Abstract
Little is known about middle and inner ear development during the second and third parts of human fetal life. Using ultra-high resolution Microcomputed Tomography coupled with bone histology, we performed the first quantitative middle and inner ear ossification/mineralization evaluation of fetuses between 17 and 39 weeks of gestational age. We show distinct ossification paces between ossicles, with a belated development of the stapes. A complete cochlear bony covering is observed within the time-frame of the onset of hearing, whereas distinct time courses of ossification for semicircular canal envelopes are observed in relation to the start of vestibular functions. The study evidences a spatio-temporal relationship between middle and inner ear structure development and the onset of hearing and balance, critical senses for the fetal adaptation to birth.
Highlights
Different patterns of inner ear developments have been suggested, some advocating a prenatal maturation of the bony labyrinth based on the observation of complete ossification of the surrounding otic capsule by seven months in utero[4], and others claiming that the temporal bone undergoes further postnatal changes[5]
In most previous works, investigations of fetal inner and middle ear ossification in human fetuses were based on histological examination of decalcified temporal bones specimens[6] and/or on three-dimensional (3D) images extrapolated from serial histological slices[7], which made accurate measurements quite challenging
In order to provide a more comprehensive information of human ear development, we describe in the present report the use of two complementary techniques so far never integrated for this purpose, namely μCT and undecalcified histomorphometry for the spatio-temporal evaluation of both middle and inner ear ossification and mineralization in fetuses from 17 to 39 weeks of gestational age
Summary
On the posterior part of the membranous labyrinth, the inner ear balance system consists of three semicircular canals (SCC), functioning as gyroscopes which detect rotations, and two gravity receptors, the utricule and saccule (otolith system) which respond to both linear acceleration and gravity These structures allow the vestibule to act as a high sensitive sensor, which detects head movements along any axis, and serves three main functions: (1) the control of spinal reflexes involved in posture www.nature.com/scientificreports/. The development in the bone and skeletal research field of histological and histomorphometric techniques for imaging in praiseworthy morphological details[11] and analyzing quantitatively[12] undecalcified specimens has allowed for years the direct evaluation of human bone structure, development and remodeling Such detailed analysis is of direct relevance to the fields of audiology and otologic surgery in order to develop accurate diagnosis, better operation and care strategies. In order to provide a more comprehensive information of human ear development, we describe in the present report the use of two complementary techniques so far never integrated for this purpose, namely μCT and undecalcified histomorphometry for the spatio-temporal evaluation of both middle and inner ear ossification and mineralization in fetuses from 17 to 39 weeks (wks) of gestational age
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