Spontaneous Regeneration of Recurrent Laryngeal Nerve Following Long-Term Vocal Fold Paralysis in Humans: Histologic Evidence

Objectives/Hypothesis: To validate the occurrence of spontaneous regeneration of the recurrent laryngeal nerve (RLN) in patients with symptomatic vocal fold paralysis (VFP). Study Design: Histologic study. Methods: Between June 2008 and February 2009, 29 patients with symptomatic unilateral VFP caused by thyroid surgery were continuously enrolled in this study, with 30 normal RLNs serving as the control. The denervation course was from 7 to 74 months. Intraoperative exploration was performed to identify the sites and types of RLN lesions. The status of RLN regeneration was detected by histologic examination, and the number of myelinated axons was counted. Results: Intraoperative exploration showed that RLN was transected in 24 cases, and the continuity of the RLN stump was recognized in the five other cases. Connective tissue connected the distal and the proximal ends of all transected RLNs under a surgical microscope. Light microscopy showed varying numbers (17-259) of abnormal myelinated axons in these injured RLNs; the maximum was less than 40% of those of normal RLNs (658 +/- 79). Electron microscopy also demonstrated that abnormal myelinated axons with small diameters commonly existed in all injured RLNs, with dark myelin clumps without axons (Bungner bands) and fibrotic components. Conclusions: The present study demonstrates that a varying degree of spontaneous RLN regeneration is substantially engaged in the process of subclinical reinnervation following laryngeal denervation in humans, which may account for different clinical characteristics and outcomes of VFP.