[Degeneration and regeneration characteristics of nerves and muscles after recurrent laryngeal nerve injury].

We investigated the degeneration and regeneration characteristics of nerves and muscles after different degrees of recurrent laryngeal nerve (RLN) injury, and then discussed the possible relations between them. Ninety-five Sprague Dawley (SD) rats were used in this study, 2 rats died of infection, 2 died during surgery and 1 died in transit. The rest 90 SD rats were classified as having complete injuries (transection,43 rats), incomplete injuries (crush, 43 rats) and conrtol group (4 rats). The characteristics of nerve injuries were evaluated by endoscopic examination, laryngeal electromyography (LEMG), and histopathologic examination at 6 hours, 12 hours, 1 day, 3 day, 5 day, 1 week, 2 weeks, 3 weeks and 4 weeks after the injury. All the vocal folds kept fixation in the completely injury group, where as 41/43 vocal folds in imcompletely injury group got normal activity 2 weeks after surgery, 1 at 3 weeks and 1 at 4 weeks. Fibrillation potentials were found 1 day after transection, and rennervation potentials appeared 4 weeks after transection. LEMG was normal 3 weeks after RLN was crushed. The average muscle fiber number of the left thyroarytenoid (TA) decreased with the time in the completely injury group, which increased in the second week after crush. Degeneration appeared more seriously in the distal region after transaction, and a small amount of large myelinated nerve fibers appeared at 4 weeks after injury. The most serious nerve degeneration appeared in the first day after crush, and 1 week later the ultrastructures of RLN were almost normal. The phagocytosis of Schwann cells occurred within 2 weeks after injury, 3 weeks later we found the apperance of Schwann cells who did not wrap around nerve fibers, especially in the proximal region. In the crush group, the phagocytosis of Schwann cells occurred within 1 week after injury, apoptosis and degeneration appered occasionally. Inflammatory response was more severe in the transection group, the number of fibroblasts and collagen fibers in the mesenchy increased. The degeneration is more severe in the distal nerve when RLN is traversed. Nerve regeneration appears in the fourth week after RLN is traversed. Injuried nerve has the ability to repair itself. Schwann cells play a role in phagocytosis after injury, and immature Schwann cells are found. Nerve fiber disintegration product can accelerate the migration of macrophage activation.