Facial surface analysis by 3D laser scanning and geometric morphometrics in relation to sexual dimorphism in cerebral–craniofacial morphogenesis and cognitive function

Abstract

Over early fetal life the anterior brain, neuroepithelium, neural crest and facial ectoderm constitute a unitary, three-dimensional (3D) developmental process. This intimate embryological relationship between the face and brain means that facial dysmorphogenesis can serve as an accessible and informative index of brain dysmorphogenesis in neurological and psychiatric disorders of early developmental origin. There are three principal challenges in seeking to increase understanding of disorders of early brain dysmorphogenesis through craniofacial dysmorphogenesis: (i) the first, technical, challenge has been to digitize the facial surface in its inherent three-dimensionality;(ii) the second, analytical, challenge has been to develop methodologies for extracting biologically meaningful shape covariance from digitized samples, making statistical comparisons between groups and visualizing in 3D the resultant statistical models on a 'whole face' basis; (iii) the third, biological, challenge is to demonstrate a relationship between facial morphogenesis and brain morphogenesis not only in anatomical-embryological terms but also at the level of brain function. Here we consider each of these challenges in turn and then illustrate the issues by way of our own findings. These use human sexual dimorphism as an exemplar for 3D laser surface scanning of facial shape, analysis using geometric morphometrics and exploration of cognitive correlates of variation in shape of the 'whole face', in the context of studies relating to the early developmental origins of schizophrenia.

Three-Dimensional Laser Surface Imaging and Geometric Morphometrics Resolve Frontonasal Dysmorphology in Schizophrenia

“…Previous work (Hennessy et al 2005) has shown that results are largely insensitive to the number of pseudo-landmarks provided this is greater than approximately 300. Here, 1694 pseudo-landmarks distributed over the entire facial surface were selected to provide sufficient resolution for visualisation of facial features, particularly the mouth and frontonasal prominences (Hennessy et al 2005).…”

“…Facial surfaces were recorded using a portable, handheld Polhemus FastScan laser scanner (Hennessy et al 2002(Hennessy et al , 2005. A typical surface, consisting of ~80,000 points, is shown in Figure 1.…”

“…interpolated landmarks] over the whole facial surface, a smooth interpolation using thin plate splines was employed (Hutton et al 2003), as described recently in detail (Hennessy et al 2005). Briefly, a facial surface of low resolution is generated as a template and edited to remove surface points above the supraorbital ridge and below the inferior mandibular margin.…”

“…As an interim approach, we have recently elaborated facial dysmorphology in patients with schizophrenia using limited 3D configurations reconstructed from linear measurements . However, 3D digitisation technologies now allow facial surfaces to be recorded in their entirety and landmark coordinates obtained (Hennessy et al 2002(Hennessy et al , 2005Hammond et al 2004); in a complementary manner, geometric morphometrics, which analyses 3D landmark coordinates directly, provides the basis for relating shape to other biological variables both statistically and visually (Hennessy et al 2005;O'Higgins and Jones 1998;Dryden and Mardia 1998). We have recently applied portable, hand-held 3D laser surface imaging to specify statistically and anatomically the nature of sexual dimorphism in human facial morphogenesis (Hennessy et al 2002) and the relation of facial shape to cognitive function (Hennessy et al 2005(Hennessy et al , 2006.…”

“…However, while this substantial increase in detail over the facial surface indicated topographically distinct abnormalities of facial shape in developmental disorders such as velocardiofacial syndrome (Hammond et al 2004), statistical approaches to comparative analysis have been lacking. We have recently implemented an algorithm elaborated from this procedure to analyse, both statistically and visually, sexual dimorphism and its relationship to cognitive function in normal subjects using interpolated landmarks over the entire facial surface (Hennessy et al 2005).…”