Unilateral Vocal Fold Paralysis

Excerpt

Vocal fold immobility is a broad term that can be used to describe the abnormal movement of the true vocal folds. It can be unilateral, where only one true vocal fold is affected, or bilateral, in which both true vocal folds are affected. The abnormal movement can be characterized as being paretic, meaning some movement is present, albeit reduced or paralyzed, with complete cessation of vocal fold movement. If a true vocal fold is paralyzed, it can be described as being paralyzed in a midline, paramedian, or lateral position. This review will focus specifically on unilateral vocal fold paralysis.

It is imperative to understand the neuroanatomy of the true vocal folds to understand vocal fold paralysis. The vagus nerve innervates the larynx and its associated muscles. The vagus nerve is comprised of nerve fibers that arise from the nucleus ambiguus in the medulla portion of the brainstem. Upper-motor cortico-bulbar neurons originate from the cerebral cortex and descend to synapse onto these lower-motor vagal nerve fibers, which originate from the nucleus ambiguus.

After arising from the brainstem, the vagus nerve then exits the skull base at the jugular foramen and descends into the neck to give off three main branches (the pharyngeal branch, the superior laryngeal nerve [SLN], and the recurrent laryngeal nerve [RLN]). The SLN supplies sensation to the larynx above the glottis and innervates the cricothyroid muscle. The RLN descends further into the neck, loops around the subclavian artery (on the right) or the aortic arch (on the left), and ascends back up into the neck in the tracheoesophageal groove, where it enters the larynx posteriorly, near the cricothyroid joint. The RLN innervates all remaining intrinsic muscles of the larynx including the posterior cricoarytenoid, interarytenoid, lateral cricoarytenoid, and thyroarytenoid muscles.