Unilateral Vocal Fold Paralysis

Excerpt

Vocal fold immobility is a broad term referring to the abnormal movement of the true vocal folds. The abnormal movement can arise from reduced mobility (paretic) or complete cessation of any vocal fold movement (paralytic). The condition can be unilateral or bilateral. Unilateral vocal fold paralysis (UVFP) is more common than the bilateral type.

Vocal Fold Anatomy

The vagus nerve innervates the larynx and its associated muscles. Vagal nerve fibers arise from the nucleus ambiguus in the brainstem medulla. Upper-motor corticobulbar neurons descend from the cerebral cortex to the nucleus ambiguus, stimulating these vagal nerve fibers. The fibers coalesce and exit the brainstem via the jugular foramen as the 10th cranial nerve.

The vagus nerve then descends inferior to the skull base, passes into the neck, and gives off 3 main branches: the pharyngeal branch, superior laryngeal nerve (SLN), and recurrent laryngeal nerve (RLN). The SLN is responsible for laryngeal sensation in the superior glottic aspect and cricothyroid muscle motion.

The RLN classically descends further into the neck and thorax, loops around the subclavian artery on the right and aortic arch on the left, and ascends back into the neck in the tracheoesophageal groove. The RLN then enters the larynx posteriorly, near the cricothyroid joint. However, a small proportion of the population has a "nonrecurrent laryngeal nerve" that directly innervates the larynx without passing the thorax.

The RLN provides sensation to the glottis and subglottis and motor innervation to all remaining intrinsic laryngeal muscles, including the posterior cricoarytenoid, interarytenoid, lateral cricoarytenoid, and thyroarytenoid muscles. The cause of unilateral vocal fold paralysis can arise in the larynx and anywhere along the RLN pathway. The role of SLN injury in UVFP pathophysiology is insignificant.[73]