Cochlear Fluid Space Dimensions for Six Species Derived From Reconstructions of Three‐Dimensional Magnetic Resonance Images

TLDR

The study aims to determine the dimensions and volumes of cochlear fluid spaces in six species (human, guinea pig, bat, rat, mouse, and gerbil). Using magnetic resonance microscopy, the authors reconstructed cochlear fluid spaces from isotropic 25‑µm³ serial slices and quantified length, cross‑sectional area, and volume via voxel counting and a midpoint‑following algorithm. The reconstructions revealed that endolymphatic spaces are consistently longer than perilymphatic scalae, Reissner's membrane was unresolved in human specimens, guinea pig fluid volumes were lower than prior histology, and the quantified dimensions will aid accurate modeling of solute transport in the inner ear.

Abstract

To establish the dimensions and volumes of the cochlear fluid spaces.Fluid space volumes, lengths, and cross-sectional areas were derived for the cochleas from six species: human, guinea pig, bat, rat, mouse, and gerbil.Three-dimensional reconstructions of the fluid spaces were made from magnetic resonance microscopy (MRM) images. Consecutive serial slices composed of isotropic voxels (25 microm3) representing the entire volume of fixed, isolated cochleas 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 that followed the midpoint 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.Length, volume, and cross-sectional areas are provided for six 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.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.