gms | German Medical Science

Fourth International Symposium and Workshops: Objective Measures in Cochlear Implants

Medical University of Hannover

01.06. bis 04.06.2005, Hannover

Use of pre-operative CT imaging for optimizing hearing preservation with cochlear implantation

Meeting Abstract

  • corresponding author C. James - Service ORL, Hôpital Purpan, Toulouse, France
  • B. Fraysse - Hôpital Purpan, Toulouse
  • O. Deguine - Hôpital Purpan, Toulouse
  • A. Sevely - Hôpital Purpan, Toulouse
  • C. Cognard - Hôpital Purpan, Toulouse
  • B. Escudé - Clinique Pasteur, Toulouse

Medical University of Hannover, Department of Otolaryngology. Fourth International Symposium and Workshops: Objective Measures in Cochlear Implants. Hannover, 01.-04.06.2005. Düsseldorf, Köln: German Medical Science; 2005. Doc05omci066

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Veröffentlicht: 31. Mai 2005

© 2005 James et al.
Dieser Artikel ist ein Open Access-Artikel und steht unter den Creative Commons Lizenzbedingungen (http://creativecommons.org/licenses/by-nc-nd/3.0/deed.de). Er darf vervielf&aauml;ltigt, verbreitet und &oauml;ffentlich zug&aauml;nglich gemacht werden, vorausgesetzt dass Autor und Quelle genannt werden.


Gliederung

Text

Introduction

To determine the feasibility of using pre-operative high resolution CT images as an aid in limiting depth of insertion of cochlear implant electrodes in order to better preserve low-frequency residual hearing. Recent results for hearing conservation with the Nucleus 24 Contour Advance electrode array show that where insertion depths exceed 400 degrees there is a rapid decrease in hearing conservation despite soft-surgery procedures being strictly adhered to. In addition, insertion depth angles vary considerably from 300° to 430° degrees.

Materials and Methods

Pre-operative CT scans were analysed using rotational tomography software. A two dimensional view of the basal turn of the cochlea was developed by displaying the darkest voxels in a 1.0 mm layer. A characteristic measure of cochlear size was obtained by finding the largest distance between the round window and the lateral wall. Post-operative X-rays were obtained from patients implanted with the Nucleus 24 Contour Advance electrode array using a linear insertion depth of 17mm in order to better preserve residual hearing for electro-acoustic stimulation. These X-rays were analysed using the method of Xu to obtain the insertion depth angles for individual electrodes.

Results

The largest distance between the round window and the lateral wall varied between 8.6 and 10.0 mm (e.g a range of 1.4 mm). The mean variation of insertion depth angle with linear distance for apical electrodes was computed as 48.2°/mm.

Conclusions

Variations in cochlear size may thus account for significant variations in insertion depth angle, approximately 50°/mm. Thus, in small cochleae, further reducing the length of electrode introduced by 1.0 mm may better conserve low-frequency hearing without compromising access to spiral ganglia with characteristic frequencies at and above 500Hz.