A 3D analysis of growth trajectory and integration during early human prenatal facial growth

Sella turcica and facial bones: Morphological integration in the human fetal cranium

OBJECTIVES

The cranial base plays a significant role in facial growth, and closer analyses of the morphological relationship between these two regions are needed to understand the morphogenesis of the face. Here, we aimed to study morphological integration between the sella turcica (ST) and facial bones during the fetal period using geometric morphometrics.

MATERIALS AND METHODS

Magnetic resonance images of 47 human fetuses in the Kyoto Collection, with crown-rump lengths of 29.8-225 mm, were included in this study. Anatomical homologous landmarks and semilandmarks were registered on the facial bones and the midsagittal contour of the ST, respectively. The shape variations in the craniofacial skeleton and the ST were statistically investigated by reducing dimensionality using principal component analysis (PCA). Subsequently, the morphological integration between the facial bones and ST was investigated using two-block partial least squares (2B-PLS) analysis.

RESULTS

PCA showed that small specimens represented the concave facial profile, including the mandibular protrusion and maxillary retrusion. The 2B-PLS showed a strong integration (RV coefficient = 0.523, r = .79, p < .01) between the facial bones and ST. The curvature of the anterior wall of the ST was highly associated with immature facial morphology characterized by a concave profile.

CONCLUSION

The strong integration between the two regions suggested that the anterior ST may be associated with facial morphology. This result quantitatively confirms previous studies reporting ST deformities in facial anomalies and induces further research using postnatal subjects.

A Geometric Morphometric Study on Sexual Dimorphism in Viscerocranium

The level of sexual dimorphism manifested by human bones is an important factor for development of effective sex estimation methods. The aim of the study was to investigate the sexual dimorphism in the size and shape of the viscerocranium using geometric morphometric techniques. It also aimed to explore the sex differences in distinct viscerocranial regions and to establish the most dimorphic region with regard to size and shape. Computed tomography images of 156 males and 184 females were used in the study. Three-dimensional coordinates of 31 landmarks were acquired. Five landmark configurations were constructed from the viscerocranium and its orbital, nasal, maxillary, and zygomatic region. Generalized Procrustes superimposition, principal component analysis, and discriminant analysis were applied to each configuration. The significance of the sex differences in size and shape was assessed and significant differences were found in all configurations. The highest accuracy was obtained from both shape and size of the whole viscerocranium. Based on size only, the highest accuracy was achieved by the nasal region. The accuracy based on shape was generally low for all configurations, but the highest result was attained by the orbital region. Hence, size is a better sex discriminator than shape.

Morphometric analysis of secondary palate development in human embryos

Rapid shelf elevation and contact of the secondary palate and fusion reportedly occur due to a growth-related equilibrium change in the structures within the oro-nasal cavity. This study aimed to quantitatively evaluate complex three-dimensional morphological changes and their effects on rapid movements, such as shelf elevation and contact, and fusion. Morphological changes during secondary palate formation were analyzed using high-resolution digitalized imaging data (phase-contrast X-ray computed tomography and magnetic resonance images) obtained from 22 human embryonic and fetal samples. The three-dimensional images of the oro-nasal structures, including the maxilla, palate, pterygoid hamulus, tongue, Meckel's cartilage, nasal cavity, pharyngeal cavity, and nasal septum, were reconstructed manually. The palatal shelves were not elevated in all the samples at Carnegie stage (CS)21 and CS22 and in three samples at CS23. In contrast, the palatal shelves were elevated but not in contact in one sample at CS23. Further, the palatal shelves were elevated and fused in the remaining four samples at CS23 and all three samples from the early fetal period. For each sample, 70 landmarks were subjected to Procrustes and principal component (PC) analysis. PC-1 accounted for 67.4% of the extracted gross changes before and after shelf elevations. Notably, the PC-1 values of the negative and positive value groups differed significantly. The PC-2 value changed during the phases in which the change in the PC-1 value was unnaturally slow and stopped at CS22 and the first half of CS23. This period, defined as the "approach period", corresponds to the time before dynamic changes occur as the palatal shelves elevate, the tongue and mandibular tip change their position and shape, and secondary palatal shelves contact and fuse. During the "approach period", measurements of PC-2 changes showed that structures on the mandible (Meckel's cartilage and tongue) and maxilla (palate and nasal cavity) did not change positions, albeit both groups of structures appeared to be compressed anterior-posteriorly. However, during and after shelf elevation, measurements of PC-1 changes showed significant changes between maxillary and mandibular structures, particularly positioning of the shelves above the tongue and protrusion of the tongue and mandible. These results suggest an active role for Meckel's cartilage growth in repositioning the tongue to facilitate shelf elevation. The present data representing three distinct phases of secondary palate closure in humans can advance the understanding of morphological growth changes occurring before and after the horizontal positioning of palatal shelves and their fusion to close the secondary palate in humans successfully.

