Electromyographic and histologic evolution of the recurrent laryngeal nerve from transection and anastomosis to mature reinnervation
ABSTRACT Objectives:To describe the natural evolution of recurrent laryngeal nerve (RLN) reinnervation in an animal model.Study Design:Twenty Sprague Dawley rats underwent unilateral RLN transection and anastomosis. Animals were sacrificed at 4, 8, 12, 16, and 20 weeks. Prior to sacrifice, each rat underwent electromyography (EMG) and visual grading of vocal fold motion. Bilateral RLNs were harvested and evaluated histologically.Results:EMG revealed synkinetic reinnervation at all time periods except at 4 weeks. EMG evolution plateaued at 16 weeks. Vocal fold motion was slight in three rats at 4 weeks but was otherwise absent except for one rat at 12 weeks. Histologic changes of the axons and their myelin sheaths were consistent at each time period. At 16 weeks, histologic changes plateaued.Conclusions:Consistent EMG, histologic, and vocal fold motion changes occur at specific time periods during RLN reinnervation after transection and anastomosis in a rat model. Reinnervation is mature at 16 weeks. Findings corroborate theories of preferential and synkinetic reinnervation after RLN transection. Use of a rat model to investigate the effect of interventions on RLN reinnervation requires a minimum of 16 weeks between transection and investigation to allow for maturation of reinnervation. Laryngoscope, 2011
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ABSTRACT: After microsurgery preparation, the endings of the nerve trunk, which have been freed from epineurium, are approxiamated on top of a gelatin platelet (gel foam) which has been soaked in a nutrient solution. The gelatin platet is then formed like a tube and wrapped around the ends of the anastomosis. Using this procedure, suture-induced reactions in the vicinity of the anastomosis are prevented. The connection is sufficiently firm so as to withstand tension incurred in chewing and in movement of the head. Additionally, the gelatin coating prevents early onset of fibrosis, which as a process is normally induced by the surrounding tissues onto transplants. Simultaneously, nutrition of the transplant is guaranteed during the first post-operative days. In all cases operated hitherto, good to satisfactory return of function has been observed. The earliest onset of function-return was observed at four (4) months after the operation and the latest completion occurred at eighteen (18) months. Thus far, no negative results have been observed using this method.Laryngologie, Rhinologie, Otologie 03/1979; 58(2):154-6.
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ABSTRACT: Motoneurons supplying the posterior crico-arytenoid (PCA), thyro-arytenoid (TA), lateral crico-arytenoid (LCA), and crico-thyroid (CT) laryngeal muscles were localized in the cat, the rabbit, and the 6-week-old kitten by using the technique of intramuscular injection of horseradish peroxidase. Each muscle was found to be innervated by a single, ipsilateral pool of motoneurons, a result which was reliably established only after controlling adventitious spread of the label to nontarget muscles by prior denervation of adjacent musculature. The laryngeal motoneuron column extended in the nucleus ambiguus for a distance of 5-6 mm caudally from the facial nucleus. CT motoneurons were located in the rostral third of this column while the PCA, TA, and LCA motoneurons were located more caudally. These results are in general agreement with earlier degeneration studies (Lawn, '66a; Szentágothai, '43). Although labelled cells were widely dispersed in the nucleus, particularly in the adult cat, a limited amount of topographical structure could still be discerned in the arrangement of recurrent laryngeal nerve motoneurons. In the cat, the PCA pool was located in the ventral part of the recurrent laryngeal nerve representation and did not extend as far caudally as the TA or LCA pools; the LCA pool was located in the caudal and dorsomedial part of the recurrent laryngeal nerve pool; TA motoneurons appeared to overlap the PCA and LCA pools on all three anatomical planes. TA motoneurons were more numerous than PCA or LCA motoneurons, the numbers of cells in the three pools being estimated at 170, 111, and 112, respectively. In the cat bilateral labelling of different pools pointed to certain differences in morphology between cells from these pools and also suggested a functional basis for such differences. The mean soma diameter for the PCA and CT motoneurons was each significantly smaller than that for the TA and LCA motoneurons. The rabbit data were similar. The findings on motoneuron morphology are considered in relation to anatomical and physiological characteristics known to have been established for individual laryngeal muscles and with which they appear to be consistent.The Journal of Comparative Neurology 12/1984; 230(1):13-32. · 3.66 Impact Factor
Article: The innervation of the human larynx.[show abstract] [hide abstract]
ABSTRACT: To investigate the gross anatomy of the recurrent and superior laryngeal nerves (RLNs and SLNs) in 10 human larynges. Whole larynges were processed to clear all soft tissue while leaving nerves stained. Then the main laryngeal nerves and the muscles they innervate were dissected and analyzed. It was found that in all larynges the RLNs and SLNs are connected by nerve branches other than Galen's anastomosis. The most consistent connection is in the interarytenoid muscle, where RLNs and internal SLNs combine in a neural plexus. A less consistent connection occurs in the piriform fossa, where a continuation of the external SLN passes from the cricothyroid muscle to the thyroarytenoid muscle. Based on these findings it is proposed that there are significant neural connections between the RLN and SLN systems. In addition, limited cross-innervation is seen from side to side in the area of the interarytenoid muscle. Other findings concern the innervation patterns within the laryngeal muscles. The posterior cricoarytenoid, cricothyroid, and thyroarytenoid muscles all appear to be composed of separate bellies based on the configuration of their nerve supply. Most notable is the region of the thyroarytenoid muscle at the vocal cord margin that is innervated by a nerve plexus of extreme complexity. The details of the innervation patterns suggest functional differences within and between laryngeal muscles.Archives of Otolaryngology - Head and Neck Surgery 10/1993; 119(9):934-9. · 1.78 Impact Factor