Morphogenesis of Myodural Bridges: A Histological Study in Human Fetuses

Fibrous connections between the suboccipital muscles and the spinal dura mater (DM), known as myodural bridges (MBs), have been extensively described in adults, but their embryological development and morphogenesis remain incompletely understood. This study examines the development of these structures, along with the posterior atlanto-occipital and atlanto-axial membranes (AOM and AAM), in human fetuses, to clarify their origin and potential functional relevance.

This study examined the histological sections of 40 human embryos and fetuses from 8 to 14 weeks of development (WD). The used sample belongs to the collection of the department of anatomy and embryology of the Complutense University of Madrid and was examined under light microscopy.

At 8 WD, the DM, AOM, and AAM formed a common mesenchymal anlage, while the ligamentum nuchae (LN) developed separately. At 9 WD, the common anlage differentiated into DM and AOM-AAM. By 10 WD, the DM and AAM separated, forming the epidural space and allowing the establishment of connective tissue junctions. Between weeks 11 and 12 WD, the lower third of the AOM became continuous with the DM, forming a "fibrous intersection" composed of the DM, AOM, rectus capitis posterior minor (RMI), and LN. Between 13 and 14 WD, the DM thickened through the incorporation of connective fibers from the AOM, AAM, RMI, rectus capitis posterior major (RMA), obliquus capitis inferior (OCI), and LN.

This study shows that dense, regular fibrous connective tissue connections integrate into the DM originated from the AOM, AAM, RMI, RMA, OCI, and LN. The MB may help prevent dural infolding during upper cervical extension, as previously suggested, and the LN-DM junction could be a pathway used by veins to drain the epidural venous plexus. In our opinion, head movements and these connections would facilitate venous return.