- Congenital anomalies of nerve roots are rare.
- This possibility should be considered in cases of failed back surgery for herniated disc.
- Classification system of Cannon et al:
- Type 1 anomalies:
- Conjoined nerve root (2 nerve roots arise from a common dural sheath).
- They separate at various distances from the thecal sac,
- They exit through the same or separate neural foramina.
- Neurosurgeons need to be aware of this anomaly to avoid inadvertent injury e.g. during surgery for herniated disc
- Type 2 anomalies:
- 2 nerve roots exit through one foramen.
- Variants:
- leaves an unoccupied neural foramen
- all foramina occupied, but one foramen has 2 nerve roots
- Type 3 anomalies:
- adjacent nerve roots are connected by an anastomosis
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