Comparative histology and vibration of the vocal folds: Implications for experimental studies in microlaryngeal surgery

Objectives/Hypothesis: To determine the most suitable animal model for expe rimental studies on vocal fold surgery and function by a histological compa rison of the microflap surgical plane and laryngeal videostroboscopy (LVS) in different species of animals. A second goal was to determine how the lay ered vocal fold structure in humans and three different animal species affe cts surgical dissection within the lamina propria Study Design Prospective laboratory. Methods: Three larynges each from dogs, monkeys, and pigs were compared with three ex vivo human larynges. Microflap surgery was performed on one vocal fold from each larynx. Both the operated and nonoperated voca l folds were examined histologically using stains specific for elastin, mat ure collagen, and ground substance. Based on the histological results, LVS was performed on two dogs and two pigs after first pet-forming a tracheotom y for ventilation and airflow through the glottis. Arytenoid adduction sutu res were placed to facilitate vocal fold adduction Results: The distributio ns of the collagen and elastin fibers were found to differ among the specie s with concentrations varying within species. Unlike the human vocal fold, which has a higher elastin concentration in the deeper layers of the lamina propria, both the pig and the dog had a thin band of elastin concentrated just deep to the basement membrane zone in the superficial layer. Just deep to this thin band, the collagen and the elastin were less concentrated The monkey vocal fold had a very thin mucosal layer with less elastin througho ut the mucosa. The microflap dissections in each of the dog, pig, and human vocal folds were similar, being located within that portion of the superfi cial lamina propria where the elastin and mature collagen are less concentr ated. The microflap plane in the monkey vocal fold was more deeply located near the vocalis fibers. Despite the differences in elastin concentration, the microflap plane in both the dog and the pig was found to be similar to that in humans. The dog anatomy was much more suitable for microsuspension laryngoscopy and stroboscopic examination The dog vocal folds vibrated in a similar fashion to human vocal folds with mucosal waves and vertical phase differences, features not seen in the pig vocal folds. Conclusions: Based on both the histological and stroboscopic results, the dog was believed to be a more suitable animal model for studies on vocal fold surgery, acknowle dging that no animal's laryngeal anatomy is identical to that of the human. The dog LVS model presented allows for longitudinal laryngeal studies requ iring repeated examinations at multiple time periods with histological corr elation applied at sacrifice.