Cochlear Size and Shape Variability and Implications in Cochlear Implantation Surgery

HYPOTHESIS: To study variations in cochlear size and shape with potential implications for cochlear implants. BACKGROUND: A comprehension of the cochlear morphology is essential for nontraumatic electrode insertion and hearing preservation in individual surgery. METHODS: A total of 310 normal developed cochleae with three-dimensional multiplanar reconstructed computed tomography images were studied. We measured the linear length of the half (1/2TL) and three quarters (3/4TL) of the basal turn, the first turn (1TL), the first two turns (2TL), and the cochlear length. The length and width of the cochlear base as well as the tilt angle within the first turn (α) and the angle between the first and second turns (γ) of the cochlea were also measured. RESULTS: The measurement results showed that cochlear size and shape vary greatly among individuals. The length and width of cochlear base had positive correlations with 1/2TL (r = 0.526 and r = 0.625), 3/4TL (r = 0.633 and r = 0.729), 1TL (r = 0.658 and r = 0.754), 2TL (r = 0.677 and r = 0.795) and cochlear length (r = 0.622 and r = 0.769) respectively. The mean tilt angle α was 9.72 ± 1.85 degrees while the angle γ was 14.90 ± 1.36 degrees, and both had significant positive correlations with the ratio of length to width of cochlear base (p = 0.040 and p = 0.013). CONCLUSION: The significant variations of the cochlear anatomy suggest that personalized cochlear implant is needed. The width of cochlear base has a stronger association with the linear length of cochlea. And the angle within the first turn and between the first and second turns can be predicted by the ratio of length to width of cochlear base.