Predicting Round Window Niche Visibility via the Facial Recess Using High-Resolution Computed Tomography

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Abstract

Objective

To predict round window niche (RWN) visibility using high-resolution computed tomography (HRCT).

Study design

Case series with chart review.

Setting

Academic tertiary care center.

Subjects and methods

We retrospectively reviewed 70 cochlear implant ears that underwent presurgical axial HRCT with a surgical video recorder. The visibility of the RWN was classified into three types: 17 as invisible or nearly invisible, 22 as partially visible, and 31 as fully visible. Next, we measured the following three radiologic parameters: 1) the angle of the external auditory canal (EAC) relative to the cochlear basal turn, 2) the width of the facial recess, and 3) the relative location of the facial nerve (FN) to the cochlear basal turn. These were compared with the RWN visibility. Subsequently, to predict the RWN visibility, a line was created parallel to the EAC line and along the anterior lateral FN. The location of the line relative to the round window membrane was compared with the RWN view.

Results

In cases that had poor RWN visibility, the angle of the posterior canal wall portion of the EAC relative to the cochlear basal turn was significantly smaller and the location of the FN to the cochlear basal turn was closer. The location of the prediction line to the round window membrane highly predicted the RWN view during the surgery.

Conclusion

The RWN visibility and the preoperative HRCT findings showed a high correlation. Drawing the prediction line is a simple and useful way for preoperatively predicting the RWN visibility in cochlear implant surgery.

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