Midmodiolar Reconstruction as a Valuable Tool to Determine the Exact Position of the Cochlear Implant Electrode Array

Abstract

A midmodiolar reconstruction with multislice computed tomography could potentially be used clinically to determine the cochlear implant electrode array position if the technique was validated with a cadaveric temporal bone study. Several radiologic studies using sophisticated techniques have been described. This study was designed to validate a standard multislice computed tomography scan technique to determine the electrode array position. This ex vivo study was conducted on 18 cadaveric temporal bones without malformation. Cochlear electrode dummies were implanted by a single experimented surgeon with the Advance Off-Stylet technique. After randomization, the placement was processed through an anteroinferior or superior cochleostomy for respective scala tympani or vestibuli positioning with direct location of the basilar membrane. Cadaveric temporal bones were then scanned (Philips Brilliance 40 computed tomographic scan) and reconstructed into the midmodiolar computed tomography scan plane (± 45 degrees, z-axis in the cochlear coordinate system). Two independent neuroradiologists, who were unaware of the implanted scala, evaluated the electrode array position on a computed tomographic scan through the midmodiolar reconstruction. In the end, the microanatomic study was the criterion standard to determine the exact scala localization of the electrode array. Nine electrodes were inserted into the scala tympani, and 9 were inserted into the scala vestibuli. According to our anatomic criterion standard, the midmodiolar reconstruction sensitivity and the specificity for the scala tympani position were 0.875 (range, 0.722-1.0) and 1.0, respectively; the sensitivity and specificity for dislocation and the scala vestibuli position were both 1.0. The radioanatomic concordance was 0.94 (range, 0.89-0.98) for determining the electrode array position into scalae with midmodiolar reconstruction. Our cadaveric study validates midmodiolar reconstruction as a valuable tool to routinely determine the precise position of the cochlear implant electrode array. This study opens the field for further clinical studies.