Basis Cranii Interna in Metopism: A Comparative Geometric Morphometric Study

The cranium is a highly integrated structure composed of partially independent yet interrelated modules with different origin and developmental pathways. Throughout growth, these modules interact extensively in response to various intrinsic and extrinsic factors, ultimately forming a cohesive and functionally unified structure. Consequently, morphological changes in one cranial unit are expected to influence the development and shape of others. Considering the known vault alterations associated with metopism, we assume that the cranial base is also modified in metopic skulls. To test this hypothesis, we compared shape and size of the internal cranial base in metopic (46) and control (183) dry crania of contemporary adult Bulgarian males using geometric morphometric techniques. The crania were scanned using an industrial µCT system. Three-dimensional coordinates of 37 (9 midsagittal and 14 bilateral) landmarks were recorded on the endocranial surface. The landmarks were grouped into four configurations outlining the internal cranial base and its compartments: anterior cranial fossa, middle cranial fossa, and posterior cranial fossa. No significant size differences were observed between the metopic and control series. Shape comparisons revealed significant differences in all configurations except the posterior cranial fossa. However, Principal Component Analysis did not demonstrate clear separation between the groups, indicating that the observed shape variation cannot be attributed solely to the persistence of the metopic suture.