ABSTRACT Purpose: To present a detailed, reproducible, cost-efficient surgical model for controlled subepithelial endoscopic vocal fold injury in the rat model. Methods: Six male Sprague Dawley rats were enrolled in the experiment. The left vocal folds were used to carry out the injury model, and the right vocal fold served as control. After deep sedation, the rats were placed on a custom operating platform. The vocal fold injury by subepithelial stripping was carried out using custom-made microsurgical instruments under endoscopic guidance. Data were analyzed for procedural time and post-procedural pain. Microcomputed tomography (micro-CT) scan and histologic images were obtained to assess the length, area, and depth of injury to the vocal fold. Results: The mean procedural time was 112 s. The mean control vocal fold length was 0.96 ± 0.04 mm. The mean vocal fold injury length was 0.53 ± 0.04 mm. The mean vocal fold surface was 0.18 ± 0.01 mm2 with a mean lesion area of 0.05 ± 0.00 mm2. Mean vocal fold injury depth was 375.4 ± 42.8 μm. The lesion length to vocal fold length ratio was 0.55 ± 0.03, as well as lesion area to vocal fold surface area was 0.29 ± 0.02. Conclusions: Our described experimental vocal fold injury model in rats is found to be fast, safe, cost-efficient, and reproducible with a rapid learning curve.

SUMMARY: The objective of the study was to provide a detailed anatomical description of the rat’s ear anatomy that will prove insightful to different experimental otologic surgical procedures regardless of scope. Three male Wistar rats were enrolled in the study. Candidates were screened for systemic and otologic pathology. External ear canal endoscopy was carried out with a 30˚ rigid endoscope through an image capture system. Middle ear anatomical elements were analyzed under stereomicroscopy. 3D computer tomography image reconstruction was realized with a micro-CT to describe the anatomy. Image data from all three rats were analyzed. Anatomical annotations and surgical exposure recommendations were added for key elements. The most relevant images from all three rats were selected for representation. Detailed visualization of the structural elements of the tympanic cavity were clearly visible: promontory, round window, stapedial artery, stapes, incus, and tympanic membrane were all constant findings. We describe a step wise ventral surgical approach of the middle and inner ear for which we found that the clavotrapezius muscle was a reliable landmark. For the transtympanic approach the endoscopic transcanal access was an easy and reliable method for which a detailed anatomical representation was depicted. Further, anatomical similarities to humans were observed by stereomicroscopy and Micro-CT imaging reiterating that the rat model is suitable for otologic research. The endoscopic approach to the tympanic membrane is comfortable and less expensive than a microscope. The tendon of the clavotrapezius muscle can be a reliable landmark for discovering the tympanic bulla when considering a ventral approach. 3D Micro-CT reconstruction allows intact evaluation of the samples, simultaneously being a diagnostic and also a learning tool.

RESUMEN: El objetivo de este trabajo fue proporcionar una descripción anatómica detallada de la anatomía del órgano vestíbulococlear de la rata que resultará útil para diferentes procedimientos quirúrgicos otológicos experimentales, independientemente del alcance. En el estudio se usaron tres ratas Wistar macho. Los ejemplares fueron evaluados por patología sistémica y otológica. La endoscopía del meato acústico externo se realizó con un endoscopio rígido de 30˚ a través de un sistema de captura de imágenes. Los elementos anatómicos del oído medio se analizaron bajo estereomicroscopía. La reconstrucción de la imagen de tomografía computarizada en 3D se realizó con un micro-CT para describir la anatomía. Se analizaron los datos de imagen de las tres ratas. Se agregaron anotaciones anatómicas y recomendaciones de exposición quirúrgica para elementos clave. Las imágenes más relevantes de las tres ratas fueron seleccionadas para su representación. La visualización detallada de los elementos estructurales de la cavidad timpánica era claramente visible: promontorio timpánico, ventana coclear, arteria estapedial, estapedio, yunque y membrana timpánica eran hallazgos constantes. Describimos un abordaje quirúrgico ventral escalonado del oído medio e interno para el cual encontramos que el músculo clavotrapecio era un punto de referencia confiable. Para el abordaje transtimpánico, el acceso transcanal endoscópico fue un método fácil y confiable para el cual se describió una representación anatómica detallada. Además, se observaron similitudes anatómicas con los humanos mediante estereomicroscopía e imágenes Micro-CT, lo que reitera que el modelo de rata es adecuado para la investigación otológica. El abordaje endoscópico de la membrana timpánica es cómodo y menos costoso que un microscopio. El tendón del músculo clavotrapecio puede ser un punto de referencia fiable para descubrir la bulla timpánica cuando se considera un abordaje ventral. La reconstrucción 3D Micro- CT permite la evaluación intacta de las muestras, siendo simultáneamente una herramienta de diagnóstico y también de aprendizaje.