Analysis of facial skeletal asymmetry during foetal development using μCT imaging

Abstract

Structured Abstract 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.

Application of geometric morphometrics for facial congenital anomaly studies

“…Either types of data can be used in GM [10][11][12] and the latter is often used for the visualization of GM results. [13][14][15][16] Surface data represent "data on the object's surface," and are constructed as polygons. Surface data can be created by regional segmentation from volumetric data by stacking contours extracted from…”

“…The volume data contain all information, including the inside of the objects, while the surface data contain only surface information, thus having less data. Either types of data can be used in GM 10–12 and the latter is often used for the visualization of GM results 13–16 …”

Assessment of facial landmarks for bone asymmetry in geometric morphometric studies: A review

“…Also, we notice that individual landmarks do not have a clear definition of their position in some studies. 33,37,43 These discrepancies limit comparisons between individual landmarks with the same name among different studies.…”

Symmetry and fluctuation of cell movements in neural crest-derived facial mesenchyme

“…Indeed, precise comparisons of lip fusion in several mouse strains (normal and cleft lip liable) found that the timing of when fusion was initiated was more variable in the cleft lip-liable strains ( Wang et al, 1995 ). There is also asymmetry of the jaw skeleton, derived from cranial neural crest cells in the normal human fetus ( Katsube et al, 2019 ).…”