Classification of bony malformations of the CVJ according to embryogenesis
Clinically significant CVJ bony malformations
Malformations of central pillar
Malformations of surrounding rings
Disturbance of axial component of occipital sclerotome, proatlas and C1 resegmented sclerotome
Odontoid dysgeneses
Basioccipital dysgeneses
- Aplasia/hypoplasia of odontoid components
- Disturbance of odontoid synchondroses (IBZ)
- Os odontoideum
- Ossiculum terminale persistens
- Abnormal resegmentation of proatlas centrum
- Os avis
- Failed midline integration of basal dental segment
- Bifid dens
- Failed midline integration of basioccipital primordium
- Bifid clivus
- Basioccipital dysplasia
- Basilar impression
- Platybasia
- Retroflexed dens
- Basilar invagination
- Basilar kyphosis
Disturbance of lateral component and hypochordal bows of proatlas and C1 resegmented sclerotome
Proatlas anomalies
C1 sclerotome anomalies
- Hyperplasia of hypochordal bow of proatlas
- Third occipital condyle
- Pre-basioccipital arch
- Hyperplasia of exoccipital sclerotome
- Hypertrophic occipital condyle
- Non-resegmentation of proatlas (anterior homeotic transformation)
- Atlas assimilation
- Posterior homeotic transformation
- Aplasia of hypochordal bow of C1
- Aplasia and hypoplasia of anterior C1 arch
- Aplasia/hypoplasia of lateral sclerotome
- Posterior C1 arch agenesis
- Combined hypochordal bow and lateral sclerotome dysplasia
- Aplasia of lateral mass and anterior C1 arch
- Combined anterior and posterior C1 arch defects
- Bifid anterior and posterior C1 arch
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