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Craniovertebral Junction (CVJ) anomalies are congenital or acquired abnormalities affecting the junction between the skull base (occipital bone) and the upper cervical spine (atlas [C1] and axis [C2]).
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This region is structurally complex and houses critical neural and vascular structures, making imaging essential for diagnosis, surgical planning, and follow-up.
| Structure | Description |
|---|---|
| Occipital bone | Includes the foramen magnum |
| Atlas (C1) | Ring-shaped; articulates with occipital condyles |
| Axis (C2) | Contains the odontoid process (dens) |
| Ligaments | Cruciate, alar, apical, tectorial membrane – stabilize CVJ |
| Neural structures | Lower medulla, upper cervical cord, spinal accessory nerve |
| Vascular | Vertebral arteries traverse the transverse foramina |
Congenital:
| Condition | Features |
|---|---|
| ‣ | Upward migration of odontoid into foramen magnum |
| ‣ | Flattened skull base angle (>143°) |
| ‣ | Fusion of atlas to occiput |
| ‣ | Accessory ossicle replacing normal odontoid tip |
| ‣ | Congenital fusion of cervical vertebrae |
| ‣ | Often associated with bony CVJ anomalies |
| Achondroplasia / OI / Cleidocranial dysostosis | Syndromic associations with skull base anomalies |
Acquired:
| Etiology | Examples |
|---|---|
| ‣ | Pannus formation and ligamentous laxity → atlantoaxial instability |
| Trauma | Dens fractures, ligament injury |
| Infections / TB / Osteomyelitis | Vertebral collapse or abscess formation |
| ‣ | Paget’s, osteomalacia – skull base softening (platybasia) |