Two cases of large bregmatic bone along with a persistent metopic suture from necropoles on the northern Black Sea coast of Bulgaria

Abstract

The co-occurrence of a bregmatic bone and metopism is an extremely rare finding. In the present study we investigate, compare, and describe this uncommon combination in two skulls of a child and an adult male. Both samples were from the osteological collection of the Institute of Experimental Morphology, Pathology and Anthropology with Museum, Bulgarian Academy of Sciences. The skulls were obtained from archaeological excavations of two necropoles located on the northern Black Sea coast of Bulgaria. The samples were macroscopically observed and measured. A CT scan was also performed in order to investigate the internal structure and the relation between the calvarial bones. Both bregmatic bones were slightly prominent unpaired structures wedged into the frontal and parietal bones with a developed diploic space. In the child, the frontal sinus was underdeveloped, whereas in the adult the frontal sinuses were well developed on both sides of the metopic suture. In the latter, an osteoma on the left side of the sinus was observed. The retention of the metopic suture along with the formation of a bregmatic bone could be considered as indispensable accessory sites for the regulation of the bone growth as a response to the increasing brain mass requirements under specific circumstances. This could be a mechanism for maintaining the optimal balance between the calvarial shape and size for a maximal effectiveness and stability in the presence of some developmental abnormalities.