Atlantooccipital
Junction Anatomy
Vertebral
artery Hypoglossal canal, Posterior margin of foramen magnum, Posterior
atlantooccipital membrane, Posterior arch of atlas (C1), Nuchal ligament, Ligamentum
flavum, Posterior atlantoaxial membrane, Spinous process of axis (C2), Hypoplastic
dens, Os odontoideum with fibrous union and narrowing of vertebral canal with
head in extension,
Lowest level of occipital bone, McGregor’s line, from
posterior nasal spine of hard palate to lowest point of occipital bone., Average
normal position of tip of dens is 1.32 mm above this line, with standard deviation
of _2.6 mm as measured on standard lateral radiograph. Tip _4.5 mm above line
is considered to indicate basilar impression. Abnormalities of dens, most often
associated with skeletal dysplasias such as Klippel-Feil, Down, or Morquio
syndromes, Tectorial membrane, Apical ligament of dens, Superior longitudinal
band of cruciate ligament of atlas, Anterior atlantooccipital membrane, Anterior
arch of atlas (C1), Articular cavity, Dens of axis (C2), Transverse ligament of
atlas, Inferior longitudinal band of cruciate ligament of atlas, Anterior
longitudinal ligament, Posterior longitudinal ligament
