Background: Recent advances in the techniques of MRI have enabled us to visualize and measure the endolymphatic spaces in the inner ear, leading to a new paradigm for the diagnosis of Meniere's disease and other inner ear disorders. For proper interpretation of inner-ear MRI, otolaryngologists and radiologists need to have a precise understanding of the three-dimensional (3D) configuration of each compartment in the membranous labyrinth. However, resources for learning the complex anatomy of the bony and membranous labyrinth have been remained limited to histological sections. The aim of the present study was to provide serial images as reference information for a more precise interpretation of inner-ear MRI.

　Methods: We used 3D model data, that are freely available, of a healthy human inner ear, including the cochlear duct, the saccule, the utricle, the three semicircular canals, and the bony labyrinth, generated by micro-computed tomographic scanning. The 3D model was converted into serial images on the axial plane using a computational approach. The endolymphatic and perilymphatic spaces are shown in black and gray, respectively. The area ratio of the endolymphatic space to the sum of the endolymphatic and perilymphatic spaces in the vestibule was calculated for each section.

　Results: Serial cross-sectional images similar to delayed intravenous contrast-enhanced MRI in the normal ear were obtained. The images clearly illustrate the anatomical orientation of the cochlear duct, the saccule, the utricle, and the ampullae and duct of the semicircular canals. The calculated area ratio of the endolymphatic space in the vestibule was up to 61%.

　Conclusion: These serial images can be a powerful educational resource for understanding the relationship of the 3D anatomy of the endolymphatic spaces and the 2D morphology seen in inner-ear MRI.