Cochlear fluid space dimensions for six species derived from reconstructions of 3-D magnetic resonance images.

Marc Thorne,  Alec N. Salt,  John E. DeMott,  Miriam M. Henson,

O. W. Henson Jr., Sally L Gewalt.

Abstract

Objectives: To establish the dimensions and volumes of the cochlear fluid spaces.
Study Design: Fluid space volumes, lengths and cross-sectional areas were derived for the cochleae from six species; human, guinea pig, bat, rat, mouse and gerbil.
Methods: Three-dimensional reconstructions of the fluid spaces were made from magnetic resonance microscopy (MRM) images. Consecutive serial slices composed of isotropic voxels (25 µm3) representing the entire volume of fixed, isolated cochleae were obtained.  The boundaries delineating the fluid spaces, including Reissner's membrane, were resolved for all specimens, except for  the human, in which Reissner's membrane was not consistently resolved. Three-dimensional reconstructions of the endolymphatic and perilymphatic fluid spaces were generated.  Fluid space length and variation of cross-sectional area with distance were derived by an algorithm which followed the mid-point of the space along the length of the spiral. The total volume of each fluid space was derived from a voxel count for each specimen.
Results: Length, volume and cross-sectional areas are provided for 6 species. In all cases, the length of the endolymphatic fluid space was consistently longer than that of either perilymphatic scala, primarily as a result of a greater radius of curvature.  For guinea pig specimens, the measured volumes of the fluid spaces were considerably lower than those suggested by previous reports based on histological data.
Conclusions: The quantification of cochlear fluid spaces provided by this study will enable the more accurate calculation of drug and other solute movements in fluids of the inner ear during  experimental or clinical manipulations.
 

This study was supported by the National Institutes of Health through the National Institute on Deafness and other Communication Disorders, Grant number DC01368

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