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Objective: To predict round window niche (RWN) visibility using high-resolution computed tomography (HRCT) in children under 12 months old. Methods: RWN visibility was determined by a senior surgeon with surgical videos. We use St Thomas's classification for the visibility of RW during CI as follows: Type I RWM is entirely exposed. Type II RW is partial exposure and is subdivided into type IIa, more than 50% but less than 100% of the RWM is exposed and type IIb, the exposure is less than 50% but more than 0%. Type III, the RWM cannot be identified Next, we measured the following four radiologic parameters: 1) the angle of the line of posterior membrane of RWN to facial nerve outer margin relative to the cochlear basal turn(angle A), 2) the angle of the external auditory canal (EAC) relative to the cochlear basal turn(angle B), 3) the width of the facial recess, 4) the relative location of the facial nerve (FN) to the cochlear basal turn. These were compared with the RWN visibility. Subsequently, we draw a line parallel to the EAC line and along the anterior lateral FN. Results: 80 ears of 40 children were included in the study. Angle A and angle B had a significant correlation with the RWN visibility. The location of the prediction line to the round window membrane highly predicted the RWN view during the surgery. Conclusion: Preoperative temporal HRCT can predict RWN visibility in cochlear implant surgery. Drawing the prediction line is a simple and useful way for preoperatively predicting the RWN visibility. [ABSTRACT FROM AUTHOR]