57 - Anatomy of the Round Window: Visibility Prediction from Preoperative CT Scanners in Cochlear Implantation: Literature Criteria Study and Three-dimensional Reconstruction Evaluation

Poster Board Number: 57
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Abstract Body : Introduction: During cochlear implantation, round window membrane visibility through posterior tympanotomy is associated with type of cochleostomy used. Limiting bone drilling helps preserve residual hearing. Studies of preoperative scanner sections were proposed to anticipate its visibility with variable results. Based on preoperative scanner three-dimensional reconstruction the purpose of this study is to evaluate the predictive capacity of the round window membrane.

Materials and methods: Prospective monocentric observational study conducted at Reims University Hospital Center on all patients who were candidates for cochlear implantation from December 2018 to May 2019. The exposure of the round window membrane is classified as "good exposure" and "bad exposure" according to the St Thomas' Hospital classification, on three-dimensional (3D) reconstruction and on the basis of intraoperative vision, blind to each other. The criteria in the literature measured on the scan sections were also studied.
Their correlation is then evaluated, as well as the diagnostic performance of the 3D analysis to predict the intraoperative exposure of the round window membrane.


Results :
25 procedures were carried out in 10 children and 15 adults. Among literature criteria only the distance from the facial nerve to the membrane of the oblique sagittal round window is statistically significantly associated with intraoperative exposure of the membrane of the round window (good exposure: 5.5 ± 0.6[4.7-6.7] mm versus poor exposure: 4.8 ± 0.6[3.9-5.3] mm ; p=0.05). Exposure of the round window membrane in 3D reconstruction is associated with intraoperative exposure of the round window membrane in a statistically significant manner (p=0.0005).

Discussion :
In our study, among literature criteria only distance from facial nerve to round window membrane in oblique sagittal plane is statistically significantly associated with intraoperative exposure of the round window membrane. For a safe cochlear implantation, we propose a new criterion using petrous 3D reconstructions which is strongly associated with intraoperative exposure of the round window membrane.