The posterior atlantooccipital membrane is a broad, thin fibrous sheet connecting the posterior arch of the atlas to the posterior margin of the foramen magnum. A lateral opening in the membrane forms an arcuate foramen through which the vertebral artery and suboccipital nerve (C1 dorsal ramus) pass as they enter the cranium. The membrane represents the superior continuation of the ligamentum flavum.
Reinforces the posterior craniocervical junction, limits flexion at the atlantooccipital joint, and protects the vertebral arteries and suboccipital nerves as they pass through its lateral arcuate openings.
The posterior atlantooccipital membrane can calcify or ossify around the arcuate foramen, compressing the vertebral artery and causing vertebrobasilar insufficiency with position-related dizziness and headache, known as posterior cervical sympathetic syndrome or Barre-Lieou syndrome. Surgical decompression requires careful dissection to protect the vertebral artery. The membrane is an anatomical landmark during posterior occipitocervical fusion procedures.
Calcification of the posterior atlantooccipital membrane around the C1 arcuate foramen compresses the vertebral artery, producing position-related vertigo, occipital headache, and vertebrobasilar symptoms requiring MR angiography and occasionally surgical decompression.
