Quantitative evaluation of craniofacial growth in the third trimester human.

A detailed understanding of fetal craniofacial growth is necessary for understanding the mechanisms underlying the growth process and how altered growth patterns may give rise to specific craniofacial anomalies. Although descriptive studies of human fetal craniofacial growth are abundant, quantitative studies are less common; most employ only lateral cephalograms or tracings of sectioned specimens. In this study, we compared growth rates in the individual bones of the facial and basicranial regions in a large sample of spontaneously aborted, third trimester fetuses. Growth in the individual dimensions of most bones is not significantly different from isometry when compared with body weight, but comparisons of dimensions within bones show clear changes in shape. In particular, the mandible is characterized by a deepening of the corpus, probably in association with development of the teeth. The maxilla also shows a relatively rapid height increase associated with dental development. The temporal bone grows faster in superoinferior height as opposed to anteroposterior width. The lateral and inferior margins of the zygomatic bone grow faster than the orbital margin. The basioccipital bone, cited in radiographic studies as growing substantially slower than the facial region, actually changes in shape more rapidly than any other skeletal component examined in this study, with widths growing much faster than lengths. Our findings demonstrate that craniofacial development in the third trimester is characterized by localized variation in the rate of growth within and between individual skeletal components, and that gross characterizations of regional rates of growth inadequately characterize craniofacial development.