Use of MRI to determine cochlear duct length in patients undergoing cochlear implantation

OBJECTIVES: It is recognised that CT can be used to determine the cochlear duct length (CDL) when selecting an electrode for cochlear implantation. It is the practice of our institution to routinely use MRI as the sole modality of pre-operative imaging in the assessment of children referred for consideration of cochlear implantation. We therefore wanted to determine whether MRI could be reliably used to determine cochlear duct length. METHODS: An analysis of 40 ears that had undergone MRI and CT of the temporal bones was undertaken. The diameter of the basal turn was independently measured for each ear using the two modalities, and CDL was then calculated. RESULTS: The mean error of measurement was 0.26 mm (range 0-0.8 mm), leading to a difference in calculated CDL of 0.96 mm (range 0-2.92 mm). CDL did not predict full insertion of 28 mm cochlear implant electrodes in 30 ears. CONCLUSIONS: MRI can be used to reliably determine cochlear duct length.