An Approach to the Vestibular Nerve in Chinchillas

Abstract Problem: Although there are many physiological and anatomic studies regarding the cochlear efferent system, its functional role in auditory processing is not fully understood. Sectioning of the vestibular nerve in chinchillas could thus create an experimental model for further in-depth study of this system. Methods: Eight adult male chinchillas were deeply anesthetized with an intramuscular association of ketamine chloridrate and xylasin. Surgery was performed on the right side under a light microscope. The skin and subcutaneous tissues were incised to expose the occipital muscles that were detached. The osteotomy was performed as far as possible from the sigmoid sinus, the dura was incised to allow aspiration of the posterior lateral part of the cerebellum, enabling the visualization of the fossa for the parafloccular lobe of the cerebellum and the internal acoustic meatus with all its nerves. The vestibular nerve was sectioned outside the internal acoustic meatus. Results: This approach allowed an adequate visualization of the important landmarks and a successful section of the vestibular nerve in all animals. The postmortem craniotomy revealed that no harm had been inflicted on the cochlear and facial nerves. Conclusion: Detailed anatomic description of the temporal bone medial side in chinchillas and the suggested surgical pathway may facilitate laboratory experiments in such animals and offers several advantages: (1) shorter surgical duration, (2) no need for the drill pin, (3) no need for venous sinus isolation, and (4) lesser manipulation of neighboring structures. Significance: The complete understanding of the surgical technique to reach the vestibular nerve is imperative to many experimental trials undertaken in the otology field, especially regarding the efferent system study. Support: None reported.