Morphogenesis of the middle ear ossicles and spatial relationships with the external and inner ears during the embryonic period

Abstract

We describe the three-dimensional morphogenesis of the middle ear ossicles (MEOs) according to Carnegie stage (CS) in human embryos. Seventeen samples including 33 MEOs from CS18 to 23 were selected from the Kyoto Collection. The primordia of the MEOs and related structures were histologically observed and three-dimensionally reconstructed from digital images. The timing of chondrogenesis was variable among structures. The stapes was recognizable as a vague condensation of the mesenchymal cells in all samples from CS18, whereas the malleus and incus were recognizable at CS19. Chondrogenesis of all MEOs was evident in all samples after CS21. The chondrocranium was recognizable in all samples by CS18, and the perichondrium border of the auricular cartilage and otic capsule was distinct in all samples at CS23. At CS19, the MEOs were positioned in the anterior to posterior direction, following the order malleus, incus, stapes, which adjusted gradually during development. The MEOs connected in all samples after CS22. The stapes was located close to the vestibular part of the inner ear, although the basal part was not differentiated into the "footplate" form, even at CS23. The handles of the malleus were close to the tubotympanic recess at CS23, but were distant from the external auditory meatus. Determining the timeline of the formation of MEOs and connection of the external and inner ears can be informative for understanding hearing loss caused by failure of this connection. These data may provide a useful standard for morphogenesis, and will contribute to distinguishing between normal and abnormal MEO development. Anat Rec, 299:1325-1337, 2016. © 2016 Wiley Periodicals, Inc.

Development of the Human Incus With Special Reference to the Detachment From the Chondrocranium to be Transferred into the Middle Ear

“…Mesenchyme in the first pharyngeal arch seems to form the incus as well as Meckel's cartilage, but the origin of the first pharyngeal arch should not be considered equivalent to the origin of Meckel's cartilage. According Ozeki-Satoh et al 2016, the incus was no contiguous with the malleus at CS 19.…”

Morphogenesis of the Middle Ear during Fetal Development as Observed Via Magnetic Resonance Imaging

“…This study is the first observe the initiation of TC formation using 3D imaging methods. Our previous study involving histological sections revealed that the handle of the malleus approached the tubotympanic recess—which later differentiates into the TC—while remaining distant from the external auditory meatus at CS23 (Ozeki‐Satoh et al, ). In samples exhibiting a CRL of 86 mm, the recess contained a thin yet distinct cavity attached to the external auditory meatus on the convex surface, which later developed into the tympanic membrane.…”

“…The os goniale becomes ossified between 26.5 and 34 mm CRL, corresponding to CS23 or later. Previously, we detected the os goniale in histological sections, as this structure is too thin to observe using MRI or phase‐contrast computed tomography (CT) due to limitations in resolution (Ozeki‐Satoh et al, ). Previous studies have reported attachment of the anterior process to the main region in fetuses with a CRL of 120 mm (Richany et al, ), 85 mm, and 93 mm (Rodríquez‐Vázquez et al, 1991).…”

“…Recently, our research group has utilized serial histological sections to investigate the morphogenesis of the middle ear, which corresponds to the period of MEO cartilage formation (Ozeki‐Satoh et al, ). Our findings also demonstrated the 3D position and relationship of the MEOs to the external auditory meatus and inner ear, providing useful information regarding the morphological growth processes of the middle ear in the embryonic period between CS18 and CS23.…”

3D Analysis of Human Embryos and Fetuses Using Digitized Datasets From the Kyoto Collection

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