Description
- The recurrent laryngeal nerve (RLN) provides both sensory and motor innervation to the larynx.
- Supplies motor function to all intrinsic muscles of the larynx except for the cricothyroid muscle (innervated by the external branch of the superior laryngeal nerve).
- Supplies sensory innervation to the vocal cords and subglottis.
- The RLN innervates all of the intrinsic laryngeal muscles except for the cricothyroid (innervated by the external branch of the superior laryngeal nerve). Specifically, all of the muscles that are innervated by the RLN (e.g., lateral cricoarytenoid, interarytenoid, vocalis, etc.), except for the posterior cricoarytenoid (only vocal cord abductor), adduct the vocal cords.
- Coughing, gagging, and laryngospasm result from the efferent limb of the RLN
- Originates as a branch of the vagus nerve (CN X).
- The right and left vagus nerves exit the skull base via the jugular foramens.
- In the neck, the right and left vagus nerves descend in the right and left carotid sheaths, respectively, between the internal jugular vein and internal carotid artery, and into the thoracic outlet.
- Within the thorax, the vagus nerve gives off the recurrent laryngeal nerve.
- The right RLN loops around the right subclavian artery at the level of the innominate artery and ascends along the tracheoesophageal groove behind the common carotid artery.
- The left RLN follows the carotid artery into the mediastinum, loops around the aortic arch lateral to the ligamentum arteriosum.
- Once the RLNs enter the larynx, they divide into motor and sensory branches.
- The left RLN has a longer course (~12 cm from aorta to cricothyroid) compared to the right RLN (~5–6 cm from subclavian to cricothyroid), which may make it more prone to injury (1).
- Blood supply to the RLN is provided by the inferior thyroid artery.
Physiology/Pathophysiology
- Injury to the RLN can occur from:
- Inadvertent injury during surgical procedures
- Tumor
- Aortic aneurysms (hoarseness may be one of the first presenting signs)
- Trauma
- Neurotoxic drugs
- Viral or bacterial infections
- Vascular insult
- Surgical injury to the RLN can occur anywhere along the nerve's course: Neck, chest, or skull base.
- Most common surgical procedures citing RLN injury include
- Recurrent laryngeal nerve transmission may be transiently blocked when a supraclavicular, interscalene, or stellate ganglion block is performed. It typically manifests as hoarseness.
- Recurrent laryngeal nerve paralysis
- May be difficult to assess because many patients can be asymptomatic, especially if caused by slow growing tumor.
- Unliateral palsy
- Partial: Abductors are more vulnerable to injury. Therefore, partial nerve damage may result in a selective abductor paralysis with a VC that lies in the midline (adducted position)
- Complete: Affects both adductors and abductors and results in a vocal cord that lies midway between adduction and abduction, just lateral to the midline.
- Bilateral palsy
- Partial: When the abductor is more severely affected than adductors, both vocal cords meet in the midline and cause complete airway obstruction
- Complete: Vocal cords are positioned midway between abduction and adduction. Breathing is still possible with a glottic opening smaller than normal.
- Intraoperative nerve monitoring (spontaneous electromyelography [EMG]) has gained increasing popularity as a means of identifying the RLN during surgical procedures. The EMG detects and records muscle electrical activity continually. Mechanical irritation of the RLN triggers motor unit potential discharges and aids with detection of the nerve during surgical dissection as well as inadvertent manipulation and injury (retraction, cautery, scalpel). It requires the use of specialized equipment and precautions (3):
- Use of a specialized endotracheal tube with electrodes at the level of the glottis.
- Electrodes should make contact with the medial surface of the vocal cords (bilaterally) to allow monitoring.
- An antisialagogue such as glycopyrrolate may help reduce saliva pooling at the vocal cords that can impede monitoring.
- Frequent intraoperative suctioning may be required for saliva pooling.
- Use short-acting muscle relaxants for intubation as long-acting neuromuscular blockers will prevent effective neuromonitoring.
- The endotracheal tube may migrate after positioning for surgery with neck extension and should be considered if adequate EMG signal cannot be obtained.
- Regional anesthesia of the RLN and proper preparation can significantly aid successful awake fiberoptic intubation (4):
- Thoroughly discuss procedure and reassure patient.
- Administer adequate sedation for a calm, cooperative patient.
- An antisialagogue such as glycopyrrolate can decrease secretions and improve visualization during fiberoptic guidance.
- Topical local anesthetic can be applied through a variety of ways: Aerosol spray, atomizer, nebulizer, and gargling.
- Translaryngeal nerve block delivers local anesthetic to areas supplied by the sensory component of the RLN (subglottis, upper trachea).
- Identify structures by extending the patient's neck and palpating the midline of the cricothyroid membrane. Insert a 20G or 22G needle with an attached 5 cc syringe (filled with 3–5 cc of local anesthetic) using the dominant hand and constantly aspirating. The nondominant hand is usually "anchored" to the patient and helps stabilize the needle. The presence of air bubbles in the syringe is an indicator of proper needle placement. Prior to injection, ask the patient to forcefully inhale, which will help spread local anesthetic. Potential complications of a translaryngeal block include bleeding, puncture of the membranous portion of the trachea, and systemic local anesthetic toxicity. Use with caution in patients where significant coughing is undesirable or those at high risk for aspiration as their cough reflex will be greatly impaired.
