- Discussion:
- various stages of Fusion of the the basiocciput may be seen;
- ranging from partial fusion, either anterior or posterior, to
complete occipitalatlantal fusion;
- atlantal-axial fusion anomalies are seen w/ equal frequency;
- aplasia / Hypoplasia may involve any portion of the ring of C1 and
C2;
- may simulate fracture on radiographs;
- smooth sclerotic margin at ring anomaly suggest congenital deficiency;
- fractures tend to have lucent irregular margins;
- Normal Variants of Dens:
- rare but may be misinterpreted as a fracture;
- dens may be completely absent, hypoplastic, or incompletely fused to
body of
C2 (lesion called
Os Odontoideum)
-
Os Odontoideum is smaller than normal dens and is fixed to anterior
ring of C1; (2 move as a unit);
- Normal Variant of the Lower Cervical Spine:
- fusion of the vertebral bodies or fusion of the posterior elements
-
Spina Bifida occulta (incomplete fusion of the posterior ring)
- has smooth sclerotic margins that help differentiate from frx;
- hypoplastic lesions in lateral masses are best appreciated w/
AP
- look for thinning of hypoplastic portion & relative hypertrophy
and sclerosis of the contralateral lateral mass;
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Effect of C1-C2 rotation on canal size.
