Modelling 3D craniofacial growth trajectories for population comparison and classification illustrated using sex-differences

Harold S Matthews,Nicola M Kilpatrick,Yi Fan,Peter D Claes,Rita Hardiman,John G Clement,Anthony J Penington

doi:10.1038/s41598-018-22752-5

Abstract

Many disorders present with characteristic abnormalities of the craniofacial complex. Precise descriptions of how and when these abnormalities emerge and change during childhood and adolescence can inform our understanding of their underlying pathology and facilitate diagnosis from craniofacial shape. In this paper we develop a framework for analysing how anatomical differences between populations emerge and change over time, and for binary group classification that adapts to the age of each participant. As a proxy for a disease-control comparison we use a database of 3D photographs of normally developing boys and girls to examine emerging sex-differences. Essentially we define 3D craniofacial ‘growth curves’ for each sex. Differences in the forehead, upper lip, chin and nose emerge primarily from different growth rates between the groups, whereas differences in the buccal region involve different growth directions. Differences in the forehead, buccal region and chin are evident before puberty, challenging the view that sex differences result from pubertal hormone levels. Classification accuracy was best for older children. This paper represents a significant methodological advance for the study of facial differences between growing populations and comprehensively describes developing craniofacial sex differences.

Highlights

Many disorders present with characteristic abnormalities in craniofacial shape, emerging through abnormal pre- or postnatal growth
Growth may differ in terms of growth rate, growth direction or in some combination of the two
In this study we introduce a framework for describing and analysing the emergence of shape differences between populations and apply the method to the question of how differences in craniofacial shape emerge between males and females

Summary

Introduction

Many disorders present with characteristic abnormalities in craniofacial shape, emerging through abnormal pre- or postnatal growth. 3D photography and advances in image analysis have achieved rapid, automatic measurement of the entire outer surface of the craniofacial soft tissue[2,3,4] This allows the anatomy to be quantified as a dense cloud of point co-ordinates providing a high resolution description of the surface. Averaging these corresponding points within a disease group and within a control group to produce ‘prototypical’ faces provides a spatially dense description of the differences between the two groups[5,6,7,8,9,10] These representations have been used to learn classification models for diagnosis from craniofacial shape[5,8]. The combination of state-of-the-art methodology and a large sample size spread over childhood and adolescence makes this, to the best of our knowledge, the most comprehensive analysis of the emergence of sexual dimorphism to date

Methods

Results

Conclusion