# Basis Cranii Interna in Metopism: A Comparative Geometric Morphometric Study

## TL;DR

This study investigates how the persistence of the metopic suture in adults relates to the shape of the cranial base using geometric morphometrics.

## Contribution

The study introduces a comparative geometric morphometric analysis of the internal cranial base in metopic and control crania.

## Key findings

- No significant size differences were found between metopic and control crania.
- Shape differences were observed in the anterior and middle cranial fossae but not the posterior.
- Principal Component Analysis showed no clear separation between metopic and control groups.

## Abstract

Metopism, defined as the persistence of the metopic suture into adulthood, represents a variation in cranial morphology. Although often considered an isolated feature of the frontal bone, its occurrence may reflect integrated developmental processes involving the cranial base. The cranial base plays a central role in coordinating craniofacial growth, serving as a structural and functional platform for the developing brain and facial skeleton. Consequently, variations in its growth pattern, synchondrosis activity, or overall geometry could influence the development of the entire craniofacial complex. This study explores the relationship between metopism and cranial base morphology by examining differences in shape and size using geometric morphometric approaches. Understanding this developmental relationship provides insight into both normal and variant cranial growth, with implications for developmental biology, clinical assessment, and the study of craniofacial integration.

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.