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Ontogeny of the human fetal tongue, mandible, and hyoid cartilage Khayat, Raid


BACKGROUND: Growth characteristics of the human craniofacial region during the fetal stages of development remain largely unexplored. This project investigates the growth of the human tongue, mandible and hyoid cartilage, during the early fetal stage, using a rare collection of preserved fetal head tissues. These structures differ in the tissue types that they are comprised of, however, they share common developmental origins. We hypothesized that the growth of these tissues exhibits a strong positive correlation during prenatal human life. MATERIALS AND METHODS: Human fetal heads were obtained from elective terminations between nine and nineteen postconceptional weeks (n=16). They were contrast-enhanced with phosphotungstic acid (PTA) and imaged with high-resolution micro-CT. Segmentation of the tongue, mandible, and hyoid cartilage was performed, three-dimensional models were constructed, and their volumes were calculated. To assess the relationship between the variables, correlations between different tissues were determined. Additionally, regression analyses were performed after normalization of data to permit comparisons between the different tissues. A single-rater interclass correlation coefficient was performed for 5 randomly selected samples, to study the measurement reliability. iii RESULTS: PTA contrast enhancement provides excellent visualization and allows for accurate digital segmentation of hard and soft tissues of the craniofacial regions in the fetal head samples. Pearson’s correlation coefficients of 0.96, 0.85, and 0.91 were calculated between the growth of the tongue – hyoid, tongue – mandible, and mandible-hyoid, respectively. The mandibular bone showed a similar growth trajectory as the tongue and the hyoid cartilage. However, the growth of the tongue was found to precede the mandibular growth, albeit slightly, at day 109.6 pc. Interclass correlation coefficient for all repeated measurements were > 0.9 with a P < .001. CONCLUSION: Contrast-enhancement followed by high-resolution 3D scanning provides an important resource to study hard-soft tissue correlations within the fetal craniofacial region during development. Our data indicate a strong positive correlation between the tongue, mandible, and hyoid cartilage, during the early fetal stage of human growth. These structures seem to begin a growth spurt between the end of the 13th to the 15th postconceptional weeks.

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