Comparison of Inner Ear Volume Between Humans and Sheep Using MRI

In preclinical research, animals are used to perform clinical experiments. The use of large animals with human-like anatomies and structural size appears to be essential. For auditory function research, we needed to identify an animal model whose dimensions are close to those of the human inner ear for future research. In the present study, we investigated measurements of the human and sheep inner ear using 3 T Magnetic Resonance Imaging (MRI) to evaluate the suitability of a sheep model for studying the inner ear.

Inner ears were compared between 8 ears from 4 normal humans (women) and 8 ears from 4 normal sheep (female). Cranial MRI of both species' cochleae were acquired and analyzed, with specific measurements for key anatomical features, including the cochlea length and width, the length and width of the inner auditory canal, the number of spiral turns of the cochlea and the cochlea volume. The size ratios between sheep and human cochlear structures were calculated and compared.

Overall cochlear dimensions of the sheep were approximately 2/3 that of human cochleae across most measurements, except for the internal auditory canal. The internal auditory canal of the sheep was 1/3 of the size of that in humans. The number of spiral turns in the cochlea was equivalent between the two species.

Given the proportionally similar dimensions to humans, the sheep cochlea appears to be a promising model for inner ear research, specifically to develop pathological models, to study the pathophysiological mechanisms of inner ear diseases, and/or to improve treatment with implantable prostheses.