From the Guidelines
The posterior cricoarytenoid (PCA) muscles are the only laryngeal muscles that have bilateral innervation from the recurrent laryngeal nerves (RLNs). This means that each PCA muscle receives nerve fibers from both the ipsilateral (same side) and contralateral (opposite side) RLNs. This bilateral innervation is clinically significant because it provides a protective mechanism against complete vocal cord paralysis in cases of unilateral RLN injury. The PCA muscles are the primary abductors of the vocal cords, responsible for opening the glottis during inspiration. Their bilateral innervation ensures that some degree of vocal cord abduction can be maintained even if one RLN is damaged, which helps prevent complete airway obstruction. All other intrinsic laryngeal muscles, including the lateral cricoarytenoid, thyroarytenoid, cricothyroid, and interarytenoid muscles, receive unilateral innervation from their respective RLNs or, in the case of the cricothyroid muscle, from the external branch of the superior laryngeal nerve.
Some key points to consider:
- The RLN is a mixed nerve with sensory and motor fibers, originating from the thoracic portion of the vagus nerve 1.
- The right RLN lies in a more superficial plane, along the lateral esophageal edge and is traditionally considered at higher risk of injury 1.
- The knowledge of highly variable relationships between the RLN and inferior thyroid artery (ITA) is critical to a better neural identification 1.
- Non-recurrent laryngeal nerve is a rare variant (incidence 0.3-1.6%) observed more frequently on the right side, still representing a surgical challenge 1.
In terms of clinical significance, the bilateral innervation of the PCA muscles is crucial for maintaining vocal cord function and preventing airway obstruction in cases of unilateral RLN injury. This is particularly important in thyroid surgery, where the RLN is at risk of injury 1. The use of intraoperative neural monitoring (IONM) can help identify and prevent RLN injury, and has been shown to be beneficial in reducing the risk of vocal cord paralysis 1.
Overall, the bilateral innervation of the PCA muscles is a critical aspect of laryngeal anatomy and function, and is essential for maintaining vocal cord function and preventing airway obstruction in cases of unilateral RLN injury.
From the Research
Laryngeal Muscles with Bilateral Innervation from RLN
- The interarytenoid muscle is bilaterally innervated by both recurrent laryngeal nerves (RLNs) as well as branches of both superior laryngeal nerves (SLNs) 2.
- The internal branch of the superior laryngeal nerve (iSLN) provides no functional efferent motor innervation to the interarytenoid muscles, but rather exclusively evokes an interarytenoid motor response via afferent activation of central neural circuits that mediate the laryngeal reflex arc 3.
- The interarytenoid muscle receives motor innervation from both the recurrent and superior laryngeal nerves, with the proportion of motor axons varying from 6% to 31% in the internal branch of the superior laryngeal nerve 4.
- Significant neural connections between the RLN and SLN systems exist, including a neural plexus in the interarytenoid muscle where RLNs and internal SLNs combine 5.