Anatomical appearances of endolymphatic sac in three laboratory rodents

Objective To explore the anatomical location of endolymphatic sac (ES) and its similarities and differences among common laboratory animals, in order to provide an anatomical basis for endolymphatic sac disease studies. Methods Adult guinea pigs, SD rats and KM mice were selected. The bilateral temporal and occipital bone were removed, and ES location and its adjacent landmarks were identified. Then the occipital and temporal bone were separated and vestibular aqueduct external aperture was marked. Histological sections were utilized for verification of our works. Results All endolymphatic sacs were located posteroinferior to the internal auditory canal and lateral to the bone cover beneath the posterior semicircular canal. Those bone covers showed different physical appearance in the three common laboratory rodents. The bone cover was a thin bone plate in guinea pigs, a long apophysis in SD rats, and a slightly longer apophysis in KM mice. Vestibular aqueduct external orifice could be seen under the bone cover clearly. It was verified with the histological section results. Conclusion The anatomical location of ES is roughly the same among the three common rodent animals, only anatomical marks or histomorphology shows slight differences.