More on vault thickness. As we commented in the previous post, the cranial vault can be divided in three layers: external table, diploe and internal table. Many previously studies provided information about skull thickness and density, but generally were based on a scarce number of measurements and with limited small sample size. Digital anatomy allows to go beyond many limits and constraints when working on this topic. Arne Voie and coauthors published a study based on parametric mapping and quantitative analysis of the human cranium. This team from San Diego, California, working mainly on neuroscience and radiological investigations, described how the thickness and density of the human skull changes depending on the anatomical regions (frontal, temporal, parietal and occipital bones). Measurements were computed on 51 dried crania of modern humans (males and females, ranging from 53 to 97 years old) and were analyzed by using 2000 points positioned on the three layers. Thickness and density distribution were calculated by using an algorithm to detect dense point of both extra and intra cranial boundaries and the lower density values of the diploic layer. The density results were mapped parametrically on each cranium to display their thicker areas and their distribution. The analysis evidenced a marked variation among the specimens. The thicker regions of the skull, namely the parietal, occipital, and frontal bones, have a mean value of 10.14 mm. In almost half of the sample the denser areas are the coronal and sagittal sutures, especially in their meeting point, while in the rest of the sample the density varies widely. The study cannot evidence sexual differences in both thickness and density.
Gizéh Rangel de Lázaro
Cranial vault consists of two cortical tables (inner and outer) sandwiching a layer of trabecular bone (diploe). Cranial vault thickness (CVT) is the distance between endocranial and ectocranial surfaces of vault bones. Several studies have pointed out that CVT differs not only between hominids but also among modern human populations. This morphological trait is mainly influenced by systemic and local stimuli, such as brain growth and development, mechanical forces (at the muscles attachments), circulating hormone levels, formation of sutures etc. Marisol Anzelmo and colleagues have recently published a study of ontogenetic changes in CVT in a modern sample of Homo sapiens. They tested age differences in CVT and if these changes are associated with changes in endocranial volume (EV), which reflect brain size. CT cranial images of 143 individuals (males and females) from 0 to 31 years were used to obtain, among others, a thickness mean measure (TMM), a measure of endocranial volume (EV), and a 3D topographic mapping of CVT, which indicates thickness distribution at different regions through a chromatic scale. A topographic mapping is very useful for picturing differences across vault regions in every age group, and it also reveals development of the regions during ontogeny and the onset of adulthood. The results of this study show that TMM increases during ontogeny without sex differences. Most accelerated growth rates of TMM occur during the first 6 years of life. Also, association between TMM and EV was significant only in this period (infants and children). Furthermore, adult pattern of thickness distribution seems to begin early in ontogeny. Increase of CVT in early ontogeny is directly linked to brain protection. However several mechanisms are involved in CVT formation, such as sutures patterning and vessels development. The vault bones dynamic in later ontogeny and in adulthood may be then influenced by different type of muscular activity and mechanical demands or, most commonly, by systemic factors associated with hormones, physical activity, nutrition.