infront, inbetween or behind the inferior thyroid artery
• Recurrent Laryngeal Nerve branches outside of the Larynx in 1/3 of pts
  • Posterior branch is sensory
  • Anterior branch (more vulnerable) is motor

Innervation

• All muscles of the Larynx (except Cricothyroid – supplied by the External Laryngeal Nerve – Branch of Superior Laryngeal Nerve)
  • All motor fibres in both nerves are from cell bodies in the Nucleus Ambiguus derived mainly via the cranial part of the accessory nerve
• Supplies mucous membrane of the folds and Larynx below the level of the Vocal Folds
  • The mucous membrane ABOVE the vocal folds supplied by the Internal Laryngeal Nerve
• Right Recurrent Laryngeal Nerve also innervates Cricopharyngeus

Non-Recurrent Right Recurrent Laryngeal Nerve

• Due to abnormal origin of the Right Subclavian Artery (Arteria Lusoria)
  • Arise from Aortic Arch distal to origin of Left Subclavian Artery
  • Passes to the right behind the Oesophagus – possible cause of dysphagia
• Without normal Right Subclavian Arch, Right Recurrent Laryngeal Nerve runs down the side of the Larynx – possible hazard in thyroidectomy
• Reported incidence: Right nerve non-recurrent in 0.5% or 1 in 200

Embryology of recurrent laryngeal nerve

• Origin from the Vagus Nerve (Cranial Nerve X)
  • Develops from the fourth and sixth pharyngeal arches. See Pharyngeal Arches, Pouch and Cleft
  • Initially follows a straight course to the developing larynx
• Relationship to the Aortic Arch System
  • The six paired aortic arches supply the pharyngeal region in early development
  • Only some arches persist, influencing the RLN pathway:
    • Fourth aortic arch →
      • Left: Contributes to the aortic arch
      • Right: Forms part of the proximal right subclavian artery
    • Sixth aortic arch →
      • Forms the pulmonary arteries
      • Left side also forms the ductus arteriosus
• Descent of the Heart and Great Vessels
  • As the heart descends into the thorax, the RLNs are dragged down with it
  • The nerves become trapped under different structures:
    • Right RLN loops under the right subclavian artery
    • Left RLN loops under the ductus arteriosus (later ligamentum arteriosum) and aortic arch
  • This leads to the longer intrathoracic course of the left RLN compared to the right
• Postnatal Changes
  • The ductus arteriosus regresses to form the ligamentum arteriosum
  • RLNs remain in the tracheoesophageal groove and enter the larynx via the cricothyroid membrane
• Clinical Significance of Embryology
  • Non-recurrent RLN (NRLN)
    • Occurs if the right fourth aortic arch regresses instead of forming the right subclavian artery
    • Associated with an aberrant right subclavian artery (Arteria Lusoria)
  • Left RLN vulnerability
    • Long intrathoracic course makes it more prone to compression by aortic aneurysms, mediastinal tumors, or lung cancer
  • Congenital vascular anomalies
    • Right-sided aortic arches or double aortic arches can alter the RLN pathway, increasing surgical risks