Posterior Atlantooccipital Membrane, Lateral View

Description

Arcing from the posterior margin of the foramen magnum to the superior border of the posterior arch of the atlas (C1), the posterior atlantooccipital membrane spans the atlantooccipital interval in lateral profile. Deep to it, the vertebral canal continues cranially toward the cranial cavity, bounded by the occipital bone superiorly and the ring of the atlas inferiorly. The membrane lies posterior to the atlantooccipital joint and immediately superficial to the dura, with the C1 lamina (posterior arch) forming a firm osseous reference point. Adjacent upper cervical elements, including the posterior arch of C1 and the cervical curve, orient the relationship between skull base and cervical spine. Clinically, this is the membrane you think about when planning a posterior approach to C1, because it acts as a thin roof over the vertebral artery groove on the superior surface of the posterior arch before the artery turns medially to enter the foramen magnum. A small but real hazard zone. Ossification or thickening of the posterior atlantooccipital membrane can form an arcuate foramen (ponticulus posticus), a variant associated with vertebral artery irritation and relevant when placing C1 lateral mass screws or interpreting lateral cervical radiographs and CT. The same layer is also encountered in posterior atlantooccipital decompression, where distinguishing membrane from dura helps prevent unintended dural violation. Use this lateral view for gross anatomy and neuroanatomy teaching on craniovertebral junction landmarks, and for surgical education materials covering C1 instrumentation, suboccipital craniectomy, or vertebral artery exposure at the atlas. It also fits radiology and chiropractic medicine publications that discuss ponticulus posticus and other atlas ring variants in relation to headache and cervicogenic symptoms. Anatomical accuracy verified by SciePro's Medical Advisory Board.