Aims: To establish normative data on the size of the basal turn of the cochlea using high-resolution computed tomography of the temporal bone in adults and children. To determine whether final insertion depth angle for a perimodiolar cochlear implant electrode varies according to cochlear size. Methods: Forty-two patients screened for cochlear anomaly using computed tomography were randomly selected from patients with otologic disease. Reconstruction of the full basal turn was performed for both ears using a 1.0-mm layer, minimum intensity projection. The largest distance from the round window to the lateral wall (distance A) and the perpendicular distance (B) were measured. Distances were averaged between ears for each individual. In addition, 15 patients were implanted with the Nucleus 24 Contour Advance electrode array using a linear insertion depth of either 17 mm (n = 9) or 19 mm (n = 6). Postoperative X-rays were analyzed using the method of Xu et al. [Am J Otol 2000;21:49–56] to obtain the insertion depth angles for individual electrodes. Results: Mean distance A was 9.23 mm (SD = 0.53, range 7.9–10.8 mm). Perpendicular distance B was significantly correlated with distance A (r2 = 0.57, p < 0.001). The mean difference in insertion depth angle between the 17 and 19 mm groups was 80°. A statistically significant correlation (r2 = 0.51) was found between distance A and the insertion depth angle for the 17 mm group. Conclusions: The cochlear size measure distance A was repeatable to within the resolution of the high-resolution computed tomography image data. The basal turn of the normally formed cochlea is variable in size. These variations in size would produce >5.0 mm variation in the length of the lateral wall to the point consistent with an insertion depth angle of 360°. Cochlear size influenced final insertion depth angles obtained for the perimodiolar Nucleus 24 Contour Advance electrode.

Adunka O, Unkelbach MH, Mack MG, et al: Predicting basal cochlear length for electric-acoustic stimulation. Arch Otolaryngol Head Neck Surg 2005;131:488–492.
Dimopoulos P, Muren C: Anatomic variations of the cochlea and relations to other temporal bone structures. Acta Radiol 1990;31:439–444.
Fraysse B, Ramos A, Sterkers O, et al: Residual hearing conservation and electro-acoustic stimulation with the Nucleus 24 Contour Advance cochlear implant. Otol Neurotol 2006;27:624–633.
Greenwood DD: A cochlear frequency-position function for several species – 29 years later. J Acoust Soc Am 1990;87:2592–2605.
Gstoettner W, Kiefer J, Baumgartner WD, Pok S, Peters S, Adunka O: Hearing preservation in cochlear implantation for electric acoustic stimulation. Acta Otolaryngol 2004;124:348–352.
Hardy M: The length of the organ of Corti in man. Am J Anat 1938;62:291–311.
James C, Albegger K, Battmer R, Burdo S, Deggouj N, Deguine O, Dillier N, Gersdorff M, Laszig R, Lenarz T, Manrique Rodriguez M, Mondain M, Offeciers E, Ramos Macias A, Ramsden R, Sterkers O, von Wallenberg E, Weber B, Fraysse B: Preservation of residual hearing with cochlear implantation: how and why. Acta Otolaryngol 2005;125:481–491.
Kawano A, Seldon HL, Clark GM: Computer-aided three-dimensional construction in human cochlear maps: measurement of the lengths of organ of Corti outer wall, inner wall and Rosenthal’s canal. Ann Otol Rhinol Laryngol 1996;105:701–709.
Ketten DR, Skinner MW, Wang G, Vannier MW, Gates GA, Neely JG: In vivo measures of cochlear length and insertion depth of Nucleus cochlear implant electrode arrays. Ann Otol Rhinol Laryngol 1998;107:1–16.
Skarzynski H, Lorens A, Piotrowska A: A new method of partial deafness treatment. Med Sci Monit 2003;9:CS20–CS24.
Xu J, Xu SA, Cohen LT, Clark GM: Cochlear view: postoperative radiography for cochlear implantation. Am J Otol 2000;21:49–56.
Yoo SK, Wang G, Rubinstein JT, Vannier MW: Three-dimensional geometric modeling of the cochlea using helico-spiral approximation. IEEE Trans Biomed Eng 2000;47:1392–1402.
Copyright / Drug Dosage / Disclaimer
Copyright: All rights reserved. No part of this publication may be translated into other languages, reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying, recording, microcopying, or by any information storage and retrieval system, without permission in writing from the publisher.
Drug Dosage: The authors and the publisher have exerted every effort to ensure that drug selection and dosage set forth in this text are in accord with current recommendations and practice at the time of publication. However, in view of ongoing research, changes in government regulations, and the constant flow of information relating to drug therapy and drug reactions, the reader is urged to check the package insert for each drug for any changes in indications and dosage and for added warnings and precautions. This is particularly important when the recommended agent is a new and/or infrequently employed drug.
Disclaimer: The statements, opinions and data contained in this publication are solely those of the individual authors and contributors and not of the publishers and the editor(s). The appearance of advertisements or/and product references in the publication is not a warranty, endorsement, or approval of the products or services advertised or of their effectiveness, quality or safety. The publisher and the editor(s) disclaim responsibility for any injury to persons or property resulting from any ideas, methods, instructions or products referred to in the content or advertisements.
You do not currently have access to this content.