Characteristics of Experimental Recurrent Laryngeal Nerve Surgical Injury in Dogs

Objectives: We characterized various recurrent laryngeal nerve (RLN) injuries in dogs. Methods: Sixteen dogs were classified as having complete injuries (transection) or incomplete injuries (ligation, half-section, and crush). The characteristics of nerve injuries were evaluated by endoscopic examination, laryngeal electromyography (LEMG), and histopathologic examination at 0 to 12 months after the injury. Results: After the RLN injury, the average muscle fiber diameter and the average muscle bundle diameter of the affected muscles were decreased, and the average number of muscular cell nuclei per square inch increased. Fibrillation potentials were found I to 3 months after injury, and reinnervation potentials appeared 3 to 6 months after incomplete injury. For nerve transection and ligation, there was no reaction with LEMG instantly after injury involving vocal fold fixation. Vocal fold motion did not improve in members of the complete injury group, whereas all of the vocal folds in the members of the nerve ligation subgroup had limited activity in the later period. Various forms of vocal fold mobility were observed after injury in the half-section subgroup. Animals in the crush subgroup had normal EMG signals combined with abnormal LEMG signals with lower amplitudes after injury. Vocal fold fixation was not observed in this subgroup. Conclusions: We found the causes of nerve injury, in order of decreasing severity, to be transection, ligation, half-section, and crush.