New insight into the bony labyrinth: a microcomputed tomography study

To visualize and quantify the morphology and mineralization of the developing fetal human bony labyrinth, using 3D-microcomputed tomography (3D-microCT) imaging.

Eleven right temporal bones from late second and third trimester fetuses were used in this prospective pilot study. After fixation in 10% formalin solution, all samples underwent a microcomputed tomography (microCT) scan, permitting the 3D imaging of the bony labyrinth as well as the quantitative assessment of mineral density, angular distances and dimensions of inner ear components the progression of ossification was precised with histological observations.

Our findings show different rates of growth among the semicircular canals, the vestibular aqueduct, the oval window, the round window and the cochlea. The final sizes of the cochlea and round window are achieved at 23 weeks of gestation, with heights of 5mm and 2mm, respectively. The oval window reaches adult size at 35 weeks, whereas the vestibular aqueduct will attain adult size after birth. An increasing degree of torsion of each semicircular canal is observed during fetal development. The superior semicircular canal achieves adult size at 24 weeks, before the posterior and the lateral canals (25 weeks). The time-course of ossification and mineralization observed in structures and confirmed by histology.

During this developmental period poorly studied until now, our findings suggest that each part of the bony labyrinth follows distinct growth and ossification kinetics trajectories, some of these reaching their adult size only after birth.