Quantitation of nasal development in the early prenatal period using geometric morphometrics and MRI: a new insight into the critical period of Binder phenotype

3D atlas of the human fetal chondrocranium in the middle trimester

The chondrocranium provides the key initial support for the fetal brain, jaws and cranial sensory organs in all vertebrates. The patterns of shaping and growth of the chondrocranium set up species-specific development of the entire craniofacial complex. The 3D development of chondrocranium have been studied primarily in animal model organisms, such as mice or zebrafish. In comparison, very little is known about the full 3D human chondrocranium, except from drawings made by anatomists many decades ago. The knowledge of human-specific aspects of chondrocranial development are essential for understanding congenital craniofacial defects and human evolution. Here advanced microCT scanning was used that includes contrast enhancement to generate the first 3D atlas of the human fetal chondrocranium during the middle trimester (13 to 19 weeks). In addition, since cartilage and bone are both visible with the techniques used, the  endochondral ossification of cranial base was mapped since this region is so critical for brain and jaw growth. The human 3D models are published as a scientific resource for human development.

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.

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

Significant shape changes in the human facial skeleton occur in the early prenatal period, and understanding this process is critical for studying a myriad of congenital facial anomalies. However, quantifying and visualizing human fetal facial growth has been challenging. Here, we applied quantitative geometric morphometrics (GM) to high-resolution magnetic resonance images of human embryo and fetuses, to comprehensively analyze facial growth. We utilized non-linear growth estimation and GM methods to assess integrated epigenetic growth between masticatory muscles and associated bones. Our results show that the growth trajectory of the human face in the early prenatal period follows a curved line with three flexion points. Significant antero-posterior development occurs early, resulting in a shift from a mandibular prognathic to relatively orthognathic appearance, followed by expansion in the lateral direction. Furthermore, during this time, the development of the zygoma and the mandibular ramus is closely integrated with the masseter muscle.

Analysis of facial skeletal asymmetry during foetal development using μCT imaging

OBJECTIVES

Asymmetry has been noted in the human craniofacial region in several pathological conditional and growth abnormalities, often with a directional predilection. Physiological asymmetry has also been reported in normal adults and adolescents, with certain regions of the cranioskeleton, such as the mandible, displaying prevalent asymmetry. However, the timing at which such asymmetries arise has not been evaluated. The objectives of this study were to assess the degree of asymmetry in facial bones during the foetal stages of human development.

MATERIAL AND METHODS

Twenty-one preserved conceptuses from the Congenital Anomaly Research Center at Kyoto University, between ages 15 and 20 weeks of gestation, were studied using high-resolution μCT imaging. Asymmetry analysis was performed on digitally segmented facial bone pairs, using geometric morphometric (GM) approaches as well as adapted deformation-based asymmetry (DBA) methods.

RESULTS

GM analysis revealed that the developing facial bones display statistically significant fluctuating and directional asymmetry. DBA methods suggest that the magnitude of asymmetry in facial bones is low and does not appear to be correlated to the estimate of overall size of conceptus. Additionally, the patterns of asymmetry are highly variable between individual specimens.

CONCLUSIONS

The developing foetal facial skeleton displays variable patterns of low magnitude asymmetry. GM and DBA methods offer unique advantages to assess facial asymmetry quantitatively and qualitatively.

Critical Growth Processes for the Midfacial Morphogenesis in the Early Prenatal Period

BACKGROUND

Congenital midfacial hypoplasia often requires intensive treatments and is a typical condition for the Binder phenotype and syndromic craniosynostosis. The growth trait of the midfacial skeleton during the early fetal period has been assumed to be critical for such an anomaly. However, previous embryological studies using 2-dimensional analyses and specimens during the late fetal period have not been sufficient to reveal it.

OBJECTIVE

To understand the morphogenesis of the midfacial skeleton in the early fetal period via 3-dimensional quantification of the growth trait and investigation of the developmental association between the growth centers and midface.

METHODS

Magnetic resonance images were obtained from 60 human fetuses during the early fetal period. Three-dimensional shape changes in the craniofacial skeleton along growth were quantified and visualized using geometric morphometrics. Subsequently, the degree of development was computed. Furthermore, the developmental association between the growth centers and the midfacial skeleton was statistically investigated and visualized.

RESULTS

The zygoma expanded drastically in the anterolateral dimension, and the lateral part of the maxilla developed forward until approximately 13 weeks of gestation. The growth centers such as the nasal septum and anterior portion of the sphenoid were highly associated with the forward growth of the midfacial skeleton (RV = 0.589; P < .001).

CONCLUSIONS

The development of the midface, especially of the zygoma, before 13 weeks of gestation played an essential role in the midfacial development. Moreover, the growth centers had a strong association with midfacial forward growth before birth.

Blechschmidt Collection: Revisiting specimens from a historical collection of serially sectioned human embryos and fetuses using modern imaging techniques

Along with the Carnegie Collection in the United States and the Kyoto Collection in Japan, the Blechschmidt Collection (Georg-August-University of Göttingen, Germany) is a major historical human embryo and fetus collection. These collections are of enormous value to human embryology; however, due to the nature of the historical histological specimens, some stains are fading in color, and some glass slides are deteriorating over time. To protect these specimens against such degradation and ensure their future usefulness, we tried to apply modern image scanning and computational reconstruction. Samples of histological specimens of the Blechschmidt Collection were digitized into images using commercial flatbed scanners with a resolution of 4800 pixels per inch. Two specimens were reconstructed into three-dimensional (3D) images by using modern techniques to vertically stack two-dimensional images of the slices into 3D blocks. The larger specimen of crown-rump length (CRL) 64.0 mm, a series of very large histological sections in human embryology, was reconstructed clearly, with its central nervous system segmented before stacking. The smaller specimen of CRL 17.5 mm was also reconstructed into 3D images. The outer surface of the embryo was intact, and its development was classified according to the widely used Carnegie stages (CSs). The CS of the specimen was identified as the later half of CS 20. The invaluable Blechschmidt Collection can be revisited for further research with modern techniques such as digital image scanning and computational 3D reconstruction.