Histopathologic investigation of the dimensions of the cochlear nerve canal in normal temporal bones.

Objective: Establish normative histopathologic data on the dimensions of the cochlear nerve canal (CNC).

Background: Evidence suggests that when the CNC is stenotic, the cochlear nerve may be hypoplastic. There is clear agreement in the literature that an internal auditory canal less than 2 mm in diameter is a relative contraindication to cochlear implantation in children. However, there has only been recent recognition in research that a narrowed CNC may lead to diminished ability to interpolate and use auditory information delivered through a cochlear implant. However, there is no consensus in the literature on the normal diameter of the CNC and what parameters should be used to determine stenosis. In addition, no normative histopathologic data is available for CNCs.

Methods: This study evaluated histopathologic axial sections from normal human temporal bones to measure the cochlear nerve canal in 110 individuals, aged 0-100 years. The maximum CNC diameter in each normal patient was identified and measured.

Results: The mean CNC diameter was 2.26 mm with a standard deviation of 0.25 mm. There were no differences in the CNC diameters between males and females or with increasing age.

Conclusion: These measurements should provide a normative reference for comparison in histopathologic and radiographic assessment of any patient with suspected cochlear nerve canal stenosis.