Vascular microforamina and endocranial surface: Normal variation and distribution in adult humans

The term craniovascular traits refers to the imprints left by arteries and veins on the skull bones. These features can be used in biological anthropology and archaeology to investigate the morphology of the vascular network in extinct species and past populations. Generally, the term refers to macrovascular features of the endocranial cavity, like those associated with the middle meningeal artery, venous sinuses, emissary foramina, and diploic channels. However, small vascular passages (here called microforamina or microchannels) have been occasionally described on the endocranial surface. The larger ones (generally with a diameter between 0.5 and 2.0 mm) can be detected through medical scanners on osteological collections. In this study, we describe and quantify the number and distribution of these microforamina in adult humans (N = 45) and, preliminarily, in a small sample of children (N = 7). Adults display more microchannels than juvenile skulls. A higher frequency in females is also observed, although this result is not statistically significant and might be associated with allometric cranial variations. The distribution of the microforamina is particularly concentrated on the top of the vault, in particular along the sagittal, metopic, and coronal sutures, matching the course of major venous sinuses and parasagittal bridging veins. Nonetheless, the density is lower in the region posterior to bregma. Beyond oxygenation, these vessels are likely involved in endocranial thermal regulation, infection, inflammation, and immune responses, and their distribution and prevalence can hence be of interest in human biology, evolutionary anthropology, and medicine.