"type A: failure of posterior midline fusion of the two hemiarches"
"type B: unilateral defect"
"type C: bilateral defects"
"type D: absence of the posterior arch, with persistent posterior tubercle"
"type E: absence of the entire posterior arch, including the tubercle"
"1: incidental imaging finding, asymptomatic"
"2: neck pain or stiffness after trauma to the head or neck"
"3: chronic symptoms referable to the neck"
"4: various chronic neurological problems"
"5: acute neurological symptoms following minor cervical trauma"
"median cleft(s) of the posterior arch"
"Arnold-Chiari malformation"
"Currarino triad"
"In cases of doubt (e.g. post-traumatic symptoms not clearly related to the anomaly, type C or D without symptoms) imaging studies may include 7:"
Expected headings
"Classification"
"Embryology"
"Associations"
"Mechanism"
"When patients with arch anomalies present with trauma, the radiographs may be confusing and misleading. Hence thorough knowledge of these abnormalities is essential to avoid misinterpretation as an osteolytic lesion, fracture or dislocation, e.g. atlantoaxial subluxation."