Differences in Cochlear Nerve Cross-Sectional Area between Normal Hearing and Postlingually Deafened Patients on MRI

Abstract

Objectives. To demonstrate that parasagittal constructive interference in steady state (CISS) magnetic resonance imaging (MRI) can be used to accurately measure cochlear nerve cross-sectional area and thereby evaluate for statistically significant differences in the cochlear nerve cross-sectional areas of postlingually deafened and normal-hearing adults. Study Design. Cross-sectional study. Setting. Tertiary care medical center. Subjects and Methods. Parasagittal CISS MRIs of postlingually profoundly deafened cochlear implant candidates and normal-hearing patients at a tertiary care academic medical center between 2006 and 2009 were retrospectively identified. Two independent and blinded investigators measured the cochlear nerve height and width and calculated the cross-sectional area [π(H/2)(W/2)] at the fundus of the internal auditory canals. Measurements of both investigators were analyzed for reliability and agreement with an Altman plot, and deafened patient measurements were compared with results of the normal-hearing patients via Wilcoxon rank sum tests. Results. The cochlear nerve cross-sectional area of postlingually deafened patients (mean ± SD = 0.61 ± 0.16 mm2) was less than normal-hearing patients (0.94 ± 0.28 mm2). The difference was statistically significant ( P = .002). There was good agreement between independent observer measurements. Conclusion. Parasagittal CISS MRI can be used to measure the cochlear nerve with good interobserver agreement, and there is a significant difference between the cross-sectional area of postlingually deafened and normal-hearing adults. The cross-sectional area may correlate with residual spiral ganglion cells and provide a prognostic indicator for post–cochlear implant performance, which is the focus of our ongoing research.