Fine structures of the human fetal cochlea were observed by scanning electron microscopy. The study aimed to make the knowledge on the developmental microanatomy of the cochlea more accurate. The temporal bones of fetuses were removed and the membranous portions of the cochleas were prepared for observation.
In a 14-week 6-day old fetus, the hair cells were arranged mainly in four rows. The sensory hairs differed in appearance from those in the adults. The innermost or first row hair cells corresponded to the inner hair cells and revealed certain characteristic structures. From the second to the third or outermost row, a rather uniform hair pattern with a bud-like appearance was noted. Neither W nor V letter formation of sensory hairs was found. One strong kinocilium was identified with its thick base; it was located lateral to the outermost stereocilia.
With older fetuses, 22 weeks 2 days and 24 weeks 0 day of age, the hair patterns closely resembled those of the adult with the exception of the presence of a short kinocilium on the outer hair cells and a slim kinocilium on the inner hair cells.
The present study indicates that structures including the sensory hairs and their attachment to the tectorial membrane, the Reissner's membrane and the stria vascularis essentially complete their morphological development in 6 months after gestation.