Laryngeal abductor function after recurrent laryngeal nerve injury in cats.
OBJECTIVE
To determine the influence of severity of neural injury of t he recurrent laryngeal nerve on recovery of laryngeal abductor function and the importance of synkinesis.


METHODS
The recovery of laryngeal abductor function was studied in 30 cats after crushing (second-degree injury) or transection followed by neurorrhaphy (fifth-degree injury) of the recurrent laryngeal nerve, with a reinnervation period of 10 weeks.


METHODS
Recovery of laryngeal abductor function was evaluated by videolaryngoscopy of spontaneous laryngeal abduction during respiration and electromyography of the posterior cricoarytenoid and vocalis muscles. Neural lesions were applied unilaterally, and recovery of laryngeal function was compared with the contralateral unimpaired hemilarynx. Reinnervation was confirmed by histologic examination.


RESULTS
After the recurrent laryngeal nerve was crushed, laryngeal abductor function was similar to normal after a 10-week reinnervation period in 19 of the 20 cats; after neurorrhaphy, no notable recovery of laryngeal abduction resulted in any of 10 cats. Electromyographic recordings disclosed synkinesis after neurorrhaphy and recovery of normal activity patterns after crush injuries.


CONCLUSIONS
Severity of neural injury to the recurrent laryngeal nerve influences the recovery of laryngeal abductor function. Damage to the endoneurium leads to misdirection of regenerating axons, inappropriate reinnervation, and synkinesis. No effective laryngeal function can then be expected.
van Lith-Bijl
J T
JT
Department of Otolaryngology, Head and Neck Surgery, University of the Vrije Universiteit, Amsterdam, The Netherlands.
Mahieu
H F
HF
Stolk
R J
RJ
Tonnaer
J A
JA
Groenhout
C
C
Konings
P N
PN
D000818:Animals; D002415:Cats; D004576:Electromyography; D005260:Female; D007828:Laryngoscopy; D007830:Larynx / Q000503:physiopathology*; D009119:Muscle Contraction; D009409:Nerve Crush; D009416:Nerve Regeneration; D010699:Phonation; D012009:Recurrent Laryngeal Nerve / Q000473:pathology / Q000503:physiopathology; D061226:Recurrent Laryngeal Nerve Injuries; D012119:Respiration; D014743:Videotape Recording