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Original Investigation |

The Effect of Round Window vs Cochleostomy Surgical Approaches on Cochlear Implant Electrode Position A Flat-Panel Computed Tomography Study

Nicole T. Jiam, BA1,2; Patpong Jiradejvong, MS2; Monica S. Pearl, MD3; Charles J. Limb, MD2
[+] Author Affiliations
1Medical student, Johns Hopkins University School of Medicine, Baltimore, Maryland
2Department of Otolaryngology–Head and Neck Surgery, University of California San Francisco School of Medicine
3Department of Radiology, Johns Hopkins University School of Medicine, Baltimore, Maryland
JAMA Otolaryngol Head Neck Surg. 2016;142(9):873-880. doi:10.1001/jamaoto.2016.1512.
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Importance  The round window insertion (RWI) and cochleostomy approaches are the 2 most common surgical techniques used in cochlear implantation (CI). However, there is no consensus on which approach is ideal for electrode array insertion, in part because visualization of intracochlear electrode position is challenging, so postoperative assessment of intracochlear electrode contact is lacking.

Objective  To measure and compare electrode array position between RWI and cochleostomy approaches for CI insertion.

Design, Setting, and Participants  Retrospective case-comparison study of 17 CI users with Med-El standard-length electrode arrays who underwent flat-panel computed tomography scans after CI surgery at a tertiary referral center. The data was analyzed in October 2015.

Exposures  Flat-panel computed tomography scans were collected between January 1 and August 31, 2013, for 22 electrode arrays. The surgical technique was identified by a combination of operative notes and imaging. Eight cochleae underwent RWI and 14 cochleae underwent cochleostomy approaches anterior and inferior to the round window.

Main Outcomes and Measures  Interscalar electrode position and electrode centroid distance to the osseous spiral lamina, lateral bony wall, and central axis of the modiolus.

Results  Nine participants were men, and 8, women; the mean age was 54.4 (range, 21-64) years. Electrode position was significantly closer to cochlear neural elements with RWI than cochleostomy approaches. Between the 2 surgical approaches, the RWI technique produced shorter distances between the electrode and the modiolus (mean difference, −0.33 [95% CI, −0.29 to −0.39] mm in the apical electrode; −1.42 [95% CI, −1.24 to −1.57] mm in the basal electrode). This difference, which was most prominent in the first third and latter third of the basal turn, decreased after the basal turn.

Conclusions and Relevance  The RWI approach was associated with an increased likelihood of perimodiolar placement. Opting to use RWI over cochleostomy approaches in CI candidates may position electrodes closer to cochlear neural substrates and minimize current spread. These findings need to be interpreted in light of the increased potential for osseous spiral lamina trauma with reduced distances between the electrode array and modiolus.

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Figure 1.
Flat-Panel Computed Tomography (CT) Visualization of the Electrode Array With Respect to the Round Window

A, The round window (black arrowhead) is visualized on an oblique coronal view of the cochlea. B, The electrode array is observed to be anterior to the round window (black arrowhead) and is inserted at the site demarcated by the white arrowhead. C, The electrode array is traced in 3 dimensions (3D) and visualized in 3 different windows (coronal, axial, and sagittal oblique views) using the 3D curved multiplanar reconstruction settings. D, A bony cleft (blue arrowhead) sits between the round window (black arrowhead) and the electrode array insertion site (white arrowhead). The red line tracing depicts the cochlear implant on a 2D CT image. This tracing helps demonstrate the site of the electrode array insertion because the line is a dark red at that particular location. The shades of red provide spatial depth to the figure by indicating how close the line tracing is to that particular cut of the CT. Darker shades of red are used to illustrate portions of the electrode array that are spatially close to the CT cut, whereas lighter shades of red are used to demonstrate portions of the electrode array that are more distal to the CT section at present view.

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Figure 2.
Sagittal and Coronal Oblique Views of the Cochlea

The top 8 images in each panel make up the round window insertion group and the remaining 14 images make up the cochleostomy group. Red dots indicate the 12 electrode contacts in the standard electrode array. Numeric identifiers indicate individual patients (demographic characteristics are detailed in the eTable in the Supplement). L indicates cochlear implant in the left ear, and R, in the right ear.

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Figure 3.
Example of a Digital Composite Image

A, Preoperation multislice computed tomography (CT) scan. B, Postoperation flat-panel CT secondary reconstruction. C, Algorithmically constructed digital composite image of A (green color channel) and B (purple color channel).

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Figure 4.
Electrode Centroid Distance in Millimeters From 3 Landmarks

Electrodes are designated in numerical order, where 1 is the most basal electrode and 12 is the most apical electrode. Error bars indicate 95% confidence intervals, and dots, individual patients.

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