Ossification and midline shape changes of the human fetal cranial base

Abstract

An appreciation of ontogenetic changes to the cranial base is important for understanding the evolution of modern human skull form. Using geometric morphometric techniques, this study explores midline shape variations of the basicranium and midface during human prenatal ontogeny. In particular, the analysis sets out to explore shape variations associated with endochondral ossification and to reassess shape variations previously observed on the basis of angular measures.Fifty-four formalin-preserved human fetuses were imaged using high-resolution MRI. Coordinates for 10 landmarks defining the midline basicranium and midface were acquired and areas of ossification in the midline basioccipital, basisphenoid, and presphenoid cartilages were measured as percentages of overall cranial base area. The results show shape variations with increasing fetal size that are consistent with cranial base retroflexion, anterior facial projection and dorsal facial rotation. These growth variations are centered on the midsphenoid area and are associated with disproportionate variations of sphenoid height and length. Small but significant correlations were observed between ossification of the presphenoid cartilage and components of shape that described, among other variations, sphenoid shortening. While ossification cannot be directly linked with the shape variations observed, it seems likely that bone formation plays a role in modulating the influence of other factors on the fetal cranial base.

Cranial base angulation and growth of the human fetal pharynx

“…To my knowledge, there are no other fetal studies of the external cranial base angle (PNS-H-Ba). However, a non-Euclidean shape analysis of the same sample clearly illustrated that the external surface of the fetal basicranium retroflexes due mostly to anterior facial rotation (Jeffery and Spoor, 2004). This is in close agreement with the findings of the present study.…”

“…All measurements were computed from landmark coordinates taken from midline hrMR images or parasagittal images close to the midline with the ImageJ software package (Wayne Rasband) and Align3D plugin (Nick Parker). Previous studies have shown that this is a precise and accurate method for studying fetal morphology (Jeffery, 2002;Jeffery and Spoor, 2004). It should be remembered, however, that previous studies also indicate that head orientation influences laryngeal position (Magriples and Laitman, 1987).…”

“…This is in close agreement with the findings of the present study. The finding that the external cranial base angle retroflexes more rapidly than the internal cranial base angle probably reflects the greater anterior projection and rotation of the facial block (PNS-H) compared with rotation of the anterior cranial base (Pp-Fc) (Jeffery and Spoor, 2004).…”

The use of geometric morphometry to study facial asymmetries: relationship between basicranial shape and maxillofacial and occlusal pathologies

“…The role of the base of the cranium in the genesis of maxillofacial dysplasias is the subject of an on-going debate [1][2][3][4][5]7,17,[20][21][22][23]29 ; some authors suspect that the base of the cranium is responsible for the development of the anteroposterior dysplasias, because of the much-discussed angle of the base of the cranium as well as for the genesis of the asymmetries being linked to a primary asymmetry of the base of the brain.…”

“…The modifications of the cranial base during growth 8,18,21,32,33 , the ethnic differences, evolutionary changes between primates and homo sapiens, the relationship with encephalization, upright stature or speech are some subjects that are largely controversial. Further the published results are most often contradictory.…”