Organogenesis of inner ear and anomalies of inner ear in trisomy 18 syndrome studied by temporal bone histopathology

<p>Objectives: We examined the mechanism of development of inner ear malformation in trisomy 18 syndrome from embryonic inner ear organogenesis.</p><p>Methods: The histopathological specimen was from a fetus that died at 35 weeks gestation and was diagnosed with trisomy 18 by chromosomal testing.</p><p>Results: In the pathological specimen of trisomy 18, the cochlea was as short as two turns, and the apical turn was hypoplastic. The modiolus was short, and the aperture of the cochlear nerve canal was stenotic. The cochlear duct showed formation of the organ of Corti. There were no abnormalities in the outer and inner hair cells, and no abnormalities in the stria vascularis. The saccule was hypoplastic. The utricle had an otolithic membrane and sensory epithelium. The anterior semicircular canal showed a normal luminal structure. The lateral semicircular canal was hypoplastic, and no cupula formation was observed at the crista ampullaris of the lateral semicircular canals. The posterior semicircular canal had a small lumen structure and was hypoplastic.</p><p>Conclusions: The development of the cochlear duct in the membranous labyrinth appeared to have stopped at six to eight weeks of fetal life. However, the differentiation of the organ of Corti continued, and the ossification of the bone labyrinth also progressed.</p><p>Estimating from the differentiation of otoliths and semicircular canals, inner ear development progressed until about 20 weeks of fetal life.</p><p>In considering the mechanism of inner ear malformation, it was necessary to classify the process of development by separating the cochlear duct and organ of Corti in the membranous labyrinth, ossification of the bone labyrinth, and ossification of the otic capsule.</p>