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

Objectives: To describe how the retrotympanic structures could influence the visibility of the round window niche and the round window membrane during cochlear implant surgery, and to investigate if a round window approach is possible even in cases with unfavourable anatomy.

Methods: Video recordings from 37 patients who underwent cochlear implantation were reviewed. The visibility of the round window niche and round window membrane at different timepoints was assessed according to a modified version of the Saint Thomas Hospital classification. The structures that concealed the round window niche and round window membrane were evaluated.

Results: After posterior tympanotomy, 54 per cent of cases had limited exposure (classes IIa, IIb and III) of the round window niche. After remodelling the retrotympanum, round window niche visibility significantly increased, with 100 per cent class I and IIa cases. Following remodelling of the round window niche, visibility of more than 50 per cent of the round window membrane surface was achieved in 100 per cent of cases.

Conclusion: Remodelling the retrotympanum and the round window niche significantly increased exposure of the round window niche and round window membrane respectively, allowing round window insertion in all cases.