CT and MRI, importance of preoperative radiological assessment in pediatric cochlear implantation

Abstract

INTRODUCTION: Cochlear implantation (CI), in the past more than 30 years, has become a standard of care for children with profound sensorineural hearing loss. As it became a routine intervention, requests for pre-op images have increased in the work-up for candidates. The optimal protocol for radiodiagnostics has not yet been defined. CT and MRI are complementary methods and both being used for this purpose. The presence of a functional cochlear nerve is a key issue in pediatric CI. Cochlear nerve aplasia is the only absolute contraindication for CI and MRI is a gold standard for cochlear nerve (CN) detection. Recently, some authors have reported the relationship between bony cochlear nerve canal (BCNC) stenosis on CT and cochlear nerve deficiency (CND). OBJECTIVES: The aim of this study was to consider the importance of CT in the preoperative assessment of prelingualy deaf children and to determine whether the width of the bony cochlear canal (BCNC) can serve as a reliable predictive factor for the existence of a CND. MATERIALS AND METHODS: A total of 11 children with confirmed diagnosis of prelingual, severe sensorineural hearing loss will be included in this study. In all patients, indication for CI was confirmed and according to the preoperative protocol, high-resolution CT and MR were performed. Reconstructions at a distance of 0.6 mm of the axial plane images from the HRCT of temporal bones were used for measuring the width of the BCNC. The cochlear nerves were evaluated on axial and sagittal - oblique T2 - MRI images and classified as normal, hypoplastic or aplastic. CND is diagnosed if the cochlear nerve is absent (aplasia) or very thin i.e. smaller than the adjunct facial nerve in the internal auditory canal on MRI (hypoplasia). Two factors were reviewed retrospectively: presence of inner ear anomalies and the relationship between BCNC stenosis on CT and the existence of CND on MRI. RESULTS From a total of 22 temporal bones analyzed (22 ears in 11 patients), inner ear malformations were detected in 6 ears from 3 patients (27.27%). All three children had a bilateral malformation, in one it was Michel deformity and in two it was IP2 (incomplete partition 2). BCNC diameter ranged from 0.1mm to 2.33mm with a mean value of 1.46±0.6mm. CND was recorded in 4 of 22 ears and all were associated with stenosis of the BCNC. In a total of three ears with a stenotic canal, we obtained a normal finding for the cochlear nerve on MR. CONCLUSION: Radiological evaluation is integral in surgery planning. The optimal protocol for radio-diagnostics has not yet been defined. CT and MRI are complementary methods and both being used for this purpose. Children with BCNC stenosis on CT have a high incidence of CND on MRI. A narrowed BCNC on CT can be an indicator for the selection of children who are candidates for CI and need to be additionally referred for MRI. So, when its feasible use both imaging methods, but when not narrow BCNC on CT it’s a reliable indicator for mandatory MRI. KEYWORDS: CT, MRI, bony cochlear nerve canal, cochlear nerve, pediatric cochlear implantation.