Application of geometric morphometrics for facial congenital anomaly studies

The face is a small complex three-dimensional (3D) structure composed of various bones and essential organs. Congenital anomalies of those organs represent various deformities; therefore, their quantification has been challenging. Linear measurements, such as lengths or angles between landmarks, called conventional morphometrics, have been used to quantify their phenotypes usually using 2D images, such as photographs or X-ray images. During analysis, geometric information, which refers to the relative position of each structure, is lost. Geometric morphometrics (GM) uses shape configurations, including anatomical landmarks, which can retain geometric information throughout analysis and can help visualize the results, making it tremendously advantageous compared to conventional methods. Morphometric studies investigate variations within groups, identification of group differences, simulation of the ontogeny, or association with specific organs or genetic disorders, and GM can be applied to these purposes using multivariate statistical methods. The calculation of high-dimensional data is usually required and has prevented GM from becoming a major morphometric method. However, recent developments in computer technology and software have enabled us to perform it easily with ordinary home computers, and the number of morphometric studies applying GM for facial congenital anomalies has been increasing recently. In this article, we introduce the concept and application of GM and review previous morphometric studies with GM regarding congenital facial anomalies.

The first 3D analysis of the sphenoid morphogenesis during the human embryonic period

The sphenoid has a complicated shape, and its morphogenesis during early development remains unknown. We aimed to elucidate the detailed morphogenesis of the sphenoid and to visualize it three-dimensionally using histological section (HS) and phase-contrast X-ray CT (PCX-CT). We examined 54 specimens using HS and 57 specimens using PCX-CT, and summarized the initial morphogenesis of the sphenoid during Carnegie stage (CS) 17 to 23. The 3D models reconstructed using PCX-CT demonstrated that some neural foramina have the common process of "neuro-advanced" formation and revealed that shape change in the anterior sphenoid lasts longer than that of the posterior sphenoid, implying that the anterior sphenoid may have plasticity to produce morphological variations in the human face. Moreover, we measured the cranial base angle (CBA) in an accurate midsagittal section acquired using PCX-CT and found that the CBA against CS was largest at CS21. Meanwhile, CBA against body length showed no striking peak, suggesting that the angulation during the embryonic period may be related to any developmental events along the progress of stages rather than to a simple body enlargement. Our study elucidated the normal growth of the embryonic sphenoid, which has implications for the development and evolution of the human cranium.

The role of the nasal region in craniofacial growth: An investigation using path analysis

This study focuses on the role of the nasal region and its interactions with adjacent facial elements during early ontogeny. A series of linear measurements, areas and volumes were extracted from a collection of 227 medical CT-scans of children from 0 to 6 years of age. These measurements describe aspects of the form of the orbit, maxilla, peri-alveolar (subnasal) region, nasal area, eye, oral region, masseter, and temporal muscles. Hypothesized interactions were then examined using path analysis. Two paths were designed: the first to investigate potential interactions in, and relative contributions of the nasal derivatives and adjacent regions to overall facial growth and development; the second path sees the addition of facial soft tissue measurements and aims to assess their effects on skeletal components, and on overall facial growth and development. The results of the first path indicate a large contribution of the nasal and subnasal regions to facial development. This indicates that the nasal septum and the developing dentition provide an important but variable contribution to facial ontogeny during early years. This result is confirmed in the second path, where the soft tissue elements were added to the diagram. Results of the second path indicate that the soft tissues contribute only locally to the development of some skeletal elements of the face. This indicates that the contribution of skeletal components has a more direct effect on facial height than soft tissue matrices, however there are complex interactions between soft tissues and skeletal elements throughout ontogeny.