Cochlear Nerve Diameter in Normal Hearing Ears Using High-Resolution Magnetic Resonance Imaging

Objectives: Deficient cochlear nerves (CN) have been associated with poor cochlear implant performance. Normative data on CN diameter based on radiographic imaging have not been published. The objectives of this study were to determine if CN diameter could be reproducibly measured on parasagittal constructive interference in steady state (ClSS)-sequence magnetic resonance imaging (MRI) and to establish a normative range for CN diameter. Study Design: Retrospective review of MRI images by two independent blinded observers. Methods: Thirty patients (45 ears) with a CISS-sequence MRI done for auditory complaints in patients with normal hearing in one ear were included. CN diameters were measured in a parasagittal plane just medial to the internal auditory canal (IAC) fundus by two independent observers. Cross-sectional areas were calculated and interobserver agreement was evaluated. Results: The CN was identified in 100% of studied ears. In 93%, the diameters were able to be measured by both observers. In 7% of ears, the cochlear nerve was unable to be measured secondary to the proximity of the CN to IAC wall. The CN vertical diameter (1.4 mm +/- 0.21 mm), horizontal diameter (1.0 mm +/- 0.15 mm), and cross-sectional area (1.1 mm +/- 0.26 mm(2)) were normally distributed. There was good interobserver correlation for each measure. Conclusions: CN diameter can be reliably measured at the IAC fundus. This study establishes normative radiographic data for the CN diameter. These data may be used to evaluate the cause and treatment prognosis in patients with sensorineural hearing loss.