Cochlear Implantation: Predicting Round Window Niche Visibility Using One Measurement in High-Resolution Temporal Bone Computed Tomography

BACKGROUND: To evaluate the accuracy of a single measurement in temporal bone computed tomography in predicting the round window niche (RWN) visibility during cochlear implantation. METHODS: A prospective study was conducted on 148 patients (165 ears) who had a cochlear implant (CI) from January 2010 to December 2018 at a tertiary CI center. The measurement was done for the angle of the basal turn of the cochlea (ABTC), which we defined as the angle formed by the cochlear basal turn and the cranium mid-sagittal plane, by 2 readers blindly from the axial images of computed tomography. The RWN visibility was classified according to the observation during surgery (through posterior tympanotomy) into full visibility, partial visibility, and invisibility. The measured angle was then correlated to the intra-operative visibility of the RWN. RESULTS: The average ABTC was 57.48 degrees +/- 4.05 degrees (range: 45.0-68.0), and the RWN was found to be fully visible in 85%, partially visible in 11%, and invisible in 4% of the studied ears. The receiver operating characteristic analysis revealed a significant discriminating ability in predicting RWN visibility ( P <.001) at a threshold ABTC angle of 58.5 degrees. The mean ABTC was 56.71 degrees +/- 3.74 degrees, 61.00 degrees, and 63.86 degrees +/- 2.67 degrees for fully visible, partially visible, and invisible RWN, respectively. A statistical significant difference was found ( P = .0002) when comparing the ABTC in patients with partially visible/invisible RWN (61.80 degrees +/- 2.87 degrees) with the fully visible RWN (56.71 degrees +/- 3.74 degrees). CONCLUSION: Round window niche visibility could be predicted by measuring the ABTC in relation to the cranium's mid-sagittal plane in CT preoperatively. An ABTC bigger than 58.5 degrees could be an indication of poorly visible RWN.