Shinichiro Hashimoto

Three-Dimensional Analysis of Morphological Aspects of the Human Saccular Macula

The 3-dimensional shape of the human saccular macula and its orientation in the skull were quantitated in this study. The semicircular canals and saccular maculae were reconstructed 3-dimensionally on a computer from 3 human temporal bones. The 380 to 522 triangles in the entire area of the saccular macula were made by drawing lines between 2 adjacent points every 100-μm width of the saccular macula in each section. The angles between each triangle and each estimated standard axis in the skull obtained were calculated. This information will provide standard data regarding the 3-dimensional morphological aspects of the saccular macula for further investigations of the function of the sacculus. It was determined that the 3-dimensional shape of the saccular macula was not a plane, but was a curved surface like that of an ellipsoid. It is thought that this shape is necessary in order for the saccular macula to detect wide-range linear acceleration.

Three-Dimensional Reconstruction of the Human Semicircular Canals and Measurement of Each Membranous Canal Plane Defined by Reid's Stereotactic Coordinates

Objectives: Equations for estimating the planar relationships of the human semicircular canals were devised by Blanks et al from a dissected bony labyrinth in a human skull. However, a similar study on the membranous semicircular canal planes has never been published. Methods: In this study, the angle between each membranous canal plane and Reids stereotactic horizontal plane was measured on serial histologic sections of 7 temporal bones from Japanese adults. We reconstructed the 3 semicircular canals by computer-aided 3-dimensional analysis. The angles between each pair of both bony and membranous canal planes were measured. Results: In the bony labyrinth, the angles between the 2 canal planes of the lateral-anterior, anterior-posterior, and lateral-posterior pairs were 90.51° ± 2.98° (mean ± SD), 91.70° ± 1.85°, and 94.52° ± 3.32°, respectively. The angles between the 2 membranous canal planes of the lateral-anterior, anterior-posterior, and lateral-posterior pairs were 90.05° ± 4.74°, 91.03° ± 2.93°, and 91.92° ± 5.22°, respectively. Conclusions: The data from our study of the membranous labyrinth showed that the angles between each canal plane and the others were much closer to 90° than was found by Blanks et al for the bony labyrinth.