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Surgical Anatomy of the Human Round Window Region

Implication for Cochlear Endoscopy Through the External Auditory Canal

Fujita, Takeshi; Shin, Jung Eun; Cunnane, MaryBeth; Fujita, Kyoko; Henein, Simon; Psaltis, Demetri; Stankovic, Konstantina M.

doi: 10.1097/MAO.0000000000001074

Objective: To enable development of an endoscope for cellular-level optical imaging of the inner ear.

Study Design: A prospective study of 50 cadaveric human temporal bones to define detailed surgical anatomy of the round window (RW) region and the range of angles necessary to reach the RW membrane perpendicularly via the external ear canal.

Main Outcome Measure: The transcanal angle to the RW membrane was surgically measured in 3D intact specimens, and correlated with the angle calculated from temporal bone computed tomography (CT) scans of the same specimens obtained before and after measurements in situ.

Results: Surgically measured transcanal angles to the RW membrane correlated well with the radiographically measured angles. The angles ranged from 110 to 127 degrees, with the median of 115 degrees and the middle 50% ranging from 109 to 119 degrees. Four temporal bones were excluded because of pathology. The opening of the RW niche was located posteriorly in six bones (13%), inferiorly in 18 bones (39%), and postero-inferiorly in 22 bones (48%). The angles were not statistically different among the three orientations of the RW niche.

Conclusions: By correlating measurement from cadaveric human temporal bones and their CT scans, we defined key parameters necessary for designing an endoscope for intracochlear imaging using a minimally invasive approach through the external auditory canal. The excellent correlation between the measurement on the CT scan and the actual shape of the probe that was able to reach the RW through the ear canal enables selection of the probe using the CT data.

*Eaton Peabody Laboratories, Department of Otolaryngology, Massachusetts Eye and Ear Infirmary, Boston, Massachusetts

Department of Otology and Laryngology

Department of Radiology, Harvard Medical School, Boston, Massachusetts

§Department of Otorhinolaryngology–Head and Neck Surgery, Konkuk University Medical Center, Seoul, South Korea

||School of Engineering, École Polytechnique Fédérale de Laussane (EPFL), Lausanne, Switzerland

Address correspondence and reprint requests to Konstantina M. Stankovic, 243 Charles St Boston, MA 02114, U.S.A.; E-mail:

Authors Takeshi Fujita and Jung Eun Shin contributed equally.

This project was supported by the Bertarelli Foundation (DP, KMS), Wyss Center for Bio and Neuroengineering (DP, KMS), Lauer Tinnitus Research Center (KMS), and Nancy Sayles Day Foundation (KMS).

The authors disclose no conflicts of interest.

Copyright © 2016 by Otology & Neurotology, Inc. Image copyright © 2010 Wolters Kluwer Health/Anatomical Chart Company