Use of a Microendoscope for Transtympanic Drug Delivery to the Round Window Membrane in Chinchillas

Introduction: Systemic drug application for the treatment of inner ear diseases is restricted because of the blood-labyrinthine barrier and the limited blood supply to the inner ear. Local drug delivery to the inner ear can be an alternative method to overcome the problems with systemic application. The purpose of the present study was to describe the anatomic orientation of the round window membrane (RWM) and to examine the use of a microendoscope for transtympanic drug delivery to the RWM in the chinchilla animal model. Materials and Methods: Fourteen female chinchillas were used for anatomic dissections (n = 4, 8 ears) and comparison of oto-microscopy (n = 5, 10 ears) with otoendoscopy (n = 5, 10 ears) for visualization and transtympanic application of methylene blue to the RWM of the animals. Results: The external auditory meatus in chinchillas is S-shaped, and the RWM is not accessible through the tympanic membrane in otomicroscopy. The use of a special microendoscope makes it relatively easy to have an accurate transtympanic access to the RWM. The working channel of the microendoscope permitted successful delivery of methylene blue to the RWM in all tested chinchillas. Conclusion: The present study is the first published study that shows the feasibility of a microendoscope for transtympanic drug delivery to the RWM in animal models. Minor technical modifications are recommended, which will make the microendoscope an easy tool for future studies on local drug delivery to the RWM in the chinchilla animal model.