The traces of the middle meningeal artery (MMA) can be observed on dry skulls. For this reasons, it is often investigated in paleoneurology. The vessels run between the two layers of dura mater, along with the endosteal (periosteal) layer which is adherent to the inner surface of the skull. The MMA display connections with other vascular networks, but it is largely independent of the cerebral vascular system. Apparently, in adults there is only scarce or absent blood flow in MMA at rest, and activation may be triggered by thermal stress or other emergency responses (see Bruner et al. 2011). In a recent paper, Niknejad and colleagues (2018) test the possibility of using the MMA as a donor vessel in cerebrovascular bypass procedures, as an alternative to the superficial temporal artery (STA) which is standardly used for this purpose. The authors performed cadaveric dissections on 12 specimens and compared size, diameter and feasibility of both the MMA and the STA for the bypass to the middle cerebral artery. Their results confirmed that the MMA can be a suitable donor vessel. The premise of the donor potential of the MMA is based on its dispensability. Nevertheless, the authors note that the MMA may play an important role in case of the moyamoya disease, in which conditions MMA forms an important collateral network. In addition, this study provides valuable empirical data on the MMA morphology. Authors were able to identify three main branches in all specimens, with the dominant anterior petrosquamosal branch in all the cases. The diameter of the MMA was measured at its ostium and was 2.4 mm in average.
This month we have published a review on craniovascular traits and anthropology, freely available to download from the Journal of Anthropological Sciences. The article describes many vascular traits that can be analyzed on skulls, through the traces they leave on the bone surface or within the bone itself. The traces of the middle meningeal vessels, the traces of the venous sinuses, the diploic channels, and the endocranial foramina, can provide information on the vascular networks and, indirectly, on the physiological processes associated with their growth and development. The functional information available from these imprints is partial and incomplete, but it is the only one we have on blood flow when dealing with fossils, archaeological remains, or forensic cases. Methods are an issue, because of the difficulties with small samples, scoring procedure, statistics of ordinal and nominal variables, and with an intrinsic limitation in current anatomy: we still ignore the variations and processes behind many macroanatomical features, even in our own species. Previous articles on this topic deal with middle meningeal artery, vessels and thermoregulation, diploic channels, and parietal bone vascularization. Most of these papers are part of a project funded by the Wenner-Gren Foundation through an International Collaborative Research Grant, entitled “Cranial anatomy, anthropology, and the vascular system”. This beautiful drawing of a sectioned skull is by Eduardo Saiz.
Studying anatomical variability in paleontological and archaeological context is a challenge to look behind (and beyond) the bones. In the case of cranial remains we are able to make inferences not only on bone morphology but also on part of the vascular system. With computed tomography we can observe the diploic channels inside the bone matrix, and the imprints of the middle meningeal vessels on the endocranial surface of the vault. In the parietal bone both networks are particularly developed, most of all in modern humans. This month we have published a new study focusing the size and morphology of these vascular imprints in adult humans, and on their relationship with bone size and thickness. Our aim was to reveal possible influences between vascular and bone morphology. Vessels and bones share morphogenetic processes, and there can be shared functional and structural relationships between angiogenesis and osteogenesis. Shared growth factors can generate a positive correlation between bones and vessels dimensions or, conversely, biomechanical constraints between bone matrix and its embedded soft tissues can generate an inverse relationship between their volumes. We used CT data of human adult crania to measure cranial size, parietal bone thickness, and lumen size of these vascular traces. We provide a metric description of the size variation and size distribution of the diploic channels and meningeal imprints, for different orders of branches. The diploe largely influences the overall thickness of the bone. The upper part of the parietal bone shows the thickest values. The lumen size of the diploic channels and meningeal imprints is very similar, with no patent sexual or hemispheric differences. The correlation analysis did not revealed any clear relationship between vessels size, cranial size, and cranial thickness. Therefore, these results do not support the hypothesis of a reciprocal influence between bone and vascular morphology, which are likely to respond to different factors. Actually, although some vascular changes may be described in extreme cases of cranial deformation, also according to a previous survey on the endocranial vascular pattern in normal variation there is no apparent correspondence between gross cranial form and craniovascular traces.