Extracting the Cochlea from a Human Temporal Bone: A Cadaveric Protocol

Summary

This article presents a reliable method for extracting the human cochlea from the cadaver temporal bone by drill-out while following distinct anatomical landmarks.

Abstract

The extraction of the cochlea from a cadaver human temporal bone may be required for different studies of the inner ear. For histological evaluations, the inner ear must be extracted from the temporal bone to facilitate histologic processing; likewise, some micro-computed tomography devices are too small to accommodate the complete temporal bones; additionally, the image quality can be enhanced when the cochlea is isolated.

The inner ear is located within the petrous part of the temporal bone. The inner ear can be divided into the osseous labyrinth or otic capsule and the membranous labyrinth inside the otic capsule. Furthermore, the inner ear can be divided into the vestibular system (the semicircular canals and the vestibule) and the cochlea. The appreciation of the location and orientation of the cochlea within the temporal bone is difficult, as it is embedded within bony structures and thus cannot be directly visualized. Nevertheless, there are distinct anatomical structures that can help guide the process to allow a reliable drill-out of the cochlea. The landmarks in the posterior parts of the cochlea are the facial nerve, semicircular canals, and the vestibule. In the middle, the inferior borders of the cochlea are identified by the round window and the basal turn of the cochlea. In the anterior border, one encounters the carotid artery; the landmark for the superior border is the genicular ganglion (GG) of the facial nerve. The medial structures are determined by the locations of the internal auditory canal, the superior semicircular canal, and the canal of the internal carotid artery.

In this article, we present a method for extracting the cochlea reliably out of the temporal bone by drill-out while following several anatomical landmarks.

Introduction

The inner ear is a delicate organ that provides us with the sense of hearing and balance. The inner ear is located at the base of the skull in the petrous part of the temporal bone (TB). The TB encases several crucial anatomical structures that twist and turn inside the bone. Thus, the TB forms a challenging anatomical entity to comprehend¹. Rask-Andersen et al., in their review^2,discuss the history of cochlea research and understanding of its microstructures.

The inner ear includes the semicircular canals, the vestibulum, and the cochlea. The three semicircular canals and the vesti....

Protocol

This study used temporal bones (TB) gathered from the human cadaver subject post-mortem. The study was granted Institutional approval and fulfilled the Helsinki Declaration for the ethical use of human material. Approval for cadaver temporal bones was granted to the Kuopio University Hospital by the Finnish National Supervisory Authority for Welfare and Health (NRO: 9202/06.01.03.01/2013), and the study was conducted following Finnish regulations and laws. All of the bones were gathered anonymously during medical autopsy.......

Discussion

There are several landmarks to be followed for removing the cochlea, so this procedure can be done systematically if the anatomy in the TB is normal (no malformations of the TB). The most critical parts of the removal procedure are the inferior margin and medial proportion between the IAC and the ICA. We recommend maintaining a slightly greater margin and, if necessary, precisely honing any excess bone after extracting the block. It is important to avoid opening the cochlea as it might cause trauma to its delicate inner .......

Materials

Name	Company	Catalog Number	Comments
Drillblades for Drill		N/A	See below. Drillblades should be suitable for your drill system
High speed surgical drill	Medtronic	https://www.medtronic.com/us-en/healthcare-professionals/products/neurological/powered-surgical-instruments/midas-rex-mr8.html	There are numerous providers from various different cateories for surgical drills. The one with irrigation system is recommended (e.g.,Stryker, Bbraun, Medtronic, etc.)
Operating Microscope	Zeiss	https://www.leica-microsystems.com/products/surgical-microscopes/	Microscope for microsurcigal preparation of the temporal bone. Higly recommended microscopes include Zeiss, Leica, etc.
Temporal Bone holder	Stortz	N/A	Cup to fixate the temporal bone while drilling