Developmental Changes in Cochlear Orientation-Implications for Cochlear Implantation

Objectives: To investigate changes in cochlear orientation with age and discuss the implications of any change with respect to cochlear implantation. Study Design: Cross-sectional study of computed tomographic scans of the temporal bones in patients with no congenital abnormalities. Patients: One hundred fifty-nine patients were included in the study, making a total of 318 ears. The age range was 9 months to 85 years. Intervention: Axial computed tomographic scans showing the basal turn of the cochlea were identified. The angle of the basal turn of the cochlea was measured by drawing a line through the long axis of the basal turn and measuring its angle with a line drawn through the midsagittal plane. The patients were grouped according to age, and a 1-way analysis of variance was used to identify any statistically significant change in basal turn angulation. Interobserver and intraobserver errors were calculated and presented as repeatability coefficients. The basal turn angles of 3 difficult cases of cochlear implantation were related to the findings. Results: The mean basal turn angle was 54.6 degrees ( range, 46.8-63.8 degrees; standard deviation, 3.5). There was a statistically significant reduction in the angulation of the basal turn with increasing age ( F = 10.1; p = 0.002). The majority of the change occurs between the ages of 11 and 15 years. The interobserver reliability coefficient was 4.8. The intraobserver reliability coefficient was 2.0. The 3 difficult cases had basal turn angles that were at the upper limit of the reference range. Conclusion: There is a statistically significant reduction in basal turn angulation relative to the midsagittal plane with increasing age. However, care should be taken in interpreting these results in light of the inherent error in the measuring technique, although the intraobserver repeatability coefficient was only 2.0. The more obtuse angulation of the basal turn in children may have implications for cochlear implantation.