Segmental Analysis of Cochlea on Three-dimensional MR Imaging and High-resolution CT : Application to Pre-operative Assessment of Cochlear Implant Candidates

High-resolution computed tomography （HRCT） and magnetic resonance imaging （MRI） have recently become standard pre-operative examinations for cochlear implant candidates. HRCT can demonstrate ossification and narrowing of the cochlea, but subtle calcification or soft tissue obstruction may not be detected by this method alone, and so conventional T2 weighted image （T2WI） on MRI has been recommended to disclose them. In this study, segmental analyses of the cochlea were made on three-dimensional MRI （3DMRI） and HRCT in order to predict cochlear implant difficulties.The study involved 59 consecutive patients with bilateral profound sensorineural hearing loss who underwent MRI and HRCT from November 1992 to February 1998. Etiologies of deafness were meningogenic labyrinthitis （n = 9）, tympanogenic labyrinthitis （n = 12）, and others （n = 38）. Pulse sequence of heavy T2WI was steady state free precession and 3DMRI was reconstructed by maximum intensity projection method. HRCT was reconstructed by bone algorithm focusing on the temporal bone. For alternative segmental analysis, cochleas were anatomically divided into five parts and each of them was classified by three ranks of score depending on 3DMRI or HRCT findings.There was a close correlation by ranks between the total score of the five parts on 3DMRI and HRCT （rs = 0.86, P<0.001）, and a statistically significant difference was identified between causes of deafness in the total score on 3DMRI or HRCT （P<0.001, respectively）. There was a significant difference in the score among the five parts on each examination （P