Surgical anatomy of posterior tympanotomy: influence of the retrotympanum on round window exposure

Objective: To describe how the retrotympanic structures could influence the visibility of the round window niche (RWN) and of the round window membrane (RWM) during cochlear implant (CI) surgery. To investigate if a RW approach is possible even in those cases with unfavorable anatomy. Methods: Video recordings from 37 patients underwent CI were reviewed. The visibility of the RWN and RWM at different timepoints was assessed according to a modified version of the Saint Thomas Hospital classification. The structures responsible for hiding the RWN and RWM were evaluated. Results: After posterior tympanotomy 54% of cases had a limited exposure (class IIa, IIb, and III) of the RWN. After remodeling the retrotympanum, the RWN visibility achieved a significant increase, with 100% class I and IIa. Following the remodeling of RWN, a visibility >50% of the RWM surface was achieved in 100% of the cases. Conclusion: Remodeling the retrotympanum and the RWN significantly increase the exposure of the RWN and RWM respectively, allowing a RW insertion in all cases.