Digital analysis of the diploic vascular system in anatomy, archaeology and paleoanthropology and its implications in the hominid endocranial thermoregulation

Zusammenfassung

The diploic channels are placed in the cancellous bone between the vault cortical layers (external and internal). The diploic veins are large, thin-walled and valveless running through a network of microscopic channels. Diploic veins appear to be more developed in humans than in non-human primates, suggesting a key role in human evolution. Our main goal is to provide a segmentation protocol for diploic channels and computed tomography analysis (CT), a quantitative description of their variation in modern humans (non-adults and adults), non-human primates, and fossil specimens. The CT was used for the 2D and 3D visualization of diploic channels, rendering and measure. The effect of different resolution on the final anatomical rendering was evaluated. We develop a specific protocol to segment the vascular system and identify the main branches, reducing the noise introduced by the cancellous bone. We describe their vascular networks, providing quantitative comparisons and correlations between compact and cancellous bone thickness, vessels branch length and lumen size, vascular asymmetries and volumetric distribution in frontal, parietal and occipital bones. Communications between the diploic network with the meningeal artery at the temporal fossa, with the emissary veins at the occipital bone, and with the venous sinuses at the confluence of sinus were noted. The parietal areas are the most vascularized in modern humans, while human fossils and non-humans primates, show lower vascular variation and development. The use of CT at high resolution can hamper semi-automatic segmentation of the diploic channels. Optimal resolution is sufficient to reconstruct the channels without increasing noise associated with the trabecular structure. In view of probable metabolic differences and constraints associated with modern human brain size and shape, it should be evaluated whether these vascular differences can be due to endocranial thermoregulation. Therefore, considering the possible contribution of diploic vessels in brain thermoregulation and heat management, the analysis of the diploic network may be relevant in anthropology, medicine, and paleontology.