三次元MRIと高分解能CTによる蝸牛の領域分析 -人工内耳適応の術前診断への応用-

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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<0.001, respectively), and abnormal findings were more frequent in the inferior horizontal part (IHP) of the basal turn. Of the 35 patients who underwent cochlear implantation, no one had ossification in the IHP on HRCT and only one patient had an obstacle to implantation. When no signal void in the IHP on 3DMRI and no ossification in the IHP on HRCT were assumed to be the criteria for candidacy for cochlear implantation, the true negative rate was 94% and the false negative rate was 0%; which fulfilled our goal of establishing feasibility of cochlear implant. The decreased signal or narrowing of the cochlear part on 3DMRI was thought to indicate slight fibrosis or inflammatory exudate in the cochlea without signifying difficulties in implantation and the increased attenuation or narrowing of the cochlear part on HRCT was considered to be primarily ascribed to partial volume averaging effect. The segmental analysis of the cochlea on 3DMRI and HRCT provides regional information on cochlear implant candidates, i.e. fluid-filled, apparently healthy, cochlea and/or pathological findings such as ossification, fibrosis and so on, and it is consequently useful for the final decision about candidacy.
札幌医科大学の論文
2002-12-01

三次元MRIと高分解能CTによる蝸牛の領域分析 -人工内耳適応の術前診断への応用-

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